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Electrical Resistivity Tomography (ERT) can be a key tool for aiding in characterization of karst geohazard risks at proposed landfill sites. This study is proximal to the south-central Kentucky karst and Mammoth Cave National Park and possesses siliciclastic cap rock upland areas that pose relatively high groundwater-contamination risks due to adjacent ravines floored by carbonates. Complex stratigraphy associated with the Mississippian-Pennsylvanian unconformity and juxtaposition of heterolithic sedimentary rocks in general presents further challenges for demarcating hydrogeological characterization of the base of engineered landfills. A conceptual site model integrates ERT surveying and field geology that both satisfactorily characterize the site and risks to groundwater resources without conducting multiple borings. The proposed landfill site is compared to well-known and mapped caves at a landfill near Bowling Green, Crumps Cave near Smiths Grove, and River Styx Spring at Mammoth Cave. Our work entails review of ERT datasets at known cave sites and compares these to two ERT profiles that traversed the proposed landfill site, which are integrated with study of outcrops, and an excavated pit and trench. ERT data range from several low 10 s to about 400 Ω-meter values for mud rock units whereas sandy units possess ERT values from approximately 500 to several tens of thousands of Ω meters. The greatest values are indicative of basal Pennsylvanian Caseyville Sandstone, and these exceed 32,000Ω meters. In comparison, ERT values at known cave sites range from one to 100,000 Ω meters, with elevated, dry rock or possibly dry (air filled) caves interpreted from the greatest values and low values reflective of conductive underground cave streams and moist caves. An unexpected challenge specific to the Hart County landfill study includes occurrence of well-drained and highly weathered Caseyville at the highest elevations of the site causing increased electrical contact resistance during ERT surveying. The overall ERT contrast however, between quartz-rich and clay poor strata (high-resistivity rocks and regolith) and clay-rich strata (low-resistivity rocks) provides independent data consistent with the observed stratigraphy exposed in site exposures. Nonuniqueness of conductive intervals at the Hart County site contrasts with other conductive areas at depth associated with moist or wet cave passages as documented at Crumps Cave and Mammoth Cave. [ABSTRACT FROM AUTHOR]

The article is an introduction to a special issue dedicated to Ralf Littke, a prominent geologist known for his work in organic petrology, basin analysis, and petrophysics. It highlights Ralf's research on coal petrography, sedimentary environments, and basin modeling, showcasing his contributions to the field. The special issue includes studies on organic-rich sediments, coal deposits, and source rocks, reflecting Ralf's interests and scientific endeavors over his 40-year career. The article also acknowledges Ralf's impact as a teacher, supervisor, and mentor to numerous students and researchers in the geosciences. [Extracted from the article]

The North Sea Basin is the most important oil and gas producing area in Europe and the birthplace of many classic petroleum geological theories. From the perspective of multi-spheric interactions in the Earth, this study investigated the rift-foreland-rift evolution process of the North Sea Basin, which was controlled by the deep dynamic driving forces of the continental collision orogeny, mantle plume uplift, and intraplate deformation. The North Sea Basin was found to have drifted northward since the Carboniferous and passed through the low-latitude Hadley and the mid-latitude Ferrel cells. Two sets of main hydrocarbon source rocks have formed, the coals and coal measures of the Upper Carboniferous Westphalian and the marine shale of the Upper Jurassic Kimmeridge Clay Formation. We propose that the deep processes, tectonic activity, and transgression-climate evolution jointly controlled the types and horizons of the source rocks, reservoirs, and seals in different regions of the North Sea Basin. In the southern North Sea Basin, a Carboniferous-Lower Triassic gas-rich petroleum system was formed, which is characterized by transitional coal measure source rocks, desert aeolian sandstone reservoirs, and evaporite cap rocks. In the northern North Sea Basin, an Upper Triassic-Paleogene oil-rich petroleum system was formed, which is characterized by marine graben-type source rocks, deltaic sandstone and marine limestone reservoirs, and marine tight marl and shale cap rocks. The late tectonic burial and uplift in the North Sea Basin further controlled the processes of oil and gas generation and accumulation, ultimately leading to a differential distribution pattern which is oil rich in the northern part and gas rich in the southern part of the basin. In the future, there is an urgent need to re-examine the mechanisms for the petroleum generation and accumulation in large mature exploration areas (e.g., super basins such as the North Sea) and low exploration areas (e.g., the Okhotsk Sea and Arctic regions) from the perspective of multi-spheric interactions in the Earth in order to provide new theoretical support for increasing the identification of oil and gas reserves globally. The development of artificial intelligence in the petroleum industry should focus on the massive amount of exploration and geological data collected in the North Sea Basin. Through digital geological innovation, carbon neutral comprehensive utilization of oil, gas, and associated resources (e.g., helium and hydrogen) can be achieved, providing a new paradigm for global oil and gas exploration and development. [ABSTRACT FROM AUTHOR]

Fractured aquifers are heterogeneous due to the variable frequency, orientation, and intersections of rock discontinuities. A ~100-m-thick Silurian dolostone sequence provides a bedrock aquifer supplying the city of Guelph, Canada. Here, fracture network characteristics and associated influences on hydraulic head were examined using several data types obtained from 24 cored holes in a study that is novel for the quantity and quality of data. High (50–90°) angle joint orientations, heights, and terminations relative to bedding features were determined from acoustic televiewer logs and outcrop scanlines. These data were compared to high-resolution hydraulic head profiles showing head loss over depth-discrete intervals identifying zones with lower vertical hydraulic conductivity. This study reveals that the marl-rich Vinemount Member, traditionally considered the principal aquitard, corresponds to head loss in only 62% of the 24 boreholes. The vertical position of head loss varies across the 90-km2 study area and occurs in any of the lithostratigraphic units of the Lockport Group. Within this sedimentary sequence, aquitards are laterally discontinuous or "patchy" at variable depths and relate to: (1) the frequency of the high-angle joints; (2) shorter joint height; and (3) the type of joint terminations. The head loss occurs in thin (2–2.5 m) intervals where the frequency of the high-angle joints is low. Where a large proportion of small joints cross-cut marl bedding planes, head loss is negligible, suggesting that the vertical hydraulic conductivity is not reduced. Overall, these findings are potentially applicable to assessing aquitard and cap rock integrity in carbonate sedimentary sequences worldwide. [ABSTRACT FROM AUTHOR]

Deep shale has the characteristics of large burial depth, rapid changes in reservoir properties, complex pore types and structures, and unstable production. The whole-rock X-ray diffraction (XRD) analysis, reservoir physical property parameter testing, scanning electron microscopy (SEM) analysis, high-pressure mercury intrusion testing, CO2 adsorption experimentation, and low-temperature nitrogen adsorption–desorption testing were performed to study the pore structure characteristics of marine shale reservoirs in the southern Sichuan Basin. The results show that the deep shale of the Wufeng Formation Longyi1 sub-member in the Luzhou area is superior to that of the Weiyuan area in terms of factors controlling shale gas enrichment, such as organic matter abundance, physical properties, gas-bearing properties, and shale reservoir thickness. SEM is utilized to identify six types of pores (mainly organic matter pores). The porosities of the pyrobitumen pores reach 21.04–31.65%, while the porosities of the solid kerogen pores, siliceous mineral dissolution pores, and carbonate dissolution pores are low at 0.48–1.80%. The pores of shale reservoirs are mainly micropores and mesopores, with a small amount of macropores. The total pore volume ranges from 22.0 to 36.40 μL/g, with an average of 27.46 μL/g, the total pore specific surface area ranges from 34.27 to 50.39 m2/g, with an average of 41.12 m2/g. The pore volume and specific surface area of deep shale gas are positively correlated with TOC content, siliceous minerals, and clay minerals. The key period for shale gas enrichment, which matches the evolution process of shale hydrocarbon generation, reservoir capacity, and direct and indirect cap rocks, is from the Middle to Late Triassic to the present. Areas with late structural uplift, small uplift amplitude, and high formation pressure coefficient characteristics favor preserving shale gas with high gas content and production levels. [ABSTRACT FROM AUTHOR]

Large-scale geological sequestration of CO2 is one of the most effective strategies to limit global warming to below 2 °C, as recommended by the Intergovernmental Panel on Climate Change (IPCC). Therefore, identifying and characterizing high-quality storage units is crucial. The Surma Basin, with its four-way dip closed structures, high-quality reservoirs, and thick regional cap rocks, is an ideal location for CO2 storage. This study focuses on the Bokabil Formation, the most prominent reservoir unit in the Surma Basin. Detailed petrographic, petrophysical, XRD, and SEM analyses, along with mapping, have been conducted to evaluate the properties of the reservoir and cap rock within this formation. The Upper Bokabil Sandstone in the Surma Basin ranges from 270 to 350 m in thickness and consists of fine- to medium-grained subarkosic sandstones composed of 70–85% quartz and 5–12% feldspar, with good pore connectivity. Petrophysical analysis of data from four gas fields indicates that this unit has a total porosity of 21–27.4% and a low shale volume of 15–27%. Cross plots and outcrop observations suggest that most of the shales are laminated within the reservoir. The regional cap rock, known as the Upper Marine Shale (UMS), ranges in thickness from 40 to 190 m and contains 10–40 nm nano-type pores. A higher proportion of ductile materials with a significant percentage of quartz in the UMS indicates higher capillary entry pressures, enhancing its capacity to hold CO2. Using the CSLF method with a 6% cut-off of the available pore volume, it is estimated that 103 Mt, 110 Mt, 205 Mt, and 164 Mt of CO2 can be effectively stored in the Sylhet, Kailashtila, Habiganj, and Fenchuganj structures, respectively. Due to the shallow depth of the storage unit and the thick cap rock, the southern Surma Basin is the optimal location for CO2 injection. [ABSTRACT FROM AUTHOR]

