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The sandstone reservoirs of the Cretaceous Bashijiqike Formation in the Yingmaili area on the southern slope of the Kuqa Depression within the Tarim Basin demonstrate favorable physical properties and considerable potential for oil and gas exploration. However, they are characterized by strong heterogeneity and unclear patterns of oil and gas distribution. In this study, the lithology and physical properties of the middle and deep reservoirs of the Bashijiqike Formation in the Yingmaili area were analyzed using core observation, a series of thin section analyses(standard, casting, cathodoluminescence, and inclusion thin sections), scanning electron microscopy(SEM), physical property testing, X-ray diffraction, and diagenesis reconstruction and physical property recovery techniques. It aims to explore the pore characteristics and preservation mechanisms, classify reservoir types, and clarify the distribution patterns and controlling factors of favorable reservoirs.The results show that the sandstone is mainly composed of feldspathic lithic sandstone and lithic feldspathic sandstone with low matrix content and medium maturity in both composition and structure. The primary pore type of the reservoir is residual primary pores, followed by secondary pores, including intergranular and intragranular dissolution pores, classifying the reservoir as a medium-to-high porosity and permeability type. The preservation of the primary pores in the middle and deep sandstones of the Bashijiqike Formation was mainly attributed to the depositional environment and subsequent diagenetic and reservoir evolution. The sandstone was initially formed in the microfacies of distributary channels at the front edge of a braided river delta with high hydrodynamics. The constantly overlapping channels formed thick and stable composite sand bodies. The strong hydrodynamics in the area led to high concentration and good sorting of sandstone clastic particles, providing the material basis for the formation of primary pores. The burial evolution process involved early long-term shallow burial and late-stage rapid deep burial, resulting in weak compaction transformation of the sandstone. Meanwhile, late-stage deep overpressure greatly enhanced the sand body's resistance to compaction, allowing for the preservation of residual primary pores. The continuously decreasing paleogeothermal gradient in the depression further contributed to the effective preservation of residual primary pores.

The Upper Cretaceous Qingshankou Formation in the Songliao Basin contains thick, widespread, and organic matter-rich shale layers, offering abundant shale oil resources. Studying the sedimentary environment during shale formation and exploring the oil-bearing characteristics of shale oil enrichment intervals provide a theoretical basis for the prediction of the intervals and sweet spots. Based on previous research, the study compared organic carbon content, pyrolysis data, types of organic macerals, and major and trace elements of samples from two typical wells of different sags, well GY8HC in the Gulong Sag and well ZY1 in the Sanzhao Sag, in the central depression zone of the Songliao Basin. The analysis delved into the differences in oil-bearing characteristics and sedimentary environment of the Qingshankou Formation shales in two different sags, further analyzing the factors influencing these differences. The oil-bearing indicators of shales from the two wells in the Qingshankou Formation of the Songliao Basin showed that the total organic carbon (TOC) content in well ZY1 was significantly higher than that in well GY8HC. However, the free hydrocarbon content (S1) and oil saturation index (OSI) in well ZY1 were lower than those in well GY8HC. The geochemical environment during shale formation controlled organic matter enrichment. Comparing major and trace elements in samples from both wells, it was found that the climate in well ZY1 was more humid during its sedimentary period, the water body had stronger reducing conditions, and its paleoproductivity and paleo-water depth were significantly higher than those in well GY8HC. These conditions were favorable for the preservation of organic matter, thereby forming a higher organic matter abundance in the shale of well ZY1. In addition, it was found that the organic matter type in well GY8HC is mainly Type Ⅰ, sapropelic kerogen, at a mature to highly mature stage, whereas well ZY1 contains mainly Type Ⅱ1 kerogen, with less Type Ⅰ, at a low to mature stage. Therefore, the shale in well GY8HC possesses better oil generation potential.

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The earliest fossil records of Bittacidae can date back to the Triassic, with a higher diversity during the Jurassic, and lower diversity in the Cretaceous. This paper based on four well-preserved new specimens of Bittacidae from the mid-Cretaceous Kachin amber in Northern Myanmar （Hukawng Valley）, revised the diagnosis of Burmobittacus Zhao, Bashkuev, Chen & Wang, 2017, supplemented the features of head, the basal part of the wing, and genitalia of Burmobittacus jarzembowskii Zhao, Bashkuev, Chen & Wang, 2017, indicated a significant difference in the intraspecific length ratio between radial sector（RS）and R2+3. This paper also compiled a fossil genus-level key for the Bittacidae and compared the wing differences among fossil groups of Bittacidae from Mesozoic. [ABSTRACT FROM AUTHOR]

