Search Results (18)

In this study, Kerogen conversion and oil production laboratory modeling results in Bazhenov formation source rock samples (Western Siberia, Russia) are presented. Two samples from one well with a similar composition and immature type II kerogen, which were accumulated in the same deep-sea conditions, were used for this investigation. Hydrous pyrolysis was performed under 300 °C, with liquid products and a sample portion collected every 12 h to study kerogen parameters via pyrolysis and the synthetic-oil composition via GC–MS. The transformation of pyrolytic parameters was similar to the natural trend previously determined for Bazhenov source rocks with different maturities. The synthetic oils’ normal alkane composition and biomarker parameters transformed with time. Sedimentary conditions and lithology biomarker parameters presumed to be constant (Pr/Ph, Ph/C18, H29/H30, and DBT/Phen) changed depending on the heating duration. The oil maturation increased slightly. Differences between the samples were detected in hydrocarbon generation endurance (5 and 8 days), n-alkane composition, and C27/C29 and DBT/Phen. A hypothesis about the influence of kerogen variability and mineral matrix on oil production was made. This paper provides the basis for more detailed and accurate investigation of the factors affecting kerogen cracking and hydrocarbon formation. Full article

The aim of this investigation is to determine the role of temperature in hydrocarbon generation in Bazhenov formation source rocks, as hydrothermal processes in situ are supposed to be the main contributor to kerogen transformation in Western Siberia. Laboratory modeling of organic matter isothermal transformation in powdered and extracted samples by hydrous pyrolysis at 300 °C, 325 °C, 350 °C, 375 °C, and 400 °C for 24 h was performed. Heated samples were analyzed via pyrolysis, and hydrocarbons were investigated by GC and GC-MS. Results show that more than 90% of the kerogen generation potential was utilized. The amounts of liquid and gaseous products reached 82 and 126 mg of hydrocarbon/g TOC, respectively. The volume of generated gas increased while the maximum production of liquid decreased with temperatures over 350 °C. The biomarker composition of liquid products at different temperatures was similar. The characteristics of kerogen and the product composition had a high correlation with the parameters for samples naturally formed in situ under an elevated heat flow. More subtle chemical analyses are required to determine the effects of kerogen’s chemical structure and the rock mineral composition on oil and gas generation. Full article

Jurassic strata in the ST gas field of the northern West Siberia Basin have been regarded as a potential exploration target with undiscovered hydrocarbon resources. However limited research has been performed on the sequence stratigraphy of the Jurassic strata, as well as its sandstone distribution controlled by variable sea level change and sediment input. In this paper, four third-order sequences (SQ1, SQ2, SQ3, and SQ4) and nine fourth-order sequences for the Jurassic strata are interpreted based on seismic facies analysis and the lithology stacking patterns of seven wells. SQ1 is characterized by the special Bazhenov Formation which is featured by regionally distributed deep marine shales. SQ2 (J1) is composed of a coarsening upward sequence, the base of which is an unconformable surface that can be recognizable in both seismic profiles and well logging data. SQ3 (J2-J8) is composed of a complete fining-upward and coarsening-upward sequence, showing a series of transgressive and regressive successions. A complete SQ4 has not been drilled through by all the seven wells, only showing a coarsening upward succession on its top (J9) which evolves into a fining upward succession at the base of SQ3. Combined with the seismic inversion result, which predicts sandstone distribution, a sequence evolution model was built for SQ3 showing a full unit of transgressive system tract and highstand system tract (TST-HST) which often occurs in shallow marine shelves. During sequence development, most reservoir sandstones are deposited in the shelf and tidal delta environment at the bottom of the TST and the top of HST, and mudstones are deposited as shelf mudstones, especially at maximum flooding surface. That is controlled by both accommodation and sediment input. Generally, under this sequence framework, the depositional architecture can be further analyzed with implications for source rock, reservoir sandstones, and sealing rock, which may guide future gas exploration and exploitation in this area. Full article

