Exploration In China Research Articles

Facies-related diagenesis of Jurassic sandstones, central Junggar Basin, NW China: implications for reservoir quality evolution

Abstract Hydrocarbon exploration in China has recently expanded to deep tight oil and gas from the Lower Jurassic sandstone reservoirs in the central Junggar Basin. These deeply buried sandstones (>4.5 km) have generally been overpressured due to hydrocarbon saturation, but have not been intensively investigated in terms of diagenesis and reservoir quality. The Lower Jurassic sandstones are feldspathic litharenites (average Q 28 F 29 R 43 ) and were deposited in the lacustrine–deltaic environments of the high-palaeolatitude continental basin under warm, humid climatic conditions. Progressive burial with only slight uplift of the strata led to a relatively stable burial–thermal regime, resulting in minor diagenetic changes consisting of compaction, cementation by carbonates, quartz and clay minerals, and partial dissolution of feldspars and rock fragments. Despite generally similar diagenetic histories, the studied sandstones reveal considerable variations in the development of pore systems, porosity and permeability. The best reservoirs are represented by medium- to coarse-grained depositional facies with higher porosity (average 8.43%) and permeability (average 0.59 mD). All the evidence suggests that integrated consideration of the roles of depositional settings and diagenesis, linked with burial–thermal history and overpressure evolution conditions, provides a helpful means of predicting reservoir quality.

Unreliable determination of in situ stress orientation by cross multipole array acoustic logging in fractured shale reservoirs

AbstractWith the development of shale gas exploration in China, the use of conventional logging tools has been introduced, and cross multipole array acoustic logging tools have gradually been used to determine the stress orientation in shale. The direction of fast shear waves (FSWs) is generally parallel to the horizontal maximum principal compression stress (SHmax). However, the azimuth of FSWs is found to be parallel to the main strike (but not to the SHmax) direction of structural fractures in shale reservoirs. Outcrop and image logging data indicate that the natural fractures in this area strike NE‒SW. If the shear wave anisotropy is caused by only the stress around the borehole and the FSWs are known to be NE‒SW, SHmaxshould be parallel to NE‒SW; however, according to statistics of land movement in adjacent areas, anelastic strain recovery, earthquake focal mechanism, borehole breakouts, hydraulic fracturing data, deviated well data, and drilling‐induced fracture data in local regions, SHmaxis oriented in the NW‒SE direction, and the directions of FSWs are generally parallel to the structural fracture direction. This contradiction indicates that the development of structural fractures may affect the orientation of FSWs. Therefore, it is not reliable to use XMAC (Cross‐Multipole Array Acoustilog) logging only to determine the direction of in situ stress in fractured shale reservoirs. In addition, the direction of the FSWs in the middle of thick mudstones is NW‒SE, which may represent accurate information about the in situ stress direction.

Exploration of China’s Way to Carry out International Chinese Education Communication in South and Southeast Asia

Exploration of China’s Way to Carry out International Chinese Education Communication in South and Southeast Asia

Comparative Study on the Primary Control Factors of Nanopores in Transitional and Deep Marine Shale in the Southeastern Sichuan Basin, China

The deep marine shale from the Silurian Longmaxi Formation and transitional shale from the Permian Longtan Formation in the Sichuan Basin are two promising targets for shale gas exploration in China. In this study, nanopore characteristics for deep marine and transitional shale samples collected from the same well in the southeastern Sichuan Basin are investigated and compared via field emission scanning electron microscopy imaging, low-pressure gas adsorption, total organic carbon measurement, and X-ray diffraction. Results show that clay-related pores are well developed, pores within organic matter (OM) are rare, and shrinkage cracks along the OM-edge are widely prevalent in transitional shales. The deep marine shale is rich in bubble-like OM pores. The transitional shale has a larger pore volume but a lower specific surface area compared to the deep marine shale. The nanoporosity of the transitional shales is primarily controlled by clay and OM content. In deep marine shale, OM is the primary contributor to nanoporosity. Higher nanoporosity in the deep marine shales than in the middle-shallow ones was observed in this study. This occurrence is attributed to the high fluid pressure and the resulting superior preservation conditions for nanopores in deep marine shale formations.

