Thermal Evolution Degree Research Articles

Pore Structure and Its Controls of Shale in the Qingshankou Formation, Sanzhao Sag, Songliao Basin

The exploration and development of Gulong shale oil in the Songliao Basin has achieved a major breakthrough, with the result that a national shale oil demonstration area is being built. The shale in the Sanzhao Sag is abundant in organic matter and is an important replacement area. For this reason, it has recently become a focus for research and exploration. Compared with the Gulong Sag, the Qingshankou Formation in the Sanzhao Sag is relatively immature, and comparatively little is known about its pore structure. For this study, well ZY1, a key well in the Sanzhao Sag, was selected as the research object. Thin section observation, high-resolution field emission scanning electron microscopy, Modular Automated Processing Systemimaging, X-ray diffraction of whole rock and clay, TOC pyrolysis, and Low-pressure N2 adsorption were used to investigate the pore structure in the sag to determine the factors influencing pore development. The principal understandings are as follows: (1) The Qingshankou Formation in the Sanzhao Sag is predominantly clay shale, with a high content of clay minerals (32.8 to 70%) and TOC contents of 0.7 to 11%. These values indicate good hydrocarbon generation potential. (2) Interparticle pores, intraparticle pores, and organic matter pores are developed. Intergranular pores are the main type, mostly observed between granular minerals or between granular minerals and clays. Intraparticle pores are observed in pyrite mass and dissolved unstable minerals. Organic matter pores (OMP) occur in primary organic matter and migrate into solid bitumen. (3) The shale pores in the Sanzhao Sag are mainly H3-type slit pores, with specific surface areas of 5.4~22.9 m2/g and pore volumes of 0.03~0.07 cm3/g. Mesopores make the largest contribution to pore volume and specific surface area. Scanning electron microscope (MAPS) imaging shows that the pore size distribution of shale is mainly 20~30 nm and 100~200 nm and that large pores, especially pores of 100~200 nm and 1~2 μm, make the largest contribution to the facies. (4) The pore structure in the Sanzhao Sag is affected by mineral composition, abundance of organic matter, thermal evolution degree, and diagenesis. Organic-inorganic interactions influence and determine the pore structure characteristics of the Qingshankou Formation shale. This paper is intended to provide scientific guidance and technical support for evaluating the effectiveness of shale oil reservoirs and selecting sweet spots in the Sanzhao Sag.

Formation conditions and the main controlling factors for the enrichment of shale gas of Shanxi Formation in the southeast of Ordos Basin, China

Based on the dissection of the geological characteristics of typical shale gas wells, the relationship between reservoir-forming factors and shale gas enrichment is deeply analyzed, and the controlling factors of shale gas enrichment are summarized. An analysis of data from drilling, logging, testing, and shale sample has revealed that the factors contributing to the formation of shale gas reservoirs in marine–continental transitional facies of Shanxi Formation in the southeast of Ordos Basin are highly heterogeneous. This is mainly reflected in the rapid spatial change of shale organic matter, physical properties, and other parameters of the shale in this area. The shale found in the Shanxi Formation has a high content of organic carbon (TOC), with an average of 2.24%. The kerogen type is mainly type Ⅲ, and the average value of RO is 2.48%, indicating that it is in the high mature-overmature stage and is a high-quality source rock. The rock composition is rich in clay (40.5%–88.5%), mainly composed of illite-mongolian mixed layer and kaolinite, and its relatively high specific surface area is beneficial for improving the gas adsorption capacity of the shale. Thin sandstone interbeds, measuring less than 3 m are widely distributed in the Shanxi Formation and have good physical conditions. With an average porosity 3.37% and an average permeability of 0.1 mD. The natural gas generated by the shale can be transported to these sandstone interlayers (laminae) in a short distance, which is beneficial for improving the gas-bearing property of the shale. The gas-bearing property of the Shanxi Formation in the study area is affected by different lithologic assemblages. The gas-bearing property of the thick mudstone-coal assemblage of the second member of the Shanxi Formation is the best, with more than 80% of the samples having a gas content of over 1 m3/t. This study suggests that the high thermal evolution degree of shale, special marine–continental transitional facies reservoir conditions, and good preservation conditions are the main factors affecting the enrichment of shale gas in the study area. This makes the shale gas of the Shanxi Formation in the southeast of the Ordos Basin have certain potential for exploration and development, and delineates the enrichment targets of shale gas in the Zichang-Yan'an-Fuxian and Yichuan areas.

