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The vertical ranges of inocerams, belemnites, ammonites, echinoids, sponges, and brachiopods from lithologically monotonous carbonate rocks have been studied in the Kommunar section. The results obtained in the study of macrofaunistic assemblages confirm and complement the benthic foraminifera research data of distinguished units of the middle–upper Turonian, Coniacian, lower and upper Santonian, and lower Campanian basal horizon. The stratigraphically full upper Coniacian–lower Santonian interval in the Kommunar section has been identified in the Volga region for the first time. The defined macro- and microfaunistic biostratigraphic units have been correlated and discussed. The Boreal–Tethyan magnetochronological correlation of the Santonian–Campanian makes it possible to conclude that the Santonian lower boundary in different regions differs by about a million years, which is comparable to the duration of the Santonian. [ABSTRACT FROM AUTHOR]

Karbasi anticline between west-northwest parts of Jahrom town is located in northwest 40 km distance of Aghar gas anticline in interior Fars region. This anticline has asymmetric structure and some faults with large strike separation observed in its structure. The operation of Nezamabad sinistral strike slip fault in west part of this anticline caused fault plunge change in this region. Because of complication increasing of structures geometry in Fars region and necessity to exploration activities for deeper horizons especially the Paleozoic ones, the analysis of fold style elements, which is known as one of the main parts in structural studies seems necessary. In this paper because of some reasons such as Karbasi anticline structural complication, importance of drilling and hydrocarbon explorations in Fars region, it is proceed to analysis and evaluation of fold style elements and geometry with emphasis on Nezamabad fault operation in Interior Fars region. According to fold style elements analysis results, it became clear that in east part of anticline the type of fold horizontal moderately inclined and in west part it is upright moderately plunging, so west evaluation of anticline is affected by more deformation. In this research the relationship present faults especially the Nezamabad sinistral strike slip one with folding and its affection on Dehram horizon and Bangestan group were modeled. Based on received results may be the Nezamabad fault is located between G-G' and E-E' structural sections and this fault in this area operated same as fault zone. In different parts of Karbasi anticline, Dashtak formation as a middle detachment unit plays an important role in connection to folding geometry, may be which is affected by Nezamabad main fault. [ABSTRACT FROM AUTHOR]

The distribution of fracture clearance is an important factor that determines the conductivity of carbonate fractures. In this paper, the morphological analysis of acid fractures and the evaluation of acid fracture conductivity were carried out to test the characteristics of acid fracture clearance and the conductivity of acid fractures under the conditions of different acid rock reaction rates. Combined with the distribution rule of fracture clearance and the calculation formula of acid fracture conductivity under closure stress, the calculation formula of acid fracture conductivity of carbonate rocks is established and verified, and the influence rule of the distribution of fracture clearance on the conductivity of acid fractures is simulated and calculated. The results show that with the increase of the closure pressure, the conductivity of the fracture with a closure pressure of 60 MPa is about 94% lower than that of the fracture with a closure pressure of 10 MPa. The increase in acid dissolution rate is beneficial to improve the fracture conductivity under various closure stresses, and the acid dissolution is beneficial to reduce the influence of the closure stress on the fracture conductivity of acid dissolution. When the confining pressure is 10 MPa, the acid corrosion rate increases from 0.0001 to 0.0004 g/cm2 s, and the conductivity of the acid corrosion fracture increases from 27 to 420 μm2 cm. As the dissolution rate of acid solution increases, the proportion of large clearance on the fracture surface increases, the average value of total clearance increases, and the proportion of contact on the fracture surface decreases. [ABSTRACT FROM AUTHOR]

Polymer flooding is a proven chemical Enhanced Oil Recovery (cEOR) method that boosts oil production beyond waterflooding. Thorough theoretical and practical knowledge has been obtained for this technique through numerous experimental, simulation, and field works. According to the conventional belief, this technique improves macroscopic sweep efficiency due to high polymer viscosity by producing moveable oil that remains unswept after secondary recovery. However, recent studies show that in addition to viscosity, polymer viscoelasticity can be effectively utilized to increase oil recovery by mobilizing residual oil and improving microscopic displacement efficiency in addition to macroscopic sweep efficiency. The polymer flooding is frequently implemented in sandstones with limited application in carbonates. This limitation is associated with extreme reservoir conditions, such as high concentrations of monovalent and divalent ions in the formation brine and ultimate reservoir temperatures. Other complications include the high heterogeneity of tight carbonates and their mixed-to-oil wettability. To overcome the challenges related to severe reservoir conditions, novel polymers have been introduced. These new polymers have unique monomers protecting them from chemical and thermal degradations. Monomers, such as NVP (N-vinylpyrrolidone) and ATBS (2-acrylamido-2-methylpropane sulfonic acid), enhance the chemical resistance of polymers against hydrolysis, mitigating the risk of viscosity reduction or precipitation in challenging reservoir conditions. However, the viscoelasticity of these novel polymers and their corresponding impact on microscopic displacement efficiency are not well established and require further investigation in this area. In this study, we comprehensively review recent works on viscoelastic polymer flow under various reservoir conditions, including carbonates and sandstones. In addition, the paper defines various mechanisms underlying incremental oil recovery by viscoelastic polymers and extensively describes the means of controlling and improving their viscoelasticity. Furthermore, the polymer screening studies for harsh reservoir conditions are also included. Finally, the impact of viscoelastic synthetic polymers on oil mobilization, the difficulties faced during this cEOR process, and the list of field applications in carbonates and sandstones can also be found in our work. This paper may serve as a guide for commencing or performing laboratory- and field-scale projects related to viscoelastic polymer flooding. [ABSTRACT FROM AUTHOR]