Science in Transnational Settings: Knowledge Exchange in Expeditions in 1920s Republican China

The 1920s to the 1930s in Republican China witnessed rising academic interest in exploring Chinas frontier regions, both from abroad and within the nation. This paper examines the nature of foreign exploration in China at that time and the resulting exchange of knowledge that shaped sciences development worldwide. The exchange was facilitated through an elite network of international specialists in Beijing, while Chinese academics and local residents became increasingly indispensable to foreign investigatorsthanks to their local knowledge and control over the sites. Together, they not only contributed to the establishment of indigenous scientific institutions but advanced the geology, archaeology, and paleoanthropology fields internationally. However, the nominally objective work of Western scholars often masked hegemonic inclinations, both explicit and implicit, which tended to vary according to the country sponsoring each investigator. By the late 1920s, rising Chinese objections to foreign exploration caused conflicts between imperialist motivations and nationalistic powers. Thus, it would be equally a reductionist reading of history to simply assume Republican Chinas intelligentsia were the victims of imperialist aggression or to draw a rosy picture of transnational collaboration. This paper suggests that early twentieth-century Republican China offers a rich example of the intersection of scientific internationalism, imperialism, and nationalism.

Restoration of sedimentary environment and geochemical features of deep marine Longmaxi shale and its significance for shale gas: A case study of the Dingshan area in the Sichuan Basin, South China

With the urgent need to increase shale gas production and reserves, deep shale gas has gradually become an important target for further exploration in China. However, there is still a lack in systematic research on the quality of different lithofacies types of shales in deep shale gas reservoirs. The overmature shales have a common problem, that is, the organic matter (OM) quality could not be clearly characterized by using conventional organic geochemical indicators, hindering the process of fine shale gas exploration. In this study, the deep marine Longmaxi (LMX) shale samples in the Dingshan area, southeastern Sichuan Basin were selected as a study case to investigate their lithofacies types, sedimentary environment and organic matter accumulation (OMA) mechanism, and restore the original OM attributes including original organic carbon content (TOCo) and original hydrogen index (HIo) for the different shale types to identify the favorable lithofacies for shale gas enrichment. The results show that the LMX shale can be divided into five different lithofacies, such as the OM-rich siliceous (RS) shale, OM-rich mixed (RM) shale, OM-lean siliceous (LS) shale, OM-lean mixed (LM) shale and OM-lean argillaceous (LA) shale, with a gradually decrease of their TOC contents. The TOC content of the LMX shale has a positive synergy with the indicators of paleoproductivity and redox conditions. However, since the studied area is close to the underwater highland with a high oxygen content in the bottom water and a great input of terrigenous debris, the OMA mainly depends on the level of high paleoproductivity. The analysis of sedimentary environment indicates that the OM amount and quality in various lithofacies shales are different. The RS shale at the lower part of the LMX shale has a better OM quality and a greater TOCo, which result in the greater effective organic carbon (TOCe), gas production potential, and retained gas content. It is followed by the RM, LS, and LM shales. In contrast, the LA shale lacks material base for shale gas enrichment. Combined with the available data from other deep blocks in the southern Sichuan Basin, the original OM attributes of RS and RM shales are always better than those of LM, LS, and LA shales. For deep and ultra-deep Longmaxi shale gas exploration, the RS shale should be the first choice, and then the RM shale.

Exploration of China's Internet Finance Business Model: Taking Ant Financial Services Group as an Example

In today's rapidly developing Internet economy, China, as one of the most developed countries in the Internet industry, has seen the emergence of many competitive Internet finance companies. Compared with the traditional banking system, these Internet finance companies have greatly facilitated people's lives and provided them with more comprehensive financial services. In order to explore the business model of China’s Internet finance companies and provide suggestions for their future development, this paper analyzes the Ant Financial Services Group, the largest Internet finance company in China. Through exploring the business model of Ant Financial Services Group and collecting relevant data, the advantages of its business model are analyzed, and suggestions are made for the future development of Ant Financial Services Group and China's Internet finance industry, this paper suggests that Ant Financial Services Group should expand its overseas market, lay out social field, focus on its Fin-Tech positioning, pay attention to relevant policies and reduce its dependence on Alibaba Group. For government departments, the legal system for Internet finance industry should be improved as soon as possible to regulate the development of Internet finance industry. By reading this article, readers can gain a deeper understanding of the current situation of Ant Financial Services Group and the development of Internet finance in China.