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To clarify the mechanical characteristics of tight sandstone in the Cretaceous Bashijiqike Formation of Kuqa Depression in Tarim Basin, and address field issues in deep and ultra-deep oil and gas exploration and development, triaxial compression experiments were used to quantitatively study the patterns of changes in rock mechanical properties influenced by confining pressure, fluid, and loading rate, with a preliminary analysis of their causes. The results showed that the maximum principal stress difference and elastic modulus of the sandstone samples increased significantly with confining pressure. The micro-reason was that the increase in confining pressure reduced the distance between particles inside the rock, enhancing the rock's cohesion and making particle dispersion less likely. Sandstone samples exhibited a progression from brittleness under low confining pressure to brittle-ductile transformation, and to ductile deformation under high confining pressure. Compared with dry sandstone samples, the reduction in the elastic modulus of samples soaked in pure water, 150 g/L solution, 250 g/L solution, and 350 g/L solution were 67.71%, 61.45%, 64.69%, and 57.32%, respectively, with pure water soaking causing the greatest reduction. Increasing fluid salinity could mitigate the weakening trend in rock mechanical parameters. Crystallization on crystal surfaces and changes in the electric double layer thickness were important controlling factors for these patterns. At lower loading rates, the values for maximum principal stress difference, elastic modulus, and Poisson's ratio of the sandstone samples were smaller, but they increased faster with increasing loading rates. When the loading rate reached a certain critical value (around 0.05 mm/min in this experiment), the rate of increase in rock mechanical parameters slowed down.

Based on the geological and geophysical data of Mesozoic oil-gas exploration in the sea area of Bohai Bay Basin and the discovered high-yield volcanic oil and gas wells since 2019, this paper methodically summarizes the formation conditions of large- and medium-sized Cretaceous volcanic oil and gas reservoirs in the Bohai Sea. Research shows that the Mesozoic large intermediate-felsic lava and intermediate-felsic composite volcanic edifices in the Bohai Sea are the material basis for the formation of large-scale volcanic reservoirs. The upper subfacies of effusive facies and cryptoexplosive breccia subfacies of volcanic conduit facies of volcanic vent-proximal facies belts are favorable for large-scale volcanic reservoir formation. Two types of efficient reservoirs, characterized by high porosity and medium to low permeability, as well as medium porosity and medium to low permeability, are the core of the formation of large- and medium-sized volcanic reservoirs. The reservoir with high porosity and medium to low permeability is formed by intermediate-felsic vesicular lava or the cryptoexplosive breccia superimposed by intensive dissolution. The reservoir with medium porosity and medium to low permeability is formed by intense tectonism superimposed by fluid dissolution. Weathering and tectonic transformation are main formation mechanisms for large and medium-sized volcanic reservoirs in the study area. The low-source “source-reservoir draping type” is the optimum source-reservoir configuration relationship for large- and medium-sized volcanic reservoirs. There exists favorable volcanic facies, efficient reservoirs and source-reservoir draping configuration relationship on the periphery of Bozhong Sag, and the large intermediate-felsic lava and intermediate-felsic composite volcanic edifices close to strike-slip faults and their branch faults are the main directions of future exploration.

A pyrolysis hydrocarbon generation experiment was conducted on low-maturity marine shale from the Second White Specks (2WS) Formation of the Cretaceous Colorado Group in the Western Canada Basin. Using GC-MS, quantitative analysis of aromatics in naturally evolved and thermally simulated samples was performed to systematically compare the geochemical characteristics of aromatics in both sets of samples. The results indicated that: (1) In the naturally evolved series of 2WS shale, the absolute contents of trimethylnaphthalene (TMN), tetramethylnaphthalene (TeMN), phenanthrene (P) and methylphenanthrene (MP) were relatively higher andincreased with the degree of evolution. In the thermally simulated series, the absolute contents and trends of P and MP remained consistent with those of naturally evolved series at higher thermal evolution levels, whereas the absolute contents of TMN and TeMN were relatively lower and showed different trends, increasing initially and then decreasing with maturity. (2) The trimethylnaphthalene ratio (TMNR) values of the naturally evolved series increased gradually with burial depth, while the TMNR values of the thermally simulated series decreased initially and then increased. The tetramethylnaphthalene ratio (TeMNR) and methylphenanthrene index (MPI) values of both series showed a consistent pattern: TeMNR values decreased initially and then increased with maturity, while MPI values increased with maturity, suggesting that phenanthrene series compounds effectively indicated shale maturity under both thermal simulation and natural evolution conditions. (3) The thermal simulation experiment was capable of effectively replicating the thermal evolution process of aromatics within a certain temperature range. Specifically, TMNR values of the simulated shale deviated from the naturally evolved shale before 350 ℃ but became consistent after 350 ℃. Similarly, alkyl phenanthrenes-related parameters aligned with those of the naturally evolved shale before 425 ℃ but diverged significantly beyond 425 ℃. This divergence was primarily influenced by the change in aromatic evolution mechanisms when the temperature reached a critical value, as well as by factors such as heating rate and the state of organic matter.

