Search

Copyright of Natural Gas Geoscience is the property of Natural Gas Geoscience 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.)

Copyright of Acta Sedimentologica Sinica is the property of Acta Sedimentologica 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.)

The shale reservoirs of the Lower Cambrian Qiongzhusi Formation are widely distributed in the Sichuan Basin and have abundant gas resources. However, the shale lithofacies of the Qiongzhusi Formation are complex due to frequent sea level changes. The reservoir pore structure characteristics and gas content of different shale lithofacies vary significantly, which makes identifying the 'sweet spot' a challenging task. In this study, core observation and X-ray diffraction (XRD) were used to analyze the lithofacies types and characteristics of the study area. The pore types of different shale lithofacies were observed using field emission-scanning electron microscopy. Pore structures were studied using low-temperature gas (including N2 and CO2) physisorption, and the pore volume (PV), specific surface area (SSA) and pore structure were systematically characterized. The primary factors influencing pore formation in different types of shale lithofacies were analyzed by combining geochemical experiments and mineral contents. The results indicate that the lithofacies of the Qiongzhusi Formation shale in the study area can be classified into five categories according to mineral compositions: Siliceous argillaceous shale (CM-1), Argillaceous siliceous mixed shale (M-2), Argillaceous siliceous shale (S-3), Siliceous rock (S) and Calcareous siliceous shale (S-2). Pores are abundant in S-3 shale, M-2 shale and CM-1 shale. The S-3 shale is more enriched in organic pores and clay mineral pores compared to other lithofacies shales, and the pore morphology is mainly wedge-shaped and plate-like. M-2 shale and CM-1 shale are rich in clay minerals and mainly develop clay mineral pores and are mainly wedge-shaped and plate-like. The S shale and S-2 shale mainly develop interparticle pores and clay mineral pores, which are mainly slit-like. The results show that TOC, pyrite content, quartz and feldspar mineral content, clay mineral type and content affect the pore structure in the study area. Quartz and feldspar content have a negative effect on micropore and mesopore volumes. TOCs have a weak positive correlation with micropore volume and micropore SSA. Clay mineral content has significant positive effects on the PV and SSA of micropores and mesopores, indicating that clay mineral content is the main factor affecting the pore structure of shale. [ABSTRACT FROM AUTHOR]

The Lower Cambrian Qiongzhusi Formation in Sichuan Basin and on its periphery is rich in shale gas resources, and it has become one of the important shale gas development intervals in Sichuan Basin. Controlled by complex sedimentary setting, the silty shale reservoir in Qiongzhusi Formation has various lithofacies and strong heterogeneity longitudinally, which restricts the exploration and development of shale gas. Therefore, it is urgent to study the sedimentary characteristics, sedimentary facies and sedimentary models. Based on the previous understanding of tectonic setting and sequence stratigraphy, and through detailed analysis of rock data, well logging data, geochemistry data and paleontology data, this paper clarifies the Early Cambrian sedimentary background of combined ocean-paleoland influence, moderate water depth and widespread reduction of Sichuan Basin and its periphery. The paper also believes that the Qiongzhusi Formation is mainly deposited in shore facies and continental shelf facies. The continental shelf facies are dominated, including shallow water continental shelf subfacies and deep water continental shelf subfacies. Based on the analysis of the combined action of wave and tide, seawater evaporation, suspension, rising ocean current, sedimentary paleogeomorphology and other fine-grained sedimentary influencing factors, and combined with the spatial distribution characteristics of sediments, the fine-grained sedimentary model of the Lower Cambrian Qiongzhusi Formation in Sichuan Basin and on its periphery is established, i.e., in the early stage of sedimentation, the effect of differential sedimentation is significant, the sequence thickness varies greatly, and the sedimentary characteristics and influencing factors differ greatly in different regions. In the middle stage of sedimentation, the effect of differential sedimentation is diminished and the difference of sequence thickness decreases continuously. In the late stage of sedimentation, with steady sedimentation, it enters the "open basin" stage, and the sequence thickness tends to be consistent.

