Potential Hydrocarbon Reservoirs Research Articles

An extensional syn-sedimentary structure in the Early Jurassic Trento Platform (Southern Alps, Italy) as analogue of potential hydrocarbon reservoirs developing in rifting-affected carbonate platforms

This work focuses on the 3D modeling and structural analysis of the Monte Testo syn-sedimentary structure, developed in the Early Jurassic Calcari Grigi Group of the Trento carbonate platform (Southern Alps, Italy). Significant changes in the facies architecture of the platform sedimentary units, occurred across a global perturbation of the Carbon cycle at the Sinemurian-Pliensbachian boundary, are associated with evidences of syn-sedimentary tectonics. In particular, an early cemented oolitic sedimentary body with a high initial porosity (Loppio Oolitic Limestone) was broken-up and tilted by a pulse of rifting and overlain by tight marls and marly limestones (lower Rotzo Formation) that display sharp changes in thickness across the syn-sedimentary faults. This complex setting creates conditions potentially favorable to hydrocarbon accumulation. In this work, the Monte Testo structure is presented as a conceptual analogue of a hydrocarbon reservoir that may develop thanks to the overlap of the effects of extensional tectonics and climate change-induced modifications in the carbonate platform facies. A 3D geo-model was realized to obtain information about the genesis and tectonic evolution of the structure. Hence, a potential porosity distribution in the 3D model was evaluated showing that such extensional structure, which has a vertical extent of 500 m and covers an area of 15 km2, could have been associated to a total pore volume of 2.24 × 107 m3 at the time of its formation. Results suggest that in rifting contexts the combined effect of syn-sedimentary faulting and facies variations related to perturbations in the global carbon cycle could generate potential reservoirs in carbonate platforms.

Three-dimensional imaging of porous media using confocal laser scanning microscopy.

In the last decade, imaging techniques capable of reconstructing three-dimensional (3-D) pore-scale model have played a pivotal role in the study of fluid flow through complex porous media. In this study, we present advances in the application of confocal laser scanning microscopy (CLSM) to image, reconstruct and characterize complex porous geological materials with hydrocarbon reservoir and CO2 storage potential. CLSM has a unique capability of producing 3-D thin optical sections of a material, with a wide field of view and submicron resolution in the lateral and axial planes. However, CLSM is limited in the depth (z-dimension) that can be imaged in porous materials. In this study, we introduce a 'grind and slice' technique to overcome this limitation. We discuss the practical and technical aspects of the confocal imaging technique with application to complex rock samples including Mt. Gambier and Ketton carbonates. We then describe the complete workflow of image processing to filtering and segmenting the raw 3-D confocal volumetric data into pores and grains. Finally, we use the resulting 3-D pore-scale binarized confocal data obtained to quantitatively determine petrophysical pore-scale properties such as total porosity, macro- and microporosity and single-phase permeability using lattice Boltzmann (LB) simulations, validated by experiments.

A Neuro-Fuzzy Approach to Screening Reservoir Candidates for EOR

The challenge of discovering new reserves coupled with the current dwindling oil price has necessitated the need to generate and sustain long-term production from existing fields through improved or enhanced oil recovery (IOR/EOR) processes. There is however, no established mechanism to match the thousands of candidate reservoirs worldwide to the subtle and critical variations in reservoir properties that control the success of the many different EOR options. We present a neuro-fuzzy approach to screening potential hydrocarbon reservoirs for enhanced oil recovery (EOR) applications. First, reservoir field data from multiple successful thermal, miscible, chemical and biological EOR projects across different petroleum systems worldwide were trained to establish knowledge pattern and represent it using fuzzy rules. This is achieved by combining fuzzy technique with neural network learning capability to deduce knowledge from the EOR data in a form akin to linguistic rules. Then, the extracted knowledge pattern was validated and used to determine the combination of reservoir properties which could best characterise the key heterogeneities that control EOR success. The model output can be used in screening potential reservoir for EOR application.

