Facies Heterogeneity Research Articles

Lateral facies heterogeneity and carbonate productivity changes during the Lower Jurassic of the Traras Mountains (NW Algeria): local versus regional controls

Lateral facies heterogeneity and carbonate productivity changes during the Lower Jurassic of the Traras Mountains (NW Algeria): local versus regional controls

3D stochastic simulation of a deep-water turbidite system: An example from the Los Molles Formation, southern region of the Neuquén Basin, Argentina

A recurring challenge in geological modeling is bridging the gap between different scales. For example, difficulties arise when connecting outcrop data through production to exploration scale models. An object-based stochastic simulation was performed using outcrop data from the Arroyo La Jardinera area in the southern region of the Neuquén Basin, Argentina. This simulation involved four depositional sequences in a vertical succession that includes turbidites and associated deep marine facies. The aims of this study are (a) to determine the best geological model consistent with field and aerial image data; (b) to validate the application of object modeling to determine facies distribution; (c) to evaluate uncertainties from models based on scarce data. The studied interval covers a transgressive (J1) to regressive succession (J21, J22, and J23) of basin plain to slope depositional settings, featuring sandy and gravelly turbidite channels, turbidite lobes and interlobes, lobe fringes, and muddy slope and basin plain. Each depositional sequence model was constructed using specific input parameters for architectural elements, with lithological proportions based on sedimentary logs. The J1 sequence includes basin plain, lobe fringe, and minor lobe deposits; J21 features turbidite lobes, fringes, and subordinate channels; J22 accommodates turbidite channels scoured into muddy slope facies; and J23 encompasses gravelly and sandy turbidite channels carved on muddy slope facies. The geostatistical modeling of outcrop data has allowed building a quantitative sedimentological model useful for understanding subsurface facies heterogeneity in both exploration (vertical) and production (horizontal) scales.

Carbonate reservoir characterization and permeability modeling using Machine Learning ـــ a study from Ras Fanar field, Gulf of Suez, Egypt

Predicting facies and petrophysical properties along and between wells is challenging in carbonate reservoir modeling. In the Nullipore carbonate reservoir, Ras Fanar field, depositional and long-term diagenetic processes result in a high degree of heterogeneity and complex distribution of facies, which in turn affect the reservoir quality. This provides a significant obstacle to building accurate geological models. This study integrates thin sections, routine core analyses, and well logging data to overcome such difficulties and model the Nullipore carbonate facies and permeability. The detailed petrographic analysis revealed the existence of seven microfacies in the reservoir, which are summed up into three facies associations (FAs), each of which represents a specific reservoir rock type (RRT): (1) supratidal FA, (2) intertidal FA, and (3) shallow subtidal FA. The three FAs were correlated with the gamma-ray logs to create facies logs for the studied wells, which were further populated via the Truncated Gaussian Simulation method. Cross-validation was used to evaluate the model's accuracy. The analysis of the available core data infers that the three RRTs are prospective and have a wide permeability distribution. However, RRT3 constitutes the best reservoir quality. The sedimentological analysis revealed that the long-term diagenetic events, involving the dolomitization of limestone and the dissolution of allochems have a major role in improving the pore connectivity and permeability of the reservoir. Fracture characterization discloses that fractures play a significant role in fluid storage and migration. Three Machine Learning (ML) models, including Adaptive boosting (AdaBoost), Gradient Boosting (GB), and Extreme Gradient Boosting (XGB), were developed to integrate the RRTs, porosity, and permeability to improve permeability prediction. Statistical analysis revealed that the XGB model outperforms other models and exhibits the highest prediction performance. The present study provides further insights into the characterization and modeling of facies and permeability of complex carbonate reservoirs. It can be applied in similar geological settings to better interpretation of depositional and diagenetic controls on reservoir quality assessment and aid in the field development plan.