Petrophysical parameters were assessed using comprehensive log data coming from two wells (Ns-2, Ns-4) located within the Mishrif, Rumaila, Ahmadi, and Mauddud formations within the Nasiriya oil field, Iraq. The logs were digitized using Techlog 2015 software, and environmental modifications were implemented to guarantee precise interpretations. The shale volume used to be determined using gamma ray (GR) logs, subsequently leading towards the calculation of the effectiveness porosity. Water saturation is used to be calculated alongside Archie's equation. The investigation indicated that the lithology regarding the Mishrif, Rumaila, Ahmadi, and Mauddud formations happens to be predominantly limestone, alongside calcite like the principal mineral within the matrix. All formations were found to contain water like the fluid type, except within favor regarding the Mishrif formation at the 2013–2046 m within Ns-2, and 2000–2060 m within Ns-4, where hydrocarbons were identified. The top strata for these depths comprise substantial shale alongside limited effective porosity, serving like cap rock at the depths from 2013 to 2016 m within Ns-2, and 2000 towards 2006 m within Ns-4. [ABSTRACT FROM AUTHOR]

Field and petrographic studies of the Qishn Formation provide insights in to sequence stratigraphic and reservoir attributes of the formation. The reservoir properties are controlled by complex interaction between depositional textures and diagenetic products. The Barremian-Aptian Qishn Formation was deposited between Precambrian basement rocks and marl-dominated Albian Kharfort Formation. The Qishn Formation consists of lower sandstone (Shabon Member), middle unit dominated by lime mudstone (Hinna Member), and upper bioclastic limestone with dolostone interbeds (Hasheer Member). The formation defines a transgressive-regressive sequence with maximum flooding surface (MFS) at the top of the Hinna Member. The petrographic and diagenetic analyses indicate that Shabon and Hasheer members constitute good reservoirs. The Shabon Member is dominated by friable medium- to coarse-grained arkose to lithic arenite with porosity as high as 20%. Despite a burial depth of ~ 5 km, the sandstone maintains most of its intergranular pores. The diagenetic features include early calcite cement followed by burial compaction. However, since most of the pores were already filled by calcite cement, volumetric reduction due to compaction was minimal. Post-compaction dissolution of the early calcite cement resulted in restoration of the intergranular pores. The Hasheer Member consists of extensively cemented bioclastic packstone to rudstone with porosity < 6% and sucrosic dolomite with intercrystalline and vuggy pores reaching up to 15%. The mud-dominated Hinna Member can be considered as potential cap rock for any fluids within the Shabon Member, whereas the marls of the Kharfot Formation constitute potential caprock for the preservation of fluids in the Hasheer Member. [ABSTRACT FROM AUTHOR]

To prevent or reduce the loss caused by land subsidence in delta region, the land subsidence of the Zhuangxi–Wuhaozhuang oil area in Shengli Oilfield is predicted based on the elastic theory of porous medium and classical consolidation theory, and the prediction results are analyzed and verified by numerical simulation. The influencing factors and mechanism of land subsidence in delta resource exploitation area are studied. The research shows that: (1) the land subsidence in delta resource exploitation area is mainly caused by the underground brine exploitation, oil exploitation, consolidation of loose sediments, shallow groundwater exploitation, and soil load consolidation. The maximum land subsidence rate obtained by numerical simulation is 22 mm/a for single oil well and 81 mm/a for single brine well. (2) Pore pressure, physical and mechanical parameters of oil and brine reservoirs, development mode, and development degree are influencing factors of land subsidence in delta resource exploitation area, and pore pressure, permeability, and reservoir burial depth are controlling factors. (3) The exploitation wells in the Zhuangxi–Wuhaozhuang oil area are dense, and the influence range of land subsidence of different exploitation wells overlaps, which further aggravates the uneven land subsidence, and makes the result of InSAR subsidence monitoring larger. [ABSTRACT FROM AUTHOR]

Porous sandstone geothermal water is an important geothermal resource, which is a low-carbon and clean resource, but lacks systematic research on a regional scale. The northern part of Jinan City is rich in geothermal resources, specifically porous sandstone thermal reservoirs. However, there is still incomplete research on the mechanism of geothermal genesis and the hydrochemical characteristics of geothermal water in porous sandstone. This study aims to address this gap by collecting 21 groundwater samples from northern Jinan and comparing their conventional ion and isotope characteristics to investigate the hydrochemical characteristics during the formation of geothermal water and uncover the genesis mechanism of porous sandstone geothermal water. The results indicate that the geothermal water is classified as Na-Cl type and Na-SO4-Cl type. The hydrochemical characteristics of geothermal water are primarily influenced by water–rock interaction and groundwater mixing. The water source primarily comes from the atmospheric precipitation in the Taiyi mountains, with an altitude of 910.75–1542.2 m.s.a.l.. The estimated temperature of the thermal reservoir ranges from 51 to 78 °C, and the depth of geothermal water circulation is estimated to be between 1316 and 2216 m. Based on the characteristics of the geothermal field, including the "cap rock, water source, heat source, reservoir, and channel," a conceptual model of the porous sandstone geothermal water flow system is proposed. This model offers novel insights into the genesis mechanism of geothermal water under similar geological conditions. [ABSTRACT FROM AUTHOR]

Hydrocarbon enrichment in faulted basins is often controlled by the activity of faults with some degree of sealing capacity. However, the rules that control the migration and accumulation of hydrocarbons in reservoirs dominated by faults are poorly understood. The Liuzhuang fault in the Bohai Bay Basin is selected for hydrocarbon migration and accumulation research. Interpretation of seismic and log data, tests of rock mechanics, and quantitative fluorescence analysis are used to quantitatively evaluate the migration of hydrocarbons. The results reveal that the Liuzhuang fault has been a long-term active fault since the Cenozoic with gradually reduced fault activity from the NE to the SW. At least four fault-bounded traps with various degrees of trap filling in the lower segment of the first member of Shahejie Formation (Es1L) were identified in the hanging wall of this fault. This differences in the degree of filling are related to the continuity of the smear structure that formed from the Es1m cap rock in the brittle‒ductile transition stage. The development degree of the smear structure, which is quantitatively evaluated by the shale smear factor (SSF) and shale gouge ratio (SGR), directly affected the fault sealing capacity. Therefore, three cases of hydrocarbon migration and accumulation, i.e., continuous smearing along the fault and complete fault sealing with SSF values of < 3, reduced continuity of the smear structure and partial fault sealing with SSF values in the range of 3–5, and discontinuous smearing and ineffective fault sealing with SSF values of > 5, were defined. The new results have implications for further exploration in faulted basins, including the Bohai Bay Basin. [ABSTRACT FROM AUTHOR]

Thermal pressurization of the trapped pore fluid is considered to be a widespread fault weakening during fluid injection in confined geological formations. Tremendous amounts of heats will be generated within the narrow shear zone during fault slip. Considering the melting of the fault gouge, the fault seal zone is adopted to construct the fluid pressurization model, thermal pressurization implemented in Comsol Multiphysics is established to illustrate the fault weaken coefficient and effective normal stress during fluid injection. The friction weakening coefficients mT and mF are proposed to research the performance of fault weakening during fluid injection. The results indicate that, the friction coefficients mT and mF both exhibit the initially decreasing and then increasing tendency, and thermal-induced fault weakening of CO2 injection occurs earlier than that of water injection. It was found that initial pore pressure and fault sealing porosity have a negligible influence on the evolutions of friction weakening and effective normal stress. Initial normal stress and fault sealing permeability have certain obvious influences on fault weakening during CO2 injection. Fault thickness is the primary factor influencing the friction weakening coefficient. When the fault thickness is over 1 mm, the variation of fault weakening is totally different from that when the thickness is less than 1 mm. This investigation of friction weakening during fault slip provides an effective reference for fluid injection. [ABSTRACT FROM AUTHOR]

The Campi Flegrei caldera is characterized by the phenomenon of bradyseism, as evidenced by stratigraphic records of alternate oceanic and continental sediments dating back over a thousand years. Since 2005, the caldera has been in a phase of unrest, which is increasing volcanic deformations and associated seismicity around the region, resulting in a growing concern over the dense population in the inhabitation. Recent studies have highlighted that the caldera dynamics are driven by a combination of endogenous processes and modulation phenomena induced by exogenous processes, e.g., rainfall, atmospheric pressure, and tidal loading. Although the complex feedback mechanisms of both endogenous and exogenous processes are still under debate, the present study is focused on the increased potential of modulation due to exogenous processes with the increase or evolution in the degree of inflation of the magma chamber. Specifically, Campi Flegrei volcanic system shows sensitivity to seasonal hydrological cycles during slower rates of inflation and to short-period tidal modulations during higher rates of inflation. The observed seasonal modulations of seismic activity are explained in terms of water infiltration into the shallow aquifers, basins, and vent depression system of the caldera. The rainfall-induced pore pressure build-up also favours the instability of the brittle cap rock, promoting seismicity. In addition, this study suggests that the tidal loadings provide horizontal NS extensions to the mostly NW–SE, NE–SW, and EW-oriented scattered fractures and further contribute towards fracture propagation. During this process, a cyclic opening and sealing of fractures by volatile outgassing and silicate settling may, respectively, produce the episodic behaviour of the seismicity. The seismicity in relation to exogenous processes imposed by seasonal rainfall and tidal loadings shows that the degree of correlation depends on the different rates of inflation. The long-period seasonal modulations and short-period tidal modulations during the evolution of the degree of inflation are finally interpreted in the framework of the fault resonance destabilization model, under rate-and-state dependant frictional formalism. [ABSTRACT FROM AUTHOR]

