CO2 huff‐n‐puff is a promising technique for enhancing oil recovery while contributing to carbon capture, utilization and storage (CCUS). CO₂ huff-n-puff physical simulations monitored by low-field nuclear magnetic resonance (LF-NMR), combined with digital rock technology integrated with scanning electron microscopy (SEM) were conducted on calcareous shale samples from the upper member of the Paleogene Lower Ganchaigou Formation (UMLG) in the Yingxiongling structural belt of the Qaidam Basin, northwestern China. Six shale samples were classified into four lithofacies, namely laminated dolomitic limestone (LDL), laminated calcareous dolostone (LCD), bedded calcareous dolostone (BCD), and bedded mixed shale (BMS). Intercrystalline pores associated with dolomite and ankerite dominate the pore system across all lithofacies. Among them, BCD exhibits the most favorable reservoir properties and pore connectivity. LDL, LCD, and BMS display similar oil mobilization dynamics, with most oil recovered during the first two cycles and limited production thereafter. In contrast, BCD demonstrates sustained oil mobilization across all four cycles, ultimately achieving a recovery factor of 70.3%. Oil production proceeds from macropores to nanopores and from free to adsorbed oil, with effective mobilization of adsorbed oil only occurring in samples with well-connected pore networks. Dolomite and ankerite enhance oil recovery, whereas clay minerals impair it. Bedded structures and clustered distribution of dolomite and ankerite favor connected pore networks, while laminated structures and dispersed distribution result in poorly connected or even isolated pores. Based on these findings, a lithofacies-guided three-step screening workflow is proposed for CO₂-EOR optimization in calcareous shale reservoirs.

Based on the analysis of typical lacustrine shale oil zones in China and their geological characteristics, this study elucidates the fundamental differences between the enrichment patterns of shale oil sweet spots and conventional oil and gas. The key parameters and evaluation methods for assessing the large-scale production potential of lacustrine shale oil are proposed. The results show that shale oil is a petroleum resource that exists in organic-rich shale formations, in other words, it is preserved in its source bed, following a different process of generation-accumulation-enrichment from conventional oil and gas. Thus, the concept of "reservoir" seems to be inapplicable to shale oil. In China, lacustrine shale oil is distributed widely, but the geological characteristics and sweet spots enrichment patterns of shale oil vary significantly in lacustrine basins where the water environment and the tectonic evolution and diagenetic transformation frameworks are distinct. The core of the evaluation of lacustrine shale oil is "sweet spot volume". The key factors for evaluating the large-scale production of continental shale oil are the oil storage capacity, oil-bearing capacity and oil producing capacity. The key parameters for evaluating these capacities are total porosity, oil content, and free oil content, respectively. It is recommended to determine the total porosity of shale by combining helium porosity measurement with nuclear magnetic resonance (NMR) method, the oil content of key layers by using organic solvent extraction, NMR method and high pressure mercury intrusion methods, and the free oil content by using NMR fluid distribution secondary spectral stripping decomposition and logging. The research results contribute supplemental insights on continental shale oil deliverability in China, and provide a scientific basis for the rapid exploration and large-scale production of lacustrine shale oil.

Interactions between mountain building, weathering and climate draw significant attention within the geoscience community. In this study, the mixed rocks from the Eocene Lower Ganchaigou Formation (LGCG) of the Qaidam Basin are employed for weathering intensity evaluation by petrology, mineralogy, and geochemistry. Lithological characteristics indicate high‐frequency sedimentary cycles (<10 m) of the LGCG mixed rocks, which are identified by a single cycle with four lithofacies from bottom to top: massive sandstones, laminated silty shales, laminated silty limestones, and bedded dolomites. Provenance analysis suggests a predominant felsic volcanic source within a continental island arc background for these mixed sediments. Chemical weathering intensity indices (CIA, chemical index of weathering, and plagioclase index of alteration) show a high coherence with sedimentary cycles, initially increasing and gradually decreasing in a single cycle. Chemical index of alteration values ranged from 51.1% to 67.2%, indicating weak to moderate weathering intensity. Additionally, correlation analysis reveals that the cyclical variations of chemical weathering intensity correlate strongly with regular paleoclimate evolution and terrigenous input changes, which were controlled by the shift of the westerlies. During the westerly strengthening periods, stronger precipitation results in a warm and humid paleoclimate conditions, leading to higher terrigenous input dominated by fine‐grained clay minerals with moderate chemical weathering intensity. During the westerly weakening periods, less rainfall leads to a cold and dry paleoclimate conditions, resulting in lower terrigenous input dominated by coarser clastic sediments and weak weathering intensity. Our study provides new evidence and insights into the westerly shift and paleoclimate evolution in the Eocene from the perspective of high‐resolution chemical weathering records.