Seismic acquisition parameters analysis for deep weak reflectors in the South Yellow Sea

The Mesozoic-Paleozoic marine residual basin in the South Yellow Sea (SYS) is a significant deep potential hydrocarbon reservoir. However, the imaging of the deep prospecting target is quite challenging due to the specific seismic-geological conditions. In the Central and Wunansha Uplifts, the penetration of the seismic wavefield is limited by the shallow high-velocity layers (HVLs) and the weak reflections in the deep carbonate rocks. With the conventional marine seismic acquisition technique, the deep weak reflection is difficult to image and identify. In this paper, we could confirm through numerical simulation that the combination of multi-level air-gun array and extended cable used in the seismic acquisition is crucial for improving the imaging quality. Based on the velocity model derived from the geological interpretation, we performed two-dimensional finite difference forward modeling. The numerical simulation results show that the use of the multi-level air-gun array can enhance low-frequency energy and that the wide-angle reflection received at far offsets of the extended cable has a higher signal-to-noise ratio (SNR) and higher energy. Therefore, we have demonstrated that the unconventional wide-angle seismic acquisition technique mentioned above could overcome the difficulty in imaging the deep weak reflectors of the SYS, and it may be useful for the design of practical seismic acquisition schemes in this region.

Hydrothermal dolomitization: simulation by reaction transport modelling

AbstractReaction transport modelling (RTM) has been successfully used to simulate dolomitization and to predict the lateral extension of dolomitized bodies as potential hydrocarbon reservoirs in the subsurface as well as to give insights into the dolomitization process itself. Geological configurations that have been tested include reflux dolomitization, thermal convection and dolomitization in compactional burial settings. In this study the hydrothermal dolomitization model has been tested with a RTM approach where a limestone reservoir in an intermediate burial setting is fluxed in the presence of deep feeding faults. Hydrothermal fluids migrate upwards from the deep basin areas through extensional fault conduits reaching more permeable levels in the reservoir. The fluids enter the primary interparticle porosity and dolomitize the limestone creating moldic and vuggy porosity. The simulations demonstrate the importance of faulting in this dolomitization process. An effective control on dolomitization is thus exerted by the permeability distribution. Moreover, the type and reactivity of the fluids entering the limestone reservoir exert important controls on the extent of the dolomite bodies.

Composition of Pliocene to Quaternary mixed terrigenous and calcareous sandy beds in contourite drift deposits at ODP Site 1119 off New Zealand: Insights into sandy drift development and drift petroleum reservoir characterization

ODP (Ocean Drilling Program) Site 1119 was drilled in drift successions deposited by northward flowing currents on the Canterbury slope, South Island, New Zealand. Pliocene (∼3.9 Ma) to Pleistocene drift accumulation was concomitant with tectonic uplift and sediment supply from the Alpine Fault plate boundary to the west, glacial development and eustatic sealevel change that created cyclicity in sandy input. Sand detrital and biogenic modes of very fine and fine sand fractions from 24 unconsolidated core samples (44 thin sections) were determined. Fine sand fractions contain an average of 52% bioclastic debris, with bioclasts making up 23% of the very fine sand fraction. Foraminifers are the dominant bioclasts, with pelagic more common than benthic varieties. The average proportions of monocrystalline quartz, plagioclase and potassium feldspar are similar in both size fractions (average QmKP of ∼25:12:63). In contrast, the very fine sand fractions have, on average, higher lithic (QFL%L of 16 vs. 3%), mica (Totalgrain%M of 10 vs. 6%), and dense mineral (Totalgrain%D of 8 vs. 5%) content as compared with the fine sand fractions. Younger clinoform drape (Unit I) and older mounded drift (Unit II) seismic facies showed no distinct detrital compositional differences in their sand fractions, though bioclast content ranges higher in the fine sand fraction of Unit II. Albite feldspar, metamorphic rock fragment, and chlorite components in the sand are consistent with a schist provenance. Other components such as biotite, plagioclase, and K-feldspar require a contribution from metasedimentary and volcanic rocks. Thus there is some along-slope mixing during sediment transport by south-to-north flowing currents. Cemented microporous sandstone at the base of the section provides some insight into contourite burial diagenesis. This work provides a better understanding of the compositional variability of sand components of drift successions which are potential hydrocarbon reservoirs elsewhere.