Huge and thick black shale was deposited in the Mianyang-Changning intracratonic sag of the Sichuan Basin, which is a favorable target for shale gas exploration in the future. Taking the paleofluid preserved in the Qiongzhusi Formation shale as the research object, based on the petrological and optical characteristics of fracture veins observed in cores and thin sections, the source and origin of the paleofluid were analyzed by carbon and oxygen isotope testing, the formation pressure evolution of shale gas was simulated by using BasinMod software, and the preservation conditions of Qiongzhusi Formation shale gas in the central portion and surrounding areas of the Mianyang-Changning intracratonic sag were discussed. The results show that fracture vein rarely appears in the Qiongzhusi Formation shale of wells GS17 and MX9. While multiple groups of bed-parallel and high-angle fractures appear in Well W201, which are filled with mesocrystalline to coarse crystalline calcite, fibrous calcite, saddle dolomite, barite, and quartz. Carbon and oxygen isotopes indicate that fracture veins were generated by fluids of hydrothermal solution or organic matter decarboxylation. Hydrocarbon generation, particularly the crude oil cracking, induced the strong overpressure in the Qiongzhusi Formation of the intracratonic sag and the Gaoshiti-Moxi area, and the overpressure has been preserved thus far. Although overpressure was also developed in the Weiyuan structure, it dissipated in the late tectonic movement. Compared with the intracratonic sag and Gaoshiti-Moxi area, the late preservation conditions of shale gas in the Weiyuan area were relatively harsh, but some local overpressure areas need to be focused on.

Recently, the shale gas exploration of Lower Cambrian Qiongzhusi Formation in Sichuan Basin has made a great breakthrough. However, the pore characteristics and controlling factors of the shale-gas reservoir in the Qiongzhusi Formation are not clear, which hinders further exploration and development of shale gas. This paper focuses on the Qiongzhusi Formation in the Lower Cambrian of the Sichuan Basin. On the basis of mineral composition and the lithofacies types of shale-gas reservoirs in Qiongzhusi Formation were classified by microscopic observation. Additionally, focused ion beam-scanning electron microscope (FIB-SEM), advanced mineral identification and characterization system (AMICS) analysis, large-field stitching scanning electron microscope technology (MAPS) and nitrogen adsorption experiment were employed to comprehensively determine the differential characteristics and controlling factors of pore development. The results indicate that the pore types in Qiongzhusi Formation are mainly composed of interparticle pores and intercrystalline pores. The pore structure of Qiongzhusi Formation is complex. Significant differences in pore structure parameters are observed among different lithofacies. Quartz and feldspar contribute to the preservation of primary pores due to their strong compressive resistance. Clay minerals and carbonate minerals impede pore development by occluding pores. The influence of organic matter on the pore development is relatively small. According to the mineral composition and pore parameters, laminated shale is a relatively favorable reservoir facies among different lithofacies types.

Copyright of Acta Sedimentologica Sinica is the property of Acta Sedimentologica 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.)

Copyright of Petroleum Geology & Oilfield Development in Daqing is the property of Editorial Department of Petroleum Geology & Oilfield Development in Daqing 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.)

Copyright of Acta Sedimentologica Sinica is the property of Acta Sedimentologica 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.)

Sichuan is an area where there are no fluorite deposits and no fluorite metallogenic belts. The discovery of medium-sized fluorite deposit in Mabian area is of great significance. Through field geological investigation and collection and analysis of geological data, the genesis of Yonghong Fluorite deposit in Mabian area and its enlightenment to regional prospecting are discussed. The results showed that the ore body occurs in the siltstone of Qiongzhusi Formation of Cambrian Terreneuvian, which is strictly controlled by fault. The metallogenic factors are dolomite, limestone, fluorine-containing phosphorites and fault, and there are no volcanic rock and intrusive rock. The five subtypes of hydrothermal filling type fluorite deposits summarized by predecessors have volcanic rock or intrusive rock. Therefore, it is summarized as a new subtype of hydrothermal filling fluorite type deposit-Yonghong subtype of hydrothermal filling type fluorite deposit (fault+carbonate rock+fluorophosphate); Yonghong fluorite deposit in Mabian area is a medium-sized fluorite deposit with an identified resource of 450000 t and its average content of CaF2 was 34.61%; Through the comparative analysis of metallogenic factors, Mabian-Leibo-Jinyang areas on Ebian-Jinyang fault zone have good fluorite prospecting prospects. The above results are of great significance to fill the gap of fluorite without metallogenic belt in Sichuan, guide the regional prospecting of Ebian-Jinyang fault zone and promote the economic development of Wumeng Mountains region.

