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One of the most essential and valuable applications of high-resolution sequence stratigraphy is reservoir zonation and characterization. Establishing a hierarchical chronostratigraphic framework comprising sequences at multiple scales is crucial to identify main reservoir heterogeneities that compartmentalize the fluid flow in the subsurface. In this context, this paper proposes a workflow that integrates different signal analysis techniques to identify sequences of multiple hierarchies from a series of stratigraphic data. The Continuous Wavelet Transform (CWT), Detrend Error Log (DTEL), and Integrated Detrend Error Log (INDTEL) techniques are utilized to process gamma-ray data obtained from outcrops of the Yacoraite Formation, which are conventionally employed as analogs for reservoir characterization. Our results suggest that CWT fits better with higher frequency cycles, while INDTEL shows a good fit with medium frequency cycles. In addition to these techniques, Hidden Markov Models were also applied, predicting T-R cycles as hidden states from the facies transition matrix and possible occurrence of missed beats. All these methods were scripted in the Python programming language, enabling the generation of fast and interactive outputs. This approach brings parameters that can guide the construction of stratigraphic models by automated processes. • Multifrequency transgressive-regressive cycles were obtained from spectral decompositional techniques on Gamma-Ray proxies. • High-Frequency output curve from Continuous Wavelet Transform has direct relationship with high-frequency transgressive-regressive cycles. • INDTEL method is a powerful tool to detect hidden trends and well correlation. • Hidden-Markov Models show high-frequency transgressive-regressive cycles as hidden states from facies transition • The integrated aplication of the methods proves to be a promising tool to help detect missed-beats. [ABSTRACT FROM AUTHOR]

The Lower Congo Basin is known to discharge a substantial volume of oil towards the sea surface, from more than one hundred seafloor seep sites distributed throughout the deep province of the Lower Congo Basin. A large geochemical coring survey confirmed the presence of oil on the seabed. The combination with the seismic data considerably improved the identification of the origin of the oil slicks on the seabed. Multiple specific geophysical characteristics of thermogenic hydrocarbon seep sites were highlighted in a previous detailed analysis of seismic datasets. This study aims to test the characteristics previously identified at regional-scale. The active discharge zone is limited to the distal province of the basin. It is characterised by strong compression/shortening due to the sliding of the post-salt super-sequence, resulting in numerous salt diapirs that control the location of seafloor oil seep sites. The paper describes the bathymetric, reflectivity, amplitude and sub-bottom profiler characteristics of a group of thermogenic seep sites. They correspond essentially to submarine mounds or pockmarks of complex and irregular shape surrounded by hummocky mounds. Active oil pockmarks are systematically associated with positive amplitude anomalies on the seabed and are linked to vertical high-amplitude columns rooted in the seismic reflector and associated with the base of the gas hydrate stability zone. The sub-bottom profiler data shows that the hummocky mounds are connected by a network of faults to high-amplitude bodies buried under a consistent sediment thickness. Based on the definition of specific geophysical features (seafloor mounds, complex shape and irregular pockmarks, positive anomalies of seafloor amplitude, high-amplitude vertical pipes), we identified a series of potential oil seep sites at basin scale. The mounds are particularly recognizable using the seismic curvature attribute; we have identified 2946 individual hummocks that are grouped in 50 zones with a density of 35–240 per km2. They are believed to be associated with asphalt storage on the seafloor and related to the biodegradation of heavy oils during hydrocarbon dysmigration through the sedimentary pile. Unusual double BSRs occur over the study area; these are also a specific feature of thermogenic seep sites. Barely half of the potential sites identified on the seismic datasets are associated with recurrent oil slicks at the sea surface. The proportion of remaining anomalies may be associated with inactive seep sites over the period of satellite-based monitoring or gas-dominated seep sites. • Oil seep sites corresponds to complex-shaped pockmarks and carbonate mounds. • Conical pockmark located in salt-minibasins likely release pore-water. • Double bottom simulating reflectors exclusively corresponds to thermogenic seeps. • About 40% of potential oil seepage sites are currently seeping oil from the seafloor. • Additional data improved the pre-exiting methodology of fluid flow studies. [ABSTRACT FROM AUTHOR]