Passive seismic activity measurements in the Way Ratai geothermal field are needed to identify near-surface features. In addition to the ease of measurement, passive seismic methods can be an initial solution in characterizing geological conditions. This study aims to characterize near-surface features using the dominant frequency ( f 0 ) pattern and 3D modeling of the shear wave velocity ( V s ). A total of 70 measurement points with intervals between points of approximately 500 m are scattered in the southern area of Mount Ratai. The f 0 curve was obtained using the horizontal-to-vertical spectral ratio (HVSR) method, while 3D modeling uses OpenHVSR. The characteristics of the surface rock layer identified by f 0 pattern is in the range of 0.2–2 Hz. Furthermore, the Kali Tiga and Margodadi fields show thick soft rock patterns near the surface, with an f 0 values between 0.6 and 0.8 Hz. The cross-section of the 3D model at a depth of 10 and 25 m is dominated by stiff soil layers, while at a depth of 35 m, it becomes very dense soil and soft rock. The characteristic of shear wave velocity ( V s ) in the geothermal field influenced by the clay alteration near the surface, ranging from 175 to 350 m/s. These results can explain the possibility of a thick cap rock layer feature in the Way Ratai geothermal field. [ABSTRACT FROM AUTHOR]

The hydrocarbon accumulation modes and differences in the Tethyan realm serve as a hot research topic in the petroleum geology community at home and abroad. Both the Persian Gulf Basin in the Middle East and the Sichuan Basin in China, situated on the southern and northern sides of the Tethyan realm, respectively, record the whole geological process of the opening and closure of the Prototethys, the Paleotethys, and the Neotethys sequentially, exhibiting anomalous hydrocarbon enrichment Based on the analysis of the plate tectonic evolution in the Tethyan realm, this study dissects the structures and hydrocarbon accumulation conditions of both basins. Followed by a systematic comparative analysis of the factors controlling hydrocarbon enrichment in the process of plate breakup and convergence in the Tethyan realm, this study proposes petroleum exploration targets in the realm. The results are as follows: (1) Since the Meso-Neoproterozoic, the Persian Gulf Basin and the Sichuan Basin have undergone similar tectonic evolution in the early stage but different in the late stage. Under the influence of the formation and evolution of the Prototethys, Paleotethys, and Neotethys oceans, both basins experienced multi-stage development and modification, forming two major extension-convergence cycles. Consequently, both basins are characterized by the vertical orderly superimposition of various basin prototypes in the order of rift-intracratonic basin (passive continental margin)-foreland. (2) The fact that the Tethyan realm was long located at medium-low latitudes and the local anoxic environment formed in the process of plate breakup and convergence played a vital role in the formation of extensive source rocks. The source rocks are predominantly distributed in underfilled rifts and deep depressions that were connected to the ocean in the unidirectional continental breakup process; basin-slopes and intra-shelf basins on passive continental margins; basinal lows within intracratonic basins, and underfilled foredeeps in foreland basins. The favorable areas for the formation of carbonate reservoirs include platform margins, submarine highs and paleo-uplifts within platforms, and fault zones. The evaporite cap rocks, intimately associated with the basin evolutionary stages and global dry-hot events, are critical for large-scale hydrocarbon preservation. (3) Under the influence of Tethyan evolution, the Persian Gulf Basin and the Sichuan Basin share similar primary factors controlling hydrocarbon enrichment. The moderate tectono-sedimentary differentiation and structural modification in the process of prototype basin superimposition, as well as the spatio-temporal matching of elements critical for hydrocarbon accumulation, are beneficial for the development of large oil and gas fields. The macroscopic hydrocarbon distribution is dictated by source rock-cap rock assemblages, while the local hydrocarbon distribution is governed by trap-reservoir assemblages. The critical factors determining the differential hydrocarbon enrichment in the Persian Gulf Basin and the Sichuan Basin include plate size and position, basement stability, eustatic movement, paleoclimate, and tectonic transformation. Besides, different tectonic modification intensities are closely related to the type, enrichment degree, and distribution of hydrocarbon reservoirs. [ABSTRACT FROM AUTHOR]

The sealing characteristics of the geological formation located above a CO2 storage reservoir, the so-called caprock, are essential to ensure efficient geological carbon storage. If CO2 were to leak through the caprock, temporal changes in fluid geochemistry can reveal fundamental information on migration mechanisms and induced fluid–rock interactions. Here, we present the results from a unique in-situ injection experiment, where CO2-enriched fluid was continuously injected in a faulted caprock analogue. Our results show that the CO2 migration follows complex pathways within the fault structure. The joint analysis of noble gases, ion concentrations and carbon isotopes allow us to quantify mixing between injected CO2-enriched fluid and resident formation water and to describe the temporal evolution of water–rock interaction processes. The results presented here are a crucial complement to the geophysical monitoring at the fracture scale highlighting a unique migration of CO2 in fault zones. [ABSTRACT FROM AUTHOR]

In Carbon Capture and Storage (CCS) procedures, it is important to determine the stability of the wellbore during carbon dioxide (CO2) injection and part of this involves assessing stresses on the rock near the wellbore due to changes in temperature and pressure. To address this, this study investigated the influence of cooling on the mechanical properties of a sandstone typical of those found in the central and southern North Sea. A series of uniaxial and triaxial compression tests was conducted on dry and saturated sandstone samples to determine the effects of cooling on the strength and stiffness under different confining pressures. The elastic modulus, shear modulus, bulk modulus and Poisson's ratio were determined for three temperature conditions and three pressures representing different depths in a wellbore. Two methods, the International Society of Rock Mechanics (ISRM) and Wood's (Soil behaviour and critical state soil mechanics. Cambridge University Press, Cambridge, 1990), were used to determine the mechanical properties of the rock during the Uniaxial Compressive Strength (UCS) tests. For the triaxial test, only Wood's (1990) method was applied due to the existence of confining pressure. Microstructural analysis on thin sections of the sandstones under plane and crossed polarised light conditions in the deformed and undeformed state was conducted to elucidate deformation mechanisms and aid interpretation of experimental results. It was identified that both an increase in confinement and a reduction in temperature, increased the strength of the sandstone and reduced the Poisson's ratio. Additionally, by decreasing the temperature, especially in the UCS test the material dilated less. This is an important outcome as expanding the results to a wellbore stability problem, brittle behaviour may be more apparent and damage may occur when sub-zero injection temperatures are applied, especially at the wellbore head, where confinement is low. Highlights: UCS and triaxial tests on Stainton Sandstone at 15 ℃, − 5 ℃ and − 10 ℃ were used to determine the influence of temperature drop on Poisson's ratio and different mechanical moduli. Wood's (1990) method for determining the mechanical properties of rock using critical state mechanics can also be applicable to UCS tests. Microscopic analysis of sandstone sample before and after the UCS and triaxial tests indicated dilation and grain realignment, which result in Poisson's ratios greater than 0.5. Expanding the experimental results to CCS challenges, the wellbore head is the most vulnerable to sub-zero temperatures due to lack of confinement. [ABSTRACT FROM AUTHOR]

High total organic sulfur (TOS) content (i.e., Type IIS kerogen) is well known to significantly influence kerogen transformation but the effect of TOS content on the evolution of organic porosity has only rarely and indirectly been investigated. This study demonstrates that organic porosity is generated at lower thermal maturity in mudstones containing Type IIS kerogen relative to those with Type II kerogen. To our knowledge this phenomenon has not been previously demonstrated. The implications are relevant for the characterization of organic-rich mudstones as cap rocks, hydrocarbon reservoirs, and disposal reservoirs for CO2 or nuclear waste because pore systems control storage volumes and matrix fluid flow. Five thermally immature core samples were selected from three organic-rich mudstone units with low to high TOS content: the late Devonian Duvernay Formation (Canada), middle late Miocene Onnagawa Formation (Japan), and early Jurassic Gordondale member of the Fernie Formation (Canada). Hydrous pyrolysis was used to artificially mature splits of the immature samples to four maturity stages, upon which petrophysical and organic geochemical properties were measured and compared to baseline immature samples. Most porosity growth in Type IIS samples occurred below 0.70% VRoeqv, but in Type II samples was broader and robust until 1.1% VRoeqv. [ABSTRACT FROM AUTHOR]