Markov chains and entropy tests in genetic-based lithofacies analysis of deep-water clastic depositional systems

AbstractThe aim of this study was to examine the relationship between structural elements and the so-called genetic lithofacies in a clastic deep-water depositional system. Process-sedimentology has recently been gaining importance in the characterization of these systems. This way the recognized facies attributes can be associated with the depositional processes establishing the genetic lithofacies. In this paper this approach was presented through a case study of a Tertiary deep-water sequence of the Pannonian-basin.Of course it was necessary to interpret the stratigraphy of the sequences in terms of “general” sedimentology, focusing on the structural elements. For this purpose, well-logs and standard deep-water models were applied.The cyclicity of sedimentary sequences can be easily revealed by using Markov chains. Though Markov chain analysis has broad application in mainly fluvial depositional environments, its utilization is uncommon in deep-water systems. In this context genetic lithofacies was determined and analysed by embedded Markov chains. The randomness in the presence of a lithofacies within a cycle was estimated by entropy tests (entropy after depositional, before depositional, for the whole system). Subsequently the relationships between lithofacies were revealed and a depositional model (i.e. modal cycle) was produced with 90% confidence level of stationarity. The non-randomness of the latter was tested by chi-square test.The consequences coming from the comparison of “general” sequences (composed of architectural elements), the genetic-based sequences (showing the distributions of the genetic lithofacies) and the lithofacies relationships were discussed in details. This way main depositional channel has the best, channelized lobes have good potential hydrocarbon reservoir attributes, with symmetric alternation of persistent fine-grained sandstone (Facies D) and muddy fine-grained sandstone with traction structures (Facies F)

Fold-thrust Style and Fluid Reservoir Potential of Eocene Sakesar Limestone: Sothern Surghar Range, Trans-Indus Ranges, North Pakistan

The Surghar Range western extension of the Trans-Indus ranges constitutes the southeastern frontal fold-andthrust belt of the Kohat Plateau. This structural province is comprised of various local to regional scale anticlines right from Serkia-Mitha Khattak to Kutki areas. The existing range-front anticlinal trend is well-built along the east-west trending segment of the Surghar Range. These anticlinal features reveal infantile tendency from east to west and unearthing the platform rock sequences ranging from Permian to Eocene which is unconformably overlain by the Mitha Khattak Formation equivalent facies to the Rawalpindi Group. This facies in turn has overlain by the fluvial sediments of Siwalik Group. Overall three major anticlines have been mapped from west to east as the Mitha Khattak, Makarwal and Malla Khel Anticline. Differential stratigraphic levels are exposed in cores of these anticlines which proved excellent prospect to be potential hydrocarbon reservoirs horizons. The Eocene Sakesar Limestone has been selected for details studies of his fractures and joints analysis. The Sakesar Limestone exposed along the range front making fraction of the frontal limbs of different anticlines. Various fractures networks and joints pattern has been observed in the Sakesar Limestone at different localities reveal high secondary porosity and permeability. Most of the secondary tectonically induced and primary diagenetic opening and ruptures planes are interconnected and tenders proficient conduit lattice for munificent circulation of fluids in the Sakesar horizon. Origin of fractures and joints growth is mainly associated to force folding in response to the compressional, transpressional and trans-tensional deformation being observed in the region. The studied anticlines reveal that they are the product of fault-bend and fault-propagation folding tender excellent structural fluid trapping philosophy. The range frontal flanks reveal that different level of strata thrust against the foredeep showing inconsistency in the subsurface level of basal detachment horizon which is too hopeful for the construction of structural traps at various levels. Blending of the structural style of the area with the sedimentary structural features of the Sakesar Limestone of Surghar Range urges that this structural province is significantly associated to make hydrocarbon reservoir potential at the stratigraphic level of Sakesar Limestone.