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[Objective] As an important type of coarse-grained sedimentary system and oil and gas reservoir in faulted basins, fan delta and slump fan complex deposition has been the hot topic of research on lacustrine sedimentary and reservoir formation, such as distribution area, evolution period and accumulation model. [Methods] Based on high resolution 3D seismic and drilling and logging data in the A Sag of Melut Basin in central Africa region, the sedimentary characteristics and evolution of fan delta-slump fan complex are studied by using core observation, sequence division, seismic reflection characteristics and seismic attribute analysis. [Results and Conclusions] The results showed that the types of sedimentary facies of fan in the study area included fan delta and slump fan caused by gravity flow, slump fan had two types of morphology characteristic, the first one was line source slump fan controlled by slope break, the second one was multistage slump fan with single point source controlled by steep topographic slope. Combined with seismic profiles and well logging features, five periods of fans were recognized in the Cretaceous study section. The single-stage fan all had the characteristics of retrogradation, the vertical evolution of multiple periods of fans was characterized by "first progradation and later retrogradation" . The fan distribution was the largest at the end of Renk Formation deposition in the Lower Cretaceous, reaching 148 km². However, the fan evolution was mainly influenced by tectonic activity, palaeogeomorphology, provenance supply, and base-level cycle. The fan distribution was larger in the period of strong tectonic activity, abundant provenance supply and large short-axis tectonic uplift, and the slump fan was most developed in the early period of relative base-level rising cycle and decreasing cycle. A new understanding of the sedimentary pattern transformation occurred in the Early Cretaceous and Late Cretaceous in the A Sag was put forward. The exploration potential of the fan delta and slump fan complex deposition in the faulted depression is clarified, which guided the exploration deployment. [ABSTRACT FROM AUTHOR]

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The features of the unconformity, fault and tectonic inversion in the eastern Doseo Basin, Chad, were analyzed, and the genetic mechanisms and basin evolution were discussed using seismic and drilling data. The following results are obtained. First, four stratigraphic unconformities, i.e. basement (Tg), Mangara Group (T10), lower Upper Cretaceous (T5) and Cretaceous (T4), four faulting stages, i.e. Barremian extensional faults, Aptian–Coniacian strike-slip faults, Campanian strike-slip faults, and Eocene strike-slip faults, and two tectonic inversions, i.e. Santonian and end of Cretaceous, were developed in the Doseo Basin. Second, the Doseo Basin was an early failed intracontinental passive rift basin transformed by the strike-slip movement and tectonic inversion. The initial rifting between the African and South American plates induced the nearly N-S stretching of the Doseo Basin, giving rise to the formation of the embryonic Doseo rift basin. The nearly E-W strike-slip movement of Borogop (F1) in the western section of the Central African Shear Zone resulted in the gradual cease of the near north-south rifting and long-term strike-slip transformation, forming a dextral transtension fault system with inherited activity but gradually weakened in intensity (interrupted by two tectonic inversions). This fault system was composed of the main shear (F1), R-type shear (F2-F3) and P-type shear (F4-F5) faults, with the strike-slip associated faults as branches. The strike-slip movements of F1 in Cretaceous and Eocene were controlled by the dextral shear opening of the equatorial south Atlantic and rapid expanding of the Indian Ocean, respectively. The combined function of the strike-slip movement of F1 and the convergence between Africa and Eurasia made the Doseo Basin underwent the Santonian dextral transpressional inversion characterized by intensive folding deformation leading to the echelon NE-SW and NNE-SSW nose-shaped uplifts and unconformity (T5) on high parts of the uplifts. The convergence between Africa and Eurasia caused the intensive tectonic inversion of Doseo Basin at the end of Cretaceous manifesting as intensive uplift, denudation and folding deformation, forming the regional unconformity (T4) and superposing a nearly E-W structural configuration on the Santonian structures. Third, the Doseo Basin experienced four evolutional stages with the features of short rifting and long depression, i.e. Barremian rifting, Aptian rifting–depression transition, Albian–Late Cretaceous depression, and Cenozoic extinction, under the control of the tectonic movements between Africa and its peripheral plates.

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Based on seismic and drilling data in the study area, the geological structure and kinematic process of the Termit rift basin were studied using seismic profile interpretation and balanced restoration to find out the dynamic mechanism of the basin. (1) The geological structure of the Termit Basin is represented as a narrow rift basin, with development of series of structural styles in extensional, extensional strike-slip and compressional stress setting. On plane, it is narrow in the north and wide in the south, and transitions from graben to half-graben from north to south; it features a graben controlled by the boundary faults in the north and a fault-overlapped half-graben in the south. (2) Before the Cretaceous, a series of hidden faults developed in the West African rift system, which laid the foundation for the development location and distribution direction of the Termit Basin; during the Cretaceous to Paleogene periods, the basin experienced two phases of rifting in Early Cretaceous and Paleogene, which controlled the initial structure and current structural shape of the basin respectively; during the Neogene to Quaternary, the basin was subjected to weak transformation. (3) In the Precambrian, the Pan-African movement gave rise to a narrow and long weak zone within the African plate, which provided the pre-existing structural conditions for the formation of the Termit Basin. In the Early Cretaceous, affected by the South Atlantic rifting, the Pan African weak zone was reactivated, resulting in the first stage of rifting and the basic structural framework of the Termit Basin. In the Paleogene, affected by the subduction and convergence of the Neo-Tethys Ocean, the African-Arabian plate extended in near E-W trending, and the Termit Basin experienced the second stage of rifting. The oblique extension in this period caused intense structural differentiation, and the current structural pattern of alternate uplifts and depressions took shape gradually.