Reservoir characteristics and pore fluid evaluation of Shan 23 Submember transitional shale, eastern Ordos Basin, China: Insights from NMR experiments

The Lower Permian Shanxi Formation in the Eastern Ordos Basin is a set of transitional shale, and it is also a key target for shale gas exploration in China. Three sets of organic-rich transitional shale intervals (Lower shale, Middle shale and Upper shale) developed in Shan 23 Submember of Shanxi Formation. Based on TOC test, X-diffraction, porosity, in-situ gas content experiment and NMR experiments with gradient centrifugation and drying temperature, the reservoir characteristics and pore fluid distribution of the three sets of organic-rich transitional shale are studied. The results show that: 1) The Middle and Lower shales have higher TOC content, brittleness index and gas content, reflecting better reservoir quality, while the Upper shales have lower gas content and fracturing ability. The total gas content of shale in the Middle and Lower shales is high, and the lost gas and desorbed gas account for 80% of the total gas content. 2) The Middle shale has the highest movable water content (32.58%), while the Lower shale has the highest capillary bound water content (57.52%). In general, the capillary bound water content of marine-continental transitional shale in the Shan 23 Submember of the study area is high, ranging from 39.96% to 57.52%. 3) Based on pore fluid flow capacity, shale pores are divided into movable pores, bound pores and immovable pores. The Middle shale and the Lower shale have high movable pores, with the porosity ratio up to 27%, and the lower limit of exploitable pore size is 10 nm. The movable pore content of upper shale is 25%, and the lower limit of pore size is 12.6 nm. It is suggested that the Lower and Middle shales have more development potential under the associated development technology.

Phenomenology of plume–surface interactions and preliminary results from the Tianwen-1 landing crater on Mars

The plume–surface interaction (PSI) is a common phenomenon that describes the environment surrounding the landers resulting from the impingement of hot rocket exhaust on the regolith of planetary bodies. The PSI will cause obscuration, erosion of the planetary surface, and high-speed spreading of dust or high-energy ejecta streams, which will induce risks to a safe landing and cause damage to payloads on the landers or to nearby assets. Safe landings and the subsequent scientific goals of deep-space exploration in China call for a comprehensive understanding of the PSI process, including the plume flow mechanics, erosion mechanism, and ejecta dynamics. In addition, the landing crater caused by the plume provides a unique and insightful perspective on the understanding of PSI. In particular, the PSI can be used directly to constrain the composition, structure, and mechanical properties of the surface and subsurface soil. In this study, we conducted a systematic review of the phenomenology and terrestrial tests of PSI: we analyzed the critical factors in the PSI process and compared the differences in PSI phenomena between lunar and Martian conditions; we also reviewed the main erosion mechanisms and the evolution and development of terrestrial tests on PSI. We discuss the problems with PSI, challenges of terrestrial tests, and prospects of PSI, and we show the preliminary results obtained from the landing crater caused by the PSI of Tianwen-1. From analysis of the camera images and digital elevation model reconstructions, we concluded that the landing of Tianwen-1 caused the deepest crater (depth > 40 cm) on a planetary surface reported to date and revealed stratigraphic layers in the subsurface of Martian soil. We further constrained the lower bounds of the mechanical properties of Martian soil by a slope stability analysis of the Tianwen-1 landing crater. The PSI may offer promising opportunities to obtain greater insights into planetary science, including the subsurface structure, mineral composition, and properties of soil.