Exploring the sedimentary process and organic matter enrichment mechanism of plateau saline lake basin holds unique theoretical research and practical production significance for the paleoenvironment restoration and hydrocarbon exploration in the plateau. This study aims to analyze the high-frequency sedimentary evolution and organic matter enrichment mechanism of the mixed deposits from the Eocene Lower Ganchaigou Formation (LGCG) in the Qaidam Basin on the Tibet Plateau, by means of petrology, mineralogy, and organic-inorganic geochemistry. Lithological characteristics indicated the high-frequency sedimentary sequences (<10m) of the LGCG which are identified by a single cycle with four lithofacies from bottom to top: massive sandstones, laminated silty shales, laminated limestones, and bedded dolomites. Bulk organic geochemistry data showed the periodic variations of organic matter contents in the high-frequency sedimentary cycles. Organic matter predominantly occurs in dark gray laminated limestones, followed by the laminated silty shales, with the lowest contents in the bedded dolomites and massive sandstones. Inorganic geochemical proxies implied the cyclical changes of paleowater properties, paleoproductivity and sedimentation rate in the vertical profile that conformed to the high-frequency sedimentary sequences. Correlation analysis revealed that the enrichment of organic matter in the plateau saline lake is mainly related to high paleoproductivity and low sedimentation rate (>5 cm/ka), and anoxic and low-salinity water conditions also promote the preservation of organic matter. Distinct from typical saline lake basins, the LGCG in the Qaidam Basin, a plateau saline lake, is characterized by lower organic matter abundance and higher hydrocarbon generation efficiency, due to reduced biological productivity and terrigenous input.

Abundant shale oil resources have been discovered in the upper member of the Paleogene Lower Ganchaigou Formation of the Yingxiongling area from the Qaidam Basin, China. The lithofacies of Yingxiongling shale oil exhibit strong heterogeneity vertically. Accurate lithofacies identification is the key to characterizing the potential of unconventional oil and gas resources. Traditional lithofacies identification is limited by factors such as the duration of experiments and the subjectivity of the scholars. Only a limited amount of coring section data is available for analysis, while a sea of logging data remains underutilized. Therefore, utilizing machine learning algorithms to effectively leverage logging data for constructing the accurate lithofacies identification model has become a crucial area in both academia and industry. In this paper, 15 basic logging curves were used, and algorithms of random forest (RF), support vector machine (SVM), and extreme gradient boosting (XGBoost) were selected through Python programming to establish machine learning classification models, identifying the lithofacies types of Yingxiongling shale and analyzing the results. The lithofacies classification scheme of Yingxiongling shale is based on "rock structure + mineral composition", developing 8 lithofacies types: thin-bedded/laminated dolomitic limestone, thin-bedded/laminated limy dolostone, thin-bedded sandstone, laminated shale, and thin-bedded/laminated mixed rock. Due to the differing sensitivities of various logging data in identifying rock structures and mineral compositions, the corresponding algorithms and parameters vary accordingly. Hence, an innovative stepwise prediction model integrating "sedimentary structures and mineral composition" is proposed. The model first identified the rock structure through the genetic algorithm-RF and 15 logging curves, yielding thin-bedded/laminated structures. Then, SVM and 9 logging curves were used to identify mineral composition, yielding limy dolostone, dolomitic limestone, sandstone, shale, and mixed rock. The lithofacies were obtained by integrating the predicted results from the two models. The maximum accuracy of identifying rock structure and mineral composition can reach 87.3% and 78.7%, respectively, and the maximum prediction accuracy of the separate prediction model reached 73.2%, which is 22% higher than that of the direct prediction model. The relationship between the well logging curves and the predicted results is discussed, and the reasons for errors will be explained. These understandings can further help provide new ideas and methods for the identification of shale lithofacies types and can provide scientific guidance and technical support for the exploration and development of the Qaidam Basin.