We report the geophysical characterisation of natural oil seep sites through a combination of sea surface evidence of oil leakage from spatial imagery with a large collection of seafloor and subsurface geophysical data. This paper provides a detailed characterisation of one selected active seep site and identifies possible specific feature of oil seep sites. The oil seep is a complex-shaped feature on the seafloor consisting of a cluster of heterometric pockmarks inside a main depression area and peripheral metre-scale seafloor mounds. A strong deformation related to salt tectonics controls the location of the seafloor source by fracturing the overburden. The associated thermal anomaly induces a vertical modification position of the base of the gas hydrate stability zone (BGHSZ) that is used as a fluid migration route towards the crest of the diapir. The combination of local depressions and seafloor amplitude anomalies linked with vertical high-amplitude pipes rooted on the BGHSZ suggests a focused fluid flow towards the seafloor. In peripheral areas, the seafloor mounds are linked by shallow faults to buried high amplitude patches on sub-bottom profiler sections. The combination of restricted-size seafloor mounds with a progressive deepening of the high amplitude from the seafloor suggests a substantial decrease of the hydrocarbon flow towards peripheral areas. The proximity of actively oil-supplying seafloor depressions and seafloor mounds shows that the hydrocarbon flow rapidly decreases laterally. The thermogenic seep site is affected by two consistent and sub-parallel reflections with negative polarity. The first is interpreted as the methane-related BGHSZ, the second could correspond to the base of a thermogenic BGHSZ produced by a mixture of heavier gas. The seafloor roughness and double BSR appear to be specific features of oil seep sites. The geophysical features revealed at a localised study area will be extrapolated towards a larger province for relevance validation. • We link sea surface oil slicks with seafloor pockmarks in the Lower Congo Basin. • Seafloor active oil seeps consist of heterometric pockmark cluster above salt dapirs. • The proximity of asphalt mounds and pockmarks suggest a lateral flow decrease. • The BSR is overlain by vertical pipes and underlain by massive high amplitudes. • A second deeper BSR could mark the base of stability of a mix of thermogenic gas. [ABSTRACT FROM AUTHOR]

Clastic eruptions are the surface expression of piercement structures such as mud volcanoes or hydrothermal vent complexes and involve subsurface sediment remobilisation and fluid flow processes. During these eruptions, many different processes are involved over a wide range of temporal and physical scales, which makes it a highly challenging multi-phase and multi-processes system to model. Field studies on piercement structures rarely include monitoring and detailed descriptions of clastic eruptions, and only a few attempts have been made to model fluid flow during these events. Moreover, these models have usually only considered one or two dimensions and/or have a limited spatial resolution. In this paper, we summarise the elements that are relevant for modelling fluid flow during clastic eruption: the geometry of the system, the ascending material and the host rocks. We present the main challenges associated with the identification of processes and quantification of parameters. By analogy to magmatic systems, we suggest that the type of clastic eruptions could be controlled by the liquid-gas flow pattern in the conduit. Effusive eruptions could be explained in terms of annular flows, while slug or churn flows could be expected during explosive events. We also propose that the viscosity of liquid mud controls the presence of slug flows in the conduit. We then review the two main approaches that have been proposed to model the flow dynamics in the active conduits, Darcy and Navier-Stokes, as well as their key parameters and their validity. Finally, we discuss the limits of the previously employed models and suggest further work directions to improve our understanding of clastic eruptions. [ABSTRACT FROM AUTHOR]

Hydrocarbon flow rates from tight carbonate reservoirs often depend on the distribution and properties of fractures throughout the reservoir interval. Hence, quantification of fracture parameters can contribute to understanding of reservoir characteristics and reservoir potential. In this paper, natural fractures in tight carbonate reservoir rocks of the Upper Cretaceous Shiranish Formation in the Taq Taq field (Kurdistan Region of North Iraq) were examined primarily using core samples, XRMI micro-resistivity image logs and conventional wireline logs, with additional dynamic data from well tests and mud logs. The Shiranish Formation is composed of a variety of limestones and argillaceous limestones with arithmetic mean matrix porosity and geometric mean permeability values of 1.64 ± 0.37% and 0.0223 ± 0.59 mD, respectively. However, fracturing has enhanced the permeability by up to four orders of magnitude above the maximum matrix permeability (1.79 ± 0.59 mD). Hydrocarbons are produced entirely from the fracture network in these rock types in the Taq Taq reservoir. Observed open and partially-open fractures have NE-SW orientations; these are classified as macro-fractures with average aperture of 0.17 ± 0.18 mm, arithmetic mean height of 11.70 ± 45.40 mm and arithmetic mean length of 26.7 ± 32.32 cm, where the uncertainties are standard deviations. Fracture aperture size and fracture height control fracture permeability and fluid flow. However, while fracture frequency has no effect on permeability, fracture distance distribution influences flow rates and hydrocarbon production. The dominant NE-SW trending fractures are more likely to remain open within the NE-SW oriented present day stress field at Taq Taq. Furthermore, the effect of overburden stress on the permeability and production rate was examined in laboratory tests on core plugs by increasing the confining stress during permeability measurements using constant flow rates. It was found that the magnitude of fracture permeability was reduced by 70% by applying 4000 psi of confining stress. In the reservoir, this effect would be exacerbated by reduced reservoir fluid pressures as a function of production. However, fractures with apertures greater than 0.10 mm are preserved as productive fractures even at high confining pressures and implying that hydraulic fracturing could open existing fractures significantly, enhancing production. This last observation implies that the use of hydraulic fracturing in tight carbonate reservoirs with natural fracturing is likely to be commercially viable. • Fracturing provides negligible supplementary porosity but can improve permeability by up to 4 orders of magnitude. • Open and partially cemented macrofractures are controlled fluid flow and hydrocarbon production. • Fracture frequency affects the fracture permeability distribution in carbonate reservoir rocks. • In situ confining pressure reduces the original fracture permeability by nearly one-third of that at surface pressures. [ABSTRACT FROM AUTHOR]