Differential sedimentary mechanisms of Upper Ordovician-Lower Silurian shale in southern Sichuan Basin, China

The Wufeng-Longmaxi Formations are the focus of shale gas exploration in China. Their sedimentation is affected by global and regional geological events, and the resulting heterogeneity hinders the expansion of exploration results. This study combines logging, mineralogy, and geochemistry to reconstruct the sedimentary mechanisms of shale in the southern Sichuan Basin and discusses its implications for exploration. The shale can be divided into third-order sequences, in which the Wufeng Formation and lower Long-1 Member are transgressive systems tracts (TST1 and TST2), and the Guanyinqiao Member and the middle-upper Long-1 Member are highstand systems tracts (HST1 and HST2). Volcanic eruption and glaciation evolution are the driving factors of the sedimentary environment during the TST. The area is in a cold-warm climate, characterized by anoxic conditions, slow sedimentation, booming productivity, and low terrigenous influx, thereby depositing four types of siliceous shale. The siliceous shale is rich in biogenic microcrystalline quartz and high TOC, which are the keys to becoming the “sweet spot” of shale gas. Microcrystalline quartz fills the intergranular pores to support the entire pore network framework. The organic matter undergoes thermal evolution to produce abundant organic matter pores, which constitute the main place for adsorbed gas and free gas. For the highstand systems tract, HST1 is the product of the peak of glaciation, mainly composed of calcareous shale and carbonate rocks. The sedimentation of HST2 is affected by turbidity currents and violent orogeny. The area is in a warm climate, characterized by high terrigenous influx, dysoxic-oxic conditions, medium productivity and rapid sedimentation rates. The lithofacies gradually changed from siliceous shale to mixed shale and argillaceous shale. Excessive clay minerals and low TOC make it difficult for HST2 to realize the commercial development of shale gas.

Concepts, models, and indicator systems for urban safety resilience: A literature review and an exploration in China

Safety resilient city is a frontier concept of urban safety development and a hot topic in the field of urban safety research. In this paper, the relevant research results of domestic and foreign scholars are reviewed from the perspectives of concepts and models, the evaluation indicator system of urban safety resilience is compared in terms of risk types, evaluation objects, evaluation dimensions and quantitative methods, and the development of international standards for resilient cities is discussed. Based on the literature review, the connotation of the triangular theoretical model of urban safety resilience is explained, and an urban safety resilience evaluation index system applicable to Chinese cities is proposed, which provides support for the development of the national standard “Guide for safety resilient city evaluation” (GB/T 40947-2021). It is applied to six representative cities as examples for evaluation to explore the direction of Chinese urban safety resilience improvement. The pathway for improving the safety resilience of Chinese cities is discussed.

Development and optimization a miniature Mattauch-Herzog mass analyzer

With the advancement of space exploration in China, mass spectrometers are becoming increasingly important in space missions. A miniature Mattauch-Herzog double focusing mass spectrometer was developed for mass analysis. Based on the study of the fringing field of the analyzer, the ion optical lens software SIMION8.1 was used to simulate the focusing performance of the ion beam. The 90° magnetic analyzer with asymmetric structure is adopted, which has a magnetic flux density of 0.85T. The experiment shows that the ion current is actually affected by the fringing field of electrostatic analyzer which is basically consistent with the simulation results. Besides, the performance indicators of the miniature MS are tested, the mass resolution of N2 is 75.7, the sensitivity of N2 is 4.13 × 105 V/Pa and the minimum detectable partial pressure of N2 is 2.81 × 10−7Pa.

Factors controlling the development of carbonate reservoirs of Ordovician Yingshan formation in the Gucheng area, Tarim Basin