Mississippian (Lower Carboniferous) Facies Heterogeneity and Distribution within the Mixed Carbonate-Siliciclastic Reservoirs of the Midcontinent STACK Play, Oklahoma, USA

Summary The objective of this study is to evaluate facies heterogeneity, including both lateral and vertical distributions within the mixed carbonate and siliciclastic reservoirs of the Mississippian System (Lower Carboniferous). This research and statistical approach will aid in future investigations related to determining optimal landing zones, enhancing completion designs, and providing geologic insight into fracture driven well interference studies to increase production efficiency. This study integrates well log, petrographic, sedimentologic, and conventional core analyses along a set of transects across the Anadarko Basin and includes the development of core-based facies logs. Statistical analysis indicates that the Mississippian System in the STACK play of the Anadarko Basin is fundamentally a highly layered rhythmic succession in which a variety of carbonate rock types, siliciclastic rock types, and chert tend to form couplets with siltstone. Thickness-frequency distributions and Markov chain analysis indicate that sediment thickness and lithologic transitions were stochastically regulated and that lithologic cyclicity is not apparent. Overall lithologic trends indicate a transition from carbonate to sandstone in the midramp and from carbonate to mudstone and siltstone in the outer ramp. Stratal geometry defines a series of south-prograding clinoforms, and detailed analysis of vertical trends in the distribution of mudstone, siltstone, sandstone, chert, and carbonate facilitates identification of shoaling-upward parasequences that can be correlated regionally.

Chemometric analysis on concentrations and ratios of terpanes and steranes and implications for oils from the cratonic region of the Tarim Basin, NW China

More than 2 × 109 tonnes of proved oils have been found in the cratonic region of the Tarim Basin. The source rocks for these oils remain unresolved although the source rocks are marine facies within the Cambrian and Ordovician strata with total thickness over 5 km. So far, there is no systematic classification of these oils on the basis of source facies. In this study, a practical approach was presented to select effective and sensitive biomarker parameters for source facies and maturity assessments for the studied oils on the basis of biomarker classification by hierarchical cluster analysis (HCA). Twenty-one terpanes and steranes in oils from both the Tabei (Northern Tarim) and Tazhong (Central Tarim) uplifts were classified into three groups using HCA on the basis of terpane and sterane concentrations. The result of biomarker grouping mainly reflects the differences in thermal stabilities among biomarkers for the 45 Tabei oils, providing a general thermal stability sequence for terpanes and steranes that helps the selection of effective maturity parameters. However, biomarker grouping suggests that both source facies and thermal stability have major influences on relative biomarker concentrations for the 75 Tazhong oils. The Tabei oils are mainly derived from a single source with relatively homogeneous facies while the Tazhong oils are derived from multiple sources or a single source with more heterogeneous facies. Based on the HCA results, twelve terpane and sterane ratios were selected as source facies parameters for the Tabei and Tazhong oils. These studied oils were consequently classified into four families by HCA and principle component analysis (PCA) integrating the twelve selected facies parameters of terpanes and steranes along with Pr/n-C17 and Ph/n-C18 ratios. Family 1 and 2 oils are mainly in the Tabei uplift while Family 3 and 4 oils are almost in the Tazhong uplift. Family 1 and 2 oils are derived from source rocks located at the northern, central and southern areas of the Northern Depression and the Tabei Uplift with marine mudstone facies. Family 3 and 4 oils are derived from source rocks located mainly at the southern area of the Northern Depression and the Tazhong Uplift with carbonate and evaporite facies. This study provides a practical approach to trace oil origins for oil and condensate reservoirs in the Tarim Basin and elsewhere.

Seismic sequence stratigraphy of Late Albian-Early Turonian successions in SW Iran: Implication for reservoir characterizations and potential for improved reservoir quality prediction