Gas injection has already proven to be an efficient shale oil recovery method successfully tested all around the world. However, gas-enhanced oil recovery methods have never been implemented or tested for the greatest Siberian shale oil formation yet. This article proposes numerical simulation of a hydrocarbon gas injection process into a horizontal well with multiple hydraulic fractures perforating Bazhenov shale oil formation in Western Siberia characterized by ultra-low permeability. A complex field-scale numerical study of gas injection for such a formation has never been performed before and is presented for the first time in our work. The hydrodynamic compositional simulation was performed utilizing a commercial simulator. A sensitivity study for different operating parameters including cycle times, bottom-hole pressures for the production and injection period, and injected gas composition was performed after the model was history matched with the available production data. Some uncertain reservoir properties such as relative permeability curves were also sensitized upon. Two different ways of accounting for multiple hydraulic fractures in the simulation model are presented and the simulation results from both models are compared and discussed. Eventually, huff-n-puff injection of a hydrocarbon gas resulted in a 34–117% increase in oil recovery depending on the fracture model. Full article

The paper reports comprehensive analysis of different factors affecting uranium content in oil source rocks and the relationship between uranium content and productivity of source rocks. The analysis of data for 13 wells of the Bazhenov Formation (Western Siberia, Russia) was carried out. The uranium content of the rocks was measured by gamma-ray spectrometry on core samples. In order to analyze factors affecting uranium accumulation in source rocks, we studied content and characteristics of organic matter (Rock-Eval pyrolysis), and also mineral, element, and isotope composition of rocks. We have shown that redox conditions at the sedimentation stage have the most pronounced impact on the uranium accumulation in the rocks of the Bazhenov Formation. It was also shown that productive intervals, containing increased amounts of mobile hydrocarbons, are characterized by low (<20 ppm) concentration of uranium. However, the intervals, containing phosphorite minerals may show better reservoir properties and oil saturation at higher concentration of uranium. The analysis of correlations and relationships between uranium content and Rock-Eval pyrolysis indexes (oil saturation index and productivity index) enabled formulation of criteria for selection of oil-saturated intervals using the spectral gamma and pulsed neutron spectroscopy log data. Full article

Rock swelling and rock disintegration in the presence of drilling, stimulation and completion fluids are considered to be the main reasons for operational and production problems for wells in clay-rich formations. The impact of these fluids on rock properties shall be established for the effective treatment design. This paper describes the development of the experimental setup for studying rock swelling in reservoir conditions and the application of this setup for the evaluation of swelling mechanisms of shale rock samples. Swelling quantification was performed using measuring piston displacement that was caused by rock swelling in a piston accumulator during pressure maintenance. We studied the interaction of the disintegrated rock samples with water-based and hydrocarbon-based fluids and supercritical CO₂. It was found that alkaline water solution in reservoir conditions causes swelling of the used rock samples in the amount of 1–3% vol. with a direct correlation between the rock swelling magnitude and the total clay content. The change in the rock volume in the presence of the used hydrocarbon-based fluid depends on the content of organic matter, its distribution in the rock, and the clay content. The observed swelling degree in the hydrocarbon fluid and CO₂ was significantly lower (0–0.5% vol.) than in water. The proposed methodology and obtained results can further be used for the optimization of various operations in clay-rich formations. Full article

The paper presents the results of an experimental study of heating and the structural resultant changes of source rocks under the influence of the electromagnetic field in the microwave and radio-frequency ranges. The samples from the Bazhenov Formation (West Siberia, Russia) and the Domanic Formation (Ural, Russia) have been tested. It is shown that samples from these formations demonstrate very different heating rates at the same electromagnetic field parameters and the their heating rate depends on the type of the electromagnetic field (radio-frequency or microwave) applied. The temperature of the Bazhenov Formation samples reaches 300 °C within one hundred seconds of the microwave treatment but it slowly rises to 200 °C after twelve minutes of the radio-frequency influence. The samples of the carbonate Domanic Formation heat up more slowly in the microwave field (within two hundred seconds) and to lower temperatures in the radio-frequency (150 °C) than the Bazhenov Formation samples. The study of the structure of the samples before and after experiments on the electromagnetic treatment shows fracture formation during the heating process. Numerical simulations of heating dynamics of source rock samples have been based on a simple mathematical model of the electromagnetic influence and main features of heating for different types of source rock have been revealed. The opportunities for application of electromagnetic heating for oil source rock recovery are discussed. Full article