Carbonate reservoirs are characterized by abundant reserves and are currently focal points for development in oil and gas producing regions such as the Ahdab oilfield, Tarim Basin, Sichuan Basin, and Ordos Basin. The primary method for exploiting carbonate reservoirs is waterflooding. However, due to the complex pore structure and pronounced heterogeneity of carbonate rocks, the waterflooding process often leads to an unclear distribution of remaining oil and low waterflooding recovery efficiency, significantly impacting the stable and high production of carbonate reservoirs. This paper presents a two-phase flow model of oil and water in distinct pore structures by integrating fluid flow equations and interface tracking equations. It visually represents the waterflooding process at the pore scale, elucidates the distribution and formation mechanism of remaining oil, and discusses the mechanism of microscopic displacement efficiency change. The study reveals that: 1) After waterflooding, the distribution patterns of remaining oil can be categorized into dead-end remaining oil, pressure balance remaining oil, wall-bound remaining oil, Jamin effect remaining oil, and water-encapsulating remaining oil, which are governed by microscopic pore structure, wettability, and preferential flow paths; 2) From the perspective of actual reservoir displacement efficiency, intergranular pores > intergranular dissolved pores > visceral foramen > mould pore, with this trend being more pronounced under hydrophilic wetting conditions; 3) Given the oil-wet to strong oil-wet wettability characteristics of these carbonate rocks, capillary forces pose significant resistance during waterflooding. The conclusion underscores the importance of leveraging the reservoir's microscopic pore structure and wettability characteristics for actual oil wells, elucidating the evolutionary law of the mechanical mechanism of oil-water interface advancement, clarifying oil-water percolation characteristics at the pore scale, and understanding the microscopic displacement physical mechanism, all of which are crucial for guiding the design of schemes aimed at enhancing reservoir recovery efficiency. [ABSTRACT FROM AUTHOR]

The characteristics and stages of collapse-filling in paleo-underground rivers vary in recharge-runoff-discharge zones, constraining the associated fracture-caved reservoirs in carbonate strata. This paper comprehensively uses core, fluid inclusion, and carbon-oxygen isotope to probe the evolution process and migration of collapse-filling in paleo-underground rivers in the Northern Uplift of the Tarim Basin. The results show that 1) more than three stages of collapse-filling were identified in recharge-runoff-discharge zones, and a four-stage differential collapse-filling process was proposed to summarize the evolution of paleo-underground rivers. 2) The collapse-filling process varies spatiotemporally in the recharge, runoff, and discharge zones. Hydrodynamic strength and filling capacity migrate gradually from the recharge zone to the discharge zone. 3) Collapse-filling mechanisms, including gravity, suffusion, and suction-erosion mechanisms, also vary along with the collapse-filling evolution process of paleo-underground rivers. The research provided a new insight to recognize and interpret the differential planar distribution and vertical filling of the paleo-underground river system, which can be further applied to investigate the fracture-caved karst reservoirs. [ABSTRACT FROM AUTHOR]

The Xujiashan Sb deposit located at the Mufushan fold thrust belt of the Yangtze block is one of the most important Sb deposits in this district. Stibnite in this deposit contains high and various contents of Se, but research on the distribution and enrichment of Se in stibnite remains limited. This paper conducts geochemical composition, C-H-O isotopic composition, and scanning electron microscopy morphology of the Xujiashan deposit to discuss the sources of ore-forming materials and fluid, as well as the distribution and enrichment mechanisms of selenium in stibnite. The results showed that the ores have trace element compositions comparable with the wall rocks, and Sb and Se contents are significantly higher than the average carbonate rocks. The δ13CPDB values of calcite and quartz range from −12.8‰ to 5.5‰, the δ18OSMOW values range from 20.4‰ to 24‰, and the δDV-SMOW values range from −57.8‰ to −86.9‰. Trace element and isotope compositions indicate that the ore-forming materials were mainly derived from the wall rocks (sedimentary–metamorphic rocks) that S, Se, and Sb dissolved during fluid–rock interactions. The ore-forming fluids were metamorphic water produced by metamorphism, which had experienced multistage mixing with meteoric water and organic-rich fluids. Selenium substitutes for sulfur in the stibnite crystal lattice, causing rhythmically distributed Se contents in stibnite, which resulted from multistage physicochemical changes in ore-forming fluids during crystallization. The varied patterns of Se contents are the result of different cross-sections of the stibnite. [ABSTRACT FROM AUTHOR]

The paper presents the results of studies on the transformation of the organic matter of siliceous-clayey carbonate rocks of the SemilukskoeMendymsky horizon of the Romashkino oil field in a hydrothermal fluid for an hour (with a water-to-rock ratio of 33) at 340°C and 380°C and pressures of 17 and 20 MPa. As a result of hydrothermal treatment, at 340°C and 17 MPa, based on nitrogen porosimetry and electron microscopy data, transformations of rock-forming minerals in the rock are observed. They lead to an increase in the volume and average diameter of mesopores in it and the formation of micropores, as well, which improve its filtration properties. At the same time, the amount of kerogen in the composition of the organic matter decreases and the yield of the petroleum hydrocarbon extract increases, in which, according to the SARA analysis, the content of asphaltenes increases and the content of resins, aromatic and saturated hydrocarbons decreases. In the composition of aroatic hydrocarbons, the proportion of alkyltrimethylbenzenes and dibenzothiophenes increases, phenanthrene homologues appear, and in the composition of saturated hydrocarbons, the amount of iso-structure alkanes decreases relative to the content of linear alkanes. Raising the temperature and pressure of the hydrothermal fluid to 380°C and 20 MPa increases the degree of kerogen conversion from 12.4% to 23.6%. At the same time, changes occurring in the component composition of petroleum hydrocarbon extracts remains similar to the experiments carried out at 340°C and 17 MPa; the content of naphthalenes decreases, the content of dibenzothiophenes increases and C11-C17, C19-C22 alkyltrimethylbenzenes appear. According to IR spectroscopy, with increasing temperature and pressure of the hydrothermal fluid the intensity of the absorption bands of the aromatic ring, aliphatic fragments, and oxygen-containing groups increases in resins; the structural-group composition of asphaltenes changes little: aromaticity and the content of condensed structures slightly increase. The revealed distinctive features in the composition of organic matter after hydrothermal impact on siliceous-clayey carbonate rocks confirm the concept of staged destruction of kerogen, when large structural heteroatomic blocks (asphaltenes) are split off at the initial stages. Changes occurring in the composition of petroleum hydrocarbon extracts indicate their involvement in the process of hydrothermal transformation of organic matter of siliceous-clayey carmbonate rocks with the predominant reactions of dehydrogenation of naphthenic compounds and oxidative polycondensation of aromatic structures. The data of electron microscopy and nitrogen porosimetry of rocks after hydrothermal exposure at 380°C and 20 MPa indicate a deterioration in their reservoir properties. The most optimal thermobaric conditions of the hydrothermal fluid for the generation of petroleum hydrocarbons from kerogen of siliceous-clayey carbonate deposits of the SemilukskoeMendymsky horizon of the Romashkino field, which improve their reservoir properties, are 340°C and 17 MPa; with implication of hard-to-recover heavy hydrocarbon resources and wellestablished catalytic methods of in-situ conversion. [ABSTRACT FROM AUTHOR]