The Late Albian-Early Turonian succession on the Arabian Platform stands out as one of the world's richest hydrocarbon provinces. This study delves into the Seismic Sequence Stratigraphy (SSS) of these successions to unravel reservoir characterization and characterized potential hydrocarbon plays. Utilizing data from five exploration wells, including well logs, selected core data, biostratigraphical information, and chemostratigraphy analysis, alongside a comprehensive 3D seismic volume, enabled the identification of four 3rd-order sequences and multiple 4th-order sequences within the studied successions. Sequence-1 (DS-I), dating back to the Late Albian age, features mudstone and bioclast wackestone in an open marine environment. DS-I is a key sequence, notably witnessing the disappearance of siliciclastic input from west to east in the study area. DS-II (Early Cenomanian) and DS-III (Mid-Cenomanian) were deposited on carbonate platforms with grain-supported facies in shoal and lagoonal depositional environments.A distinct regional unconformity at the Turonian base, evident on seismic sections, aligns with depleted δ18O values on the Cenomanian-Turonian Boundary. The maximum flooding surfaces of DS-I and DS-II are characterized by continuous reflectors with negative amplitude. Furthermore, the lateral grading of reservoir facies and their intercalation with non-reservoir facies within 4th-order sequences suggest that reservoir facies heterogeneity is strongly influenced by depositional processes at this scale. Potential reservoirs, particularly in the Highstand System Tract (HST) of each 3rd sequence, are highlighted, with DC-III's HST standing out, hosting patch reef facies resulting from local tectonic activities and carbonate build-up movements.

3D geophysical image translated into photorealistic virtual outcrop geology using generative adversarial networks

Outcrop analogues play a pivotal role in resolving meter-scale depositional facies heterogeneity of carbonate strata. Two-dimensional outcrops are insufficient to decipher the 3D heterogeneity of carbonate facies. Near-surface geophysical methods, notably ground-penetrating radar (GPR), can be employed to step into 3D and extend the dimensionality of the outcrops to behind the outcrop. However, interpreting geophysical images requires specific geophysical expertise, often unfamiliar to field geologists who are more familiar with the actual rock than the geophysical data. A novel generative adversarial network (GAN) application is presented that constructs a photorealistic 3D virtual outcrop behind-the-outcrop model. The method combines GPR forward modeling with a conditional generative adversarial network (CGAN) and exploits the apparent similarities between outcrop expressions of lithofacies with their radargram counterparts. We exemplified the methodology and applied it to the open-source GPR data acquired from the Late Oxfordian-Early Kimmeridgian Arabian carbonate outcrop. We interpret a 4 km long outcrop photomosaic from a digital outcrop model (DOM) for its lithofacies, populate the DOM with GPR properties, and forward model the synthetic GPR response of these lithofacies. We pair the synthetic GPR with DOM lithofacies and train them using CGAN. Similarly, we pair the DOM lithofacies with outcrop photos and train them using CGAN. We chain the two trained networks and apply them to construct an approximately 2 km long 2D and an approximately 60 m2 3D volume of photorealistic artificial outcrop model. This model operates in a visual medium familiar to outcrop geologists, providing a complementary instrument to visualize and interpret rock formation instead of geophysical signals. This virtual outcrop replicates the visual character of outcrop-scale lithofacies features, such as the intricate bedding contacts and the outline of reef geobodies.

Facies characterisation and stratigraphy of the upper Maastrichtian to lower Danian Maastricht Formation, South Limburg, the Netherlands

Abstract The Maastricht Formation is a mostly calcarenitic unit that belongs to the Chalk Group but is unlike the typical North Sea chalk in that it is much coarser and at times contains a significant terrigenous component. The formation was deposited between the late Maastrichtian and the early Danian in a proximal zone of the Chalk Sea immediately north of the Anglo-Brabant and Rhenish massifs. The formation crops out in South Limburg, the Netherlands, in the German state of North Rhine–Westphalia, near Aix-la-Chapelle (Aachen), and in the Belgian provinces of Liège and Limburg, and it is present in the subsurface in the Campine Basin and in the Roer Valley Graben, in Belgium and the Netherlands. The often spectacular fossil content of the Maastricht Formation has been extensively studied but its sedimentological aspects remain understudied. Indeed, the lithostratigraphy of the formation is largely informal and based on the abundance and morphology of flint and on the quantification of fossil content. The paucity of facies studies and the lack of a lithostratigraphic framework based on modern facies studies hampers stratigraphic correlation between outcrops and, more importantly, boreholes. A facies characterisation and facies-based lithostratigraphic framework of the Maastricht Formation in South Limburg is particularly urgent because groundwater is abstracted from aquifers in the formation and geological models currently in place fail to predict facies heterogeneity and, consequently, aquifer properties. We studied eight outcrops of the Maastricht Formation across South Limburg and carried out a (micro)facies analysis of the outcrops. We show that the Maastricht Formation can be subdivided into three lithofacies and five microfacies. The lithofacies reflect the traditional subdivision of the formation into Maastricht and Kunrade limestones. Our results suggest that the current subdivision of the Maastricht Formation into six members is untenable. The formation is best subdivided into lower and upper members. The Kunrade limestone should be afforded the status of formation. We interpret the Maastricht Formation as having been deposited in an epeiric ramp, in which facies distribution was controlled by water temperature, nutrient levels and storminess. The (micro)facies of the Maastricht Formation can be organised into two depositional stages: stage 1, representing the lower part of the formation, is characterised by heterozoan carbonates deposited under cooler, mesotrophic conditions in a nutrient-rich, more proximal region of the epeiric sea; stage 2 is characterised by heterozoan-photozoan carbonates deposited in a warmer and stormier environment with slightly lower nutrient levels.