This paper documents and describes through the use of 3D seismic data a prolific mud volcano province within the Eastern Mediterranean. As many as 386 mud volcanoes were mapped within the post-salt succession of the western slope of the Nile Cone, offshore Egypt, using high resolution 3D seismic data. The mud volcanoes within this field display significant geometrical variability in diameter (c. 550 m to c. 5660 m), height (c. 25 m to c. 510 m) and volume (c. 0.1 km 3 to c. 3.3 km 3 ) and lie at depths ranging from c. > 6000 m subsea to c. 3100 m at the seafloor. A close spatial relationship between mud volcanoes and base-salt depressions and regions of anomalous thinning within the immediate pre-salt succession, combined with documented core samples taken from mud volcanoes within this region present a powerful argument for a pre-salt source of mud. 3D seismic interpretation and volumetric analysis of these mud volcanoes and their source region permit the definition and quantification of their depletion zones. A conceptual model for a dynamic liquefaction and sediment withdrawal process is proposed whereby mud is fed into a central conduit as the depletion zone propagates radially and episodically outwards resulting in a the formation of a concentric depletion zones. Prolonged mud volcanism within this region over the last ∼5.3 Ma implies the potential for long lived pre-salt overpressure and continued mud volcanism following the catastrophic hydrodynamic impact of the Messinian Salinity Crisis. It is suggested that the scale of mud volcanism means that this region should be considered as among the largest mud volcano provinces in the world. [ABSTRACT FROM AUTHOR]

Thick evaporite sequences deposited in saline giant basins are traditionally viewed as impermeable barriers to fluid flow. This paradigm has recently been challenged by documented evidence of fluid migration pathways through several-km thick series of evaporites, such as the late Miocene (Messinian) sediments in the Mediterranean basin, deposited during the Messinian Salinity Crisis (MSC). Our paper reviews the occurrence of fluid expulsion events in these evaporites in the depocentres of the basin, and analyses their potential as seal-bypass systems. The Messinian salt giant was deposited in peculiar conditions where massive sea-level changes occurred in a relatively limited time interval, and a thick basin-centre evaporitic series was deposited between pre-MSC and post-MSC deep-water sediments. Consequently, rapid water and sediment loading/unloading events contributed to the creation of overpressures up to fracture and possibly lithostatic gradient, causing the fluids to be released in explosive events. Examples of fluid expulsion events are here grouped and classified in relation to the long and short term effects of the Messinian Salinity Crisis, as well as the local controls and pre-conditioning basin factors. While peaks of fluid expulsion activity during the short time-frame of the MSC can be mainly linked to Mediterranean-wide events, local controls appear to play a major role in post-MSC fluid mobilisation. In these cases, evaporite breach is largely dependent on the availability of pre-MSC undersaturated fluid sources and the capability of the pre-MSC sediments to be overpressured. The analysis here presented can be used as a basis to understand the controls on syn- and post-depositional movement of fluids in sedimentary basins. Moreover, the analysis of temporal and spatial distribution of fluid expulsion events can help define hydrocarbon migration style and pathways in deep-seated petroleum plays. [ABSTRACT FROM AUTHOR]

Recognition of fractures and faults related to different types of folding is important for understanding how fluids flow in folds or which parts of folds represent a better productive sector of reservoirs due to, for example, changes in the intensity and distribution of fractures. In this paper, we suggest that seismic data alone may be insufficient to determine the style of buckle folding. The differences in mechanical properties of the rock masses favour the development of two main types of internal deformation within the buckle folds, that originated as a result of layer-parallel shortening: flexural slip/flow folding and neutral-surface folding. However, it is difficult to tell from seismic data alone which type of deformation had occurred. This paper presents the advantages of analyzing structures in core combined with results of amplitude variation with azimuth (AVAZ) analysis applied on the 3D seismic survey, when compared to the use of seismic data alone. To illustrate this, we use examples of seismic-scale folds, interpreted as buckle folds formed within the Pomeranian segment of the Caledonian Foredeep Basin. The analysis of structures related to the amplification of one fold known as the Opalino Anticline leads us to conclude, that this approach allowed us to recognize that folding within the mostly homogenous, isotropic Ordovician and Silurian mudstone formations is associated with bed-parallel and bed-perpendicular veins, reverse faults, thrusts, stylolites and normal faults, which formed at different depths within the fold. We consider the structures to have developed as a result of buckling of the mudstone formations and demonstrate that the process facilitated neutral-surface folding, which caused outer-arc extension in the higher parts of the Opalino Anticline and the development of an inner-arc contraction zone in the lower parts of the anticline. We show that this approach helps to predict the distribution of structures related with folding, which in turn aids in estimating the reservoir quality. • Seismic data alone may be insufficient to determine the style of buckle folding. • Structures observed in cores, compared with seismic data and supported by the results of the AVAZ technique allow to interpret the style of folding in buckled rocks. • The strain pattern during layer-parallel shortening within the Pomeranian segment of the Caledonian Foredeep Basin was controlled by the mechanical properties of mostly homogenous, isotropic Ordovician-Silurian mudstones. • The layer-parallel shortening of the relatively homogenous, isotropic rock sequence facilitated neutral-surface folding. • Upper Silurian (Pridoli) growth strata demonstrate that folding in this part of the Caledonian Foredeep Basin occurred during the Pridoli. [ABSTRACT FROM AUTHOR]