Deep carbonate rocks are important targets for oil and gas exploration in China. In recent years, significant oil/gas discoveries have been made in the deep carbonate sequences in the Tarim, Sichuan, Ordos, and Bohai Bay basins. Despite significant oil/gas discoveries, large-scale exploration has not been conducted in the Gucheng area in the Tarim Basin. To break the bottleneck restricting the petroleum exploration in the Gucheng area, this study analyzed the factors controlling the formation of carbonate reservoirs of the Yingshan Formation in the Gucheng area in detail based on the basic geological conditions of the study area and the data from cores, thin sections, well logging, testing, and 3-D seismic survey. The inner shallow-ramp in the Gucheng area acts as the main sedimentary facies zone for the development of high-quality reservoirs. The grainstones formed in the high-energy environment of the inner shallow-ramp laid the foundation for subsequent reservoir development in the study area. The dolomitized shoal grainstones in the inner shallow-ramp have well-developed intercrystalline pores and intercrystalline dissolved pores due to later dolomitization, thus serving as high-quality reservoirs. Strike-slip faults are crucial to reservoir reformation and determine whether high production can be achieved in oil and gas exploitation in the study area. Moreover, later reformation by hydrothermal solutions also plays a constructive role in reservoir formation.

The Trend and Development of Geological Prospecting and Exploration Technology for Gold Deposits

With the rapid development of China's social economy, the demand for gold ore consumption is increasing day by day. Under this condition, it is necessary to study the key techniques of gold ore prospecting and geological exploration and carry out geological exploration smoothly. This is to further improve the efficiency of gold ore exploration in China. In practice, Chinese government workers should carefully observe the scientific and technological development of gold prospecting because of the social reality, and scientifically and reasonably choose the prospecting and technical means according to the actual requirements of social geology. It is to discover more gold resources and provide a guarantee for social and economic development.

Effectiveness of Oil Filling in Tight Sandstone Reservoirs of Yancheng Formation in Ordos Basin

The Ordos basin is one of the important oil-bearing basins in China, with abundant tight sandstone oil resources, wide distribution, and large thickness. It is the most realistic field of unconventional oil and gas exploration in China, and it is also an important oil and gas replacement resource at present. Oil accumulation in tight reservoirs is obviously different from conventional oil and gas accumulation, and the key lies in studying the effectiveness of oil filling in tight reservoirs. In order to solve this problem, this paper takes the tight sandstone reservoir of Member 7 of the Yancheng Formation in Ordos Basin as the research object, introduces the geological characteristics of this area after sorting out the previous research results, carries out the physical simulation experiment of oil filling, studies the relationship between the filling pressure and the lower limit of the filling throat, analyzes the effective accumulation space of the tight sandstone reservoir, defines the oil filling mechanism of the tight sandstone reservoir, and discusses the effectiveness and reservoir-forming effect of oil filling in different types of reservoirs. The results show that the rock types of tight sandstone reservoirs in the 7th member of the Yancheng Formation are mainly lithic feldspathic sandstone and feldspathic lithic sandstone, and the reservoirs have experienced strong compaction and carbonate cementation. The late iron-bearing carbonate cementation has further strengthened the degree of reservoir densification, and the reservoirs have been densified at the time of large-scale oil and gas filling. Through the simulation experiment of oil filling with natural cores with different physical properties, the relationship model between filling pressure and effective accumulation space of different types of tight sandstone reservoirs in Member 7 of the Yancheng Formation is established. With the change in filling pressure, the change trend and range of effective accumulation space of different types of tight sandstone reservoirs are obviously different. According to the relationship model between the filling pressure and the lower limit of the effective filling pore throat, the oil filling effectiveness of different types of tight sandstone reservoirs in the 7th member of the Yancheng Formation is determined. Class I and class II1 reservoirs are effective reservoirs for oil filling of tight sandstone reservoirs, which constitute the main oil-bearing section of tight sandstone reservoirs in member 7 of the Yancheng formation, while class II2 reservoirs are poor tight reservoirs, and class III reservoirs are basically oil-free, which are noneffective reservoirs for oil filling of tight sandstone reservoirs. The results provide theoretical data support for the next step of oil exploration and exploitation in tight sandstone reservoirs.