Major period and process of hydrocarbon accumulation of deep reservoirs — A case study of Tuoputai area in Tarim Basin, China

Deep hydrocarbon reservoirs in China's Tarim Basin are characterized by multistage accumulation, but the major period and the process of hydrocarbon accumulation are still ambiguous. By integrating analyses of fluid inclusions, light hydrocarbon and diamondoid, and reservoir bitumen, we determined the contribution of oils charged in different periods and reconstructed the hydrocarbon accumulation process of Ordovician reservoirs in the Tuoputai area, which is significant to expand deep petroleum exploration in Tarim Basin. The results show that the abundance of yellow to yellowish-green (34.6%–42.1%) and bluish-green oil inclusions (42.1%–46.2%) is relatively high, followed by the blue oil inclusions (15.4%–23.1%). The Th values of the corresponding coexisting aqueous inclusions are mainly in 70–80 °C, 90–100 °C, and 120–130 °C, respectively. The hydrocarbon charging is mainly in the late Caledonian and the late Hercynian, followed by the Himalayan. However, oils charged in the late Caledonian experienced strong biodegradation with the tectonic uplift in the early Hercynian and were transformed into heavy oils and carbonaceous bitumen. The recharged oils have not been altered by biodegradation, thermal cracking, gas washing, and thermochemical sulfate reduction, the amount of oils charged in the Himalayan was relatively small. And the calculated maturity of oils, determined by vitrinite reflectance (Rc = 1.3%–1.5%), is similar to the thermal evolution degree of the Є1y source rock in late Hercynian (1.3%–1.6%) and far less than that in Himalayan (1.8%–2.0%). Large amounts of oils accumulated in the late Hercynian made a major contribution to the current reservoirs. Deep hydrocarbon reservoirs in Tuoputai area were mainly got accumulated when the formation was shallowly buried and then preserved with the deep burial.

Microwave pretreatment of biomass for conversion of lignocellulosic materials into renewable biofuels

For the conversion of lignocellulosic material into renewable biofuels the microwave pretreatment of raw material is a new and promising technology. This work presents a numerical simulation of microwave heating of materials derived from sugar cane, african palm and green algae in microwave domestic oven. The power absorption of biomasses is studied in cylindrical and spherical shapes, with volumes varying from 10−5 m3 to 100 × 10−5 m3, as function of humidity (from 20% to 80%). Maxwell equations were employed to calculate the microwave electromagnetic field distribution in the microwave cavity and in the samples, coupled to heat equation when the humidity is varied. Penetration depth varied from 2 × 10−2 to 10 m and tanδ from 2 × 10−3 to 7 × 10−1 as function of humidity. Plots of electric field and temperature distribution inside the oven were done for sugar cane, palm oil and green algae for cylindrical and spherical samples for 30% and 65% of humidity in the samples. The coefficient of variation (COV) varied between 0.05 and 0.18. The rate of heating efficiency was evaluated using the degree of thermal runaway ΔT (5K<ΔT<75K) and evolution of average temperature T‾ (300K<T‾<370K) and their relationship with the energy absorbed by the samples and COV, respectively. The comprehensive evaluation coefficient, that describes the usability of a specific lignocellulosic material in industry, varied between 0.3 and 10.0, was calculated for the biomasses shapes and sizes as function of power and humidity.

Quantitative characterization and formation mechanism of the pore system heterogeneity: Examples from organic-rich laminated and organic-poor layered shales of the upper triassic chang 7 member in the southern Ordos Basin, China