PALYNOLOGICAL MODEL OF THE LATE NEOGENE SEDIMENTS OF EASTERN SLAVONIA (CROATIA)

By applying a palynological analysis of the Late Neogene sediments from one exploration well in the area of Eastern Slavonia, three vegetation zones (Z 1 , Z 2 , Z 3 ) as conditioned by climate sensitivity were set. On the basis of mutual percentage relations of the occurrence of individual form-species and grouping them according to the results of cluster analysis, these zones reflect the changes of warm-cold and variable humidity periods. The age of zones has been determined: zone Z 1 is Pontian, zone Z 2 is Pliocene and zone Z 3 is Pleistocene-Holocene. In the Pontian, 13 form-species of spores were determined that do not cross the Miocene/Pliocene boundary. In the Pliocene, 4 index form-species of spores were determined that were not found in the Quaternary in the study area. In the youngest sediments of the study area, i.e. Pleistocene and Holocene, 7 index form-species of spores were determined. Together with well logging (gamma ray and specific resistivity logs) of the formation, a model was constructed for the local routine provision of age in the study area. The results are generally consistent with other results obtained from Early Neogene sediments in adjacent areas in the central part of Paratethys, and may serve as a model for the correlation of contemporaneous sediments in other areas of Croatia, e.g. Sava and Drava Depressions , which in effect may contribute to the more efficient investigation of potential hydrocarbon reservoirs.

Diagenesis and reservoir quality of the Lower Cretaceous Quantou Formation tight sandstones in the southern Songliao Basin, China

The Lower Cretaceous Quantou Formation in the southern Songliao Basin is the typical tight oil sandstone in China. For effective exploration, appraisal and production from such a tight oil sandstone, the diagenesis and reservoir quality must be thoroughly studied first. The tight oil sandstone has been examined by a variety of methods, including core and thin section observation, XRD, SEM, CL, fluorescence, electron probing analysis, fluid inclusion and isotope testing and quantitative determination of reservoir properties. The sandstones are mostly lithic arkoses and feldspathic litharenites with fine to medium grain size and moderate to good sorting. The sandstones are dominated by feldspar, quartz, and volcanic rock fragments showing various stages of disintegration. The reservoir properties are quite poor, with low porosity (average 8.54%) and permeability (average 0.493mD), small pore-throat radius (average 0.206μm) and high displacement pressure (mostly higher than 1MPa). The tight sandstone reservoirs have undergone significant diagenetic alterations such as compaction, feldspar dissolution, quartz cementation, carbonate cementation (mainly ferrocalcite and ankerite) and clay mineral alteration. As to the onset time, the oil emplacement was prior to the carbonate cementation but posterior to the quartz cementation and feldspar dissolution. The smectite to illite reaction and pressure solution at stylolites provide a most important silica sources for quartz cementation. Carbonate cements increase towards interbedded mudstones. Mechanical compaction has played a more important role than cementation in destroying the reservoir quality of the K1q4 sandstone reservoirs. Mixed-layer illite/smectite and illite reduced the porosity and permeability significantly, while chlorite preserved the porosity and permeability since it tends to be oil wet so that later carbonate cementation can be inhibited to some extent. It is likely that the oil emplacement occurred later than the tight rock formation (with the porosity close to 10%). However, thicker sandstone bodies (more than 2m) constitute potential hydrocarbon reservoirs.

Bioturbating animals control the mobility of redox-sensitive trace elements in organic-rich mudstone

Bioturbating animals modify the original mineralogy, porosity, organic content, and fabric of mud, thus affecting the burial diagenetic pathways of potential hydrocarbon source, seal, and reservoir rocks. High-sensitivity, synchrotron rapid scanning X-ray fluorescence elemental mapping reveals that producers of phycosiphoniform burrows systematically partition redox-sensitive trace elements (i.e., Fe, V, Cr, Mn, Co, Ni, Cu, and As) in fine-grained siliciclastic rocks. Systematic differences in organic carbon content (total organic carbon >1.5 wt%) and quality (Δ13Corg~0.6‰) are measured between the burrow core and host sediment. The relative enrichment of redox-sensitive elements in the burrow core does not correlate with significant neo-formation of early diagenetic pyrite (via trace metal pyritization), but is best explained by physical concentration of clay- and silt-sized components. A measured loss (~–15%) of the large-ionic-radius elements Sr and Ba from both burrow halo and core is most likely associated with the release of Sr and Ba to pore waters during biological (in vivo) weathering of silt- to clay-sized lithic components and feldspar. In conclusion, this newly documented effect has significant potential to inform the interpretation of geochemical proxy and rock property data, particularly from shales, where elemental analyses are commonly employed to predict reservoir quality and support paleoenvironmental analysis.