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Structural analysis and reservoir evaluation has become increasingly important as petroleum exploration keeps making breakthroughs in the foreland of the southern Junggar Basin. However, the research on rock mechanical parameters which is closely related to them is rare. Based on the drilling core data, logging and seismic data of the Jurassic-Cretaceous in the Sikeshu sag, using the rock mechanics experiment and three-dimensional rock mechanics inversion, we defined the rock mechanics parameters in this study. The dynamic and static Young′s modulus shows a positively correlated linear relationship with the Poisson′s ratio. The rock mechanical parameters are controlled by the lithological variation. The lower K1q and J2t, J2x, J1b Formations have a higher Young′s modulus and a lower Poisson′s ratio, while the upper K1q and J1s Formations have a lower Young′s modulus and a higher Poisson′s ratio. When the Young′s modulus increases and the Poisson′s ratio decreases, the rock compressive strength increases. The inversion results of rock mechanical parameters in the Gaoquan area show that the higher the Young′s modulus and the lower the Poisson′s ratio, the higher the fracture index. The fracture index of the upper K1q and J1s Formations is lower than 0.4, indicating poor fracture development and petroleum display; while the fracture index of the lower K1q and J2t, J2x, J1b Formations is higher than 0.4, suggesting good fracture development and petroleum display. Therefore, the research results are instructive for the deep petroleum exploration in the study area.

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Distribution characteristics, organic matter development characteristics, gas-bearing characteristics, reservoir characteristics, and preservation conditions of the Shahezi Formation shale of Lower Cretaceous in the Lishu fault depression, Songliao Basin, NE China, are analyzed using organic geochemical, whole rock, and SEM analysis data, and CO2 and N2 adsorption and high-pressure mercury injection experiment data in combination with the tectonic and sedimentation evolution of the region to reveal the geological conditions for enrichment and resource potential of continental shale gas. The organic-rich shale in the Lower Cretaceous of the Lishu fault depression is mainly developed in the lower submember of the second member of the Shahezi Formation (K1sh21 Fm.) and is thick and stable in distribution. The shale has high TOC, mainly types II1 and II2 organic matter, and is in the mature to the over-mature stage. The volcanic activity, salinization, and reduction of the water environment are conducive to the formation of the organic-rich shale. The shale reservoirs have mainly clay mineral intergranular pores, organic matter pores, carbonate mineral dissolution pores, and foliated microfractures as storage space. The pores are in the mesopore range of 10–50 nm, and the microfractures are mostly 5–10 μm wide. Massive argillaceous rocks of lowland and highstand domains are deposited above and below the gas-bearing shale separately in the lower submember of the K1sh21 Fm., act as the natural roof and floor in the process of shale gas accumulation and preservation, and control the shale gas enrichment. Based on the above understandings, the first shale gas exploration well in Shahezi Formation was drilled in the Lishu fault depression of Songliao Basin. After fracturing, the well tested a daily gas production of 7.6×104 m3 marking a breakthrough in continental shale gas exploration in the Shahezi Formation (K1sh Fm.) of the Lishu fault depression in Songliao Basin. The exploration practice has reference significance for the exploration of continental shale gas in the Lower Cretaceous of Songliao Basin and its periphery.

In view of the difficulties in the study of lithofacies paleogeography and the low reliability of the distribution range of sedimentary sand bodies in the prototype basin caused by less deep drilling, complex seismic imaging and low degree of exploration in the southern margin of Junggar Basin, NW China. A new method based on the source to sink idea was used to restore lithofacies paleogeography and predict glutenite distribution. In the restoration, apatite fission track age was used to define range and uplift time of macro-provenance; the range of provenance area and the migration process of lake shoreline were restored based on the quantitative relationship between gravel diameter and transportation distance, tectonic shortening and other geological parameters; drilling cores and field outcrop sedimentary structures were analyzed, and a series of maps of lithofacies paleogeographic evolution and distribution range of glutenite bodies were compiled. It is concluded that from Early Jurassic to Early Cretaceous, in the southern margin of Junggar Basin, the provenance area gradually expanded from south to north, the lake basin expanded, shrunk and expanded, and the paleoclimate changed from humid to drought to humid. The western section always had proximal fan delta deposits from the southern ancient Tianshan provenance developed, and in the middle and eastern sections, the provenance areas evolved from far source to near source, mainly river-delta, braided delta, fan delta and other sediments developed. The boundary between provenance areas of the western and middle sections is speculated to be Hongche fault zone. In an angle open to the northwest with the current basin edge line, the restored ancient lake shoreline controlled the heterogeneity of reservoirs in the delta plain belt and delta front belt on its both sides. The ancient lake shoreline, current stratigraphic denudation line and current basin margin line limit the types and scope of favorable reservoirs. This understanding provides an important geological basis for oil and gas exploration in the deep lower source-reservoir assemblage at the southern margin of Junggar Basin.