Integrated seismic-stratigraphic, sedimentological and petrophysical approaches for characterizing the reservoir potential of early Cretaceous Alam El Bueib formation in the Meleiha concession of North Western Desert, Egypt

The Early Cretaceous late syn-rift sediments of Alam El Bueib Formation host potential, however poorly-explored reservoir targets in the north Western Desert of Egypt. The controls on depositional evolution and architecture of Alam El Bueib sedimentary facies, as well as the influence of depositional attributes on reservoir facies heterogeneity, are poorly constrained. Therefore, this study integrates seismic, sedimentological, and petrophysical data from Meleiha concession in the north Western Desert to build evolutionary models for Alam El Bueib succession and predict the architecture of the potential reservoir facies. Several channel systems were observed with a notable upward transition from complex-filled to flat-filled channels. The complex-filled channels correspond to the early highstand tidally-influenced estuarine, deltaic/estuarine sediments of Alam El Bueib-IV and Alam El Bueib-IIIG units. Matruh canyon and Alam El Bueib-IIIG fluvial sand bars were developed during a phase of forced regression, and the canyon was infilled by hemiplegic mudstones during the Late Valanginian sea level rise. The late highstand and lowstand facies of Alam El Bueib-IIIG unit present the main fluid flow conduits. The minimal degree of reservoir heterogeneity occurs in the lowstand amalgamated fluvial sandstone bars, whereas lateral and vertical reservoir heterogeneity increases in the deltaic/estuarine and estuarine successions of Alam El Bueib-IIIG and Alam El Bueib-IV, respectively. The lateral compartmentalization of the Alam El Bueib-IIIG fluvial facies against Alam El Bueib Matruh canyon shales produced excellent stratigraphic traps that should be tracked throughout the entire north Western Desert.

Facies distribution and depositional cycles in lacustrine and palustrine carbonates: The Lutetian–Aquitanian record in the Paris Basin

AbstractThe difficulty of correlating continental deposits hinders predicting lacustrine and palustrine carbonate facies variations in time and space. This study aims to understand better the factors governing these facies heterogeneities by measuring carbonate isotopes and conducting facies, petrographic and sequence stratigraphic analyses of the Lutetian–Aquitanian deposits of the Paris Basin, that record the transition from marine to lacustrine environments. Large‐scale correlations enabled the definition of two lacustrine–palustrine carbonate facies models. (1) The coastal lacustrine system (Bartonian to Rupelian), consists of fine‐grained brackish carbonate exhibiting episodic marine inputs during short‐term relative sea‐level maxima and evaporite sedimentation during relative sea‐level minima. Lacustrine sediments differ notably from marine ones with more negative δ13C and δ18O compositions that co‐vary and a biota adapted to low salinity conditions. In the associated palustrine environment, depositional sequences evolve upwards from micritic lacustrine deposits to nodular and then laminar calcretes. Microbial‐coated grains and rhizoliths indicate biological processes during repeated subaerial exposure phases in sub‐tropical to arid climates. (2) The inland lacustrine system (Rupelian and Aquitanian) was disconnected from the marine domain and showed evidence of microbial activity with microbial crusts and oncoidal rudstones. Facies rich in micritic intraclasts composed of palustrine and lacustrine facies indicate the reworking of already lithified sediments along the margins. In the palustrine domain, the calcrete facies are less abundant than breccias formed in‐situ by desiccation, limestones with root traces, or organic‐rich wackestones and marls. This system reflects a more temperate climate with more developed microbial structures and less exposed carbonates than the coastal lacustrine system. The southward migration of the depocentre and the transition from marine environments to (1) coastal and then (2) inland systems are controlled by uplift phases induced by Pyrenean and Alpine orogenesis. Third‐order relative sea‐level variations appear to control only short‐term cycles in coastal systems.