Mass-transport deposits and reservoir quality of Upper Cretaceous Chalk within the German Central Graben, North Sea

The architecture of intra-chalk deposits in the ‘Entenschnabel’ area of the German North Sea is studied based on 3D seismic data. Adapted from seismic reflection characteristics, four types of mass-transport deposits (MTDs) are distinguished, i.e. slumps, slides, channels and frontal splay deposits. The development of these systems can be linked to inversion tectonics and halotectonic movements of Zechstein salt. Tectonic uplift is interpreted to have caused repeated tilting of the sea floor. This triggered large-scale slump deposition during Turonian–Santonian times. Slump deposits are characterised by chaotic reflection patterns interpreted to result from significant stratal distortion. The south-eastern study area is characterised by a large-scale frontal splay complex. This comprises a network of shallow channel systems arranged in a distributive pattern. Several slide complexes are observed near the Top Chalk in Maastrichtian and Danian sediments. These slides are commonly associated with large incisions into the sediments below. Best reservoir properties with high producible porosities are found in the reworked chalk strata, e.g. Danish North Sea, therefore MTDs detected in the study area are regarded as potential hydrocarbon reservoirs and considered as exploration targets.

The Paleozoic Hudson Bay Basin in northern Canada: New insights into hydrocarbon potential of a frontier intracratonic basin

The Hudson Bay Basin is the largest intracratonic basin in North America, although it is the only one without any proven hydrocarbon reserves. The stratigraphic succession that fills the basin consists mainly of Paleozoic strata, with a maximum preserved thickness of about 2500 m (8202 ft). The Paleozoic succession includes Ordovician to Devonian shallow marine carbonates, reefs, and shales with locally thick Devonian evaporites. The Paleozoic strata are locally unconformably overlain by a thin Mesozoic and Cenozoic cover of nonmarine and marine strata. From 1964 to 1985, over 46,000 line-km (28,600 mi) of seismic reflection data were acquired, and four onshore and five offshore exploration wells were drilled. The data acquired at that time led to pessimistic conclusions on source rocks and the thermal rank of the basin and resulted in the stoppage of exploration activities. However, hydrocarbon shows or indicators were identified in well log data and seismic reflection profiles. The likelihood of an active petroleum system has also been recently supported by recognition of pockmarks on the seafloor and possible marine oil slicks identified on satellite images. New studies of geological, geophysical, and biostratigraphic data reveal that the Hudson Bay Basin had an irregular subsidence and uplift history. Syntectonic deposition occurred during the Late Ordovician(?) to Early Devonian and sag-basin deposition during the Middle to Late Devonian. The basin contains four unconformity-bounded sequences, with significant depocenter migration over time. Analyses of petroleum-system data indicate the Hudson Bay Basin has higher petroleum potential than previously considered. Porous platform limestones, reefs, hydrothermal dolomites, and siliciclastics form potential hydrocarbon reservoirs. Upper Ordovician organic-rich shales with type II-S organic matter are recognized at several locations in the basin. Newly acquired organic matter reflectance and Rock-Eval data indicate Ordovician–Silurian strata locally reached the oil window. Basin modeling demonstrates significant potential for oil generation and expulsion from Ordovician source rocks. Five petroleum play types are identified in the Hudson Bay Basin, including an untested fault-sag or hydrothermal dolomite play. The synthesis of the petroleum system information indicates that the Hudson Bay Basin is, at least locally, prospective for oil accumulations.