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The transformation mechanism of muddy carbonate rock by the coupling of bioturbation and diagenesis was studied based on core, cast thin section and physical property data of Cretaceous strata in the Mesopotamia Basin, the Middle East. There are 3 ways of biological transformation of rocks: (1) The living creatures transformed formations mechanically to make the rocks looser and intergranular pores increase. (2) After formation, burrows were backfilled with coarse-grained debris, and then unsaturated fluid infiltrated into the burrows during the penecontemporaneous period, resulting in dissolution. (3) Chemical alteration occurred in abandoned burrows and dolomitization produced a large number of intercrystalline pores. The coupling of bioturbation and dissolution occurred mainly in the penecontemporaneous phase, and was controlled by rock type, sea level decline, burrow abundance, infillings, and water environment etc. As the burrows had better physical properties than the matrix, unsaturated fluid preferentially migrated along the burrows, leading to dissolution and expansion of the burrows first and then dissolution of the matrix. The coupling of bioturbation and dolomitization occurred mainly in the burial phase. The rich organic matter and reducing bacteria in the burrow provided material basis, reducing conditions and alkaline environment for dolomitization. The metasomatism in the penecontemporaneous period had little effect on the physical properties of the burrows. When the burrows were separated from the deposition interface, equimolar metasomatism occurred in the burrows in a closed environment, forming euhedral fine-crystalline dolomite with intercrystalline pores. The transformation degree of bioturbation to muddy carbonate reservoir depends on rock type, density, connectivity, infillings and structure of the burrows. With the increase of the carbonate mud content, the improvement to rock physical properties by bioturbation becomes more prominent. When the burrows are filled with coarse-grained debris or fine-crystalline dolomite, the greater the density, the higher the connectivity, and the lower the tortuosity of burrows, the better the physical properties of the muddy carbonate rocks are.

Freezing method is an effective construction method for vertical shaft in deep water rich bedrock coal mine. Cretaceous sandstone has the characteristics of low strength, weak cementation and softening when encountering water. It is widely distributed in the construction of coal mine shaft in Western China. The research on the long-term strength of frozen sandstone provides scientific theoretical basis for the stability evaluation and freezing design of shaft freezing wall. Taking the saturated frozen sandstone of Cretaceous as the test object, the triaxial creep mechanical tests were carried out under different temperature (+20 ℃,-10 ℃ and-20 ℃), different confining pressure (0, 2 MPa, 4 MPa and 6 MPa). According to the creep test results, the long-term strength of frozen sandstone was calculated based on the strain isochronous curve cluster and the relationship between steady-state creep rate and stress level. The advantages and disadvantages of the two models were discussed, and the triaxial strength and long-term strength were compared and quantitatively analyzed. The results show that the inflexion of volume strain isochronous curve cluster is more obvious than that of axial strain and radial strain isochronous curve, and its response to stress level and time is more sensitive. The long-term strength calculated by inflexion of steady-state creep rate stress curve has small error of numerical value. The long-term strength of frozen sandstone calculated by volume strain isochronous curve cluster method is more suitable Li. According to the determined calculation method, the creep long-term strength of sandstone at +20 ℃,-10 ℃ and-20 ℃ is 45.7%~50.7%, 41.8%~53.4% and 51.5%~67.1% of triaxial compression strength under the same conditions, respectively. The results will provide scientific guidance for determining and predicting the long-term strength of Cretaceous water rich frozen sandstone and the possible failure time under creep load. [ABSTRACT FROM AUTHOR]

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The Cretaceous continental strata developed in eastern Northeast China are rich in animal and plant fossils and have formed important minerals such as coal and oil shale. The only records of the earliest marine strata in Early Cretaceous are also preserved here besides Tibet' which is of great significance for the study on Cretaceous geography in China. Many new discoveries have been made in the Cretaceous stratigraphy of this area in recent years' some of which have filled the gaps of strata study in Northeast China. The paper also preliminarily discusses the co-evolution of Late Cretaceous flora and fauna represented by dinosaurs in the region. [ABSTRACT FROM AUTHOR]