[Objective] Geomechanical analysis plays a crucial role in exploring and developing oil and gas reservoirs. However, the study of in-situ stress in the Yijianfang-Yingshan formations of the Middle to Lower Ordovician in the Shunbei oilfield has lagged behind. This paper compares and analyzes the rock mechanics and in-situ stress characteristics of different types of carbonate reservoirs in the Yijianfang-Yingshan formations of the Lower Paleozoic Ordovician in the Shunbei No. 4 block, and explores the control effect of micro-grain structures on the in-situ stress and rock mechanics parameters of carbonate reservoirs. It aims to provide fundamental geological data for the evaluating of ultra-deep carbonate reservoirs in the Shunbei area. [Methods] This study, based on the spring combination model, determined the rock mechanics and in-situ stress characteristics through rock mechanics experiments and array acoustic logging, and characterized the micro-pore structure of the limestone using casting thin sections and X-ray μ-computed tomography analysis. [Results] The results indicate that the Young's modulus of the Yijianfang-Yingshan formations ranges from 50 to 89 GPa, the compressive strength from 99 to 136 MPa, and the Poisson's ratio from 0.25 to 0.32. The maximum horizontal principal stress of the formations ranges from 200 to 225 MPa, while the minimum horizontal principal stress ranges from 125 to 160 MPa. [Conclusion] Significant differences in rock mechanics parameters and in- situ stress exist among different types of carbonate reservoirs in the Yijianfang-Yingshan formations. From Type I to Type III and non-reservoir carbonate rocks, the Young's modulus, compressive strength, and maximum horizontal principal stress increase dramatically, while the Poisson's ratio and minimum horizontal principal stress show little change. Compared to micritic limestone, sandy-bioclastic limestone has larger calcite particles and reduced particle cohesion, resulting in decreased compressive strength and Young's modulus. Some calcite particles appear sub-rounded or rounded with higher three-dimensional particle sphericity, also leading to weaker intergranular engagement and further reduction in compressive strength and Young's modulus. The presence of numerous pores and fractures in sandy-bioclastic limestone facilitates frictional sliding and potential failure along microfractures or particle interfaces, contributing to lower compressive strength and Young's modulus as well. In addition, micritic limestones in the Yijianfang-Yingshan formations are affected by hydrothermal activity, with some dolomite being replaced by quartz, which increases the compressive strength and Young's modulus. The macroscopic mechanical characteristics and rock mechanics parameters of the rock are constrained by the micro-grain structures. The low-value zones of the Young's modulus, compressive strength, and maximum horizontal principal stress in the Yijianfang-Yingshan formations are identified as the advantageous reservoir development zones in the Shunbei No. 4 block. [ABSTRACT FROM AUTHOR]

Beachrock is a type of coastal carbonate sedimentary rock developed in the sandy beach intertidal zone, widely distributed along the beach front, and the loss of beach sediment is the main cause of beachrock exposure. Based on the analysis of measured data of different exposure forms of beachrocks in profiles, this paper analyzes the main features and influences of non-dynamic factors, such as the exposure position and morphology, of beachrocks on the dynamic geomorphic processes of beaches. Studies have shown that (1) changes between beach energy dissipation bodies are significant features of coastal geomorphic processes under the influence of beachrocks. The first spatial mode of EOF analysis shows that the erosion position of beach-rock-exposed profiles is mainly concentrated in the protected and real sections of beachrock, and the first temporal mode indicates that the exposure of beachrock results in a lagged response of its profile to dynamic environmental changes. (2) The differences in the exposure forms of beachrocks determine the sand-holding space of the beach, and the differences in the lateral exposure positions of beachrocks determine the main areas where erosion occurs on the profile. Meanwhile, the geomorphic processes of their profiles show different degrees of feedback, and such geomorphic phenomena can serve as reference indicators for the stage-wise evolution process influenced by beachrocks. [ABSTRACT FROM AUTHOR]

The purpose of this review paper is to show the possibilities of carbonate reservoir characterization using well logging and laboratory measurements. Attention was focused on standard and new methods of well logging acquisition and interpretation including laboratory experiments to show a part of the history of carbonate rock investigations as hydrocarbon or water reservoirs. Brief information on the geology, mineralogy and petrography of carbonate rocks was delivered. Reservoir properties, i.e., porosity (including fracturing), permeability, and saturation, were defined to emphasize the specific features of carbonates, such as fractures, and vugs. Examples of methodologies were selected from the commonly used laboratory techniques (thin sections examination, mercury and helium porosimetry, X-ray diffraction—XRD) combined with the standard well logs (bulk density—RHOB, neutron porosity—NPHI, sonic slowness—DT, and deep resistivity—Rd) to show the methods that have been used since the very beginning of the scientific and engineering studies of carbonates. Novelty in well logging, i.e., resistivity and acoustic imaging, nuclear magnetic resonance–NMR, dipole shear sonic imaging–DSI, and a spectral neutron-gamma log-geochemical device–GLT combined with modern laboratory investigations (NMR laboratory experiments, scanning electron microscopy SEM), showed how continuous information on mineral composition, porosity and saturation could be obtained and juxtaposed with very detailed laboratory data. Computed X-ray tomography (CT) enabling the 2D and 3D analyses of pores and fractures was presented as a quantitative methodology, effective in pore space characterization, revealing rock filtration abilities. Deep learning and artificial intelligence were used for joining various types of data. It was shown that thanks to new computational technologies original data from very small samples (micro scale), extensively describing the flow ability of the reservoir, could be extended to mezzo scale (core samples) and macro scale (well log images). Selected examples from the published papers illustrated the review. References cited in the text, together with the issues included in them, were the rich source of the practical knowledge processed These were checked by the authors and could be used in other projects. [ABSTRACT FROM AUTHOR]