Fractured and karstified carbonate units are key exploration targets for the hydrocarbon industry as they represent important reservoirs. Furthermore, large water reserves and geothermal systems are hosted in carbonate aquifers. This paper documents the relationships between stratigraphy, structural patterns, silicification, and the spatial-morphological organization of a 3D multistorey cave system developed in a Neoproterozoic mixed carbonate-siliciclastic sequence. We found that the combination of lithology, silicification, fracture patterns (controlled by lithostratigraphic variability), and petrophysical properties control the formation of high or low permeability zones; their distribution was fundamental for the spatial organization of dissolution and the compartmentalization of the resulting conduit system in different speleogenetic storeys. We propose a deep-seated hydrothermal origin for the fluids involved in the main phases of karst formation. Warm and alkaline hydrothermal fluids caused silica dissolution, followed by chalcedony and quartz reprecipitation in pore space and fractures. Rising fluids concentrated along through-going vertical fracture zones in the lower storey, whereas sub-horizontal bedding-parallel fluid flow was focused on sedimentary packages containing highly silicified dolostones (SiO 2 >80 wt%) characterized by high permeability. The Calixto Cave is an enlightening example for the complex speleogenetic history affecting a mixed carbonate-siliciclastic succession where the combined effect of silicification and hydrothermal karst dissolution can potentially generate high-quality reservoirs. [Display omitted] • Stratigraphy and structures interplay in forming high-vs. low-permeability units. • High-permeability zones are focused in the silicified carbonates. • Mineral deposits and silica dissolution suggest a hypogene hydrothermal origin for the conduit system. • The 3D organization of the conduit system reflects the interplay among stratigraphy, fracture patterns and silicification. [ABSTRACT FROM AUTHOR]

In the Hikurangi subduction wedge (New Zealand), a strong relationship exists between tectonic structures and fluid migrations. In the study area, outcropping tubular carbonate concretions, corresponding to the shallow subsurface plumbing systems of paleo-cold seeps, are hosted by Miocene syn-subduction mudstones. New observations demonstrate the presence of migrated solid bitumen within the tubular concretions and in the fault gouge of a major fault zone. A multi-proxy approach was performed to determine the organic matter thermal maturity in the study area (organic matter petrography and solid bitumen reflectance (BR) R r % (R r : random reflectance)). We also used Rock-Eval pyrolysis, vitrinite reflectance (VR) R r %, and clay mineral reaction progress (illite Kübler-Index and clay mineral paragenesis) to determine the diagenesis grade of the rocks. Low T max values and clay minerals indicate a thermally immature sedimentary cover. The main source rock of the region, the Waipawa Formation is locally thermally mature (VR = 0.86 R r %) suggesting that tectonic thrust-sheet stacking isresponsible for a structural thickening causing local organic maturation. The seaward propagation of out-of-sequence thrusts at base of intra-slope basins could be responsible for the inititation of biogenic fluid flows sourced in the shallow sedimentary cover that is subjected to deformation above the blind thrusts, leading to the earlier generation of the first carbonate tubular concretions. With the continuation of blind thrusting, deep thermogenic fluids then migrated laterally through fault planes (primary migration) and finally vertically through the intrabasinal pre-existing tubular concretions (secondary migration). In this paper, solid bitumen is used for the identification of a fossil thermogenic fluid migration from the source rock, along faults and through tubular carbonate conduits within a subduction thrust-wedge. The study evidences a multi-genetic tubular concretion formation, related with the timing and style of the deformation, being therefore a potential reliable indicator for the evolution of tectonic activity. • Integrated analysis of a plumbing system of paleo-cold seeps on an active margin. • Samples from SR, faults and tubular concretions to determine thermal maturity, bitumen migration, clay mineral reactions. • Circulation of thermogenic fluids in cold seep systems, which correspond initially to migration of shallow biogenic gas. • Role of the shallow plumbing system of biogenic cold seeps as vertical paths for subsequent thermogenic fluid circulations. • Structural thickening due to thrust sheet stacking favor maturation, thrust faults then acting as lateral migration pathway. [ABSTRACT FROM AUTHOR]