The heterogeneity of shale pore structure is a vital problem that cannot be ignored in the process of shale oil exploration and development. The organic-rich laminated shale (ORLS) and organic-poor layered shale (OPLS) show significantly different pore system heterogeneity. In this study area, the porosity and permeability of ORLS (2.7% and 0.00053mD) are higher than those of OPLS (2.29% and 0.00041mD). The heterogeneity of the pore system in ORLS is reflected by the wider pore size range of intercrystalline pores (pore size of 0.002–5.5 μm), the stronger holistic distribution heterogeneity of intergranular pores (average △α of 1.61) and organic pores (average △f of 2.65) at local locations. The wider range and discontinuity of the pore size distribution for intergranular pores and organic pores, and the instability of the morphological structure for intercrystalline pores and microfractures, all lead to the heterogeneity of the pore system in OPLS. The micropore (<2 nm) volume and macropore (>50 nm) volume of ORLS are higher than that of OPLS, while the surface area and volume of mesopores (2–50 nm) are lower than those of OPLS. The macropore has the most obvious fractal characteristics and three fractal dimensions. The macropore volume of ORLS is positively correlated with reservoir physical and pore multifractal properties, while the mesopore volume of OPLS is positively correlated with reservoir properties and negatively correlated with fractal properties. Pore system evolution patterns of shale reservoirs are obviously controlled by the mineral composition, laminae, TOC content, thermal evolution degree and fluid pathways. The macropore volume in ORLS shows a clear positive correlation with the pyrite content. The high TOC content and high thermal evolution degree are more likely to produce erosive fluids. Laminar interfaces, microfractures and primary pores provide channels for the fluid migration. The development degree of secondary dissolution may be an important factor leading to the difference of reservoir qualities between ORLS and OPLS.

Evaluation of Hydrocarbon Generation Potential of Laiyang Formation Source Rocks in Ri-Qing-Wei Basin, Eastern Shandong

The Ri-Qing-Wei Basin is a newly discovered Late Mesozoic rift basin on the eastern Shandong coast in recent years. Thick, continuous deposited source rocks are found in the Lingshan Island scientific drilling project. Therefore, it is necessary to evaluate the distribution and hydrocarbon generation potential of source rocks in this area. Organic geochemical experiments were carried out on samples from the core of LK-1 and outcrops in the Lingshan Island, the Laoshan area, and the Jimo Zhougezhuang area to evaluate the maturity, abundance, and type of organic matter in source rocks. The results show that the cumulative thickness of the source rocks in the study area is more than 500 m, and the TOC content is generally greater than 1.0%. The organic matter type is good (mainly type II1 and type II2 kerogen) and the Ro value is more than 2.0. The thermal evolution degree of the organic matter is high with natural gas predominantly generated. We carried out Rock-Eval, PY-GC and gold tube experiments on low-maturity samples of Laikong 2 and established a chemical kinetic model to quantitatively evaluate the study area in combination with sedimentary burial history and thermal history data. The results show that the total resources of the five sags in the study area are about 476 billion cubic meters, and the average resource intensity is about 82.2 million cubic meters/km2. Among them, the resource intensities of the Lingshan Island Sag and Laoshan Sag are 112.6 million cubic meters/km2 and 98.8 million cubic meters/km2, respectively. Studied sites are “small and fertile” and may be used as favorable exploration prospect areas.

Pore structure and fractal characteristics of the marine shale of the longmaxi formation in the changning area, Southern Sichuan Basin, China

The pore structure is an important factor affecting reservoir capacity and shale gas production. The shale reservoir of the Longmaxi Formation in the Changning area, Southern Sichuan Basin, is highly heterogeneous and has a complex pore structure. To quantitatively characterize the shale’s pore structure and influencing factors, based on whole rock X-ray diffraction, argon ion polishing electron microscopy observations, and low-temperature nitrogen adsorption-desorption experiments, the characteristics of the shale pore structure are studied by using the Frenkel-Halsey-Hill (FHH) model. The research reveals the following: 1) The pores of the Longmaxi Formation shale mainly include organic pores, intergranular pores, dissolution pores and microfractures. The pore size is mainly micro-mesoporous. Both ink bottle-type pores and semiclosed slit-type pores with good openness exist, but mainly ink bottle-type pores are observed. 2) The pore structure of the Longmaxi Formation shale has self-similarity, conforms to the fractal law, and shows double fractal characteristics. Taking the relative pressure of 0.45 (P/P0 = 0.45) as the boundary, the surface fractal dimension Dsf and the structural fractal dimension Dst are defined. Dsf is between 2.3215 and 2.6117, and the structural fractal dimension Dst is between 2.8424 and 2.9016. The pore structure of micropores and mesopores is more complex. 3) The mineral components and organic matter have obvious control over the fractal dimension of shale, and samples from different wells show certain differences. The fractal dimension has a good positive correlation with the quartz content but an obvious negative correlation with clay minerals. The higher the total organic carbon content is, the higher the degree of thermal evolution, the more complex the pore structure of shale, and the larger the fractal dimension. The results have guiding significance for the characterization of pore structure of tight rocks.