Magnesian Limestone zoned dolomite (red and non-luminescent zones) now partly dedolomitized), calcite (yellow luminescence), blue luminescent albite has non-luminescent overgrowths) Mansfield Quarry, Nottinghamshire. Modern tropical carbonate sediments are generally aragonite and high-Mg calcite with high porosities (Enos & Swatsky, [16]), yet ancient carbonates (Miocene and older) are generally calcite or dolomite with far lower porosity. Dissolution of aragonite and Mg calcite with precipitation of calcite cements with 2-8 mol% MgCO SB 3 sb occur in sea water undersaturated with respect to aragonite and high-Mg calcite, but supersaturated with respect to low-Mg calcite. The Xiong et al. compilation shows that the cycles of aragonite/high-Mg calcite were more variable than previously recognised, with the first inferred transition from a high-Mg calcite to low-Mg calcite sea occurring during early Cambrian stage 3. [Extracted from the article]

Non-invasive techniques, such as close-range photogrammetry (CRP) and 3D ultrasonic tomography complemented with optical and scanning electron microscopy and mercury porosimetry, were applied to characterize the carbonate rock samples of the Calcari di Cagliari formation. The integrated approach started with the computation of high-resolution 3D models of the carbonate samples using the CRP technique to produce 3D high-resolution models texturized both with natural colors and intensity. Starting from the 3D models from previous techniques, a 3D ultrasonic tomography on each rock sample was accurately planned and carried out in order to detect the elastic properties of such rocks and relate them to textural heterogeneity or internal defects. The results indicate that the relationship between longitudinal velocity and rock properties is complex even in the same carbonate formation. Understanding the relationship between the geomatic and geophysical responses in the investigated rock properties, such as textural characteristics and especially structure and geometry of pores, type of pores, tortuosity and cementing material, is important for many practical applications and especially in the diagnostic process of the conservation state of monumental structures. The integration of the above non-invasive techniques complemented by petrographical–petrophysical data proved to be a powerful method to associate each lithotype with a different susceptibility to degradation. The results presented in this paper demonstrate that the proposed integrated use of complementary methodologies would guarantee the reproducibility of the measurements both at the laboratory and field scale for the monitoring in time of the rock condition while giving a useful contribution in making decisions on an appropriate remedial strategy. [ABSTRACT FROM AUTHOR]

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The development of oil and gas deposits in compacted rocks is a promising area of development in the oil and gas industry. The object of research in this paper is the filtration properties of compacted rocks. To develop such deposits, special extraction technologies are required. Compacted carbonate rocks are easily dissolved by most acids, but for effective use, it is necessary that working solutions have very low viscosity and surface tension coefficient. Special filtration equipment has been developed for the research, which allows pumping various liquids and gases through rock samples and measuring permeability at pressures up to 1,000 bar. To determine the effectiveness of the acid solution, three groups of samples were studied: silty sandstone with clay-carbonate cement with a permeability of 0.2–0.95 mD, compacted organogenic-detrital light gray limestone with a permeability of 0.001–0.004 mD, and organogenic-detrital gray limestone with a permeability of 0.04–0.06 mD. In the course of the study, the stimulation fluid was pumped through the samples at a pressure of 200–300 bar and a temperature of 120 °C. The efficiency was determined by the change in nitrogen permeability of the samples before and after the experiments. In general, the studied stimulation fluid allowed increasing the permeability of rocks up to 3–7 times, depending on the rock and research conditions. The solution retains its reactivity for a long time and, due to its low viscosity and surface tension, penetrates deeply into the rock and significantly increases the well treatment radius compared to conventional acid treatments. The use of the developed acid solution for well stimulation will increase the efficiency of hydrocarbon production from compacted reservoirs without the use of hydraulic fracturing. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibetan Plateau and its surrounding areas have a long and complex tectonic evolutionary history. Cratons and blocks, such as northern India, Lhasa, Qiangtang, Qaidam and Central Qilian, and their in-between orogenic belts constitute the main part of the Qinghai-Tibetan Plateau. During the Cambrian Period, most of these cratons and blocks were on the northwestern periphery of Gondwana, and were associated with the surrounding blocks, e.g. Arabian, Central Iran, Afghanistan, Tarim, Alxa, North China, South China and Sibumasu through the Proto-Tethys Ocean. The Cambrian stratigraphic sequences on these stable blocks are composed of mixed siliciclastic and carbonate rocks deposited in the shallow-water marine environments, and contain the trilobite assemblages of shelf facies. The Cambrian stratigraphic sequences in the Qilian tectonic belts, however, are characterized by the intermediate-basic igneous rocks and silicates formed in the Proto-Tethys Ocean, and contain the trilobite assemblages of deep-water slope facies. Combining with previous data, field observations and newly discovered fossils through funding by the Second Tibetan Plateau Scientific Expedition and Research, the general characteristics of the Cambrian strata in different tectonic units of the Qinghai-Tibetan Plateau and its surrounding areas have been summarized in this paper. Furthermore, efforts have been made to subdivide and correlate the Cambrian strata across these areas by utilizing available biostratigraphic and geochronological data. As a result, a comprehensive litho- and biostratigraphy chart has been compiled. Finally, from the biogeographic perspective, this paper also provides a brief overview of the Cambrian paleogeographical reconstruction of the major tectonic blocks, and discusses the problems associated with the evolution of the Proto-Tethys tectonic belt. [ABSTRACT FROM AUTHOR]