In previous studies, the "marine facies" fossils in the second member of Taizhou Formation and the second and fourth members of Funing Formation of the Subei-South Yellow Sea Basin were generally considered to be organisms associated with transgression and organisms that lived in saline lakes. However, after reviewing the data, this theory proved to be wrong: most of the foraminifera do not exist in the above mentioned members. The distributions of "marine facies" fossils are not concentrated, and the surrounding rocks do not contain gypsum-salt. The evidence of paleoclimate and paleohydrology is also contrary to lake salinization theory. Formation comparison results show that 97 foraminifera are from 4 new strata, and the remaining 3 are in the second member of Funing Formation. The source of transgression, the ancient East China Sea, does not exist, and there are no marine fossils here. The "marine facies" fossils found here are all euryhaline organisms that can also live in fresh water. During the Late Cretaceous-Paleocene lake invasion period, the ancient climate was humid and the ancient lake was deep, and the water could not be salinized. Glauconite, apatite and trace elements cannot be used as a criterion for distinguishing between marine and terrestrial facies. Different types of euryhaline organisms are usually flourishing separately, and co-exist with a large number of freshwater organisms; meanwhile, the surrounding rocks do not contain gypsum-salt. According to the evidence above, the euryhaline organisms in this area are interpreted to live in freshwater, since foraminifera can live in a freshwater environment, and there was no water salinization in the three stages, of regional lake invasion. The large scale, high quality source rocks in Mesozoic-Cenozoic terrestrial basins in China are mainly freshwater lacustrine sediments, which can provide rich oil and gas resources.

Changtian Basin is one of significant energy basins in Guangdong Province. To learn the geological structure, sedimentary material characteristics and tracer sandstone provenance in detail, microscopic identification, electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) are used to systematically study the typical sandstones of Nanxiong Group in Changtian Basin on the basis of field geological survey. The results show that the Upper Cretaceous Nanxiong Upper Subgroup is mainly composed of (carbonaceous) lithic quartz sandstone, followed by calcareous sandstone, (argillaceous) siltstone, fine sandstone, conglomerate and greywacke, generally developed with obvious secondary changes and metallization. The analysis of detrital zircons from Nanxiong Group reveals that most of the zircons in the samples have perfect oscillatory bands with Th/U values usually greater than 0.4, indicating the zircons are mainly of magmatic crystallization origin, with a few metamorphic zircons of complex origin. The U-Pb concordant ages can be roughly divided into five groups: 2506-1666 Ma, 1815-941 Ma, 510-434 Ma, 308-234 Ma, and 172-99 Ma, which correspond to the known tectonic events in northeast Guangdong, reflecting that the tectono-magmatic activities in the study area are mainly controlled by the magmatic activities in eastern China, with the characteristics of episodic development and evolution. Based on the systematic analysis of lithography, zircon U-Pb age and REE characteristics of clastic rocks from Nanxiong Group, and comparison with the possible provenance, it is concluded that the detrital materials were mainly derived from Mesozoic magmatic intrusions in the western margin of Changtian Basin. [ABSTRACT FROM AUTHOR]

The research on Meso-Cenozoic formation and evolution process of Altyn Mountain, which locates at the northern margin of Qinghai-Tibet Plateau, is the key to understand the uplift and extension of Qinghai-Tibet Plateau. The rocks in Lapeiquan area, the eastern segment of Altyn was used to reveal its uplift and cooling process since Cretaceous through zircon and apatite fission track chronology, and then comprehensively understand Meso-Cenozoic uplift and exhumation history of Altyn. The results show that zircon and apatite fission track ages mainly are divided into two groups, including 116-108 Ma and 47-19 Ma, respectively. All of the data show a cooling history of the eastern segment of Altyn since Early Cretaceous. The thermal history simulation shows that the northern margin of the eastern segment of Altyn experiences two fast cooling events at 60-48 Ma and 10-0 Ma. In the first event, because of the subduction from Indian plate to Eurasian plate, Qinghai-Tibet Plateau experiences uplift and thrust nappe from south to north, the Altyn crack starts the activity again, the eastern segment of Altyn experiences fast uplift; in the second event, because of the remote effect by collision between Indian plate and Eurasian plate, the large-scale strike slip movement of the Altyn crack leads to its rapid cooling. The average uplift rates of these two events are estimated at 2.85 ℃·Ma-1 and 4.84 ℃·Ma-1, respectively. [ABSTRACT FROM AUTHOR]

Pure shales in the first member of Qingshankou Formation (simplified as Qing 1 Member) in the southern Songliao Basin, i.e., the semi-deep and deep lacustrine shales, are characterized by a high content of clay minerals and poor hydrocarbon mobility, making the development of shale oil difficult. According to the drilling and testing results, the shale of Qing 1 Member can be classified into 3 lithofacies, i.e., bedded argillaceous shale, laminated diamictite shale, and interbedded felsic shale. The TOC and brittle minerals control the enrichment of shale oil, of them, TOC controls the total oil content, in other words, the total oil content increases with the increase of TOC; while the laminae made up of brittle minerals contain a large number of bigger intergranular pores which are favorable enrichment space for movable shale oil. In consideration of the origins of the 3 lithofacies, two shale oil enrichment models are classified, i.e., the deep lacustrine high-TOC bedded argillaceous shale (Model-I) and the semi-deep lacustrine moderate-high-TOC laminated diamictite shale (Model-II). In the Model-I, the shale is characterized by high hydrocarbon generation ability, high total oil content, abundant horizontal bedding fractures, and vertical and high angle fractures locally; the complex fracture network formed by horizontal bedding fractures and vertical fractures improve the storage capacity and permeability of the shale reservoir, increase the enrichment space for movable oil. In the Model-II, the shale is characterized by good hydrocarbon generation ability and fairly high total oil content, and as the brittle laminae contain large intergranular pores, the shale has a higher movable oil content. Based on the two models, shale oil sweet-spot areas of 2880 km2 in the southern Songliao Basin are favorable for further exploration. Aimed at the difficulties in reservoir fracturing of the lacustrine shale with a high content of clay minerals, the composite fracturing technology with supercritical carbon dioxide was used in the shale oil reservoir for the first time, realizing large-scale volume fracturing in shale with a high content of clay minerals and strong heterogeneity, marking a breakthrough of oil exploration in continental shale with a high content of clay minerals in China.