Hydrocarbon accumulation model influenced by “three elements (source-storage-preservation)” in lacustrine shale reservoir-A case study of Chang 7 shale in Yan’an area, Ordos Basin

The organic-rich shales of the Chang 7 Member in the Yan’an Formation of the Yan’an area, Ordos Basin is a hot spot for lacustrine shale gas exploration. In this paper, taking the Chang 7 Member shale in the Yan’an area as an example, the main controlling factors of lacustrine shale gas accumulation and the prediction of “sweet spots” are systematically carried out. The results show that the Yanchang Formation shale has the complete gas generating conditions. Shale gas accumulation requires three necessary accumulation elements, namely gas source, reservoir and good preservation conditions. The dynamic hydrocarbon generation process of the Chang 7 shale reservoirs is established according to the thermal simulation experiments of hydrocarbon generation, and the mechanism of catalytic degradation and gas generation in the Chang 7 Member under the background of low thermal evolution degree is revealed. The enriched authigenic pyrite can catalyze the hydrocarbon generation of organic matter with low activation energy, thereby increasing the hydrocarbon generation rates in the low-mature-mature stage. Different types of pores at different scales (2–100 nm) form a multi-scale complex pore network. Free gas and dissolved gas are enriched in laminar micro-scale pores, and adsorbed gas is enriched in nano-scale pores of thick shales, and silty laminates can improve the physical properties of the reservoir. This is because the laminar structure has better hydrocarbon generation conditions and is favorable for the migration of oil and gas molecules. The thickness of the lacustrine shale in the Chang 7 Member is between 40 and 120 m, which has exceeded the effective hydrocarbon expulsion thickness limit (8–12 m). At the end of the Early Cretaceous, the excess pressure of the Chang 7 shale was above 3 MPa. At present, horizontal wells with a daily gas production of more than 50,000 cubic meters are distributed in areas with high excess pressures during the maximum burial depth.

RETRACTED: Mineralogical and geochemical characteristics of the Mesoproterozoic sedimentary rocks in Rwanda and their implication for hydrocarbon investigation

To reduce deforestation and ensure energy security for socioeconomic advancements, Rwanda must find alternatives to wood fuel. Widely developed metasedimentary mudstones gradually became a petroleum survey object due to the progress of petroleum exploration theories and practices in the Mesoproterozoic strata all over the world. In this study, extensive field and experimental work was conducted to explore the organic features of the Mesoproterozoic strata and their relationship with the geological background, which is important for a petroleum survey of such strata. The results show that (1) the Mesoproterozoic samples have low total organic carbon (TOC) and S1+S2 and (2) except for the high degree of thermal maturity (Ro ranging from 3.71‒3.82, avg. 3.77), the low TOC is mainly caused by the hypoxia degree and dissolution of terrigenous clastic materials in shallow water environments related to the fluvial delta. Hence, the Gikoro and Pindura groups should be paid more attention in Northwestern Rwanda (offshore direction in paleography) in subsequent exploration work for their thicker mudstones. • The Mesoproterozoic samples have low TOC (less than 1.0, avg. 0.52) and S1+S2. • The samples experienced a high degree of thermal evolution. • The low TOC is mainly caused by the hypoxia degree and dissolution of clastic materials in a shallow water environment.

Controlling Effect of Wave-Dominated Delta Sedimentary Facies on Unconventional Reservoirs: A Case Study of Pinghu Tectonic Belt in Xihu Sag, East China Sea Basin