This study is focused on the mineralogical, chemical, and isotopic characterization of pyrites from the rocks of the Bazhenov Formation (Upper Jurassic–Lower Cretaceous organic-rich shales, Western Siberia, Russia). Scanning electron microscopy (SEM) revealed pyrites of different morphologies: small and large framboids, small crystals, and large euhedral crystals; all morphotypes were usually combined into aggregates. Isotope ratio mass spectrometry (IRMS) and secondary ion mass spectrometry (SIMS) showed that small framboids and microcrystalline pyrite are isotopically light, with δ³⁴SCDT varying from −55 to −20‰. Large framboids and euhedral crystals of pyrite are isotopically heavy with δ³⁴SCDT up to +26‰. Both morphology and δ³⁴S were suggested to be controlled by the redox conditions and sedimentation regime. The abundance of small framboids suggests that pyrite sedimentation occurred under anoxic conditions; the presence of the large framboids and euhedral crystals of pyrite suggest the accumulation of sediments occurred at suboxic conditions, possibly in the presence of oxygen. Full article

The present work is devoted to geochemical studies of the Bazhenov Formation in the north of the West Siberian Petroleum Basin. The object is the Upper Jurassic–Lower Cretaceous section, characterized by significant variations in total organic carbon content and petroleum generation potential of organic matter at the beginning of the oil window. The manuscript presents the integration of isotopic and geochemical analyses aimed at the evaluation of the genesis of the rocks in the peripheral part of the Bazhenov Sea and reconstruction of paleoenvironments that controlled the accumulation of organic matter in sediments, its composition and diagenetic alterations. According to the obtained data, the sediments were accumulated under marine conditions with a generally moderate and periodically increasing terrigenous influx. The variations in organic matter composition are determined by redox conditions and terrigenous input which correlate with the eustatic sea level changes during transgressive/regressive cycles and activation of currents. Transgression is associated with an intensive accumulation of organic matter under anoxic to euxinic conditions and insignificant influence of terrigenous sources, resulting in the formation of rocks with oil-generating properties. During the regression periods, the terrigenous sedimentation increased along with the dissolved oxygen concentration, and deposits with low organic matter content and gas-generating properties were formed. Full article

In situ shale or kerogen oil production is a promising approach to developing vast oil shale resources and increasing world energy demand. In this study, cyclic subcritical water injection in oil shale was investigated in laboratory conditions as a method for in situ oil shale retorting. Fifteen non-extracted oil shale samples from Bazhenov Formation in Russia (98 °C and 23.5 MPa reservoir conditions) were hydrothermally treated at 350 °C and in a 25 MPa semi-open system during 50 h in the cyclic regime. The influence of the artificial maturation on geochemical parameters, elastic and microstructural properties was studied. Rock-Eval pyrolysis of non-extracted and extracted oil shale samples before and after hydrothermal exposure and SARA analysis were employed to analyze bitumen and kerogen transformation to mobile hydrocarbons and immobile char. X-ray computed microtomography (XMT) was performed to characterize the microstructural properties of pore space. The results demonstrated significant porosity, specific pore surface area increase, and the appearance of microfractures in organic-rich layers. Acoustic measurements were carried out to estimate the alteration of elastic properties due to hydrothermal treatment. Both Young’s modulus and Poisson’s ratio decreased due to kerogen transformation to heavy oil and bitumen, which remain trapped before further oil and gas generation, and expulsion occurs. Ultimately, a developed kinetic model was applied to match kerogen and bitumen transformation with liquid and gas hydrocarbons production. The nonlinear least-squares optimization problem was solved during the integration of the system of differential equations to match produced hydrocarbons with pyrolysis derived kerogen and bitumen decomposition. Full article

The current study is devoted to the determination and interpretation of geochemical trends reflecting hydrocarbon generation, migration and accumulation in unconventional reservoirs; the study is performed on the Bazhenov shale rock formation (Western Siberia, Russia). Results are based on more than 3000 Rock-Eval analyses of the samples from 34 wells drilled in the central part of the West Siberian petroleum basin, which is characterized by common marine sedimentation environments. Pyrolysis studies were carried out before and after the extraction of rocks by organic solvent. As a result, we have improved the accuracy of kerogen content and maturity determination and complemented the standard set of pyrolysis parameters with the content of heavy fraction of hydrocarbons. The data obtained for the wells from areas of different organic matter maturity was summarized in the form of cross-plots and diagrams reflecting geochemical evolution of the source rocks from the beginning to the end of the oil window. Interpretation of the obtained results revealed quantitative trends in the changes of generation potential, amount, and composition of generated hydrocarbons in rocks at different stages of oil generation process. The analysis of geochemical trends allowed us to improve approaches for the productivity evaluation of the formation and study the effect of organic matter maturity on distribution of productive intervals of different types. Full article