Based on comprehensive analysis of core, cast thin section, logging and seismic data, the sedimentary and reservoir architectures of the MB1-2 sub-member of Mishrif Formation in Halfaya Oilfield, Iraq, are studied. The MB1-2 sub-member of Mishrif Formation has three types of microfacies, lagoon, bioclastic shoal, and tidal channel, and facies architecture controlled by sequence stratigraphy. In the 4th-order sequence, the lagoon facies aggradated vertically, and the bioclastic shoals in lenticular shape embed in the background of lagoon, the end of the sequence is incised by the “meandering river” shape tide channel, which represents the depositional discontinuity. Three types of reservoirs including tidal channel grainstone to packstone reservoirs, bioclastic shoal grainstone to packstone reservoirs and dissolved lagoon wackestone reservoirs are developed. The reservoir architectures within tidal channel and bioclastic shoal are strickly controlled by grainy facies, whereas the dissolved lagoon reservoirs controlled by both facies and dissolution are related to the sequence boundary. The reservoir sections occur mainly in the 4th sequence highstand systems tract (HST) and are separated by barriers formed in the transgressive systems tract (TST). Complicated facies architecture and dissolution modification resulted in strong heterogeneity within the reservoir, which showed the characteristics of “attic type” architecture. The results of this study can guide the development of similar reservoirs in the Middle East.

The Cretaceous oil-bearing strata in the Tarim Basin have a good exploration potential. The Shunbei area has good oil and gas shows in the Cretaceous, and a small amount of crude oil has been obtained by testing. The geochemical characteristics of the Cretaceous crude oil as well as the oil-oil and oil-source correlations were studied systematically in order to determine the genesis types and sources of crude oil in the Shunbei area. The saturated hydrocarbon chromatogram of the Cretaceous crude oil in the Shunbei area shows a unimodal distribution. The n-alkanes are intact and the distribution is unchanged without any obvious "UCM". The Pr/Ph values of crude oil range 1.65-1.71. The C21TT/C23TT ratio is >1. In biomarkers, the hopane series are dominant and the ∑tricyclic terpanes/∑hopanes ratio is < 1. The gammacerane and triaryl stanine compounds are abundant, indicating that the crude oil of continental origin is well preserved. The Cretaceous crude oil in the Shunbei area and the Yingmai, Dawanqi and Dalaoba areas around the Kuqa Sag in the north, and the Triassic Huangshanjie mudstones in the Kuqa River area show similar m/z 191 biomarker patterns, which indicates that the crude oil was sourced from the Huangshanjie mudstones in the Kuqa Sag. The thermal evolution degrees of crude oil decrease from Dawanqi, Yingmai to Shunbei. We inferred that the early terrestrial hydrocarbon was sourced in the Triassic source rocks in the Kuqa Sag, and then migrated laterally from north to south through the Cretaceous sand bodies, the T40 unconformity surface and the faults.

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Copyright of Acta Geoscientica Sinica is the property of Acta Geoscientica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to reveal the effects of carbonate rock reservoir heterogeneity on development, taking the bioclastic limestone of the Cretaceous Mishrif Formation of the M Oilfield in the Middle East as an example, based on core, cast thin section, experimental data and production test, the reservoir was studied, according to the calibration of geological genesis, physical property and development performance characteristics, in combination with production per day per meter and physical property index. The result showed that the reservoir was divided into three types. Type I was mainly developed in the high-energy shoal. Type II could be developed both in low-energy lagoon and high-energy shoal while type III was mainly developed in the lagoon. It was considered that the characteristics of different reservoirs were mainly controlled by sedimentation and diagenesis. The rock in high--energy shoal usually had good primitive physical properties, but intensive dissolution and weak cementation occurred during the diagenetic period at the top of the shoal. The reservoir porosity and permeability improved when type I developed. However, in the lower part of the shoal, it was dominated by destructive diagenesis, which resulted in weak dissolution and strong cementation, reducing the physical properties of the reservoir forming the type II. Lagoon facies rocks had low origami physical properties, and the formation of connected burrows in Iagoon provided a migration channel for diagenetic fluids with subsequent constructive diagenesis. Dissolution and dolomitization formed a large number of moldic pore, intercrystalline pores and biological cavity in the burrow and the substrate, which effectively improved rock physical properties forming the type II or type III. The new classification matched the geological understanding, revealing the reason of productivity difference between wells. The result could provide a reference basis for the classification of thick carbonate reservoirs in the Middle East. [ABSTRACT FROM AUTHOR]