In order to find the “sweet spots” of unconventional oil and gas from the Pinghu Formation in the Pinghu Tectonic Belt, we are committed to clarifying the development and distribution rules of coal-measure source rocks and tight reservoirs as well as the controlling factors. Using 3D seismic and logging data, combined with logging constraints of target lithology and pyrolysis experiments of source rock, "source and reservoir" research of uncoventional oil and gas was carried out in the Pinghu Tectonic Belt. The results show that two stages of regression and one stage of transgression occurred in the Pinghu Formation, resulting in river-controlled and wave-controlled delta-neritic facies dominated by sedimentary facies, source rocks developed in interdistributary bay and swamp microfacies, and tight sandstones in point bar and distributary channel microfacies are developed. The accumulation of coalbed methane and shale gas is controlled by the sedimentary facies and the degree of thermal evolution under the factors of burial depth. The accumulation of tight sandstone is closely related to the dominantly sedimentary facies and diagenetic modification of physical properties and faults. It is concluded that the structural type, type and distribution of faults, and depositional environment of the Pinghu Tectonic Belt in the Xihu Sag are the key factors controlling the development and accumulation of coal-measure source rocks and tight sandstone reservoirs. This understanding provides a clear direction for the deep exploration of unconventional oil and gas in the sag and provides a reference for finding reservoir “sweet spots.”

Reservoir Characteristics and Resource Potential Analysis of Transitional Shale Gas in Southern Sichuan Basin

Natural gas is a clean and efficient energy source. Shale gas, one of the unconventional natural gases, is becoming an indispensable part of natural gas. Compared with marine facies shale gas, which has large-scale exploitation, marine and continental transitional facies shale gas have greater development potential. It could be the new direction of development in the future. In this article, the basic geological characteristics, sedimentary environment, and reservoir characteristics of organic-rich transitional facies shale in the southern Sichuan basin are analyzed by lithologic characteristics, chemical element analysis, reservoir space, gas bearing characteristics, and so on and are compared with domestic and abroad transitional shale gas. The results show that the sedimentary period of transitional shale of Upper Permian Leping Formation has a high paleoproductivity level and deposition rate favorable for the accumulation of organic matter in southern Sichuan basin. It was warm and humid paleoclimatic by Sr, V, Cr, Ni, Co, and other trace elements analysis. According to the experimental test analysis of reservoir characteristics, the organic matter is mainly type Ⅲ kerogen, and the thermal evolution degree is mainly overmature in the reservoir. The reservoir space is mainly of microfractures and micropores. The main types of micropore development are intergranular pore, intragranular pore, and organic pore. Compared with other shale gas regions that form industrial airflow, the study region with large thickness, highly brittle mineral content, high level of organic carbon content, and excellent gas-bearing characteristics, it has favorable conditions for shale gas accumulation. The southern Sichuan basin could be the key area for breakthroughs in the exploration and development of transitional shale gas in the next step.

Theories, technologies and practices of lacustrine shale oil exploration and development: A case study of Paleogene Kongdian Formation in Cangdong sag, Bohai Bay Basin, China

As the main factors affecting stable and high production and the production regularity of lacustrine shale oil are unclear, the theoretical understandings, key exploration and development technologies, development effect and production regularity of lacustrine shale oil have been analyzed and summarized based on 700 m cores taken systematically from Paleogene Kong 2 Member of 4 wells in Cangdong sag, over 100 000 analysis data and formation testing data. Three theoretical understandings on shale oil enrichment and high production have been reached: (1) High-quality shale with “three highs and one low” is the material base for shale oil enrichment. (2) Medium—slightly high thermal evolution degree is the favorable condition for shale oil enrichment. (3) Laminar felsic shale is the optimal shale layer for oil enrichment in semi-deep lake facies. Key exploration and development technologies such as shale oil enrichment layer and area evaluation and prediction, horizontal well pattern layout, shale oil reservoir fracturing, optimization of shale oil production regime have been established to support high and stable shale oil production. Under the guidance of these theoretical understandings and technologies, shale oil in Cangdong sag has achieved high and stable production, and 4 of them had the highest production of over 100 tons a day during formation testing. In particular, Well GY5-1-1L had a daily oil production of 208 m3. By April, 2022, the 28 wells combined have a stable oil production of 300–350 tons a day, and have produced 17.8×104 t of oil cumulatively. It is found that the shale oil production of horizontal well declines exponentially in natural flow stage, and declines in step pattern and then tends stable in the artificial lift stage. Proportion of light hydrocarbons in produced shale oil is in positive correlation with daily oil production and decreases regularly during production test.