Sequence stratigraphy of the petroliferous Dariyan Formation (Aptian) in Qeshm Island and offshore (southern Iran)

After sea level rises during the Early Cretaceous, upper parts of the Khami Group sediments (Fahliyan, Gadvan, and Dariyan Formations) deposited over Jurassic sediments. The Lower Cretaceous (Aptian) Dariyan Formation (equivalent to the Shu’aiba Formation and Hawar Member of the Arabian Plate) carbonates, which have hydrocarbon reservoir potential, form the uppermost portion of the Khami Group that unconformably overlays the Gadvan Formation and was unconformably covered by the Kazhdumi Formation and Burgan sandstones. Detailed paleontological, sedimentological, and well log analysis were performed on seven wells from Qeshm Island and offshore in order to analyze the sequence stratigraphy of this interval and correlate with other studies of the Dariyan Formation in this region. According to this study, the Dariyan Formation contains 14 carbonate lithofacies, which deposited on a ramp system that deepened in both directions (NE—wells 5, 6 and SW—wells 1, 2). Sequence stratigraphy led to recognition of 5 Aptian third-order sequences toward the Bab Basin (SW—well 1) and 4 Aptian third-order sequences toward Qeshm Island (NE—wells 5 and 6) so these areas show higher gamma on the gamma ray logs and probably have higher source rock potential. Other wells (wells 2–4 and 7) mainly deposited in shallower ramp systems and contain 3 Aptian third-order sequences. On the other hand, rudstone and boundstone lithofacies of studied wells have higher reservoir potential and were deposited during Apt 3 and Apt 4 sequences of the Arabian Plate. The Dariyan Formation in Qeshm Island (well 6) and adjacent well (well 5) was deposited in an intrashelf basin that should be classified as a new intrashelf basin in future Aptian paleogeographic maps. We interpret that salt-related differential subsidence, crustal warping, and reactivation of basement faults of the Arabian Plate boundary were responsible for the creation of the intrashelf basin in the Qeshm area.

Applications of chemostratigraphy in Middle Jurassic unconventional reservoirs in eastern Saudi Arabia

ABSTRACT The following study was undertaken on inorganic geochemical data acquired for 1,032 core and cuttings samples taken from Middle Jurassic and Upper Jurassic sediments encountered in five wells in eastern Saudi Arabia. The study sections extend from the upper part of the Middle Jurassic Dhruma Formation to the base of the Upper Jurassic Arab Formation, though the principal focus was on the intervening Hanifa and Tuwaiq Mountain formations where potential unconventional hydrocarbon reservoirs have been encountered. The principal objective of the study was to produce a chemostratigraphic framework for these wells. A secondary aim was to utilize the geochemical data to recognize organic-rich zones and seals. The study sections mainly comprise limestones, argillaceous limestones and calcareous mudrocks, with the latter lithologies being more abundant in the Tuwaiq Mountain and Hanifa formations. Although ICP-OES (Inductively Coupled Plasma–Optical Emission Spectrometry) and ICP-MS (Inductively Coupled Plasma–Mass Spectrometry) were used to acquire data for 50 elements, the chemostratigraphic framework is based on changes in the following ‘key’ elements and ratios: Nb/Cr, Zr/Nb, Zr/Cr, Cr/Th, Cr/Ta, La/Lu, Zr/Yb, Nb/Ti and Ti/U. Variations in these parameters are dependent on changes in source/provenance, reflecting increases or decreases in the abundances of particular detrital heavy minerals. The framework comprises a hierarchical order of 5 zones, 10 subzones and 8 divisions. The zones are labeled C0, C1, C2, C3 and C4 in ascending stratigraphic order, with C2, C3 and C4 being divided into subzones. Further divisions are also recognized in some subzones. Zones C1, C2, C3 and C4 are correlative between all five wells, with the absence of C0 in three of the wells, probably explained by the existence of this zone below the present sampling intervals of these wells. Unlike most zones, some of the subzones/divisions are not identified in all wells. This is mostly explained by local variations in provenance being responsible for the presence of some subzones/divisions in certain wells but not others. In other instances the absence of particular subzones and divisions may have resulted from localized erosion/non-deposition. Lithostratigraphic boundaries are relatively easy to place in wells 1, 2 and 3 where there are similar changes in e-log response in all three study sections. However, this does not hold true for wells 4 and 5 where e-log trends are more or less obvious. In these wells it has been necessary to utilize chemostratigraphy in combination with much more subtle increases/decreases in e-log trends to identify these boundaries. In addition to enabling the placement of lithostratigraphic boundaries in wells 4 and 5, it is possible to use chemostratigraphy to produce a correlation scheme of much higher resolution than was possible by employing lithostratigraphy. For example, The Dhruma Formation was previously defined as a single lithostratigraphic unit but a fourfold chemostratigraphic zonation of this formation is now proposed for wells 1 and 2 (i.e. zones C0, C1, subzone C2-1, division C2-2a which occur in ascending order). By comparing profiles plotted for U, Mo and TOC it is possible to identify units in which there is a relatively high proportion of organic matter. Sediments producing high values of these parameters may be considered potential unconventional reservoirs, with the most organic-rich zones present in wells 1 and 2. Potential seals have been identified above the ‘reservoir’ sections of these two wells. These produce elevated values of Al and K, inferring an abundance of clay minerals which may prevent or reduce the propagation of induced fractures during future ‘fracking’ operations conducted in the vicinity of these wells.