The Lysan alkaline–ultramafic complex is located in the Sisim shear zone at the contact of the two largest tectonic structures of the accretion–collisional belt in the southwestern frame of the Siberian craton. Intrusions of the complex consist of ore-bearing olivinites, kaersutite clinopyroxenites, and banded kaersutite gabbro, which have been «cut» by albitite dykes and veins. The veins and veinlets of the carbonate rocks are mainly associated with the albitites. The present paper represents the first detailed mineralogical study of carbonate rocks and albitites in the Podlysansky Massif of the Neoproterozoic Lysan alkaline–ultramafic complex. The mineral composition was determined in situ in a polished section by scanning electron microscopy, energy dispersive spectrometry, and electron probe microanalysis. The carbonate rocks of the Podlysan Massif have been found to contain minerals that are typical of siderite–carbonatites (senso stricto), including calcite, siderite, phengitic muscovite, apatite, monazite, REE fluorocarbonates, pyrite, and sphalerite. These rocks are enriched in light rare earth elements due to the presence of monazite-(Ce), bastnäsite-(Ce), parisite-(Ce), and synchysite-(Ce). The albitites were formed as a result of the fenitization of leucocratic gabbro by alkali-rich carbo-hydrothermal fluids in zones of intense development of tectonic fractures. Infiltration was the dominant mechanism of fenitization. The obtained data significantly enhance the current understanding of the geochemical and ore specialization of rocks in the Lysan Complex. [ABSTRACT FROM AUTHOR]

The Lucaogou Formation, a typical fine-grained mixed formation in the Jimusaer Sag of the Junggar Basin, exhibits considerable potential for hydrocarbon exploration. Accurate brittle prediction is a crucial factor in determining hydraulic fracturing effectiveness. However, the area features complex lithological characteristics, including carbonate rocks, clastic rocks, volcanic rocks, and gypsum interbeds, along with thin layering and sporadic sweet spots. Traditional prediction methods offer limited resolution and there is an urgent need for a seismic brittle prediction method tailored to this complex geological environment. This paper presents a multi-mineral composition equivalent model for complex lithologies that enables the accurate calculation of Vp and Vs These ratios serve as the foundation for pre-stack elastic parameter predictions, which include Poisson's ratio and Young's modulus. By comparing the predicted parameters with well-logging measurements, the prediction accuracy is improved to 82%, with particularly high conformity in intervals characterized by high organic matter and clay content. Additionally, a three-dimensional brittle modeling approach reveals that the brittleness of the reservoir exceeds that of the surrounding rock, showing a gradual improvement in brittleness with increasing burial depth from southeast to northwest. The central area exhibits relatively good brittleness, with a stable, blocky distribution pattern. [ABSTRACT FROM AUTHOR]

In the last decades, the scientific community has paid an increasing attention on coastal karst areas, since these are highly urbanized and populated, and attract high number of tourists. This transition zone where anthropogenic, terrestrial, and marine processes simultaneously act, is intrinsically fragile, and its vulnerability to geological hazards is enhanced by the mixing between fresh and salt waters, causing a stronger dissolution on carbonate rocks. In this paper, a case study located along the coastal karst of Apulia, between the provinces of Bari and Brindisi, in one of the most touristic areas of the Region is described. In detail, this manuscript deals with description sinkholes evolution at the coastal zone and seawater intrusion in coastal aquifer. The case study highlights the influence of sinkholes in the modification of coastal geomorphology, potentially leading to natural hazards in terms for communities, urbanized land, and infrastructures. The geological setting presents the Cretaceous limestone bedrock overlain by more recent Cenozoic calcarenites and Quaternary marine terrace deposits. The topography is controlled by structural discontinuities, mainly oriented in SW-NE direction. This area is locally defined “Costa Merlata”, which means “Merlon coast”, as it resembles the merlons of a medieval castle. This is due to a strong control exerted by sinkholes in the genesis of bays and inlets. In fact, in this stretch of the Adriatic coastline, it is possible to observe important freshwater outflows, including the main spa of central Apulia (Torre Canne spa), and several evidence of sinkholes, including recent collapse at a few meters from the coastline. The morphologic evolution is characterized by different phases: individual openings of sinkholes, which evolve to small inlets showing the larger sinkhole inland, accompanied by minor openings toward the sea; the last phase is characterized by well-developed bays, deriving from coalescence of sinkholes, overall entering inland for some tens of meters, by means of progressive failures, also favored by sea-storms. In addition to the sinkhole hazards, the area is affected by inland seawater intrusion. In fact, the hydrogeological setting of the coastal stretch, extending for about 25 km, shows evidence of groundwater salinization, with salinity values ranging from 0,5 g/l to more than 5 g/l. The springs with high discharge rate are in the sand dunes zone (Fiume Grande, Fiume Piccolo, and Fiume Morello) and discharge hundreds of liters of freshwater per second, while several diffuse springs, often with unknown discharge, are submerged. In such complex zone, caves adopted as groundwater monitoring spots, especially near the sea, where fresh water and sea water meet. The latter is also carried out by monitoring of stygofauna, i.e. animal species living exclusively within groundwater. Stygofauna can be considered environmental indicator and natural tracer, since it is highly sensitive to environmental variation; therefore, studying groundwater ecosystems will allow to characterize the groundwater quality and the main freshwater pathways. [ABSTRACT FROM AUTHOR]

The Cambrian system in the Ordos Basin has good exploration potential, and the Zhangxia Formation and the Sanshanzi Formation of the Middle and Upper Cambrian are important targets for the exploration of the Cambrian system. In this paper, the characteristics, genesis and main controlling factors of the Zhangxia Formation and the Sanshanzi Formation reservoir are studied through field section observation, thin section observation, drilling and geophysical logging data combined with experimental analysis data. The reservoir space types of the Cambrian carbonate rocks in the Ordos Basin mainly include intercrystalline pores, intercrystalline dissolution pores, dissolution pores, dissolution sutures and dissolution fractures, among which intercrystalline dissolution pores, dissolution pores and dissolution fractures constitute the most important reservoir space type. There are three reservoir types: pore type, fracture - dissolution cavity type and fracture type. The development of Cambrian strata in Ordos Basin is mainly controlled by three factors: high-energy sedimentary facies zone, epigenetic diagenesis and tectonic movement. Granular beach facies and dolomite tidal flat facies are favorable zones for reservoir development in Zhangxia Formation and Sanshanzi Formation. The fault zone in the basin provides a migration channel for late hydrothermal fluid, which can significantly improve reservoir performance. Tectonic fracture itself is an effective pore system, which becomes the migration channel of geological fluid, and also plays a role in communicating pores, which plays a positive role in reservoir. [ABSTRACT FROM AUTHOR]