Dynamic reconstruction of the hydrocarbon generation, accumulation, and evolution history in ultra-deeply-buried strata

The evolution mechanism of hydrocarbons in ultra-deeply-buried and ultra-old strata is the core issue of petroleum geology moving towards Deep Earth. Reconstructing the evolutionary history of ultra-deeply-buried hydrocarbons is the key to shedding light on deep hydrocarbon accumulation and evolution mechanisms. Furthermore, it can help point out directions for oil and gas exploration in Deep Earth. Anyue gas field in the central Sichuan Basin is the Frontier of deep natural gas exploration in China. This study selected the natural gas reservoirs of the Upper Sinian Dengying Formation in the central Sichuan Basin as the research object. By integrating analysis of natural gas geochemical characteristics, source rock evaluation, reservoir bitumen-source correlation, inclusion analysis, one-dimensional and two-dimensional hydrocarbon accumulation simulations, the generation and evolution of hydrocarbons in different structural regions, namely the inherited paleo-uplift and slope area in central Sichuan Basin, have been dynamically restored and compared. The results show that: 1) The natural gas of the ultra-deeply-buried Sinian Dengying formation in central Sichuan is typical oil-cracking gas from the paleo-oil reservoir. The Sinian gas is mainly sourced from the Qiongzhusi/Maidiping Formation. 2) The formation of Sinian gas reservoirs includes three stages: the formation of paleo-oil-reservoirs; the cracking of paleo-oil-reservoirs into paleo-gas-reservoirs; the adjustment of the paleo-gas-reservoirs. 3) Source rock and reservoir evaluation, quantitative solid bitumen analysis, and hydrocarbon accumulation simulation show that the natural gas accumulation conditions in the slope area are better than in the inherited uplift area. The scale of the paleo-oil-reservoirs in the slope area may be greater than that in the inherited uplift area.

Reservoir characteristics and factors influencing shahejie marl in the shulu sag, bohai bay basin, eastern China

Shahejie marl in the Shulu Sag is a crucial resource for unconventional hydrocarbon exploration in China. Although breakthroughs have been made in tight oil exploration in this area, the mechanisms underlying the formation of this marl reservoir and factors controlling its ‘sweet spots’ have not been thoroughly studied. To understand the pore structure characteristics and factors influencing the marl reservoir, we analyzed core samples from Wells ST1 and ST3. A series of experiments was conducted on the samples, such as X-ray diffraction, focused ion beam scanning electron microscopy, micro-CT, and total organic carbon test. Additionally, the physical properties of different marl rock fabrics were studied with auxiliary tests, such as mercury intrusion capillary pressure analyses, nuclear magnetic resonance, porosity and permeability tests, and thin-section observation. The results revealed that the marl reservoir is characterized by low porosity (1.61%) and low permeability (2.56mD). The porosity and permeability (1.61% and 3.26mD) of laminated marl were better than those (0.92% and 1.68mD) of massive marl. Clay minerals and quartz content in laminated (11.8 and 8.2%) was less than in massive marl (16.2 and 13.3%). The marl pores include intercrystalline pores, dissolution pores, and microfractures. Additionally, the laminated marl pores were primarily distributed along the dark lamina, with good connectivity. A few isolated and uniform holes were observed in the massive marl. Influenced by rock fabric and mineral composition, layered fractures were mainly developed in the laminated marl, while structural fractures were the main type of microfractures in the massive marl. The primary sedimentary mechanism was the main geological action underlying the differences in marl rock fabric; this mechanism affects the physical properties of the marl reservoir, which are key factors to be considered when searching for the marl reservoir ‘sweet spots’. Particular attention should be paid to these factors during tight oil exploration and development in similar sedimentary basins.

The influence of entrepreneurial spirit on sports culture construction from the perspective of cognitive regulation.