Sedimentary facies controls on reservoir quality of the Abu Madi Formation, offshore Nile Delta Basin, Egypt

The present study investigates the sedimentological analysis and petrophysical properties of the Messinian Abu Madi reservoir (AMR), offshore Nile Delta Basin in order to determine how facies heterogeneities control reservoir quality. This approach was performed by integrating core data from Mina-1 well and BE-1 well and wireline logs from four wells (BN-1, BN-2, BE-3 and Mina-1). Based on core studies, seven clastic facies have been identified, of which five form sandstone reservoirs. These facies have accumulated within a deep incised canyon-fill during four successive fluvial sub-environments; braided fluvial channel, point bar, floodplain, and abandoned channel. These fluvial sediments were changed into tidally influenced fluvial/estuarine deposits with aggradational-retrogradational stacking patterns due to a transgressive event during the Messinian time. Based on the well log petrophysical evaluation, the Abu Madi reservoir has a total porosity of 0.20–0.26 v/v and effective porosity in the 0.18–0.25 v/v range. Shale volume ranges from 0.04 to 0.09 v/v, and water saturation ranges between 0.15 and 0.45 v/v. Four reservoir rock types were recognized and interpreted as a function of composition and therefore having different petrophysical characteristics. RRT1 and RRT2 show good petrophysical properties and good reservoir quality. The best reservoir quality occurs in massive sandstones (RRT3), which have porosities up to 26% and permeabilities up to 1440 mD. RRT4 has a poor reservoir quality with porosity of 5.4% and permeability of 0.6 mD. The reservoir porosity heterogeneities and reservoir quality have been strongly impacted by the original composition and primary depositional facies.

The upper cretaceous carbonate sediments of the Ras Budran Field, Gulf of Suez, Egypt: stacking patterns and depositional controls

The present study interprets the carbonate stacking patterns and their depositional controls in the Upper Cretaceous strata of the Ras Budran Field in the Gulf of Suez, Egypt, on the basis of integrated well logging and a geological report provided. A set of well logs was run for two wells (RB-A2 and RB-B2), comprising gamma ray, resistivity, density, neutron, sonic, and photoelectric factor. Composite logs and geological reports were also used to help deduce the lithological and biological description of the stratigraphic units under investigation. The stacking patterns of the carbonate rocks yielded three types of electro-facies. The first facies covers the lower part of the Brown Limestone (early Campanian) and reflects a cylindrical (aggrading) stacking pattern. This facies indicates keep-up carbonate deposition in a heterogeneous facies accumulated in shallow water. The second facies covers the upper part of the Brown Limestone (late Campanian) and displays a funnel (prograding) stacking pattern. This facies indicates the depositional setting of a shallow shoreline. The third facies covers the Sudr Chalk (Maastrichtian), for which a serrated stacking pattern indicates an aggradational environment. This pattern indicates a marine depositional setting both distal and deep. Therefore, the formation and evolution of the cyclical stacking pattern of the carbonate rocks reflects variations in accommodation potential that determines the environmental changes. The evolution of these deposits is mainly attributed to a combination of eustatic sea-level fluctuations and tectonic episodes within the basin.

Hydrocarbon detection and depositional environment prognosis in the Niger Delta - Integrated insights from log and seismic avo-inversion attributes

This study demonstrates the effectiveness of integrated seismic analysis and petrophysically constrained AVOinversion for reservoir evaluation and assessment of hydrocarbon potential and depositional environment in the Niger Delta. It is aimed at improved prediction of reservoir fluid, lithology, and ultimately the hydrocarbon prospects, with reduced uncertainties. The results delineate the characteristics of the reservoir sands, highlight major facies heterogeneities, unravel prolific stratigraphic features (such as channels, fan lobes), depositional fairways and provide insight into the mapped geology. These are expected to consequently reduce the uncertainties associated with the prospects for economic decision making.