The bottomhole pressure is one of the key parameters for oilfield development and decision-making. However, due to factors such as cost and equipment failure, bottomhole pressure data is often lacking. In this paper, we established a GA-XGBoost model to predict the bottomhole pressure in carbonate reservoirs. Firstly, a total of 413 datasets, including daily oil production, daily water production, daily gas production, daily liquid production, daily gas injection rate, gas–oil ratio, and bottomhole pressure, were collected from 14 wells through numerical simulation. The production data were then subjected to standardized preprocessing and dimensionality reduction using a principal component analysis. The data were then split into training, testing, and validation sets with a ratio of 7:2:1. A prediction model for the bottomhole pressure in carbonate reservoirs based on XGBoost was developed. The model parameters were optimized using a genetic algorithm, and the average adjusted R-squared score from the cross-validation was used as the optimization metric. The model achieved an adjusted R-squared score of 0.99 and a root-mean-square error of 0.0015 on the training set, an adjusted R-squared score of 0.84 and a root-mean-square error of 0.0564 on the testing set, and an adjusted R-squared score of 0.69 and a root-mean-square error of 0.0721 on the validation set. The results demonstrated that in the case of fewer data variables, the GA-XGBoost model had a high accuracy and good generalization performance, and its performance was superior to other models. Through this method, it is possible to quickly predict the bottomhole pressure data of carbonate rocks while saving measurement costs. [ABSTRACT FROM AUTHOR]

In the field of historical buildings, the wide use of lime as a binder in various contexts of application emerges from a series of artistic and archaeological evidence in the Apulia (Italy) from the 4th century BCE to the 15th century CE. The large availability of carbonate rocks in the geological substratum from Daunian Subappennines to Salento areas strongly influenced the material culture of the region. In this paper, significant study cases were presented to bring to light the technological complexity, almost completely cancelled by the widespread presence of industrial products, in the use of lime over the centuries. Through examples of use from antiquity to the modern age in Apulia (Egnatia, Lamapopoli, Tertiveri, Siponto, Lucera and Monopoli sites), technological solutions indicating an ecological dimension of production were discussed, bearing witness to technologies on a human scale and sustainability. The comparison of petrographical (POM, SEM-EDS) and mineralogical (XRPD) results indicated the technological trend and custom for lime production in the Apulian region that starts from the choice of the stone to be calcined and the aggregates and passes through the modalities of lime hydration and preparation of the mixture up to the laying. [ABSTRACT FROM AUTHOR]

The carbonate rock formations have obvious dual media characteristics, fracture development and good physical conditions, which are the main seepage channels and storage spaces for gas after the reconstruction of underground gas storage. The carbonate strata of the Ordovician system are important natural gas reservoirs in the eastern area of Sulige Gas Field in the Ordos Basin, and the identification and characterization of their fractures are of great significance for the modeling of fractures in the later stage and the improvement of the operation scheme of the gas storage. At present, there is little research on fractures, which restricts exploration and development. Therefore, taking the 39–61 gas storage reservoir in the eastern area of Sulige Gas Field in the Ordos Basin as the research object, this paper identifies and studies the characteristics of the fractures by core, microscopic, conventional logging curves, and imaging logging identification. The results show that the fracture length ranges from 5 to 15 cm and the width ranges from 0.1 to 3 mm. The fracture angles are mostly between 75° and 90° and the main direction is NW–SE. In conventional logging curves, porosity logging has a good response to fractures, while resistivity logging has a general response to fractures; In layers with more developed fractures, natural gamma values are mostly higher than 40API, rock volume density is less than 2.8 g/cm3, neutron porosity is greater than 12.5%, and acoustic time difference is greater than 160 μ s/m. This study is of great significance for improving the identification of carbonate fractures, enriching the relevant theories, and providing guidance for the construction of carbonate gas storage. [ABSTRACT FROM AUTHOR]

Ground collapse is a common geological disaster in karst area, which would bring great harm to people's life and property. The zoning evaluation on karst collapse susceptibility is beneficial to the classification and treatment of the disaster in order to ensure safety and economy. Karst ground collapse is characterized by suddenness, concealment, multi-factor, randomness and fuzziness; therefore, it is difficult to be fully quantified. The normal cloud model could effectively reflect the fuzziness and randomness of objective things, and integrate them to form the mapping between qualitative and quantitative analyses. In this paper, based on the normal cloud model, the study on susceptibility of karst collapse in Yonghe town, Liuyang City has been conducted in order to provide a basis for the classification and treatment of ground collapse in this area, and also provide a reference for the susceptibility evaluation of karst collapse in other areas. The study area is located to the northeast of Liuyang City, 24 km away from it, and its administrative division is located in Yonghe town, Liuyang City, Hunan Province. Ground collapses in this area are all developed in the distribution area of soluble rock layer. The most developed layer is the second member of the Lower Permian Qixia Formation (P1q2) with thick-layered carbonate rocks. Secondarily, ground collapses are distributed in the middle and upper Carboniferous Hutian Group (C2+3ht). The study area covers an area of 14 km2, and 38 karst collapses have occurred in this area so far. Among these collapses, 22 have been surveyed and filled. Sixteen collapses, four of which have been filled, have been investigated in detail. The collapse sites are mainly distributed in the region of soluble rock where faults are developed and surface water and groundwater are closely connected. Geographically, the collapse sites are mainly distributed in Yueshan Formation-Oujia Formation-Dahe Formation, Yongfu village, Yonghe town, Juxiang community-the old street of Yonghe-Huayuan village, Yanxi town, Nanshan Formation-Lizhen Primary School (old)-Xinwan Formation-Xinping Formation. Six evaluation indexes of karst collapse susceptibility were selected in this study, including karst development degree (dissolution rate of borehole), distance from the fault in the area, thickness of overlying soil layer, characteristics of karst water, distance from the pumping funnel center and current situation of ground collapse (ground collapse density). Firstly, according to the detailed exploration results of existing subsidence pits, the weights of six evaluation indicators of 16 existing subsidence pits were calculated and assigned based on entropy weight method. The calculation results indicate that the weight of development density of existing ground collapses is the largest, and that of the fluctuation amplitude of groundwater is the smallest. Secondly, the scoring standard for the risk level of normal cloud model was determined, and the susceptibility of karst collapse in each unit area in the study area was evaluated combined with the weight of each evaluation index. The evaluation results show that all the karst collapses that occurred are distributed in the area highly subject to karst collapse, indicating that the zoning in the evaluation of this study is reasonable. When the normal cloud model is used to evaluate the susceptibility of karst collapse, the size of grid cells could be controlled by the cloud similarity of comprehensive risk evaluation of karst collapse. For areas with high similarity and small cloud droplet dispersion, the unit area of each evaluation could be appropriately increased in order to reduce the evaluation workload. In addition, the high risk area calculated by analytic hierarchy process is 10.8% larger than that by normal cloud method, but three existing collapse pits distributed in the area at medium-level risk of karst collapse, indicating that normal cloud model takes more advantages than analytic hierarchy process in dealing with fuzzy and random problems such as the risk evaluation of karst collapse. [ABSTRACT FROM AUTHOR]