The Characterization of Shale Differences Based on Petrophysical Properties and Pore Structure: A Case Study of the Longmaxi Formation in Northern Guizhou Province and the Yanchang Formation in the Ordos Basin

The pore structure and the petrophysical properties are essential parameters during the marine and continental shale reservoir evaluation. In order to the reveal the mechanism of the pore parameters differences and discuss whether the controlling factors of pore structure have extensive influence in different lithologies. Based on the analysis of N2/CO2 isotherm adsorption, FE-SEM, and geomechanical test for the marine shale samples of Longmaxi Formation and continental shale samples of Yanchang Formation are undertaken. The results indicate that (1) Continental shale is a typical transversely isotropic, while marine shale can be considered a homogeneous rock on a centimeter scale. The lithological stratification is the main reason for the difference in petrophysical properties. (2) The thermal evolution degree has significant influence on the pore structure in shale samples except for TOC content, particularly for the micropores structure. (3) Since the matrix strength of shale is much greater than the strength of bedding planes, the continental shale tends to crack and fail along the weak surface of the bedding during the axial compression, showing a lower peak strength, while the marine shale presents main crack along the principal stress direction without activating the bedding crack.

Petrophysical Characterization and Gas Accumulation of Wufeng-Longmaxi Shale Reservoir in Eastern Margin of Sichuan Basin, SW China

Shale gas plays a significant role in meeting the increasing demand of energy resources, which enables the exploration and exploitation of gas from shale reservoir to be emphasized gradually. Aiming to serve a more responsible and efficient shale gas development, for example, to guide the hydraulic/nonaqueous fracturing operation, this work organized a comprehensive assessment on the petrophysical characterization and gas accumulation of the Upper Ordovician Wufeng-Lower Silurian Longmaxi shale reservoir (abbreviated as WL shale). Results indicate that the WL shale in Well-YC4 contains three third-order sequences (SS1-lower WL, SS2-middle WL, and SS3-upper WL), and each sequence contains a transgressive system tract (TST) and a high-stand system tract (HST), according to the logging information. Meanwhile, the SS1, SS2, and SS3 experienced variable sedimentary environment—with different relatively oxygenic and hydrodynamics. And the bottom section (SS1 and SS2) has a soft great brittle index (BI) value than the upper section (SS3), suggesting the bottom WL shale is better suited for hydraulic fracturing than the upper section. Besides, the organic matter indicates the WL shale has a decent hydrocarbon generation ability, and the thermal evolution degree is also conducive to the full generation of shale gas. The gas content of WL shale ranges in the scope of 0.76 m3/t~2.38 m3/t, in which CH4 is the primary composition and occupies 95.51%~99.36%, and the content of heavy hydrocarbon gases is limited. Besides, the drying coefficient indicates the dry gas is the dominate molecular composition in the gas content of WL shale. Hopefully, this work is instructive to a certain extent for the researchers and engineers who are working on WL shale gas in Sichuan basin.

Coupling Relationship Between Densification Characteristics and Tight Oil Accumulation of the FGSR Reservoir: A Case Study of the Chang 7 Member of the Triassic Yanchang Formation in the Zhenyuan Area of the Southwest Ordos Basin, Central China

Fine-grained sedimentary rock (FGSR) reservoirs in a deep-water sedimentary environment from the Late Triassic Yanchang Formation in the Ordos Basin in central China have huge potential for tight oil production. According to the comprehensive research of fluid inclusion experiment, scanning electron microscopy, cathodoluminescence, thin section identification, and whole rock analysis, the petrographic characteristics, fluorescence spectrum parameters, and the homogenization temperature of oil inclusions and associated brine inclusions in the FGSR reservoir were analyzed to explore the coupling relationship between densification characteristics and tight oil accumulation of the FGSR reservoir. The results show the FGSR reservoir diagenesis has experienced compaction, cementation, and multiple stages of dissolution. A comprehensive analysis of burial history shows that the Chang 7 Member FGSR reservoir in the study area has three phases of oil charging, corresponding to the geologic time range of 132–124, 120–102, and 98–97 Ma. The organic acid produced by the first-stage oil charging accelerated the dissolution of feldspar and cuttings, and the dissolution pores increased significantly. Then, the organic acid in the second-stage oil charging accelerated the dissolution, and the abnormally high hydrocarbon expulsion pressure inhibited the damage of compaction on the pores of FGSR reservoir. Finally, the thermal evolution degree of source rocks reached the highest in the third-stage oil charging. The constructive effect of large-scale organic acids on pores and the protective effect of the chlorite membrane on pores inhibited the densification process of the FGSR reservoir. In short, the FGSR reservoir has experienced a cyclical reservoir densification process of “reducing porosity–increasing porosity–preserving porosity.” The coupling of pore evolution and oil charging of the FGSR reservoir is the key to the extensive accumulation and large-scale reservoir formation of tight oil in the Chang 7 Member of the Yanchang Formation in the Zhenyuan area, southwest Ordos Basin. The significance of the study may help to understand the process of the tight oil accumulation and predict the tight oil of the FGSR reservoir distribution.