Submarine-Channel Element Architecture Demonstrates Facies Heterogeneity in Both Strike and Dip Views: Miocene Modelo Formation, Lake Piru, California, USA

Submarine channels deliver vast quantities of sediment into ocean basins and the deposits left by these systems host important archives of paleoenvironmental change and are major targets for hydrocarbon production and carbon sequestration. However, similarities between channel subenvironments often make their identification difficult, particularly because some subenvironments are transitional or quite variable. While large channel complexes can often be resolved on seismic data, only outcrop data yields high-resolution detail of their internal heterogeneity. This study integrates 10 measured sections with drone-based photography to document lateral and vertical changes in depositional architecture in a well exposed outcrop of a submarine-channel element in the Miocene Modelo Formation at Lake Piru, California. The channel-element architecture is well constrained by erosional-surface mapping and lateral and vertical facies changes. The 3-dimensionality of the outcrop provides a unique example to demonstrate this heterogeneity in both strike (i.e., cross-sectional view) and dip orientations (i.e., longitudinal view). This channel element has a predictable vertical facies succession of thin sandstones and mudstones, mass transport deposits and amalgamated sandstones. The element is capped by a siliceous mudstones that provide a unique marker of hemipelagic deposition and the presence of an abandonment surface. The amalgamated sand packages are thickest in axial locations and thin over a distance of 500 m in the dip direction, but thin over 150 m in the strike direction toward two locations along the same margin. This thinning is used to constrain the dimensions and sinuosity of the channel element. We interpret a channel-element width of 550 m, a thickness of 29 m and an aspect ratio of 19:1, which is in agreement with previously published ranges of channel-element dimensions. With the documentation of lateral facies heterogeneity in orientations slightly oblique to both strike and dip, this study provides important data for understanding channelized sediment gravity flow dynamics in submarine channels and aids in evaluating reservoir-model volume and connectivity estimates.

Characteristics of oils and their potential source rocks from the Cherokee Platform, Oklahoma

The Woodford Shale is the most prolific source rock in the Anadarko Basin and Cherokee Platform and, over the past decade, it has become renowned for its high unconventional hydrocarbon potential. Recent Woodford Shale studies have emphasized facies heterogeneity based on lithology, sequence stratigraphy, and geochemical analyses. Data presented in this paper focus on the organic geochemical characterization and genetic relationship between the Woodford Shale and oils in the Cherokee Platform area, Pottawatomie County, Oklahoma. The shale samples were screened by total organic carbon (TOC) and Rock-Eval (RE) that indicate a high-quality Type I/II kerogen. Vitrinite reflectance measurements (VR%) of 0.59% for the Woodford Shale indicate the samples are at an early maturity stage in this area. The Woodford Shale generally has been subdivided into three members (Upper, Middle, and Lower), but in this study only the Upper and the top part of the Middle Woodford were characterized. Both intervals alternate between suboxic and anoxic depositional conditions, along with water column stratification and episodic euxinia or photic zone anoxia (PZA). A PZA episode has been described for Upper Woodford for the first time where C40 carotenoids and aryl isoprenoids show maximum abundance.The second part of the investigation involved oils, collected from wells in the area, and a detailed correlation with the Woodford Shale. The oils showed a close correlation with the Woodford, but maturity based on biomarkers may suggest a deeper source rock with equivalent organofacies. Many of the oils examined showed varying levels of biodegradation and possible mixing with a lighter more mature oil. The oils were compared with each other to determine possible relationships and assess the petroleum system on the southern Cherokee Platform.