The Guantao Formation is the most important reservoir with significant faces developed, and this is different from the near-source accumulation of Nanpu sag. Guantao Formation in Matouying Uplift was found far away from the source area, which is a typical accumulation outside sources. What is the difference on accumulation condition and main controlling factors between the far-source accumulation and near-source accumulation? And what is the reasonable explanation for these reservoirs? According to the main controlling factors of Guantao Formation reservoir in Matouying Uplift, the abundant accumulation in hydrocarbon generation sag, efficient transport system and good spatial and temporal configuration of reservoir cap rock are the main controlling factors for its hydrocarbon accumulation outside sources. The hydrocarbon movement follows a migration model when it passes through a multiple faulted terrace zone and an effective connection to faults has an increase in the hydrocarbon abundance. The determination of oil sources and the correct understanding of the transport system are the keys to the reservoir understanding of the Guantao Formation in Matouying Uplift, as well as to the establishment of the reservoir model and the prediction of favorable oil and gas development areas. It provides enlightenment for the exploration of reservoir outside sources in peripheral convex and although oil and gas displays have been seen during single-well drilling, no large-scale reservoirs have been discovered until the industrial flow of oil and the results enrich the future exploration trend and potential areas in the uplift around the Nazione and Npu sag are determined. [ABSTRACT FROM AUTHOR]

The gas sealing capacity of caprock (SCC) is one of the key factors that determine whether aquifer trap can be constructed into underground gas storage (UGS). However, no standard protocol for evaluating SCC of candidate aquifers has been proposed. Based on the core observation, laboratory experiment, and well logging data, the sealing capacity of the target aquifer caprock of Permian mudstone in D5 block of Litan sag, China, is quantitatively evaluated. The important parameters of mineral brittleness, permeability, breakthrough pressure (BP), mechanical brittleness, thickness, and areal extent that affect the SCC are determined. The results of specific tests and data statistics show that the caprock of D5 block is a low permeability rock with a permeability of 10−4 mD, and the BP of undisturbed rock is greater than 38 MPa. Although the brittle mineral quartz is abundant with an average of 38.38%, the mechanical brittleness is not strong under formation conditions. The direct caprock has a thickness of greater than 50 m, and on the top of it is a high-quality indirect caprock that complements the physical closure. The results of a mathematical evaluation model show that except for the sealing index of sample 2, all the other samples have optimal sealing capacity. The field interference test shows that the optimal sealing capacity of the caprock meets the requirements of the construction of underground gas storage (UGS). The rationality of the comprehensive evaluation model can provide a reference for similar evaluation projects in the future. [ABSTRACT FROM AUTHOR]

CO2 uptake by smectites can cause swelling and self-stressing in shallow clay-rich caprocks under CO2 storage P–T and constrained conditions. However, little data exist to constrain the magnitude of the effects of CO2-H2O-smectite interactions on the sealing properties of clay-rich caprocks and faults. We performed permeability experiments on intact and fractured Opalinus Claystone (OPA) cores (~ 5% smectite), as well as on a simulated gouge-filled faults consisting of Na-SWy-1 montmorillonite, under radially constrained conditions simulating "open" transport pathways (dry and variably wet He or CO2; 10 MPa fluid pressure; 40 °C). Overall, the flow of dry CO2 through intact OPA samples and simulated smectite fault gouge caused a decrease in permeability by a factor of 4–9 or even by > 1 order, compared to dry He permeability. Subsequent to flow of dry and partially wet fluid, both fractured OPA and simulated gouge showed a permeability reduction of up to 3 orders of magnitude once flow-through with wet CO2 was performed. This permeability change appeared reversible upon re-establishing dry CO2 flow, suggesting fracture permeability was dominated by water uptake or loss from the smectite clay, with CO2-water-smectite interactions play a minor effect. Our results show that whether an increases or decreases in permeability of clayey caprock is expected with continuous flow of CO2-rich fluid depends on the initial water activity in the clay material versus the water activity in the CO2 bearing fluid. This has important implications for assessing the self-sealing potential of fractured and faulted clay-rich caprocks. Highlights: Permeability of potential clay-rich caprock (Opalinus Claystone) was systematically measured using variably wet CO2 versus He. Through-flow of dry CO2 caused a decrease in permeability of intact Opalinus Claystone and simulated smectite fault gouge by up to > 1 order, as composed to dry He. Fractured Opalinus Claystone and simulated gouge showed a permeability reduction of up to 3 orders of magnitude with through-flow of wet CO2. Permeability decrease by through-flow of variably wet CO2 appeared reversible upon re-establishing dry CO2 flow. The initial water activity in the clay material versus the water activity in the CO2 bearing fluid determines change in permeability upon CO2 flushing. [ABSTRACT FROM AUTHOR]

We present a 3D high-resolution modeling methodology based on the interpretation of gravity gradient data and its joint inversion with the simulated annealing (SA) global optimization method. The geometry of the model, used as computational domain in the solution of the forward and inverse problems, is defined with an irregular ensemble of cubic prisms that recreates the interpreted shape of the target, derived from the results of applying different interpretation methods to the gravity gradient data. In our inversion approach, the linear inverse problem resulting from the domain discretization is not solved. Instead, the cost function is explored with the SA algorithm, its low misfit region is identified, and models belonging to it are selected for obtaining the mean model, which represents the most likely model among them, as well as for estimating its uncertainty. The SA inversion algorithm we applied was numerically optimized to reduce the computational burden required by the forward problem, and it was driven by optimal tuning parameters, determined by a parametric analysis. Tests on synthetic data show the efficiency of our methodology to obtain a model that approximates the synthetic target and the usefulness of the estimated uncertainty to complement the interpretation. Finally, by applying our methodology to gravity gradient data acquired over the Vinton dome located in Louisiana, USA, we obtained results that are in agreement with geological information and previous studies. [ABSTRACT FROM AUTHOR]

Acidizing is one of the most used stimulation techniques in the petroleum industry. Several reports have been issued on the difficulties encountered during the stimulation operation of the Ahdeb oil field, particularly in the development of the Mishrif reservoir, including the following: (1) high injection pressures make it difficult to inject acid into the reservoir formation, and (2) only a few acid jobs have been effective in Ahdeb oil wells, while the bulk of the others has been unsuccessful. The significant failure rate of oil well stimulation in this deposit necessitates more investigations. Thus, we carried out this experimental study to systematically investigate the influence of acid treatment on the geomechanical properties of Mi4 formation of the Mishrif reservoir. The acid core-flood experiments were performed on seven core samples from the oil reservoir in central Iraq. The porosity, permeability, acoustic velocities, rock strength, and dynamic elastic parameters were computed before and after the acidizing treatment. To determine the optimal acid injection rate, different injection flow rates were used in the core-flooding experiments. The propagation of an acid-induced wormhole and its effect on the rock properties were analyzed and compared to that of intact rocks. Computed tomography (CT) scan and a 3D reconstruction technique were also conducted to establish the size and geometry of the generated wormhole. To analyze the influence of mineralogical variation and heterogeneity and confirm the consistency of the outcomes, acidizing experiments on different rock samples were conducted. The results demonstrate that for all the rock samples studied, the mechanical properties exhibit rock weakening post-acid treatment. The Young's modulus reduced by 26% to 37%, while the Poisson's ratio, the coefficient of lateral earth pressure at rest, and the material index increased by 13% to 20%, 23% to 32%, and 28% to 125%, respectively. The CT scan visually confirmed that the acid treatment effectively creates a pathway for fluid flow through the core. [ABSTRACT FROM AUTHOR]

We provide timestamps for the major zinc-lead (Zn-Pb) Mississippi Valley-type Black Angel deposit (Greenland) based on new pyrite rhenium-osmium (Re-Os) isotope geochemistry data: (1) a Re-Os isochron age 1,884 ± 35 million years ago (Ma – 2σ, 1.8%) for subhedral pyrite cemented by sphalerite ± galena in dolomitized clean limestone, and, (2) a Re-Os model age 1,828 ± 16 Ma (2σ, 0.9%) for epigenetic massive pyrite in siltstone/mudstone cap rock. Zinc-lead mineralization in evaporite-bearing carbonates in the Karrat Basin took place ca. 1,884 Ma at the time of far-field fluid flow associated with back-arc spreading ca. 1,900–1,850 Ma. Mineralization predates the development of the Rinkian foreland basin (ca. 1,850 – < 1,800 Ma) and a collisional stage (ca. 1,830 – < 1,800 Ma) in the context of the telescoping Rinkian and the Nagssugtoqidian Orogens. Replacement of clean carbonate and sustained acid neutralization led to significant sphalerite precipitation ca. 1,884 Ma. Conversely, precipitation of epigenetic massive pyrite in the cap rock ca. 1,828 Ma may signal (1) the lack of chemical reactivity of the cap rock for the pH-buffered conditions needed for Zn-Pb mineralization, and (2) the unfavorable impact of incipient regional Rinkian metamorphism (ca. 1,830–1,800 Ma) and tectonic compression on aquifer permeability and continued brine migration. The initial 187Os/188Os ratio (Osi-pyrite = 1.07 ± 0.32) from isochron regression identifies a crustal origin for Os and, by corollary, other metals in the ca. 1,884 Ma Zn-Pb mineralization. Although the Rae Craton basement rocks comprise the dominant source for metals (based on our Osi-pyrite and δ66Znpyrite/sphalerite data), we identify a complementary contribution in Zn (maximum 12–24%) from Paleoproterozoic sedimentary carbonate. This source of Zn in sedimentary calcite is deemed possible in the context of Paleoproterozoic seawater at high Na/Cl ratio and in the absence of Zn-based eukaryotic metabolism in shallow marine environment. [ABSTRACT FROM AUTHOR]