The study of organic matter content and composition in source rocks using the methods of organic geochemistry is an important part of unconventional reservoir characterization. The aim of this work was the structural group analysis of organic matter directly in the source rock in combination with a quantitative assessment and surface distribution analysis of the rock sample by FTIR spectroscopy and FTIR microscopy. We have developed new experimental procedures for semi-quantitative assessment of the organic matter content, composition and distribution in the source rocks and applied these procedures for the study of the samples from the Bazhenov shale formation (West Siberia, Russia). The results have been verified using the data from the study of organic matter obtained by Rock-Eval pyrolysis and differential thermal analysis. The obtained results demonstrate the prospects of FTIR spectroscopy and FTIR microscopy application for non-destructive and express analysis of the chemical structure and distribution of organic matter in rocks. Full article

The deposits of the Bazhenov formation are a unique reservoir of unconventional oil reserves in Western Siberia. They contain both solid organic matter (kerogen) and liquid light oil. The successful development of these hydrocarbons is largely determined by the adequacy of the void space models. The aim of the study is to identify the types of void space in the sediments of the Bazhenov formation and to identify the distribution patterns across the section of the researched wells. The void space was studied by electron and optical microscopy, and the mineral composition of the rocks was determined by X-ray diffraction analysis. The deposits of the Bazhenov productive formation in the territory of Western Siberia are represented by a wide complex of lithotypes, including various kinds of silicites, carbonate, clay rocks, and mixtites. The reservoir space in the reservoir rocks of the Bazhenov formation is a complex and hierarchically subordinated system, which includes voids and fractures of various sizes, configurations, and genesis. The void space of the Bazhenov formation is characterized by a fairly high degree of spatial heterogeneity, which is controlled by lithological, facies, and tectonic factors, as well as the direction of catagenetic processes. Full article

This paper addresses potential application of data on stable carbon and oxygen isotope composition of carbonates for study of organic rich source rocks on the example of the Late Jurassic–Early Cretaceous Bazhenov Formation (West Siberian petroleum basin, Russia). Geochemical studies were conducted for sections located in central (most productive) and peripheral (northern and southern) regions of the Bazhenov Formation distribution area, containing deposits formed under different conditions. We identified key factors impacting stable isotope composition of carbonate minerals and established relation of their isotope composition to the formation conditions. Using a thermodynamic model of carbon and oxygen isotope exchange in the carbonate–water–carbon dioxide system, it is shown that variations in the isotope composition of secondary carbonates are affected by isotopic composition of primary carbonates in sediments and by the isotope exchange reactions with water and carbon dioxide, generated during the source rocks transformation. Our results demonstrate that stable isotope data for carbonates in the Bazhenov Formation together with standard geochemical methods can be efficiently applied to determine sedimentation conditions and secondary alteration processes of oil source rocks. Full article

Core analysis provides the essential information necessary for the characterization and development of hydrocarbon reservoirs. High core-scale heterogeneity and anisotropy, natural in unconventional reservoirs, complicate reservoir characterization and dictate the sampling methodology used. Continuous high-resolution thermal measurements with an optical scanner and scratcher along the core column can yield benefits in a sampling strategy. This article describes some features of the suggested integration of non-destructive thermal profiling with partially destructive scratch testing applied for the study of rocks from the Bazhenov Formation (West Siberia, Russia). The spatial variation in the unconfined compressive strength and thermal conductivity components parallel and perpendicular to bedding for more than 1000 samples are demonstrated and discussed on core and log scales. The relationships between these properties are established for different rock types composing the formation. The joint analysis allows specialists to correctly define multiscale heterogeneities and facies that would be difficult or impossible to observe with logging data analysis or geological description alone. The established relationships make it possible to partially replace the semi-destructive scratch test with non-destructive optical scanning, providing UCS estimation. One more important outcome of the present work is the lessons learned regarding how to organize future works. The integration of thermal core profiling and scratch testing data looks promising for unconventional reservoir characterization. Full article