Lacustrine sedimentary processes exhibit high sensitivity to paleoenvironmental changes, often manifesting as high-frequency sedimentary cycles that control the complex variations in sedimentary structure, mineral composition, and element distribution. However, the intricate co-variation mechanism among paleoclimate and paleowater properties at a high precision level (centimeter to meter scale) is still controversial. This study focuses on conducting a high-frequency cycle analysis of lacustrine mixed rocks from the Eocene Lower Ganchaigou Formation (LGCG) in the Qaidam Basin, employing petrology, mineralogy, organic geochemistry, and elemental geochemistry techniques. The lithological variation was characterized by the superposition of three lithofacies types from the bottom to the top with a single sequence: massive sandstone, laminated silty shale, and bedded calcareous dolostone. Geochemical data revealed cyclical variations in the paleoenvironment in the vertical profile, which conformed to the high-frequency lithofacies cycles. Based on the reconstruction of the lake level and paleowater properties, a synthesized paleoclimate–sedimentary model that comprised three consecutive periods within an individual sequence was established. From the bottom to the top of each cycle, the Eocene paleoenvironment varied from reduction and desalination to oxidation and salinization, which was controlled by a decline in the lake level resulting from a transformation of the paleoclimate from warm and humid to cold and arid. The variations in petrology and geochemistry observed in the Eocene Qaidam Basin play a crucial role in comprehending the sedimentary response to paleoenvironmental changes at high precision levels within lacustrine settings.

Based on the oil and gas exploration in western depression of the Qaidam Basin, NW China, combined with the geochemical, seismic, logging and drilling data, the basic geological conditions, oil and gas distribution characteristics, reservoir-forming dynamics, and hydrocarbon accumulation model of the Paleogene whole petroleum system (WPS) in the western depression of the Qaidam Basin are systematically studied. A globally unique ultra-thick mountain-style WPS is found in the western depression of the Qaidam Basin. Around the source rocks of the upper member of the Paleogene Lower Ganchaigou Formation, the structural reservoir, lithological reservoir, shale oil and shale gas are laterally distributed in an orderly manner and vertically overlapped from the edge to the central part of the lake basin. The Paleogene WPS in the western depression of the Qaidam Basin is believed unique in three aspects. First, the source rocks with low organic matter abundance are characterized by low carbon and rich hydrogen, showing a strong hydrocarbon generating capacity per unit mass of organic carbon. Second, the saline lake basinal deposits are ultra-thick, with mixed deposits dominating the center of the depression, and strong vertical and lateral heterogeneity of lithofacies and storage spaces. Third, the strong transformation induced by strike-slip compression during the Himalayan resulted in the heterogeneous enrichment of oil and gas in the mountain-style WPS. As a result of the coordinated evolution of source-reservoir-caprock assemblage and conducting system, the Paleogene WPS has the characteristics of “whole process” hydrocarbon generation of source rocks which are low-carbon and hydrogen-rich, “whole depression” ultra-thick reservoir sedimentation, “all direction” hydrocarbon adjustment by strike-slip compressional fault, and “whole succession” distribution of conventional and unconventional oil and gas. Due to the severe Himalayan tectonic movement, the western depression of the Qaidam Basin evolved from depression to uplift. Shale oil is widely distributed in the central lacustrine basin. In the sedimentary system deeper than 2 000 m, oil and gas are continuous in the laminated limy-dolomites within the source rocks and the alga limestones neighboring the source kitchen, with intercrystalline pores, lamina fractures in dolomites and fault-dissolution bodies serving as the effective storage space. All these findings are helpful to supplement and expand the WPS theory in the continental lake basins in China, and provide theoretical guidance and technical support for oil and gas exploration in the Qaidam Basin.