The purposes of this study are to extract the essence from the in-depth study of entrepreneurial spirit and the exploration of China’s sports culture construction, find out the beneficial parts in line with China’s sports culture construction, and put forward operational suggestions and countermeasures for dealing with the relationship between entrepreneurial spirit and sports culture to help China’s sports culture construction move toward a new level. This exploration discusses the influence of entrepreneurial spirit on sports culture from the perspective of cognitive regulation, and explores the importance of entrepreneurial spirit from the aspects of social psychology, system, economy, and ethics. The structure of sports culture is analyzed, and the role of entrepreneurial spirit in promoting the construction of sports culture is expounded. Moreover, a questionnaire survey is conducted to investigate the impact of entrepreneurial spirit on the construction of sports culture from the cognitive regulation perspective. The results show that most people agree with the development of the entrepreneurial spirit and positively impact the promotion of entrepreneurial spirit. Most people are not satisfied with the attention and level of sports culture construction. In China’s sports culture, the proportion of the entrepreneurial spirit is still tiny. Thereby, entrepreneurial spirit education must be vigorously promoted to enhance the integration of entrepreneurial spirit and sports culture. The entrepreneurial spirit needs to be introduced in the construction of sports culture. It is essential to do a good job in promoting entrepreneurial spirit, improving the supporting facilities related to sports culture and strengthening the correlation between sports culture and the entrepreneurial spirit. By discussing the influence of entrepreneurial spirit on sports culture, this exploration puts forward relevant opinions for developing sports culture. It is expected that they can have some reference values. This exploration provides new ideas for promoting the combination of sports culture construction and the dissemination of entrepreneurial spirit, which has crucial theoretical and practical significance.

Geochemical Characteristics and Chemostratigraphic Analysis of Wufeng and Lower Longmaxi Shales, Southwest China

The demand for shale gas has propelled researchers to focus on precise and high-resolution stratigraphic divisions for homogeneous shales, of which the late-Ordovician Wufeng (O3w) and the early-Silurian Longmaxi (S1l) formations in southwest China are two of the best candidates for shale gas exploration in China. However, systematic chemostratigraphic work for these strata is still sparse, and the existing chemostratigraphic work either lack representativeness in terms of the proxies used or are subjective during their division procedures. Thus, automatic division process based on multi proxies and an objective statistical technique was applied to establish a quantitative, high-resolution, and robust chemostratigraphic scheme for the Wufeng and lower Longmaxi shales. The geochemical analysis unveils that the Wufeng and Lower Longmaxi shales show prominent heterogeneities in terrigenous inputs, redox conditions, and paleoproductivity, enabling the potential application of chemostratigraphy to these strata. Based on these heterogeneities, the chemostratigraphic scheme for the Wufeng and Lower Longmaxi shales has been established, and the whole strata could be divided into 13 chemozones using constrained clustering analysis. The chemostratigraphic scheme could not only be comparable to the regional sequence stratigraphic scheme but also more objective and higher-resolution. The high TOC content and brittle minerals within chemozone C1 makes it the most preferable layer for shale gas exploration and development. This research gives a systematic chemostratigraphic analysis on Wufeng and Lower Longmaxi shales, which testifies the feasibility and potential of usage of chemostratigraphy for Chinese shale gas exploration and development.

The Sequence Stratigraphic Division and Depositional Environment of the Jurassic Yan’an Formation in the Pengyang Area, Southwestern Margin of the Ordos Basin, China

Coal and organic-rich shale in the Yan’an Formation in the southwestern margin of the Ordos Basin are widely developed, which is an important fact for oil and gas exploration in China that has been widely explored for a long time. In this paper, detailed sequence division and sedimentary environment analyses of the Yan’an Formation in the Pengyang area on the southwestern margin of the Ordos Basin were conducted using field outcrops, drilling cores, logging, wavelet transform and organic geochemistry. The results showed that the succession consists of some units with distinctly different characteristics. Based on the petrographic assemblage and transform wavelet characteristics, the Yan’an Formation in this area can be divided into a long-term cycle, five medium-term cycles, and eleven short-term cycles, among which coal and carbonaceous shale were mainly developed in the short-term cycles I2, III1, III2, V1 and V2. Coal and organic-rich mud shale have been developed in the Yan’an Formation and plant debris in mudstone and coal is common, indicating the development of swamps and shallow water-covered depressions in this area. The sandstones showed parallel bedding, cross-bedding and scours, thus indicating fluvial deposits. The saturated hydrocarbon gas chromatographic parameters of mud shale showed that the pristane/phytane (Pr/Ph) ratio is 2.24–6.22, the Ph/nC18 ratio is 0.15–0.93, and the Pr/nC17 ratio is 0.97–2.78, supporting the finding that the organic matter has mainly originated from terrestrial sources.