Abstract: Drilling/coring activities onboard JOIDES Resolution for hydrate resource estimation have confirmed gas hydrate in the continental slope of Krishna-Godavari (KG) basin, Bay of Bengal and the expedition recovered fracture filled gas hydrate at the site NGHP-01-10. In this paper we analyze high resolution multi-channel seismic (MCS), high resolution sparker (HRS), bathymetry, and sub-bottom profiler data in the vicinity of site NGHP-01-10 to understand the fault system and thermal regime. We interpreted the large-scale fault system (>5 km) predominantly oriented in NNW-SSE direction near NGHP-01-10 site, which plays an important role in gas hydrate formation and its distribution. The increase in interval velocity from the baseline velocity of 1600 m/s to 1750–1800 m/s within the gas hydrate stability zone (GHSZ) is considered as a proxy for the gas hydrate occurrence, whereas the drop in interval velocity to 1400 m/s suggest the presence of free gas below the GHSZ. The analysis of interval velocity suggests that the high concentration of gas hydrate occurs close to the large-scale fault system. We conclude that the gas hydrate concentration near site NGHP-01-10, and likely in the entire KG Basin, is controlled primarily by the faults and therefore has high spatial variability. We also estimated the heat flow and geothermal gradient (GTG) in the vicinity of NGHP-01-10 site using depth and temperature of the seafloor and the BSR. We observed an abnormal GTG increase from 38 °C/km to 45 °C/km at the top of the mound, which remarkably agrees with the measured temperature gradient at the mound (NGHP-01-10) and away from the mound (NGHP-01-03). We analyze various geological scenarios such as topography, salinity, thermal non-equilibrium of BSR and fluid/gas advection along the fault system to explain the observed increase in GTG. The geophysical data along with the coring results suggest that the fluid advection along the fault system is the primary mechanism that explains the increase in GTG. The approximate advective fluid flux estimated based on the thermal measurement is of the order of few tenths of mm/yr (0.37–0.6 mm/yr). [Copyright &y& Elsevier]

Abstract: Subsurface, intra-reservoir faults have subseismic portions (the fault tail) and process zones that must be considered for a complete evaluation of their role in a reservoir setting. In this paper we show that this subseismic fault domain, generally associated with all seismically mappable faults, may extend several hundred meters beyond the seismically mapped tip point, depending on vertical seismic resolution and fault displacement gradients along strike. We use reservoir modelling and fluid flow simulation of a sandstone reservoir analogue to demonstrate how a low-permeable process zone may generate steep pressure gradients in the reservoir and affect the tortuosity of reservoir fluid flow. Results and examples combined show how small adjustments in fault interpretations in the subseismic domain may significantly affect trap definition, prospect volumes, project economics and selection of exploration well locations. For production settings, we demonstrate how low-permeable fault tails and process zones may increase flow tortuosity and delay water breakthrough, thereby enhancing sweep efficiency and recovery from otherwise bypassed pockets of hydrocarbons in the reservoir. The results also indicate that process zones may contribute to pressure compartmentalization. Finally, a simple methodology for the estimation of subseismic fault continuity is presented. [Copyright &y& Elsevier]

Abstract: Recent numerical modelling studies demonstrated how pre-existing (geologically older) fault geometries within a rock volume, strongly control both the distribution of strain and fluid flow patterns during extensional fault reactivation. Fault length is particularly important with larger faults tending to accommodate more strain than smaller faults in a given population. In this paper, we explore the effects of various pore fluid pressure gradients on strain distribution and fluid flow. Our 3D models consider a simple fault architecture, with four alternative initial pore pressure gradients based on case study data from the Timor Sea. The results indicate that, in addition to geometric factors, pore fluid pressure gradients have important effects on strain localisation and fluid flow behaviour during fault reactivation. Higher pore fluid pressure gradients lead to additional strain being accommodated and increased throws on larger faults. With lower initial pore fluid pressure gradients, less strain occurs on large faults and a greater portion of the bulk strain is partitioned onto smaller faults which develop relatively larger throws. Higher pore fluid pressures can temporarily lead to greater lateral fluid migration within the reservoir and greater upward fluid discharge along large reactivated faults. Local anomalous pore fluid pressures, such as a small lateral pore pressure gradient or local overpressure within a thin layer, do not strongly impact fault reactivation results. Only high overpressures in the whole regional system seem to markedly alter strain distribution during fault reactivation. [Copyright &y& Elsevier]