The Paleogene-Neogene strata in the Western Depression of the Qaidam Basin represent a primary focus for oil and gas exploration and development. Influenced by both terrigenous clastic influx and endogenic carbonate deposition, these strata exhibit significant variation in sedimentary systems and reservoir characteristics. This study comprehensively examines the depositional patterns and reservoir properties of the Paleogene-Neogene sequence across the inner, middle, and outer belts of the basin, employing core analysis, thin section petrography, and physical property assessment of reservoirs. Key findings include 1) The development of a concentric sedimentary system in the Western Depression during the Paleogene-Neogene period, characterized by increased carbonate mineral content and decreased clastic material from the periphery to the center of the basin. 2) Varied sedimentary facies associations across different zones, with the outer belt dominated by fan delta and braided river delta deposits, and the middle and inner belts characterized by near-shore shallow lacustrine carbonates and algal mat deposits, and offshore semi-to deep-lacustrine fine sediments, respectively. 3) The outer belt exhibits reservoirs with favorable physical properties and connectivity, while the inner and middle belts show high heterogeneity, indicating potential for lithological traps and shale oil exploration. These insights offer scientific guidance for further investigation into the depositional systems of lacustrine basins in the Western Depression of the Qaidam Basin and for identifying promising reservoirs.

Yingxiongling shale oil is considered a critical area for future crude oil production in the Qaidam Basin. However, the unique features of the Yingxiongling area, such as extraordinary thickness, hybrid sedimentary, and extensive reformation, are faced with several challenges, including an unclear understanding of the main controlling factors for hydraulic fracturing propagation, difficulties in selecting engineering sweet layers, and difficulties in optimizing the corresponding fracturing schemes, which restrict the effective development of production. This study focuses on mixed fine-grained sedimentary rocks, employing a high-resolution integrated three-dimensional geological-geomechanical model to simulate fracture propagation. By combining laboratory core experiments, a holistic investigation of the controlling factors was conducted, revealing that hydraulic fracture propagation in mixed fine-grained sedimentary rocks is mainly influenced by rock brittleness, natural fractures, stress, varying lithologies, and fracturing parameters. A comprehensive compressibility evaluation standard was established, considering brittleness, stress contrast, and natural fracture density, with weights of 0.3, 0.23, and 0.47. In light of the high brittleness, substantial interlayer stress differences, and localized developing natural microfractures in the Yingxiongling mixed fine-grained sedimentary rock reservoir, this study examined the influence of various construction parameters on the propagation of hydraulic fractures and optimized these parameters accordingly. Based on the practical application in the field, a “three-stage” stimulation strategy was proposed, which involves using high-viscosity fluid in the front to create the main fracture, low-viscosity fluid with sand-laden slugs to create volume fractures, and continuous high-viscosity fluid carried sand to maintain the conductivity of the fracture network. The resulting oil and gas seepage area corresponding to the stimulated reservoir volume (SRV) matched the actual well spacing of 500 m, achieving the effect of full utilization. The understanding of the controlling factors for fracture expansion, the compressibility evaluation standard, and the main process technology developed in this study effectively guide the optimization of transformation programs for mixed fine-grained sedimentary rocks.

Abundant lacustrine shale oil resources have been discovered in the Eocene saline lake system, Yingxiongling Sag, Qaidam Basin. Compared with the Cretaceous Qingshankou Formation in the Songliao Basin and Triassic Chang 7 Member in the Ordos Basin, the lithofacies of Yingxiongling shale are more complex, featuring thinner single-layer and faster vertical variations. How to establish a reasonable lithofacies classification and evaluate the effectiveness of different lithofacies is the key to unlocking the giant resources of Yingxiongling shale oil. Based on the total organic carbon analysis, rock pyrolysis analysis, fluorescence thin section observation, oil saturation analysis, helium porosity measurement, high pressure mercury intrusion by scanning electron microscopy, focused ion beam-scanning electron microscopy, and nitrogen adsorption analysis, the organic geochemistry, reservoir property, and oil-bearing property were comprehensively analyzed. This paper proposed a lithofacies classification scheme of Yingxiongling shale oil and systematically evaluated the quality of representative lithofacies. The key findings were as follows: (1) Eight types of lithofacies were identified based on the rock structure and mineral composition, namely, thin-bedded/laminated dolomitic limestone, thin-bedded/laminated limy dolostone, thin-bedded/laminated mixed rock, thin-bedded sandstone, and laminated shale. (2) The types and combinations of lamination varied greatly among different lithofacies. Dolomite primarily formed through calcite shrinkage during the dolomitization process, resulting in the formation of abundant intercrystalline pores. (3) More organic matter was observed in the calcite laminae, which was deposited as a result of small calcite particle flocculation. (4) The combination of laminated dolomitic limestone and thin-bedded limy dolostone formed a favorable source-reservoir assemblage, which was the pay zone for horizontal wells. These understandings could further be helpful in understanding shale oil enrichment in the Qaidam Basin and could provide scientific guidance and technical support for the exploration and development of global plateau shale oil.