The polyphasic evolution of the testimonial buttes in the central area of the Ebro basin (Los Monegros) is analysed. This is a semiarid area that favours high erosion rates. An evolutionary model of the Jubierre hills is presented that shows the environmental cycles represented by aggradational and degradative processes on the slopes that resulted in the present arrangement of talus flatiron rings. In the four studied cases, talus relicts are composed of detritic material from a disappeared caprock pediment. Four slope stages (S4 to S1) that formed under stable climate conditions are identified. Older stages (S4 and S3) are estimated by comparison with other talus flatirons in the region. The S2 stage contains Bronze Age archaeological remains and the radiocarbon age obtained was 1608–1446 years cal BC (2σ), while S1 is younger. A palaeoenvironmental interpretation was made for these aggradational stages (S4 to S1). The active erosion of these hills led to a relief inversion, and talus flatirons remain as the only features revealing the presence of the relict hills and past human occupations. [ABSTRACT FROM AUTHOR]

Absence of a permeability log necessary to assess reservoir quality and injectivity for potential CO2 storage in the heterogeneous and complex South Georgia Rift (SGR) basin provides the motivation for this study. The focus of this study was on the Triassic-Jurassic red beds buried, entrenched beneath the Cretaceous-Cenozoic Coastal Plain sediments. Moreover, the significant cost typically between $10 M and $100 M associated with drilling and logging for in situ permeability coupled with the limited resolution of existing core data further makes this work necessary. The purpose is to relate, use the interpretation of the predicted permeability distribution to assess feasibility for safe and long-term CO2 sequestration. This study also intends to establish the impacts of active and passive tectonism that has shaped and/or re-shaped the evolution of the basin on the present-day permeability. A methodology was applied that utilizes the pore space and geohydraulic properties of the reservoir from existing laboratory and well data to produce a newly derived permeability log. It shows a non-uniform distribution with depths possibly due to geologic changes in the confined and heterogeneous red beds. The derived log displays characteristics consistent with observations from the porosity and resistivity logs. The interpretation of these logs provides evidence for the presence of low permeable, tightly cemented, and compacted red beds. We conclude that the low permeability aided by the low resistivity depicted in the red beds suggests increased confining stress and reduced injectivity, and that the uncharacteristically low permeability reflects a deformed basin shaped with episodes of uplift and erosion. [ABSTRACT FROM AUTHOR]

This study evaluates the chemo-mechanical influence of injected CO2 on the Morrow B sandstone reservoir and the upper Morrow shale caprock utilizing data from the inverted 5-spot pattern centered on Well 13-10A within the Farnsworth unit (FWU). This study also seeks to evaluate the integrity of the caprock and the long-term CO2 storage capability of the FWU. The inverted 5-spot pattern was extracted from the field-scale model and tuned with the available field observed data before the modeling work. Two coupled numerical simulation models were utilized to continue the study. First, a coupled hydro-geochemical model was constructed to simulate the dissolution and precipitation of formation minerals by modeling three intra-aqueous and six mineral reactions. In addition, a coupled hydro-geomechanical model was constructed and employed to study the effects of stress changes on the caprock's porosity, permeability, and ground displacement. The Mohr–Coulomb circle and failure envelope were used to determine caprock failure. In this work, the CO2-WAG injection is followed by the historical field-observed strategy. During the forecasting period, a Water Alternating Gas (WAG) injection ratio of 1:3 was utilized with a baseline bottom-hole pressure constraint of 5500 psi for 20 years. A post-injection period of 1000 years was simulated to monitor the CO2 plume and its effects on the CO2 storage reservoir and caprock integrity. The simulation results indicated that the impacts of the geochemical reactions on the porosity of the caprock were insignificant as it experienced a decrease of about 0.0003% at the end of the 1000-year post-injection monitoring. On the other hand, the maximum stress-induced porosity change was about a 1.4% increase, resulting in about 4% in permeability change. It was estimated that about 3.3% of the sequestered CO2 in the formation interacted with the caprock. Despite these petrophysical property alterations and CO2 interactions in the caprock, the caprock still maintained its elastic properties and was determined to be far from its failure. [ABSTRACT FROM AUTHOR]

Bridges designed following a conventional approach minimize the risk of collapse, but often require challenging, costly, and time-consuming restoration after an earthquake occurs. The new seismic design philosophy requires bridges to maintain functionality even after severe earthquakes. In this context, this paper proposes a controlled rocking pile foundation (CRPF) system and numerically evaluates bridges′ degree of seismic resilience. The CRPF system allows a pile cap to rock on a pile foundation and dissipate seismic energy through inelastic deformations of replaceable bar fuses that connect a pile cap and piles. Following the conceptual design of the CRPF system, two analytical models were developed for a bridge pier utilizing the CRPF system and a pier designed to develop a plastic hinge in its column. The analytical results indicate that, after experiencing a severe earthquake, a conventionally designed bridge pier sustained substantial damage in its column and exhibited significant residual displacement. In contrast, a pier using the CRPF system showed negligible residual displacement and maintained elastic behavior except, as expected, for bar fuses. The damaged fuses can be rapidly replaced to recover bridge seismic resistance following an earthquake. Therefore, the CRPF system helps to achieve the desired post-earthquake performance objectives. [ABSTRACT FROM AUTHOR]

In this study, it is aimed to characterize the Early pliocene sandstone (EP-SD) and the Late Miocene-Early Pliocene Mangaa sandstone reservoirs and the efficiency of their sealing cap rocks using the petrographical and petrophysical data of these sandstone zones in northern Taranaki basin, New Zealand. The prospective potential reservoirs were studied using impregnated thin sections, XRD data analysis, and well log data (self-potential, gamma-ray, sonic, density, neutron, shallow\deep resistivity and PEF) to characterize the reservoir zones, in addition to Mercury intrusion capillary pressure data (MICP) to check the efficiency of some potential seals. The EP-SD and the Mangaa sandstone units are typically poorly consolidated very fine sandstone to siltstone, with porosities averaging 25%. The sands are composed of quartz (38.3–57.4%), with common feldspars (9.9–15.2% plagioclase, and 2.7–6.3% K-feldspars) and up to 31.8% mica. In Albacore-1 well to the north of the Taranaki Basin, the Mangaa formation includes three separate for each of the EP-SD zones (EP-SD1, EP-SD2, and EP-SD3), and the Mangaa sequence (Mangaa-0, Mangaa-1, and Mangaa-2). The thin section studies indicate that, the studied samples are grouped into greywackes, arenites and siltstone microfacies with much lithic fragments and feldspars, sometimes with glauconite pellets. From the XRD data, it is achieved that the mineral composition is dominated by quartz, mica/illite, feldspars, and chlorite. The petrophysical investigation revealed absence of pay zones in the EP-SD zones, and presence of thin pay zone with net thickness 5.79 m and hydrocarbon saturation of about 25.6%. The effective porosities vary between 23.6 and 27.7%, while the shale volume lies between 12.3 and 16.9%. Although the shale content is relatively low, the relatively high API (50–112 API of average 75 API) is contributed by the relatively high K-feldspar content and intercalations with thin siltstone and muddy siltstone beds. Sealing units include the intra-formational seals within the Mangaa sequence, mudstones and fine grained units overlying the Mangaa and further intra-formational mudstones, within the shallower EP-SD units. The efficiency of these seals indicates the capability to trap 16.4–40.6 m gas or 17.4–43.0 m oil which is relatively low in correlation with their efficiency in the central parts of the Taranaki Basin Overlying the primary seals, mudstones of the Giant Foresets Formation provide additional regional seal. [ABSTRACT FROM AUTHOR]

Coalbed methane is a risk of coal mining safety while being an important energy source, and gas extraction is the most effective treatment method. However, roadway and borehole surrounding rock fracture lead to air leakage and thus reduce gas extraction efficiency. To determinate the surrounding rock fracture zone and improve the borehole sealing effect, this work proposed a new method based on constant-pressure gas injection. The feasibility of this method is validated by combining theoretical analysis, numerical simulation and field tests. Results showed that: (1) as the drilling depth grew from 5 to 13 m, the injected-gas flow rate dropped quickly from 41.2 to 10.0 L/min, and then fluctuated slightly to 11.7 L/min, obtaining the minimum flow rate at 9 m, which indicated that the width of the roadway surrounding rock fracture zone was 9 m. (2) The mathematical model of coal stress, permeability and damage evolution were built to describe the gas flow during the gas injection in different borehole depths. The numerical simulation reflects that the injected gas mainly leaks through walls of the roadway rather than along the borehole, with the former being 6.5 times of the latter. (3) The gas extraction concentration increased from about 20% to more than 30% when the sealing depth grew from 8 to 10 m, which indicated the sealing depth of gas extraction boreholes shall be slightly larger than 9 m. This proves that the constant-pressure gas injection method can offer effective references in determining the roadway surrounding rock fracture zone and gas extraction boreholes sealing depth. Highlights: A new method for determining the sealing depth based on the constant-pressure gas injection was proposed. The mathematical model of coal stress, permeability and damage evolution was built. The leakage characteristics during gas injection in borehole were investigated. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing is widely accepted as a geotechnical application that can be used to enhance productivity in unconventional reservoirs. However, if the hydraulic fracture is not contained within a single stratigraphic interval, the fracture treatment could harm the integrity of the caprock, and even threaten underground drinking water. Thus, for the purpose of effectively and economically recovering oil/gas from reservoirs, it is critical for the industry to understand the key parameters needed to restrict the vertical growth of massive hydraulic fractures. To this end, we introduce a comparative hydro-mechanical coupling finite element model to describe the initiation and propagation of a hydraulic fracture. The material properties and the stress field of the model are determined by the field logging data and field hydraulic fracture test. The significance of key parameters to fracture height were concluded from a statistical perspective, to thoroughly investigate the effects of key factors in determining fracture height containment, we present an uncertainty analysis of the in situ stress and intrinsic properties of the target sandstone layer and overlying mudstone. The results show that the minimum horizontal in-situ stress contrast at the caprock/reservoir interface, referred to as a stress barrier, is the most important factor for hydraulic fracture containment. A larger stress barrier hinders the fracture height elongation and increases the fracture width. Under the same stress contrast conditions, the effect of a material barrier on fracture containment is dominated by the contrast of Poisson's ratio at the caprock/reservoir interface, once the fracture tip penetrates the interface, the caprock a with lower Poisson's ratio would effectively hinder fracture propagation, the Young's modulus contrasts are probably not an important parameter in terms of directly controlling the fracture height, whereas a higher Young's modulus in both the caprock and reservoir would generally enhances the fracture height. [ABSTRACT FROM AUTHOR]