Abstract: This paper presents a computational model for mapping the regional 3D distribution in which seafloor gas hydrates would be stable, that is carried out in a Geographical Information System (GIS) environment. The construction of the model is comprised of three primary steps, namely: (1) the construction of surfaces for the various variables based on available 3D data (seafloor temperature, geothermal gradient and depth-pressure); (2) the calculation of the gas function equilibrium functions for the various hydrocarbon compositions reported from hydrate and sediment samples; and (3) the calculation of the thickness of the hydrate stability zone. The solution is based on a transcendental function, which is solved iteratively in a GIS environment. The model has been applied in the northernmost continental slope of the Gulf of Cadiz, an area where an abundant supply for hydrate formation, such as extensive hydrocarbon seeps, diapirs and fault structures, is combined with deep undercurrents and a complex seafloor morphology. In the Gulf of Cadiz, the model depicts the distribution of the base of the gas hydrate stability zone for both biogenic and thermogenic gas compositions, and explains the geometry and distribution of geological structures derived from gas venting in the Tasyo Field (Gulf of Cadiz) and the generation of BSR levels on the upper continental slope. [Copyright &y& Elsevier]

Abstract: In this paper, the diagenesis from either side of a major Cenozoic reverse fault in the Northern Oman Mountains is documented. Detailed petrographical and geochemical analysis of calcite-filled fractures in carbonate strata of Late Triassic and Early Cretaceous age in the hanging wall and footwall in Wadi Ghalilah reflect a different diagenetic history. In both hanging wall and footwall most of the fractures are pre-burial, extensional in origin, formed by a crack-seal mechanism, and the calcite vein infill has a host-rock buffered signature. In the hanging wall, the fluid responsible for calcite precipitation of these extensional fractures was a marine fluid at 60°C. These veins predate deep burial and contractional tectonic deformation and consequently do not provide any information about syntectonic fluid flow. Neither do the pre-burial extension fractures in the footwall which are also host-rock buffered. The fractures post-dating the tectonic stylolitization in the footwall, by contrast, show evidence of syntectonic migration of saline formation waters at temperatures between 80 and 160°C during contractional deformation. These fluids probably were sourced from the subsurface via the reverse fault, which acted as a fluid conduit. At the same time, however, this fault functioned as a permeability barrier towards the hanging wall, since no evidence of syntectonic fluid flow is present here. In this way compartmentalization of the hanging wall and footwall block was realized. [Copyright &y& Elsevier]

This paper integrates major, minor, trace and rare-earth element (REE) data into C-, O-, Sr-isotopes, fluid-inclusions microthermometry of replacive matrix dolomite and vug/fracture-filling saddle dolomite and calcite of the Lower Cretaceous Qamchuqe Formation, the Kurditan Region of Iraq, in order to get further insights into the origin and geochemical evolution of their parent diagenetic fluids. Multiple generations of dolomite have been observed. These dolomites constitute replacive matrix dolomite and saddle dolomite cement, dominantly poorly ordered, non-ferroan, non-stoichiometric, with an average of 59.4 and 60 mol% CaCO 3 , respectively, and have low Sr, Fe and Mn concentrations. Replacive matrix dolomites display fairly comparable REE patterns to saddle dolomite, but with light REE (LREE) enrichment, and moderate low (∑REEs) contents (18.9–1111.5 and 16.6–593.4 ppb, respectively). Saddle dolomite has moderately positive Eu anomalies while replacive matrix dolomite has slightly less positive Eu anomalies and negative Dy, Ho and Yb anomalies. Both dolomites are characterized by slightly radiogenic 87Sr/86Sr ratios ranging from 0.707702 to 0.707839, overlapping, wide-ranging and negative δ18O values from −10.43 to −4.47 and −12.87 to −7.79 ‰ VPDB , and δ13C values ranging from 0.38 to 3.57 and −3.45 to 3.11‰ VPDB , respectively. The primary fluid inclusions microthermometry of replacive matrix and saddle dolomites yield homogenization temperatures (T h) ranging from 71.3 to 228.3 °C and 82–188 °C, respectively, and salinity values ranging between 14.4 to 25.4 and 15.6 to 27.9 wt% NaCl eq., respectively. These data suggest multiple hydrothermal fluid fluxes during and post Zagros orogeny. The geochemical data also show that these fluids derived from similar source of mixed hydrothermal and marine fluids, which caused the dolomitization of host rock and precipitation of dolomite cements. • The presence of multiple hydrothermal fluid flow events with unique geochemical footprints. • Comparable major and trace element geochemistry occur of replacement and cement dolomites. • REE, isotopes and fluid inclusions in dolomite suggest mixed marine and hydrothermal fluids. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the modeling of compaction and overpressure development in sedimentary basins during sedimentation. The modeling is based on an extension of a formulation for one-dimensional sedimentation and large-strain consolidation of sedimentary layers increasing in thickness with time. A modified formulation is presented using constitutive models for sediment compaction and permeability changes, which are based on experimental results for different clays compacted to effective stresses of up to 100MPa. The main aim of the modeling is to improve the knowledge of overpressuring generated by mechanical compaction in sedimentary basins. Parametric studies were carried out to determine the effects of deposition rate and sediment properties on predicted overpressures, effective stress, porosity and permeability in sedimentary basins. Finally, a simplified North Sea sedimentary basin is analyzed in order to illustrate the use of the model, and to gain further understanding of how pore pressures have developed in some areas in the North Sea. [Copyright &y& Elsevier]