The dendrolites composed of light gray massive micrite limestone occur at the top of the Cambrian Zhangxia Formation in Houziyu Section, Zibo, Shandong Province. Because it is very difficult to study the genesis of microbial rocks through “the function of diagenesis filter,” this paper analyzes its genetic mechanism by characterizing the sedimentary fabric and formation environment of dendrolites and it is of great significance to study microbial carbonate deposited in geological history in oil exploration. The Cambrian Zhangxia Formation in the Houziyu section is a marine deposit. The macroscopic shrub-like fabric of centimeter scale can be seen on the surface of the tree-shaped stone, with small biological burrows and remnants of calcareous mud components after filling. The microstructure observation shows that the main fabric of the dendrolites is a dark micrite matrix, bright calcite cement, clastic particles, and a calcified cyanobacteria biological community. Detailed supplementary information on the diversity of calcified microorganisms in dendrolites has been made through the study of various types of calcified cyanobacteria and calcified residual substances in the microbial membrane of calcified cyanobacteria in the dendrolites of the study area. It is clear that dendrolites are the product of the calcification of biofilms or microbial mats dominated by cyanobacteria. With the deepening of this kind of research, it is bound to raise the research of microbial carbonate to a new level in China and provide great help to find oil and gas resources in marine strata of microbial origin in China.

The geochemical analysis and experimental simulation are comprehensively used to systematically study the hydrocarbon generation material, organic matter enrichment and hydrocarbon generation model of Paleogene source rock in the Western Qaidam Depression, Qaidam Basin, NW China. Three main factors result in low TOC values of saline lacustrine source rock of the Qaidam Basin: relatively poor nutrient supply inhibits the algal bloom, too fast deposition rate causes the dilution of organic matter, and high organic matter conversion efficiency causes the low residual organic carbon. For this type of hydrogen-rich organic matter, due to the reduction of organic carbon during hydrocarbon generation, TOC needs to be restored based on maturity before evaluating organic matter abundance. The hydrocarbon generation of saline lacustrine source rocks of the Qaidam Basin is from two parts: soluble organic matter and insoluble organic matter. The soluble organic matter is inherited from organisms and preserved in saline lacustrine basins. It generates hydrocarbons during low-maturity stage, and the formed hydrocarbons are rich in complex compounds such as NOS, and undergo secondary cracking to form light components in the later stage; the hydrocarbon generation model of insoluble organic matter conforms to the traditional “Tissot” model, with an oil generation peak corresponding to Ro of 1.0%.

The potential for hydrocarbon exploration in the Kaitemilike area of the western Qaidam Basin is huge, but high-frequency sedimentary cyclic studies have rarely been explored. In this study, we determined that the lake level near the boundary of the Ganchagou Formation experienced a relatively long period of rise and fall change by Fischer plotting of natural gamma logging data from the Shangganchaigou Formation (N1) and the Upper Xiaganchaigou Formation (E32) of the deep exploratory well K2. Additionally, the characteristics of the Milankovitch cycles in the Ganchagou Formation were explored by combining spectral analysis and filtering analysis. The results show that the astronomical orbital period has a significant influence on the deposition of the Ganchaigou Formation in the study area. The Upper Xiaganchaigou Formation was deposited during the high stage of the lake level, mainly controlled by the eccentricity of the Milankovitch cycle, with a relatively warm and humid climate. The Shangganchaigou Formation was deposited during a relatively low stage of the lake level, mainly controlled by the obliquity of the Milankovitch cycle, with a relatively cold and arid climate.