Analysis of Controlling Effect of Temperature–Pressure Conditions on Hydrocarbon Generation of Source Rocks

The thermal evolution of source rocks and the generation of oil and gas were not isolated reactions of kerogen pyrolysis but were comprehensively controlled by many influencing factors. In this study, using Permian source rock samples from Junggar Basin, a large number of high-temperature thermal simulation experiments were carried out to study the characteristics of kerogen, for example, thermal evolution degree and hydrocarbon yield, and their influences under the open system, closed system, and different temperature–pressure conditions. The results show that the hydrocarbon yield under the low heating rate is higher than that under the high heating rate, and the hydrocarbon generation reaction can be fully carried out under the low heating rate, which is more favorable for hydrocarbon generation; with the increase in pressure in the reaction system, the dominant frequency of activation energy of hydrocarbon generation gradually decreases. In terms of the hydrocarbon yield, the oil yield is higher in a high-pressure environment, especially the yield of C6-14 component in hydrocarbons is obviously increased, while there is a relatively small difference between the C14+ components. The result of this research provides a scientific evidence for evaluating the evolution process, hydrocarbon generation kinetics, and hydrocarbon resource potential of source rocks under different temperature–pressure conditions.

Sedimentary Environment and Enrichment of Organic Matter During the Deposition of Qiongzhusi Formation in the Upslope Areas—A Case Study of W207 Well in the Weiyuan Area, Sichuan Basin, China

For a more in-depth analysis on the marine chemical condition during the earliest Cambrian, mechanism of organic matter enrichment and exploration potential of shale gas resources, based on the petrology, organic geochemistry, and elemental characteristics of the W207 Well, this study discuss the Early Cambrian paleo-ocean environment and factors controlling of organic matter enrichment during the deposition of black strata Qiongzhusi Formation in the upslope areas, southwestern Sichuan Basin, Yangtze Block, China. The sedimentary cycles show that during the depositon of fine-grained Qiongzhusi Fm, interactive cycles of multiple deep-water and shallow-water shelf developed, and were controlled by the rise and fall in sea level. In particular, the slope turbidite (fan) and gravity flow sediments indicate that the shallow-water shelf facies were dominant in the upslope area (SW Sichuan Basin), where not in deep water for a long time, and the sedimentary thickness of the organic rich black shale was limited. Evidence from organic geochemistry indicates that the organic matter of the Qiongzhusi Fm from the W207 Well was mainly of type I kerogen, with a high degree of thermal evolution, little residual hydrocarbon, and low capacity for hydrocarbon generation. The redox parameters indicate that the marine environment on the upslope was medium restrictive, with some upwelling. The seawater had undergone a transformation according to anoxic–oxidic. Therefore, paleo-ocean productivity in the upslope area was generally low, and exhibited a prominent downward trend from bottom to top. Given its high risk of exploration, the authors suggest that the direction of shale gas resource evaluation should change to the intracratonic sag (downslope) area, which is characterized by deep-water shelf facies.

Diagenetic facies classification and characterization of a high-temperature and high-pressure tight gas sandstone reservoir: A case study in the Ledong area, Yinggehai Basin