In this paper, we address the irregular behaviour and geometry of the gas hydrate stability zone (HSZ) inferred from reflection seismic data in relation to heat-flow measurements. The study area lies in the hanging wall of the Posolsky fault in the Southern Baikal Basin (SBB). Side-scan sonar imagery already revealed an undulating antithetic active fault structure and several isolated active vent structures. Remarkably, these fluid discharge structures occur only where the base of the hydrate stability zone (BHSZ), as inferred from seismic reflection profiles, is fluctuating and discontinuous, independent of lake floor morphology. The correlation between the interpreted BHSZ and heat-flow data across the Malenki seep is reasonable. On a seismic profile south of the fluid escape features, the BHSZ is expressed as an oscillatory, but continuous reflection, and shows poor correlation with heat-flow measurements. In nearly all cases, measured heat-flow exceeds inferred heat-flow. Additionally, the local inferred minima are anomalously low compared to the expected background values in the SBB. These observations suggest that the present-day hydrate accumulation and its (meta-)stability are more complicated than originally suspected. The limited area of these anomalies, their amplitudes and their occurrence in the immediate vicinity of faults and fluid escape features suggest that fluid convection cells disturb local gas hydrate stability conditions. [Copyright &y& Elsevier]

This paper presents a comprehensive analysis of multiscale geological, petrophysical and rock mechanical data acquired from 35 m of outcrop well core from the Late Jurassic (Kimmeridgian) Upper Jubaila Formation, Saudi Arabia. In this location the sequence is a typical shallow marine heterogeneous carbonate sequence and a direct analogue to a part of the prolific Arab D reservoir sequence in the subsurface towards the east. Four main lithofacies types were identified with a general shoaling upwards trend, varying from nodular bioturbated peloidal mudstone/wackestone facies to sharp-based intraclast-peloidal, skeletal rudstone/floatstone facies. The mineralogy in the upper section of the well cores is predominantly calcite, while the lower section is also comprised of some dolomite and quartz. Stratiform dedolomitization as a telogenetic overprint is only evident in the upper 18 m of the core and controlled by vertical flow of meteoric fluids. The core plug porosity distribution is lower than that of the subsurface equivalent reservoir zones, and is attributed to meteoric cementation. Thalassinoides burrow features in mudstone and wackestone facies in the upper sections of the core control horizontal permeability distribution at the centimeter to meter-scale. Micrite morphology and dedolomitization appear to be key controls on plug permeability, rock strength and sonic velocity. Based on the trends observed in compressive rock strength, p-wave velocity and plug porosity distributions, the cored section was divided into five main rock mechanical layers. Despite reduced porosity, the average compressive rock strength in the outcrop core is lower than that of the Arab-D subsurface equivalent rocks, indicating overall 'weakening' of the rock due to telogenetic processes and surface weathering. • Multi-disciplinary data analysis used to study 35 m of Arab-D equivalent outcrop well cores. • Multi-scale petrophysical, rock mechanical and digital rock image database. • Paleo flow barrier influenced distribution of diagenetic products. • Bioturbation, dedolomitization and micrite morphology impact rock petrophysical and geomechanical properties. • Discussion of implications to subsurface reservoir management. [ABSTRACT FROM AUTHOR]

This paper integrates Mg-, C-, O-, Sr-isotopes, fluid-inclusions microthermometry, and radiometric dating of dolostones and vug-filling saddle dolomite and calcite of the Upper Cretaceous Bekhme Formation, the Kurdistan Region of Iraq, provide new insights into the origin, timing and geochemical evolution of hydrothermal dolomitizing fluids. Similar isotopic compositions and fluid-inclusion microthermometry of the dolostones and saddle dolomite suggest formation by similar fluids. The U–Pb ages of dolostones and saddle dolomite suggest that dolomitization (74.8 Ma) was accomplished in 300 Ka at near Earth's surface by flow of hydrothermal fluids followed by dolostone dissolution and precipitation of vug-filling saddle dolomite (73.8 Ma). Mg isotopic compositions of the dolomites (26Mg DSM3= −0.81‰ to −0.76‰) are interpreted to indicate derivation of Mg from marine connate waters entrapped in overpressured basinal mudstones. Relatively high Sr-isotope ratios of the dolomites precludes the role of ophiolites as an important source of Mg in the basin. • Similar ranges of isotopes and microthermometry values of the dolostones and saddle dolomite suggest formation by similar fluids. • Dolomitization was accomplished in 300 Ka at near earth's surface by flow of hydrothermal fluids. • The source of Mg is interpreted to be basinal marine connate waters. [ABSTRACT FROM AUTHOR]