The Los Humeros Volcanic Complex has been characterized as a suitable target for developing a super-hot geothermal system (> 350 °C). For the interpretation of geophysical data, the development and parametrization of numerical geological models, an extensive outcrop analogue study was performed to characterize all relevant key units from the basement to the cap rock regarding their petrophysical properties, mineralogy, and geochemistry. In total, 226 samples were collected and analyzed for petrophysical and thermophysical properties as well as sonic wave velocities and magnetic susceptibility. An extensive rock property database was created and more than 20 lithostratigraphic units and subunits with distinct properties were defined. Thereby, the basement rocks feature low matrix porosities (< 5%) and permeabilities (< 10–17 m2), but high thermal conductivities (2–5 W m−1 K−1) and diffusivities (≤ 4·10–6 m2s−1) as well as high sonic wave velocities (≥ 5800 m s−1). Basaltic to dacitic lavas feature matrix porosities and permeabilities in the range of < 2–30% and 10–18–10–14 m2, respectively, as well as intermediate to low thermal properties and sonic wave velocities. The pyroclastic rocks show the highest variability with respect to bulk density, matrix porosity (~ 4– > 60%) and permeability (10–18–10–13 m2), but feature overall very low thermal conductivities (< 0.5 W m−1 K−1) and sonic wave velocities (~ 1500–2400 m s−1). Specific heat capacity shows comparatively small variations throughout the dataset (~ 700–880 J kg−1 K−1), while magnetic susceptibility varies over more than four orders of magnitude showing formation-related trends (10–6–10–1 SI). By applying empirical correction functions, this study provides a full physiochemical characterization of the Los Humeros geothermal field and improves the understanding of the hydraulic and thermomechanical behavior of target formations in super-hot geothermal systems related to volcanic settings, the relationships between different rock properties, and their probability, whose understanding is crucial for the parametrization of 3D geological models. [ABSTRACT FROM AUTHOR]

One of the most effective approaches to identifying possible precursors of eruptions is the analysis of seismicity patterns recorded at volcanoes. Accurate locations of the seismicity and the estimate of source mechanisms can resolve fault systems and track fluid migrations through volcanoes. We analysed the six main swarms recorded at Campi Flegrei since 2000, using them as a proxy of the processes involved in the long-term-unrest of this densely populated caldera. We re-located the earthquakes comprised in these swarms and estimated the focal mechanisms, which appear in agreement with the fault systems of the caldera and with tomographic images. The focal mechanisms are in agreement with the tensional stress induced by the caldera uplift. Most of the swarms and remaining seismicity delineate a highly fractured volume extending vertically below the Solfatara/Pisciarelli vents, where gases find preferential paths to the surface triggering earthquakes. The main swarms are located below this volume where the presence of a rigid caprock is still debated. We interpreted the current unrest in term of a gradual increment in the activity of a wide hydrothermal system whose most evident manifestation is the enlargement of the fumarolic-field of Pisciarelli and the increment of the earthquakes occurrence rate. [ABSTRACT FROM AUTHOR]

Geologic carbon storage in deep saline aquifers has emerged as a promising technique to mitigate climate change. CO2 is buoyant at the storage conditions and tends to float over the resident brine jeopardizing long-term containment goals. Therefore, the caprock sealing capacity is of great importance and requires detailed assessment. We perform supercritical CO2 injection experiments on shaly caprock samples (intact caprock and fault zone) under representative subsurface conditions. We numerically simulate the experiments, satisfactorily reproducing the observed evolution trends. Simulation results highlight the dynamics of CO2 flow through the specimens with implications to CO2 leakage risk assessment in field practices. The large injection-induced overpressure drives CO2 in free phase into the caprock specimens. However, the relative permeability increase following the drainage path is insufficient to provoke an effective advancement of the free-phase CO2. As a result, the bulk CO2 front becomes almost immobile. This implies that the caprock sealing capacity is unlikely to be compromised by a rapid capillary breakthrough and the injected CO2 does not penetrate deep into the caprock. In the long term, the intrinsically slow molecular diffusion appears to dominate the migration of CO2 dissolved into brine. Nonetheless, the inherently tortuous nature of shaly caprock further holds back the diffusive flow, favoring safe underground storage of CO2 over geological time scales. [ABSTRACT FROM AUTHOR]

Does your hometown have any mathematical tourist attractions such as statues, plaques, graves, the café where the famous conjecture was made, the desk where the famous initials are scratched, birthplaces, houses, or memorials? The top view in Figure 4 shows the part of the pattern that is evident on the surface, but there is also jointing within the horizontal beds of the sandstone below the surface (see Figure 1). When these layers solidify under pressure from overlying layers and water flows through, the grain size and porosity affect the amount of flow and hence the amount of iron that leaches out of the particles [[10], [15]]. The bottom line is that some thin compaction bands of sandstone are more resistant to erosion, and when the softer surrounding sandstone erodes away, very thin layers of modified sandstone will remain. [Extracted from the article]

A temporary solution to massive anthropogenic CO2 emissions can be the capture of industrial CO2 from flue gas and sequestering it in geological formations. For safe and effective storage of CO2, interaction processes in the rock-pore fluid–CO2 system should be known. Investigation of natural CO2 accumulations provides valuable examples to what physical and chemical effects could be expected during CO2 influx at future CO2 storage sites. One of the key controlling factors of the processes occurring in natural CO2 reservoirs is the lithology of the storage rocks, which is primarily determined by the formation conditions of these rocks. In this respect, the lithologies of individual CO2 accumulation areas influence the processes between the host rock, the pore fluid, and the CO2 in different ways. In the current study, we focus on a well-studied natural CO2 storage reservoir, namely the Mihályi-Répcelak area, NW Hungary. We provide insight into the so far unstudied conglomerate reservoirs that represent a stratigraphically deeper reservoir unit with significantly different lithology and pore water compositions compared to the sandstone reservoirs. Our results indicate that dawsonite /NaAlCO3(OH)2/ formation also affected the conglomerate reservoirs, which indicates that at least part of the CO2 could be trapped in mineral form. An important role of salinity in reducing the CO2 mineral trapping capacity of the storage system is also demonstrated. Furthermore, H isotope analysis of diagenetic kaolinite was applied to trace the origin of the pore water that was present during the rock formation. Based on the data, dawsonite formation was induced by the flux of meteoric water that infiltrated during a warm and humid period and mixed with ascending CO2. [ABSTRACT FROM AUTHOR]

The use of key beds in the cap rocks of the oil reservoirs is crucial. Lack of awareness of these key beds will have serious risks and damages. The Gachsaran oil field is located 220 km southwest of Ahwaz-Iran. The former caprock consists of six key beds (A, B, C, D, E, and F). At the time of writing this paper these key beds are being used during excavations and drilling to determine the site of casing points. What has made utilizing these key beds during excavations difficult however, is use of diamond drill bits which results in the shattering of excavated samples. As such, it has become challenging to learn more about these key beds through studying petrographic thin sections in microscopy. These key beds were observed during the investigation at the drill sites. Later, the excavated samples were studied in the Energy-Dispersive X-ray Spectroscopy (EDS) machine, using a semi-quantitative method to analyze the elemental differences in those key beds. In addition to the identification of various lithological and diagenetic properties of the caprock, this study leads to the introduction of four new key beds based on geochemical properties. Some of the most important differences within the formation include those between the caprock anhydrite and the non-caprock anhydrite, namely the presence of potassium and titanium and the absence of chlorine and sodium in the caprock section. The four new key beds introduced from this study using elemental differences were named as key beds-1, 2, 3, and 4. [ABSTRACT FROM AUTHOR]