This paper presents a new method to obtain a semi-analytical solution for bottom hole pressure (BHP) of a horizontal well in fracture-cavity reservoirs. The basic building block of the method is to build a new source function suitable for the seepage of carbonate rock for the first time and obtain BHP step by step. This paper uses Laplace transform and Perturbation method to solve the diffusivity equation, which is different from the traditional method of using Green's function presented by Gringarten and Ramey. We validated it with the available published analytical solution and numerical simulation. The sensitivity analysis of pressure and pressure derivative is carried out, and the influence of fracture number, fracture angle, fracture half-length, skin factor, horizontal well segment length, and horizontal well segment spacing on pressure and pressure derivative is analyzed in detail. The findings of the research have led to the conclusion that the number of fractures and fracture direction mainly affect the radial flow stage. In contrast, the length of horizontal subsection and skin factor mainly affect the karst cave fluid flows to the fracture stage. The matrix fluid flows to the fracture stage that is more obvious when the fracture half-length and the horizontal sublevel interval of the horizontal well are small. The advantage of this method is to incorporate well geometry (skin factor) and hydraulic fracturing design (fracture parameters), which are helpful to improve the accuracy of well test interpretation. In addition, this new method has the characteristics of easy calculation. The findings of this study can help for better understanding of transient pressure behavior of horizontal well in fracture-cavity reservoirs. [ABSTRACT FROM AUTHOR]

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Pore space of tight sandstone samples exhibits fractal characteristics. Nuclear magnetic resonance is an effective method for pore size characterization. This paper focuses on fractal characteristics of pore size from nuclear magnetic resonance (NMR) of tight sandstone samples. The relationship between the fractal dimension from NMR with pore structure and water saturation is parameterized by analyzing experimental data. Based on it, a pore structure characterization and classification method for water-saturated tight sandstone and a water saturation prediction method in a gas-bearing sandstone reservoir have been proposed. To verify the models, the fractal dimension from NMR of 19 tight sandstone samples selected from the gas-bearing tight sandstone reservoir of Shahejie Formation in Nanpu Sag and that of 16 of them under different water saturation states are analyzed. The application result of new methods in the gas-bearing tight sandstone reservoir of Shahejie Formation in Nanpu Sag shows consistency with experimental data. This paper has facilitated the development of the NMR application by providing a non-electrical logging idea in reservoir quality evaluation and water saturation prediction. It provides a valuable scientific resource for reservoir engineering and petrophysics of unconventional reservoir types, such as tight sandstone, low porosity, and low permeability sandstone, shale, and carbonate rock reservoirs. [ABSTRACT FROM AUTHOR]

Deep and ultra-deep carbonate reservoirs are the focus of exploration and development in future. However, the problems of high pressures in the treatment process, a limited effective etching distance of acid, great acid leak-off, and poor adaptability of the acid system are encountered in this type of oil and gas reservoir. The mechanism of acid fracturing stimulation under different processes and parameters is not clear. Aiming at these issues, the treatment schemes, process optimization, parameter optimization, and liquid system screening are studied in this paper, try to clarify the acid fracturing stimulation mechanism, and the following conclusions are drawn: The acid network fracturing could activate natural fracture to generate a complex fracture network to the greatest extent, and thereby a high output could be achieved; By using of weighted fracturing fluid, the wellhead injection pressure, as well as the performance of equipment required, could be effectively reduced; With 20% gelling acid and 20% retarded acid system, the non-uniform etching could be realized to improve the effective etching distance of acid liquid. The conclusions in this paper shed light on the acid fracturing treatment of deep and ultra-deep carbonate rocks. [ABSTRACT FROM AUTHOR]

This document is an editorial for a special issue of the journal Minerals, focusing on the heterogeneities of carbonate reservoirs. The editorial emphasizes the importance of understanding these heterogeneities for optimizing exploration and production strategies, as they influence fluid flow behavior and the recoverable reserves within the reservoir. The editorial also highlights the need for further research to explore the implications of heterogeneities at a broader scale and recommends the use of advanced technologies and multidisciplinary approaches. The document provides a summary of five papers included in the special issue, which cover topics such as the genetic mechanism of dolomite reservoirs, diagenetic alterations in the Chiltan Formation, the formation mechanism of dolomite-mottled limestone reservoirs, characteristics of crystalline dolomites in the Sanshanzi Formation, and facies variations in the Sarvak Formation. The research presented in this special issue contributes to our understanding of ancient carbonate platforms and dolomite reservoirs and provides a framework for future studies in oil and gas exploration. [Extracted from the article]