Study on the Reservoir Heterogeneity of Different Volcanic Facies Based on Electrical Imaging Log in the Liaohe Eastern Sag

The volcanic rocks of the Es3 Formation (the third member of the Eocene Shahejie) in the Liaohe Eastern Sag can be divided into four facies and twelve subfacies. The porosity spectrum, porosity bin, variation coefficient (VC), and porosity width derived from electrical imaging log data were applied to study and characterize the heterogeneity of four facies and nine subfacies, both qualitatively and quantitatively. However, the VC and porosity width cannot be used to quantitatively classify heterogeneity when the VC is small and the porosity width is large. In the present study, the authors propose a new parameter, Pvcd = variation coefficient × porosity width. Based on this parameter, using a combination of porosity spectra, porosity bin features, VC, and porosity width, lithofacies heterogeneity is divided into three categories. The first is weak heterogeneity, which has a Pvcd < 1.1, a VC < 0.15, and a porosity width < 6. The second is moderate heterogeneity, which has a Pvcd 1.1–1.6, a VC 0.15–0.25, and a porosity width 6–9. The third is strong heterogeneity, which has a Pvcd > 1.6, a porosity VC > 0.25, and a porosity width > 9. In these three cases, the porosity spectra mainly display unimodal features, the porosity bins are concentrated, the bimodal features with tails and porosity bins are less concentrated, or the multimodal features with tails and porosity bins are scattered, respectively. Favorable reservoirs of volcanic rocks are controlled by lithofacies. In the study area, the favorable reservoirs appear to be the diatreme subfacies with low or medium heterogeneity, the pyroclastic flow subfacies with low heterogeneity, the compound lava flow subfacies with low or medium heterogeneity, and the outer zone subfacies with strong heterogeneity.

Effect of litho-facies on nano-pore structure of continental shale in shuinan formation of Jiaolai Basin

Continental shale lithofacies has an important influence on nano-pore structure? However, nano-pore distribution heterogeneity (NDH) in continental shale lithofacies is not well documented. Continental shale was collected from the Shuinan Formation in the Jiaolai Basin, and the shale lithofacies of all samples are identified based on the mineralogical composition and TOC content. Nano-pore size distributions are characterized by LPN2 and CO2GA tests. Then, micro-pore (0.3∼2 nm) and meso-pore (2∼100 nm) distribution heterogeneity of different facies are discussed by single and multi-fractal model. Finally, the pore structure mechanism in shale lithofacies is clarified, and the results are as follows. The lithofacies of all shale samples are classified into three types, (A) calcareous shale lithofacies is characterized by the higher siliceous minerals and highest TOC content; (B) Calcareous/siliceous mixed shale lithofacies is characterized by middle TOC content; (C) Siliceous shale lithofacies is characterized by higher clay minerals and lowest TOC content. Micro- and meso-pore volume and A shale lithofacies NDH is much lower than that of B and C, which indicates that the lithofacies type has a great influence on the nano-pore structure. Felsic mineral and TOC content has a weak negative correlation with nano-pore structure, and there is a linear relationship between clay mineral content and nano-pore volume, indicating that clay mineral content is the main factor that can affect nano-pore structure. Moreover, fractal characteristics of the nitrogen desorption curve have been proved, and there are obvious differences in the fractal values of adsorption and desorption curves among those different lithofacies. Single fractal dimension D1 derived from LPN2 and CO2GA tests has a linear correlation with the multifractal parameter D-10-D0, which shows that a lower pore volume of pore diameter determines NDH variation. In conclusion, siliceous rich shale can provide a larger pore volume and specific surface area, and it acts as the dominant lithofacies for shale gas drainage in the study area.

Reconstruction of Tournaisian-Viséan tectonic and climatically induced event histories of the Mobarak carbonate platform along depositional strike in the northeastern margin of Gondwana: Constraints from high-resolution cycle and sequence stratigraphy