Sedimentary geology of the middle Carboniferous of the Donbas region (Dniepr-Donets Basin, Ukraine).

The Paleozoic Dniepr-Donets Basin in Belarus, Ukraine, and Russia forms a major hydrocarbon province. Although well- and seismic data have established a 20 km thick stratigraphy, field-studies of its sediments are scarce. The inverted Donbas segment (Ukraine) exposes the middle Carboniferous part of the basin's stratigraphy. Here, we provide detailed sedimentological data from 13 sections that cover 1.5 of the total of 5 km of the Bashkirian and Moscovian stages and assess the paleoenvironment and paleo-current directions. Middle Carboniferous deposition occurred in a shelf environment, with coal deposition, subordinate fluvial facies, and abundant lower and middle shoreface facies, comprising an intercalated package of potential source and reservoir rocks. Sedimentary facies indicate a paleodepth range from below storm wave base to near-coastal swamp environments. Sedimentation and subsidence were hence in pace, with subtle facies changes likely representing relative sea-level changes. Paleocurrent directions are remarkably consistently southeastward in time and space in the different sedimentary facies across the Donbas Fold Belt, illustrating a dominant sedimentary infill along the basin axis, with little basin margin influence. This suggests that the middle Carboniferous stratigraphy of the Dniepr-Donets basin to the northwest probably contains significant amounts of fluvial sandstones, important for assessing hydrocarbon reservoir potential.

Improved stratigraphic interpretation using broadband processing – Sergipe Basin, Brazil

Mike Saunders, Laurie Geiger, Dan Negri, Jaime A. Stein, T. Altay Sansal and John Springman demonstrate that de-ghosting and bandwidth extension using the Continuous Wavelet Transform (CWT) technique can produce broadband data that allows for improved identification and mapping of thinner potential hydrocarbon reservoirs. The Sergipe Basin originated in the Early Cretaceous and is a relatively mature hydrocarbon province on the northeast coast of Brazil, comprising 44,370 km² both onshore and offshore. The onshore portion of the basin (12,620 km²) is considered mature, with more than 2 billion bbls in place and 816 wells drilled since 1935. The offshore Sergipe Basin is gaining prominence as Petrobras has made several discoveries since 2010, including the 2010 Barra well (1-SES-158) and the subsequent Barra 1 appraisal well (3-SES-165). These wells targeted oil and gas charged Maastrichtian sandstones that display readily identifiable AVO anomalies on 2D seismic profiles. Approximately 16,000 km of long offset 2D seismic data was acquired in 2014 using a flat streamer towed at a depth of 15 m. The data was processed through pre-stack time migration using conventional techniques, and through prestack depth migration including conventional and broadband processing techniques. The broadband processing included proprietary pre-migration de-ghosting and bandwidth extension phases. The application of these two technologies resulted in seismic data with a vertical resolution as fine as 5 m to 10 m. Improvements in the resolution can be quantified by analysing the sequence stratigraphic interpretation which was done on both the conventionally processed data set and a broadband data set.