Fractures are developed in carbonate rock areas, and the fracture water flow significantly influences the heat exchange between buried pipes and the rock mass by induing heat convection, providing the carbonate rock area a strong heat exchange capacity and preferable conditions for shallow geothermal development and utilization. In this paper, the calculation method of heat exchange capacity of buried pipes based on fracture distribution characteristics is proposed and deduced, featuring such advantages as quick speed and low cost. Taking an actual project in carbonate rock area as an example, the heat exchange capacity of buried pipes was obtained by the following two methods: in-situ thermal response test and calculation based on fracture distribution characteristics. In the thermal response test, the initial ground temperatures of the two test holes were 15.18 °C and 12.72 °C. By fitting the linear equation of time and average temperature with a linear thermal source model, the heat exchange capacities were 57.21 W/m and 58.22 W/m, the thermal conductivities were 3.56 W/(m·K) and 2.32 W/(m·K), the thermal diffusivities were 1.71 × 10−6 m2/s and 1.12 × 10−6 m2/s, and the volume specific heat capacity was 2.08 × 106 J (m3·K). The test results indicated that the thermal property parameters of rock and soil mass were higher than those of other areas, with obvious wide-range distribution characteristics. Through the statistical analysis of outcrop fracture characteristics, combined with the cube law to calculate the fracture water flow and convective heat transfer, an alternative method for the calculation and optimization of buried pipe heat transfer in fractured rock mass area is also proposed in this paper. According to the measured fracture distribution characteristics of the field outcrop, the heat exchange capacities of the two holes were 57.26 W/m and 58.56 W/m, which were basically consistent with the thermal response test values and verified the reliability of the calculation method of heat exchange capacity of buried pipes based on fracture distribution characteristics. [ABSTRACT FROM AUTHOR]

Carbonate rocks of the Triassic deposits of the South Mangyshlak basin are investigated in this paper for their boundary values, which are important for interpretation of field geophysical data as well as perforation and blasting. Based on their lithological composition, Triassic deposits are classified as either terrigenous or carbonate reservoirs. Carbonate reservoirs are found in the Middle Triassic strata containing volcanogenic dolomite and volcanogenic limestone rocks. A complex type of reservoir characterizes these rocks: porous-fractured, porouscavernous, and fractured. Upper Triassic sediments are formed by the intercalation of tuffaceous, siltstone-sandy, and mudstone rocks overlying Middle Triassic sedimentary rocks. Oil deposits are confined to polymictic sandstones, which are oil-saturated to varying degrees. In order to substantiate the quantitative criteria of the reservoir, experimental studies of the core samples were carried out in the laboratory. Fluid flow studies were performed where physical and hydrodynamic characteristics were determined when oil was displaced by displacing reagents. On the basis of the parameters obtained, correlations between reservoirs and non-reservoirs were constructed. Based on relationships between reservoir properties such as porosity and permeability versus residual water content, as well as effective porosity and permeability versus dynamic porosity, the boundary values were determined. Using these results, the porosity limit for the Middle and Upper Triassic strata has been determined to be 7%, the permeability limit for the Middle Triassic has been determined to be 0.02 X 10-3 µm², and the permeability limit for the Upper Triassic has been determined to be 0.3 X 10-3 µm² . [ABSTRACT FROM AUTHOR]

There have been several foam field applications in recent years. Foam treatments targeting gas mobility control in injectors as well as gas blocking in production wells have been performed without causing operational problems. The most widely used injection strategy of foam has been injecting alternating slugs of surfactant in brine with gas injection. This procedure seems to be beneficial as injection is easy to perform and control below fracturing pressure. Simultaneous injection of surfactant solution and gas may give difficulties, especially with interpretation of the tests, if fracturing pressure are exceeded during the injection period. This paper reviews critical aspects of foam for reservoir applications and intends to motivate for further field trials. Key parameters for qualification of foam are: foam generation, propagation in porous medium, foam strength and stability of foam. Stability is discussed, especially in the presence of oil at reservoir conditions. Data on each of these topics are included, as well as extracted summary of relevant literature. Experimental studies have shown that foam is generated at low surfactant concentration even below the CMC (critical micelle concentration). Results indicate that in situ foam generation in porous medium may depend on available nucleation sites. In situ generation of foam is complex and has been found to be especially difficult in oil wet carbonate rocks. Foam propagation in porous medium has been summarized, and propagation rate for a given experiment seems to be constant with time and distance. Laboratory studies confirm a propagation rate of 1–3 m/day. Field tests performed have not given reliable information of foam propagation rate, and future field pilots are encouraged to include observation wells in order to gain information of field-scale foam propagation. Foam strength is generally high with all gases. The exception is CO2 at high pressure where CO2 becomes supercritical. Stability of foam has been studied in laboratory and field tests, and has confirmed long-term stability of foam. [ABSTRACT FROM AUTHOR]

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A set of low-grade clastic metamorphic and carbonate rocks, and greenschists outcropping in the southwestern (SW) margin of the North China Craton (NCC), was originally classified as the Paleoproterozoic Xiong'er Group according to stratigraphic correlation. To verify the age, this paper carried out detrital zircon U–Pb LA-ICP-MS dating of low-grade clastic metamorphic rocks exposed in the Changqing area at the SW margin of the Ordos Block in the SW part of the NCC. Results from detrital zircon dating indicate that the metamorphic and carbonate rocks can be classified into the Neoproterozoic Nanhua System, which is the only Nanhua System stratum in this block so far, and it probably could provide new clues to Rodinia break-up and Snowball Earth of the NCC. The nine peak ages of the low-grade clastic metamorphic rocks reflected its relatively complex provenance, and almost all major geological events experienced by the NCC basement since the Neoarchean, but some age peaks were difficult to correspond to that of the NCC, indicating that the southwestern part of the Ordos Block was also affected by the Qinling and Qiliang orogenic belts during Nanhua System of Neoproterozoic. Combined with provenance analysis, it was revealed that the current southwest boundary of the Ordos Block was the previous southwest boundary of the Ordos Block during the Qingbaikou-Nanhua Period of the Neoproterozoic. [ABSTRACT FROM AUTHOR]

Copyright of Iraqi Journal of Chemical & Petroleum Engineering is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)