Kusatsu-Shirane volcano hosts numerous thermal springs, fumaroles, and the crater lake of Yugama. Hence, it has been a particular study field for hydrothermal systems and phreatic eruptions. On 23 January 2018, a phreatic eruption occurred at the Motoshirane cone of Kusatsu-Shirane, where no considerable volcanic activity had been reported in observational and historical records. To understand the eruption process of this unique event, we analyzed seismic, tilt, and infrasound records. The onset of surface activity accompanied by infrasound signal was preceded by volcanic tremor and inflation of the volcano for ~ 2 min. Tremor signals with a frequency band of 5–20 Hz remarkably coincide with the rapid inflation. We apply an amplitude source location method to seismic signals in the 5–20 Hz band to estimate tremor source locations. Our analysis locates tremor sources at 1 km north of Motoshirane and at a depth of 0.5–1 km from the surface. Inferred source locations correspond to a conductive layer of impermeable cap-rock estimated by magnetotelluric investigations. An upper portion of the seismogenic region suggests hydrothermal activity hosted beneath the cap-rock. Examined seismic signals in the 5–20 Hz band are typically excited by volcano-tectonic events with faulting mechanism. Based on the above characteristics and background, we interpret that excitation of examined volcanic tremor reflects small shear fractures induced by sudden hydrothermal fluid injection to the cap-rock layer. The horizontal distance of 1 km between inferred tremor sources and Motoshirane implies lateral migration of the hydrothermal fluid, although direct evidence is not available. Kusatsu-Shirane has exhibited unrest at the Yugama lake since 2014. However, the inferred tremor source locations do not overlap active seismicity beneath Yugama. Therefore, our result suggests that the 2018 eruption was triggered by hydrothermal fluid injection through a different pathway from that has driven unrest activities at Yugama. [ABSTRACT FROM AUTHOR]

Establishing effective seismic survey parameters in complex structural areas, such as salt domes, is of vital importance for accurate imaging. Shot and group intervals, maximum offset, recording time and profile length, to image the subsurface structures, are critical 2-D parameters. Geometry, aspect ratio of a recording patch and number of in-line and cross-lines are key additional parameters for 3-D seismic design. This study provides a workflow for determining optimal 2-D and 3-D seismic survey parameters as exemplified by a Texas salt dome case. The Pierce Junction oil field, in proximity to the salt dome, is located in Houston, Texas, and has been one of the most prolific hydrocarbon producers in the region. Engineered caverns in the salt dome itself are now used for fluid storage. Design parameters for the future seismic surveys are partially informed by previous seismic data shot over the structure (where the top of the salt is at about 290 m depth and overlying cap rock, 210 m). Existing 2-D seismic data, crossing the salt dome, are processed to extract the velocities of the salt, cap rock, and near-surface sediments. In the following step, 2-D and 3-D velocity models of the study area are constructed using legacy well data as well as gravity measurements which were acquired as part of this study. Synthetic shot gathers are next modeled with a finite difference method using the acoustic wave equation. To generate images of the constructed model, reverse time migration (RTM) is applied to the synthetic data. By assessing the coverage and continuity of the imaged salt boundaries using a variety of decimated input data sets, the optimal survey parameters are determined. In this case, 20 m group and 40 m shot interval, 3000 m maximum offset, and 8 km profile length with a 4 s recording time are found to be most favorable 2-D acquisition parameters. Using similar coverage and continuity criteria, group and shot intervals of a 3-D seismic survey are determined as 25 m and 50 m, respectively. The receiver and shot line intervals are chosen as 250 m in an orthogonal geometry with 33 in-lines and 33 cross-lines distributed in the 8 × 8 km2 survey area. The aspect ratio of any patch with 13 in-lines and 13 cross-lines is accepted as 1:1. This forward modeling and migration procedure, using a range of decimated data sets, can inform decisions on the final field parameters. [ABSTRACT FROM AUTHOR]

Subvolcanic hydrothermal systems can lead to hydrothermal eruptions as well as unrest phenomena without an eruptive event. Historical eruptions and recent unrest events, including ground inflation, demagnetization, and a gradual decrease in the plume height, at Mt. Tokachidake, central Hokkaido, Japan, are related to such a subvolcanic hydrothermal system. This study investigates the three-dimensional (3-D) resistivity structure of Mt. Tokachidake to image its subvolcanic hydrothermal system. A 3-D inversion of the magnetotelluric data, acquired at 22 sites around the crater area, was performed while accounting for the topography. Our resistivity model was characterized by a high-resistivity layer at a shallow depth (50–100 m) and two conductors near the active crater and dormant crater. The high-resistivity layer was interpreted to be composed of dense lava, which acts as a caprock surrounding the conductor. The high conductivity beneath the active crater can be explained by the presence of hydrothermal fluid in fractured or leached zones within the low-permeability lava layer, as the sources of ground inflation and demagnetization were identified within the conductive zone immediately beneath the resistive layer. The resistivity structure was used to estimate the volume of hydrothermal fluid within the pore space. The minimum volume of hydrothermal fluid beneath the active crater that can explain the resistivity structure was estimated to be 3 × 106 m3. This estimate is comparable to the water volume that was associated with the long runout and highly fluidized lahar in 1926. The resistivity structure and volume of hydrothermal fluid presented in this study can be used as a reference for further numerical simulations, which aim to reveal the mechanisms of recent unrest events and assess the risk of hazards, such as lahar. [ABSTRACT FROM AUTHOR]

Formation sampling while drilling (FSWD) technology has become a research hotspot in oilfield development at home and abroad. The technology is characterized by a comparatively short operation time. Since the operation time is short, the obtained formation data are closer to the real situation in the reservoir. After the formation fluid enters the sample chamber from the sampling module, sealed, and returns from the downhole to the surface, the change in ambient temperature and pressure causes the sample volume to shrink and the sample pressure to decrease correspondingly. The change in temperature and pressure leads to irreversible phenomena such as phase transformation or degassing, which can affect the quality analysis of the sample. To avoid the phenomenon, the pressure in the sample chamber is maintained above the bubble point pressure by pre-charging nitrogen on the ground and boosting adjustment in the downhole, so that the formation sample fluid is consistent with the phase state in the original formation when it is retrieved from the ground. The described method is used to provide results close to the real parameters in the reservoir. As the pre-charged nitrogen and the final sample occupy different cavities of the same vessel, and the volume of the vessel is constant, the change in the parameters, including the sampling volume, temperature difference, and pressure difference between the ground and the well bottom, will cause a change in the pressure of the pre-charged nitrogen. Therefore, the problem of ensuring sample fidelity has become the key to sampling technology. To solve the problem, the method of combining ground pre-charged nitrogen pressure with downhole sample chamber pressurization has been introduced. [ABSTRACT FROM AUTHOR]

This work attempted to understand the behavior of the Upper Cretaceous Nezzazat and Lower Cretaceous–Carboniferous Nubia sandstone reservoirs in response to production-induced depletion and fluid injection for enhanced hydrocarbon recoveries from the October oil field, Gulf of Suez, Egypt. Pore pressure (PP), vertical stress (Sv) and minimum horizontal stress (Shmin) magnitudes were modeled based on well logs, drilling data and subsurface measurements. The latest measurements indicated 11.7–12.7 MPa pressure drop (ΔPP) in the Nezzazat reservoirs, while the Nubia sandstone reservoir was depleted by 19–21 MPa. Revised PP and Shmin gradients offer a narrow mud weight window of 9–10.7 PPG (pore pressure gradient) if the entire Lower Miocene–Carboniferous section was planned to be drilled with a single casing in the infill/injector wells. A more conservative approach will be to drill the depleted reservoirs with 5.5–9.3 PPG mud window and case separately, although that may incur an additional cost. Based on the PP–Shmin poro-elastic coupling, stable stress path values of 0.61 and 0.65 are interpreted in the Upper and Lower reservoirs, indicating depletion-induced normal faulting is unlikely to occur at the present rate of depletion. The reservoir stability threshold during pressurization was assessed for fluid injection optimization to sustain production and curtail the bypassed oil. The maximum allowable pressure build-up during injection was estimated using various possible pore pressure–stress coupling scenarios at their maximum depletion state. Based on the PP–Shmin coupling approach, maximum pressure increments of 23 and 27 MPa can be permitted in the depleted Nezzazat and Nubia sandstone reservoirs during injection, without exceeding the lower limit of caprock Shmin, as applicable for both the reservoirs. This will ensure the geomechanical stability of the reservoirs as well as the caprock integrity. This geomechanical study provides crucial comprehensions regarding the optimization of drilling, production, and fluid injection by reducing the risk of reservoir instabilities and formation integrity. [ABSTRACT FROM AUTHOR]

Although reservoir characterization has been carried out by many researchers on the sedimentary package of the Bengal basin hydrocarbon province, integration of petrophysical and seismic sequence-based reservoir evaluation is rarely taken into account. This paper focuses on the identification of gas zones, reserve estimation and identification of new prospects in Srikail gas field within the eastern fold belt of Bengal basin integrating four wireline logs and 2D seismic data. Our study finds seven hydrocarbon-bearing zones (A, B, C, D, E, F and G) within the measured depth between 2429.5 and 3501 m. Petrophysical properties of seven hydrocarbon-bearing zones indicate that they are good quality reservoir sands. The gas horizons were mapped on seismic sections which reveal that the NW–SE anticlinal structure is largely affected by channels in the crest and western flank. The channels are infilled by fine-grained sediments which act as cap rock on northern and western parts of the structure. Thus, the anticlinal structure and fine-grained sediments make a potential trap for hydrocarbon accumulation and laterally and vertically well-distributed sequence remnants are the main reservoir rocks in this area. Volumetric reserve estimation of these sands provided a total gas initially in place as 552 billion cubic feet. Moreover, all the four wells are drilled in the southern block of the structure, and since there is a structural continuity from south to the north, it is highly recommended to drill a well up to 3000 m depth in the northern block to test its hydrocarbon potentiality. Overall, the outcomes of this study contribute new insights for reservoir characterization and identification of new prospects in an efficient way. [ABSTRACT FROM AUTHOR]