A high-temperature and high-pressure tight gas sandstone reservoir, located in the Ledong area of the Yinggehai Basin, shows considerable resource potential. However, the diagenetic characteristics of this reservoir remain unclear. In this study, reservoir petrology and diagenetic characteristics were systematically investigated through different experimental methods. Further, the porosity and diagenetic evolution models were constructed. The methods employed included petrophysical analysis, observation of core and thin sections, and grain-size distribution analysis. Furthermore, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, cathodoluminescence, carbon and oxygen isotope analysis, digital image analysis, mercury injection capillary pressure tests, and micro-CT imaging were also employed. In the study area, gravity-flow channel sediments composed of feldspathic litharenite primarily developed in a restricted submarine canyon. And tight sandstones in target formation have an average porosity of 9.34% and permeability of 1.79 mD. Mechanical compaction and cementation (mainly illite and ferrocalcite) were regarded as crucial roles in the densification process. Further, the diagenetic evolution model indicated that the reservoir underwent a high degree of thermal diagenetic evolution. Five diagenetic facies types were classified and characterized at multiple scales. Moreover, a vertical distribution model of different diagenetic facies was also developed considering the overpressure, depth of formation, thickness and frequency of mudstones, and injection concentration of the CO2. This study helps to improve the understanding of the diagenetic characteristics and diagenetic facies types in high-temperature and high-pressure clastic reservoirs.

Experimental study on reservoir characteristics and oil-bearing properties of Chang 7 lacustrine oil shale in Yan’an area, China

Abstract The Chang 7 Member shale of the Upper Triassic Yanchang formation in the Ordos basin is a hot spot in petroleum geology research. In this study, considering the Chang 7 shale in the Yan’an area as an example, the full-scale pore size characterization of lacustrine shale was realized based on the scanning electron microscopy image gray correction method, nitrogen and carbon dioxide adsorptions, and high-pressure mercury intrusion tests. In addition, the pore structures and oil-bearing properties of the Chang 7 shale were systematically studied. The results show that the Chang 7 shale is rich in organic matter, with an average total organic carbon value of 4.69% and an average R 0 value of 0.9%. It is in the mature-wet gas (crude oil-associated gas) stage. There are certain differences in the development characteristics and pore size distribution of different types of pores in shale. The statistical results showed that the pore diameters of the intergranular pores and intragranular dissolved pores were significantly larger than the intercrystalline pores of clay minerals and the organic pores. The organic pores in solid bitumen are extremely developed, whereas the organic pores in kerogen are relatively underdeveloped. The lower limit of the effective pore size of shale is 20 nm. The network system composed of inorganic pores-microcracks-organic matter-organic pores and siltstone laminae provides important channels and retention spaces for the migration of shale oil and gas within the source. This study found that the proportion of movable oil in sandy layers is relatively high, followed by shale with sandy laminae, whereas pure shale has the lowest proportion of movable oil. Therefore, the degree of sandy laminar development, the abundance of organic matter, and the degree of thermal evolution are the key geological factors that control the porosity and oil-bearing properties of shale oil reservoirs.

FÓSSEIS MOLECULARES DA MATÉRIA ORGÂNICA SILURIANA DA FORMAÇÃO TIANGUÁ (BACIA DO PARNAÍBA), NORDESTE DO BRASIL: IMPLICAÇÕES PALEOAMBIENTAIS E MATURAÇÃO TÉRMICA

MOLECULAR FOSSILS FROM SILURIAN ORGANIC MATTER OF THE TIANGUÁ FORMATION (PARNAÍBA BASIN), NORTHEASTERN BRAZIL: PALEOENVIRONMENTAL IMPLICATIONS AND THERMAL MATURATION. The Parnaíba Basin covers an area of 665,888 km2 between the northern and northeastern regions of Brazil. It is completely made up of siliciclastic sedimentary and volcanic rocks with ages varying between the Silurian and the Cretaceous. Among the formations of the Basin, the Tianguá Formation is considered a potential source rock. However, there are few geochemical and/or geological studies and no research work on the molecular parameters of the organic matter (OM) present in its outcropping rocks (OR). Thus, the objective of the present work is to characterize the OM, concerning the depositional paleoenvironment and the degree of thermal evolution, through molecular parameters and OM content. The OM was extracted using the Soxhlet system, chromatographed by classical methods, and analyzed using GC-MS and GC-MS/MS. The samples exhibited low total organic carbon values (TOC &lt;1) and the molecular parameters of saturated and aromatic hydrocarbons suggested a marine depositional environment, with algae, bacteria, and terrestrial plants input. The C30 biomarkers (24-n-propylcholestane), identified using synthetic standards and usually associated with the Chrysophyte algae, corroborated the marine origin of the depositional environment. In addition, some molecular parameters suggested little thermal evolution.