This paper investigates the spatial link between fluid escape pipes and underlying faults in the Ceduna Sub-basin. The Ceduna Sub-basin is the largest depocentre of the Mesozoic Bight Basin that formed as a result of rifting between Australia and Antarctica beginning in the Middle Jurassic. The study area is in the northwest of the Ceduna Sub-basin, within which sets of fluid escape pipes were identified in 3D seismic data along the study area's south-western edge. Set 1 pipes are observed within the siliciclastic Wobbegong and carbonate Dugong Supersequences of Paleocene to Pleistocene age, while Set 2 pipes are observed within the top 400 ms (~485 m) of Santonian to Maastrichtian deltaic Hammerhead Supersequence. Dimensions of Set 1 and Set 2 pipes range from 50 ms (60 m) to 400 ms (485 m) in height and 70–180 m in width. Roots of the fluid escape features overlie the upper tips of normal faults within the Hammerhead Supersequence. The spatial distribution of fluid escape features and predominant underlying faulting style within the Hammerhead Supersequence varies within the study area; randomly distributed fluid escape features overlie polygonal faults to the northeast, whilst linear clusters of fluid escape features overlie normal faults in the southwest. Spatial statistics analysis of fluid escape features and underlying faults support the interpretation that the faults have acted as fluid migration pathways. The polygonal and normal faults developed in the Late Cretaceous and are interpreted to have transmitted fluids probably sourced from the Lower-Upper Cretaceous Blue Whale Supersequence, and the Late Cretaceous White Pointer and Tiger Supersequences. These supersequences have been identified as containing potential source rocks, and geochemical analysis them suggest that hydrocarbon generation initiated as early as the mid-Cretaceous (~95 Ma) and continued through to the Cenozoic (~15 Ma). • Documentation of a fluid escape features in the Bight Basin that have not been analysed in published literature. • Fluid escape features are underlain by normal faults. • Spatial distribution of fluid escape features linked to type of dominant fault that underlies them. • Fluids potentially sourced from deeper hydrocarbon source rocks within the basin. [ABSTRACT FROM AUTHOR]

It has been shown that ankerite in clastic reservoirs can preserve an extended record of diagenesis and thus the fluid flow history in sedimentary basins. Ankerite cements with distinct zoning textures are well developed in gravity-flow sandstones associated with magmatic intrusions in the Linnan Sag, Eastern China. This example offering a rare opportunity to investigate the history of complex diagenetic fluid flow events in a lacustrine rift basin. An integrated study including thin section petrography, fluid inclusion micro-thermometry, carbon and oxygen isotope, SEM-EDS, XRD, CL, BSE-EPMA, LA-ICP-MS analyses was undertaken. The aim is to resolve the mineralogical, geochemical and isotopic composition of the sandstone and constitutional minerals. The sandstones are mainly of lithic arkoses (Q 43 F 34 L 23), with an average carbonate cements of approximately 8.2 wt %. The carbonate cements are dominated by zoned ankerite appearing as rhombohedral and poikilotopic blocky crystals. Calcite, ferroan calcite, dolomite and siderite cements are also present. Non-carbonate cements including barite, authigenic clay minerals, and quartz overgrowth are common in the sandstone. The δ13 C values of ferroan calcite range from −4.2‰ to +1.2‰ PDB. Ferroan calcite was re-precipitated at a temperature of 93.1 °C at the expense of the dissolution of eodiagenesis carbonate cement in the sandstone. Ankerite was precipitated at temperature ranges from 107.8 to 140.9 °C, accompanied with the formation of pore-filling barite. The δ13C values of ankerite range from −1.8‰ to +1.1‰, and δ18O values range from −14.8‰ to −10.5‰, indicating an involvement of hydrothermal fluids in the formation of the zoned ankerite. The hydrothermal fluids were probably related to the mafic magmatic activities and migrated into the sandstones along faults. These fluids are rich in iron and magnesium, and also contains abundant inorganic carbon dioxide and sulphate, episodic charging into the reservoir. The abundances of most of the elements, including magnesium, iron, REEs and trace elements in the zoned ankerite consistently decrease away from the magma intrusion centres. We therefore conclude that multiple magmatic activities were primarily responsible for the zoned ankerite precipitation in the research area. The intimate relationship between magmatic activity and carbonate cementation in sandstone reservoirs documented in this paper may have significant implications for studying fluid flow in lacustrine rift basins. • Carbonate cements are dominated by zoned aankerite exhibit as rhombohedral and poikilotopic blocky crystals. • Geochemical data induced the origin of a zoned ankerite effect of hydrothermal fluid. • The multiple period of magma extrusion and the associated hydrothermal fluid flow is the main reason for zoned ankerite precipitation. [ABSTRACT FROM AUTHOR]