The microstructure and mineralogy of volcanic rocks is varied and complex, and their mechanical behaviour is similarly varied and complex. This review summarises recent developments in our understanding of the mechanical behaviour and failure modes of volcanic rocks. Compiled data show that, although porosity exerts a first-order influence on the uniaxial compressive strength of volcanic rocks, parameters such as the partitioning of the void space (pores and microcracks), pore and crystal size and shape, and alteration also play a role. The presence of water, strain rate, and temperature can also influence uniaxial compressive strength. We also discuss the merits of micromechanical models in understanding the mechanical behaviour of volcanic rocks (which includes a review of the available fracture toughness data). Compiled data show that the effective pressure required for the onset of hydrostatic inelastic compaction in volcanic rocks decreases as a function of increasing porosity, and represents the pressure required for cataclastic pore collapse. Differences between brittle and ductile mechanical behaviour (stress-strain curves and the evolution of porosity and acoustic emission activity) from triaxial deformation experiments are outlined. Brittle behaviour is typically characterised by shear fracture formation, and an increase in porosity and permeability. Ductile deformation can either be distributed (cataclastic pore collapse) or localised (compaction bands) and is characterised by a decrease in porosity and permeability. The available data show that tuffs deform by delocalised cataclasis and extrusive volcanic rocks develop compaction bands (planes of collapsed pores connected by microcracks). Brittle failure envelopes and compactive yield caps for volcanic rocks are compared, highlighting that porosity exerts a first-order control on the stresses required for the brittle-ductile transition and shear-enhanced compaction. However, these data cannot be explained by porosity alone and other microstructural parameters, such as pore size, must also play a role. Compactive yield caps for tuffs are elliptical, similar to data for sedimentary rocks, but are linear for extrusive volcanic rocks. Linear yield caps are considered to be a result of a high pre-existing microcrack density and/or a heterogeneous distribution of porosity. However, it is still unclear, with the available data, why compaction bands develop in some volcanic rocks but not others, which microstructural attributes influence the stresses required for the brittle-ductile transition and shear-enhanced compaction, and why the compactive yield caps of extrusive volcanic rocks are linear. We also review the Young's modulus, tensile strength, and frictional properties of volcanic rocks. Finally, we review how laboratory data have and can be used to improve our understanding of volcanic systems and highlight directions for future research. A deep understanding of the mechanical behaviour and failure modes of volcanic rock can help refine and develop tools to routinely monitor the hazards posed by active volcanoes. [ABSTRACT FROM AUTHOR]

One of the main problems related to mature oilfields is the decreased pore pressure due to hydrocarbon production. Therefore, to maintain the production rate of a reservoir, the lost pressure must be compensated. A very traditional method to increase the pressure is to inject natural gas into the reservoir. This technique is widely used in SW Iranian reservoirs because of the readily available supply of this type of gas. Reactivation of pre-existing faults and inducing new fractures into the reservoir and cap rock are some of the potential risks regarding gas injection. In this article, using data such as well logs, pore pressure estimates, and rock mechanical test results, the geomechanical simulation of the Asmari reservoir in the Gachsaran oilfield, SW Iran has been carried out. For this purpose, the current stress field was determined using elastic moduli of reservoir rocks and formation integrity test (FIT) results. Then, by applying analytical methods such as Mohr diagrams and slip tendency, the reactivation possibility of four faults in the field was analyzed, and the maximum sustainable pore pressures were estimated. In the next step, numerical simulations were conducted using ABAQUS software to investigate the injected gas flow path, leakage potential through the cap rock, possible fault reactivation due to gas injection, and shear stress build-up and plastic strain development in different parts of the reservoir. Results of Mohr diagrams and slip tendency showed that all the faults are stable in the current stress state, and fault F2 has the potential to sustain a maximum pore pressure of 55 MPa in the field. On the other hand, fault F3 has the proper conditions (i.e., strike and dip referring to σHmax orientation) for reactivation. Results of numerical simulations suggested that an injection pressure of 30 MPa would not induce any new fracture or fault slip within 5 years of injection. In this period, the injected gas plume moves upward through the damage zone and reaches the shallower parts of the cap rock. It was also shown that by applying an injection pressure of 60 MPa, slip would occur on fault F4 after 10 days of injection. [ABSTRACT FROM AUTHOR]

One of the well-known geothermal potential areas in Iran is the Abgarm in Mahallat region. Due to existence of several hot springs, the Abgarm area is of particular importance in geothermal studies. To investigate the geothermal mechanism at Abgarm, geophysical surveys of magnetometry and magnetotelluric (MT) were utilized near hot springs to image the geometry of all geological requisites for trapping a geothermal reservoir. The ground magnetic data were inverted in 3D to construct a magnetic susceptibility model, where a deep intrusive igneous rock (as a heat source) and a shallow magmatic lava were inferred from the physical model. Euler depth estimation also provided insight to a shallow granodiorite unit embedded in a thick sequence of sediments. Dimensionality and strike analysis of the MT data were performed through the phase tensor method to investigate the general geometry of the sought reservoir for running a 2D TE + TM mode inversion scheme. Through 2D inversion of the MT data along three profiles across the favorable zones, the electrical resistivity models were used to image sedimentary units (i.e., cap rock, top soil, bedrock and reservoir) and magmatic rocks. Considering both geophysical properties led to illustrate a plausible geothermal reservoir in the area. [ABSTRACT FROM AUTHOR]

This study aimed to identify the geochemical reactivity of basaltic tuff as a cap rock in the Janggi Basin, Korea, and its effect on porosity changes by CO2–water–rock interactions. The basaltic tuff used in this study is composed of mainly smectite, zeolite, plagioclase, and pyroxene and contains high amounts of divalent cations that are required to form carbonate minerals. Batch experimental and modeling studies were carried out for CO2–water–rock interactions over 84 days at 50 °C and 100 bar. In this study, increases in porosity are observed from 14.9 to 18.7% by mercury intrusion porosimetry (MIP) and from 15.1 to 20.7% by images from 3D X-ray CT scans (XCT) because of the predominant dissolution reactions of the primary minerals. Among the primary minerals, analcime dissolves the most from fitting geochemical modeling to experimental measurements of cation concentrations and backscattered electron (BSE) analysis. Notably, the dissolution of analcime contributes more than 80% of the total reduction in rock volume according to the change in volume of each mineral calculated using the results of geochemical modeling. This outcome indicates that the dissolution of analcime among primary minerals contributes the most to the increase in porosity of the basaltic tuff. However, long-term research is required to discuss the role of analcime in sealing capacity because analcime is only 6.3% by weight in the basaltic tuff. [ABSTRACT FROM AUTHOR]

Flow of fluids through porous media such as soil, rocks, bones, wood and concrete has been an area of interest for engineering communities that deal with porous materials. The tools developed to describe flow through porous regions are generally applied to bulk materials with single composition. In this paper, however, we demonstrate their applicability to an interface of any two contacting surfaces particularly those of the elastomer and metal in the context of sealing applications. We propose a relationship to account for change in the permeability and the thickness of the seal interface with contact pressure at the interface and fluid pressure of fluid flowing through the interface. We hence develop a porous-media-based model to describe leak of gas through metal–elastomer interface. We validate the model using nitrogen gas leak experimental data for different elastomer–metal interfaces. [ABSTRACT FROM AUTHOR]

Background: Existing research provides estimates of the biophysical potential for increasing soil organic carbon (SOC) stock, however additional research is needed to enhance our understanding of the economic potential for agricultural soils to offset or help reduce CO2 emissions. This study derives the marginal cost to increase SOC sequestration by combining SOC sequestration potential estimates developed using the Intergovernmental Panel on Climate Change (IPCC) factors with an existing payment scheme that was designed to increase no-till (NT) adoption on U.S. cropland. The marginal costs of increasing SOC is a function of the amount of SOC that could be increased through NT and the expected cost to landowners of changing management to use NT. Results: The variability in SOC sequestration rates due to different land-use, management histories, climate, and soils, combined with the 48 unique payment rates to adopt NT, yield over 5,000 unique marginal cost values for increasing SOC sequestration. Nearly 95 percent of the biophysical potential SOC sequestration increase on U.S. cropland (2802 Tg CO2 from 140.1 Tg CO2 year−1 for 20 years) could be captured for less than $100 Mg−1 CO2. An estimated 64 to 93 percent of the biophysical potential could be captured for less than the low and high estimated costs to capture CO2 for geologic storage of $36.36 to $86.06 Mg−1 CO2, respectively. Conclusions: Decreasing tillage intensity through adoption of no-till agriculture offers a cost-effective way to offset a portion of increasing global CO2 emissions. This research demonstrates that increasing SOC stocks through NT adoption can offset CO2 emissions at a lower cost than some other options for preventing CO2 from entering the atmosphere. [ABSTRACT FROM AUTHOR]