The sedimentary succession of the Oligocene Lower Shangganchaigou Formation in the western Qaidam Basin, formed under cold paleoclimate conditions, is currently an important object of regional tight oil exploration and development, with little research on the evidence of astronomical forcing. In this study, natural gamma (GR) logging data and magnetic susceptibility (MS) are applied as paleoclimate proxies. The astronomical forcing of paleoclimate during the deposition of favorable sections of lacustrine tight reservoirs was investigated through well A in the Gasi area. The MS data show anomalously high values in the favorable section of the tight reservoirs. Prove of noteworthy Milankovitch cycles was recognized from spectral analysis of GR. By application of correlation coefficient (COCO) and evolutionary correlation coefficient (eCOCO) analysis, the sedimentation rate was estimated to be 3.8 cm/kyr. Using the 405-kyr long-eccentricity extracted from the tuned GR, a ~8.9 Myr floating astronomical time scale was established for the Lower Shangganchaigou Formation. Combining evolutionary fast Fourier transform (FFT) and the model of dynamic noise, the high-water sedimentary system formed during the period of lake level rise controlled by humid climate is conducive to the enrichment of high-quality hydrocarbon source rocks in tight sandstone reservoirs. The long-term obliquity (~1.2 Myr) is the main astronomical force driving the shift to humid climate. This study provides technical support for the next step of tight oil exploration and development in the basin with cyclostratigraphy.

The Paleogene upper Xiaganchaigou Formation (E32) is the most important source rock and reservoir in the Qaidam Basin. However, there are few studies on the processes of hydrocarbon accumulation in this formation; therefore, its hydrocarbon resource potential has not been estimated reasonably. This paper evaluates the hydrocarbon generation properties in light of an improved hydrocarbon generation and expulsion potential model. According to the geochemical characteristics of source rocks and the petrological features of reservoirs, the potentials of different resource types, including conventional oil, tight oil and shale oil, are quantified by combining the buoyancy-driven hydrocarbon accumulation depth (BHAD) and the lower limit for movable resource abundance. The results show that the source rocks are characterized by a large thickness (more than 1000 m), moderate organic matter content, high marginal maturity and a high conversion rate (50% hydrocarbons have been discharged before Ro = 1%), which provide sufficient oil sources for reservoir formation. Moreover, the reservoirs in the Qaidam Basin consist mainly of low-porosity and low-permeability tight carbonates (porosity of 4.7% and permeability less than 1 mD). The maximum hydrocarbon generation, expulsion, retention and movable retention intensities at present are 350 × 104 t/km2, 250 × 104 t/km2, 130 × 104 t/km2 and 125 × 104 t/km2, respectively. The thresholds of hydrocarbon generation, expulsion and BHAD were 0.46% Ro, 0.67% Ro and 0.7% Ro, respectively. Moreover, the dynamic evolution process of hydrocarbon accumulation was divided into three evolution stages, namely, (a) initial hydrocarbon accumulation, (b) conventional hydrocarbon reservoir and shale oil accumulation and (c) unconventional tight oil accumulation. The conventional oil, tight oil and movable shale oil resource potentials were 10.44 × 108 t, 51.9 × 108 t and 390 × 108 t, respectively. This study demonstrates the good resource prospects of E32 in the Qaidam Basin. A comprehensive workflow for unconventional petroleum resource potential evaluation is provided, and it has certain reference significance for other petroliferous basins, especially those in the early unconventional hydrocarbon exploration stage.