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Copyright of Special Oil & Gas Reservoirs is the property of Special Oil & Gas Reservoirs Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To clarify the genesis of the Cretaceous Mishrif Formation carbonate reservoirs in the M oilfield, Iraq, analyses were carried out based on core samples, casting thin sections, experimental data and logging. Systematic microfacies analysis was used to determine the depositional environment, in particular the differences between facies in the reservoir rock. This showed that the Mishrif Formation in M oilfield was a ramp with barrier shoal, in which a lagoon margin flat, lagoon, point shoal, back shoal, tidal channel, barrier shoal, the front shoal and the open shallow shelf were identified. The medium- and high-permeability reservoirs were mainly developed in high-energy environments such as the barrier shoal and the front shoal, in which the bioclastic reservoirs and the front shoal reservoirs exhibit a broad range of physical properties. The pores in the high-energy reservoirs are mainly intergranular and dissolved-pore types, with large pore throats developed. The low-energy reservoirs in the lagoon margin flat, lagoon, point shoal and back shoal possess a wide porosity range, and are mainly of low- or ultra-low permeability. The pore types were mainly matrix-host micropores, granular-host micropores, moldic pores and intercrystalline pores. The throats are mainly micro-throat size, and the sorting is better. From this it was concluded that the facies controlled the diagenesis via their components. The diagenesis in the high-energy environment was mainly dominated by dissolution and cementation. The physical properties of the reservoirs were a function of the pore and throat cementation The strong heterogeneity of the low-energy environment reservoirs is the result of differential diagenesis. Complex pores developed by selective dissolution, and dolomitization associated with bioturbation, mud crystallization, cementation, non-selective dissolution and Dorag dolomitization influenced the reservoir property. [ABSTRACT FROM AUTHOR]

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According to the research on cretaceous formation distribution and characteristics in Longdong area, we find that Longdong area is located in the east of Helan fold belt, which belongs to the tectonic system of Qilian Mountain, Lyuliang Mountain and Helan Mountain. The cretaceous strata in this area are fluvial and lake facies clastic deposits up to 2 000 m thick, and they are composed of three rock formations of Huanghehuachi formation, Luohandong formation and Jingchuan formation of the lower cretaceous Zhidan group. The lithology is mainly argillaceous siltstone, silty mudstone, medium and fine sandstone, and partially sandwiched thin layer mudstone, argillaceous limestone and so on. The rock physical mechanics and rock structure analysis data of 107 groups of samples show that the cretaceous strata are all soft rocks with weak lithology, low strength, poor local diagenesis, gentle occurrence, obvious dry-wet effect and strong plastic deformation, and the physical and mechanical properties are easily affected by environmental factors. And Cretaceous rock mass has low compressive and shear strength, poor deformation resistance, poor slip resistance, low bearing capacity of foundation, weak erosion resistance and poor local permeability stability. Based on the above research results, the distribution rules and characteristics of cretaceous strata, physical and mechanical parameters of rocks, and engineering geological characteristics of rock mass in Longdong area were preliminarily determined, and the treatment measures for bad engineering geological characteristics were proposed. [ABSTRACT FROM AUTHOR]

The core observation and casting thin section authentication, combined with physical properties, scanning electron microscope, X-ray diffraction and mercury intrusion experiment, were employed to characterize the controlling factors on physical properties of Cretaceous Nahr Umr Formation sandstone reservoir in Halfaya oilfield. Iraq. The results show that the tide-controlled deltaic sandstone reservoir of core B of Nahr Umr Formation in Halfaya oilfield has medium porosity and permeability, and the reservoir space includes intergranular pore and dissolved pore; the pore throat changes greatly and the heterogeneity is strong; the controlling factors of reservoir physical properties include sedimentation and diagenesis; sedimentation affects pore space type and pore structure; reservoirs with good physical properties are developed with strong hydrodynamic conditions and good rock composition; diagenesis plays a significant role on the physical properties of reservoir; the compaction and cementation cause a large amount of pore filling, and the authigenic and clay minerals not only reduce the pore space, but also cause blockage of the throat, resulting in plugging of the pore throat and deterioration of the physical properties; the secondary pores produced by dissolution improve the reservoir physical properties; the highest-quality reservoir develops at the cross-laminated sandstone in tide-controlled distributary channel facies, and has the characteristics of large grain size, well sorting, relatively high content of quartz, low contents of clay mineral and cement, and large size of pore throat; the corresponding porosity and permeability are medium-high and high respectively, which are the focus of characterization and modeling of reservoir in the research area. [ABSTRACT FROM AUTHOR]

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