Lava-Sediment Interaction and Drainage-System Development In A Large Igneous Province: Columbia River Flood Basalt Province, Washington State, U.S.A

Abstract Large Igneous Provinces (LIPs) have been implicated in some of the largest environmental perturbations to have affected the Earth through geological time. Yet the impact of LIP development on drainage and ecosystem development in the immediate vicinity of these provinces are still poorly constrained to date. Based on a detailed, integrative facies scheme we characterize the interaction between volcanism and fluvial, lacustrine, and wetland environments in the Miocene Columbia River Flood Basalt Province (CRBP) LIP exposed in central Washington State, USA. The facies scheme proposed here comprises a detailed description and interpretation of siliciclastic, bioclastic (diatomite), volcaniclastic, and paleosol facies and subfacies intercalated with lavas of the Columbia River Basalt Group (CRBG). Facies and facies associations of individual interbeds are further correlated to reconstruct changes in sedimentary settings and topography of lava fields during deposition. Field observations and facies analysis help to explain the effects of flood-basalt volcanism on drainage-system development. We propose a generic model of lava–drainage interplay and distribution of sedimentary settings in flood-basalt provinces, which will contribute to our understanding of sedimentological, environmental, and volcanic processes in the CRBP. Hydrocarbon exploration in volcanic terrains requires detailed information on the distribution and development of sedimentary settings. This model will help to better predict the character and distribution of sedimentary bodies and potential hydrocarbon reservoirs in volcanic terrains.

Zircon U-Pb SHRIMP ages from the Late Paleozoic Turpan-Hami Basin, NW China

Permian volcanic rocks are widely distributed in the Turpan-Hami Basin, which is part of the Central Asian orogenic belt. Here we present SHRIMP zircon data for the rhyolite in Well Baocan 1, one of the deepest wells in the basin. The 283.9±2.7 Ma reported in our study provides the best precise age determination for the Yierxitu Formation, the oldest Permian layer of Hami Depression, one of the three substructural units of the Turpan-Hami Basin, and a potential hydrocarbon reservoir in this basin. Our data refines earlier imprecise 39Ar-40Ar ages and shows that the volcanic rocks both inside the Turpan-Hami Basin and along its margin are almost coeval. We delineate a collisional orogenesis, and the new age of 283.9±2.7 Ma may limit the latest time of the collision orogenesis.

Geochemical dynamics of the gas hydrate system in the Qilian Mountain Permafrost, Qinghai, Northwest China

The gas hydrate system in the Qilian Mountain permafrost region exists as an epigenetic hydrocarbon reservoir situated over a deep-seated potential hydrocarbon reservoir. This system is characterized by a particular series of geochemical processes and elemental behaviors, which control the origin of the gases, associated mineralization processes, and the geochemical migration and enrichment of different elements. In this study, we discuss these processes based on compositional analyses of the hydrate-bound gases, associated minerals, fracture fluid, and major, trace, and rare earth element behaviors. Most of the hydrate-bound gases are thermogenic in origin, with minor additional mixed microbial and thermogenic methane that is sourced from sapropelic kerogens in the underlying hydrocarbon reservoir. Episodes of mineralization that formed pyrite, alstonite, and ankerite along rock fractures were likely caused by decomposition of nearby gas hydrate, due to shrinkage of the gas hydrate stability zone. Major element concentration anomalies partly result from ion-precipitation that occurred in the pore and fracture fluid during hydrate formation and decomposition. Most of the anomalies in the measured trace element concentrations are interpreted to demarcate the base of the gas hydrate layer, as low-temperature hydrate has a strong sealing ability. Some of these enriched elements are shown to have migrated into the pyrite crystals, causing their anomalously high concentrations. In addition, the pyrite REE pattern varies with depth and, for pyrites with the same origin, the presence of a hydrate reservoir may be the major cause of fractionation of REE into pyrite. This study provides a new description of the geochemical dynamics of a gas hydrate system operating in a region of permafrost.