Cyclic successions are one of the most important types of deposits in the carbonate platform of the Mississippian (Tournaisian-Viséan) in Gondwanan and Laurussian margins. The importance of climatically induced events impact on the amplitudes and frequencies of sea-level fluctuations in Mississippian of Iran is significant because the beginning, extent, duration, and significance of periods of climatically induced events in northern margin of Gondwana are not well recognized. A high-resolution sequence architecture in integration with paleoenvironmental reconstruction and foraminiferal biozonation from the Tournaisian-early Visean carbonate successions of the Mobarak Formation in Alborz basin along depositional strike (E-W- a distance of c. 340 km) suggests a mosaic-like pattern of deposition and compartmentalization of the depositional settings (homocline ramp to distally steepened ramp). According to the recognized facies, the stacking pattern of high-frequency cycles across the platform, and major accommodation events recognized on the correlated Fischer plots, six 3rd-order sequences (DS1–DS6) were identified. Detailed analysis on high-frequency cycles representing a highly variable number of shallowing-upward cycles, types, thicknesses, and facies heterogeneity along depositional strike. A combination of the episodic tectonic events along faults interacting with autocyclic processes, and inherited topographic irregularities are suggested as the driving mechanism for the cycle development. Six stages of Mobarak carbonate platform evolution based on understand the interplay of autocyclic and allocyclic controls are recognized in a hierarchical 3rd-order sequence stratigraphic framework and a chronological order: (1) early Hastarian corresponds to post-glacial transgressive episode with progressive backstepping of facies belts of early TST of DS1 throughout the region; (2) middle to late Hastarian corresponds to a major transgressional phase of DS1 following global temperature rise superimposed on different subsidence/uplift rates with the deformation of the platform along depositional strike; (3) Hastarian–Ivorian boundary corresponds to TST of DS2 with facies heterogeneity along depositional strike related to continuation of different subsidence/uplift rates. The absence of any systematic changes in the amplitude and period of cyclicity or lowstand deposits and subaerial surfaces during this phase shows the lack of influence of mid-Tournaisian glaciation and concurrent eustatic regression in northern margin of Gondwana. (4) early to middle Ivorian coincides with the RST of DS2 and TST of DS3 showing by remarkable topographic irregularities in the basin physiography and change in the position of the depocenter axis from a E–W trend to the center; (5) late Ivorian-early Moliniacian coincides with the RST of DS3 and DS4 showing by the Late Tournaisian thermal period and eustatic rise superimposed on uplift and subaerial exposure of the western part and subsidence in the central and eastern parts of the basin; (6) Moliniacian coincides with DS5-DS6 sequences showing by change from fault-related topography to major tilted fault-block topography accompanied by eustatic sea-level fall caused indirectly by the Viséan and Serpukhovian glaciations phases.

Assessment of the Nature of the Achimov Reservoir Saturation from Well Log Data Under Low Permeability and Facies Heterogeneity Conditions

Assessment of the Nature of the Achimov Reservoir Saturation from Well Log Data Under Low Permeability and Facies Heterogeneity Conditions

Evaluation of facies heterogeneity in reef carbonate reservoirs: A case study from the oil field, Perm Krai, Central-Eastern Russia

Reef deposits of the Upper Devonian oil fields in the north of the Perm Krai (Russia) are a primary hydrocarbon-bearing reservoir rock. This study provides new insights into carbonate reef reservoirs' sedimentation and formation processes. It also creates an essential basis for a large-scale and comprehensive analysis of carbonate reef reservoir properties. In this study, a comprehensive classification of rocks was performed using geological, petrophysical, and well-logging data. The rock types were determined based on the description and study of 250 core samples, including using X-ray microtomography, SEM, XRD, and XRF analysis. These integrated analyses allowed five facies to be identified: bioherm core, upper and lower parts of the deposit band, bordering the foot of the upland, shallow-marine facies, and reef slope. The cyclic nature of these carbonate deposits was identified, despite their identical mineralogical basis. The cyclicity of the deposits is shown by the structural features of the sediments of the various facies types and is controlled by the periodicity of tectonic movements and sedimentation processes. Lithological–facies maps were constructed for six cyclists of the productive Upper Devonian deposits of the Gagarinskoe field, which reflect the distribution of the main facies belts. The performed reservoir property analysis of the core samples made it possible to establish differences between different facies types; accordingly, the facies zonality of the reef reservoir and its relationship with reservoir properties were analyzed. Based on the results of the core sample study and geophysical studies of wells, the facies zonality of the reef reservoir of the Gagarinskoe field was determined. A detailed study of the void space of the core samples revealed various fracture types, including fractures mostly healed by calcite, which do typically not play a significant role in fluid filtration, and long and short fractures, which can considerably affect fluid filtration. The study of various fracture types and their impact on well productivity represents a key task for further research.