柴达木盆地保存了巨厚的完整连续的新生代沉积层序,为研究沉积旋回提供了良好的场所.位于盆地西部尕斯地区的上干柴沟组是典型的陆相碎屑岩地层之一,由多层砂岩和泥岩频繁相互叠置而成,高精度的沉积旋回研究鲜有讨论.综合运用频谱及滤波方法来深入分析地处柴西尕斯地区的YP2、YQ17井自然伽马测井数据.结果显示,天文轨道周期比值和中高频旋回厚度之间比值的对应性相对较好.在此基础上结合沉积速率及古气候两个方面的因素进行讨论,发现尕斯地区上干柴沟组的地层中保存了较为完整的米兰科维奇旋回.其中,短偏心率周期引起的地层旋回厚度变化为10.48～11.26 m;轴斜率长周期引起的地层旋回厚度变化为5.85～5.87 m;轴斜率短周期引起的地层旋回厚度变化为4.22～4.57 m;岁差长周期引起的地层旋回厚度变化为2.42～2.61 m;岁差短周期引起的地层旋回厚度变化为1.97～2.12 m.

The Qaidam Basin in the northeastern part of the Tibetan Plateau preserves a continuous and thick Cenozoic sedimentary succession, which is of great significance to studying the aridification of inland Asia. Based on the normalized concentrations (element/Al) and chloride content records of the lacustrine sediments in deep drilling well SS9 in the western Qaidam Basin, the change in the aridity of inland Asia during the late Middle Eocene was investigated. The results show that the Al-normalized concentrations of Na and Cl, which are indicator elements of saline lake sediments, increased sharply at similar to 38 Ma. The peaks in the Ga/Al and chloride values indicate that the salinity of the lake was extremely high at similar to 38 Ma. Based on these results, the sudden decrease in the sedimentation rate, the chemical weathering index, the hematite content, and the (smectite + illite/smectite)/illite ratios, the Qaidam Basin experienced abrupt aridification during this period. The decrease in water vapor transport caused by the final retreat of the Paratethys Sea from the southern Tarim Basin may have been the main reason for the changes in the arid environment in the Qaidam Basin during the late Middle Eocene. Long-term global cooling and the uplift of the Altyn Tagh may have played a role in the background conditions.

尼玛盆地地处青藏高原腹地,由于环境恶劣交通不便等问题,导致尼玛盆地沉积旋回和层序地层研究程度极低.收集盆地内第1口探井(尼1井)的地球物理数据,利用自然伽马测井曲线对尼1井牛堡组一段进行频谱分析,共识别出405 kyr周期旋回37个、100 kyr周期旋回148个、54 kyr周期旋回274个、41 kyr周期旋回362个和23 kyr周期旋回646个,各周期对应旋回沉积厚度分别为17.7305、4.4623、2.3680、1.7873、1.0886 m,平均沉积速率44.03 m/Ma,沉积时限14.8 Ma.在此基础上,结合带通滤波变化趋势分析,认为该地区的气候反常现象由印度板块与亚欧板块的碰撞隆升引起,风化作用与焚风作用共同控制了高原内部的气候变化.

利用钻井岩心、铸体薄片、扫描电镜、物性分析、包裹体测温等资料,结合盆地埋藏演化史,研究东营凹陷胜坨地区沙四上亚段浊积扇致密砂砾岩储层成岩作用及孔隙度演化过程.结果 表明:研究区沙四上亚段浊积扇致密砂砾岩储层现今孔隙度为8.75％,发育压实作用、胶结作用、溶蚀作用及两期油气充注;典型成岩油气充注序列表现为早期绿泥石胶结早期油气充注早期溶蚀作用石英次生加大/自生石英压实作用黏土胶结方解石胶结 白云石胶结晚期油气充注石英溶蚀晚期溶蚀作用 晚期黄铁矿胶结,储层成岩阶段达到中成岩B期;恢复储层原始孔隙度为34.53％,压实作用减孔率达到72％,各期胶结作用持续降低孔隙度,溶蚀作用调整和保存孔隙,浊积扇砂砾岩储层经历早期成藏致密边成藏边致密的过程.该研究结果可为东营凹陷致密储层的研究提供参考.

以鄂尔多斯盆地南缘平凉组烃源岩为研究对象,从烃源岩的物质组成、发育规模及地球化学特征等方面,对开阔台地和深水斜坡环境中发育的烃源岩进行了对比研究.