The Lower Cambrian Qiongzhusi formation and the Lower Silurian Longmaxi Formation are the two most important shale strata. Although differences between these two shales have become the focus of current research, a comparative study of the depositional environments has not been performed. Using cores of both Longmaxi and Qiongzhusi formations of well W201, the in situ comparison of the sedimentary environment was realized, and the interference of other factors was eliminated, which made the results more reliable. In this study, 72 samples from both formations were collected from well W201, Weiyuan shale gas field, Sichuan Basin. A systematic study, including total organic carbon (TOC) content, mineral composition, and major/trace elemental analyses, was conducted to elucidate the paleoenvironments of the Qiongzhusi and Longmaxi formations. The results show both formations were deposited in non-sulfidic environments. The depositional conditions of the Longmaxi formation varied from reducing to oxidizing from bottom to top. The detrital flow happened during the deposition of the Qiongzhusi formation, which resulted in three stages of the redox conditions, from anoxic to oxic and then to anoxic from bottom to top of the Qiongzhusi formation. The anoxic conditions of the Qiongzhusi formation were considerably stronger than those of the Longmaxi formation. Both formations were deposited in warm and humid climates. Ratios of Eu/Eu*, Y/Y*, LaN/YbN, light rare earth element (LREE) and heavy rare earth element (HREE) revealed that the Longmaxi formation was primarily controlled by seawater, whereas the Qiongzhusi formation was jointly influenced by seawater and hydrothermal fluid. The organic matter enrichment for the Longmaxi and Qiongzhusi formations was controlled by paleoproductivity and redox conditions. Due to the slightly lower paleoproductivity and influence of detrital input, the degree of organic matter enrichment in the Qiongzhusi formation was lower than that in the Longmaxi formation. [ABSTRACT FROM AUTHOR]

To deeply analyze the thalassochemical conditions and organic matter enrichment mechanism during the Early Cambrian (541-509 Ma)and actively evaluate the potential of shale gas resources of the Lower Cambrian Qiongzhusi Formation(Fm) in the southwestern Sichuan Basin, based on the analysis of the petrology, organic geochemistry, element characteristics, pore structure and adsorption capacity of Qiongzhusi Formation, Well W-207, Weiyuan area, this study has discussed the Early Cambrian paleo-ocean environment, organic matter enrichment control factors and gas-bearing properties of shale gas in the upslope area of the Upper Yangtze Platform. Sedimentary cycle shows that multiple interactive conversioncycles of deep-water continental shelf and shallow-water continental shelf are developed during the fine-grained deposition period of Qiongzhusi Formation under the control of eustasy. In particular, the slope turbidite (fan) and gravity flow sediments indicate that shallow-water continental shelf facies are dominant, and the wells in the upslope of the Weiyuan area are not in deep-water for a long time, with the sedimentary thickness of organic-rich black shale limited. Organic geochemistry evidence indicates that the organic matter of Qiongzhusi Formation in Well W-207 is mainly Type-Ⅰ kerogen, with a high degree of thermal evolution, fewer residual hydrocarbons and a low hydrocarbon generation capacity. The redox parameters indicate that the marine environment on the upslope has a medium restrictive degree, and there is a certain degree of upwelling. The seawater has experienced the transformation process of "anoxic-oxidation-anoxic-secondary oxidation- oxidation". Therefore, the paleo-ocean productivity level in the upslope area is generally low, with an obvious downward trend from bottom to top. The pore structure and nitrogen adsorption curve show that the reservoirs of the Qiongzhusi Formation are mainly complex and irregular slit pores. The methane adsorption capacity is positively correlated with TOC but negatively correlated with temperature, indicating that the high-pressure and high-temperature conditions generally faced by the Qiongzhusi Fm are not suitable for methane adsorption. As a result, the geological conditions of shale gas for Qiongzhusi Fm in the upslope area are complex. With high exploration risk, this study suggests that the resource evaluation direction should change to the intracratonic sag (downslope area), which is characterized by deep-water continental shelf facies.

The shale reservoirs of the Lower Cambrian Qiongzhusi Formation are widely distributed in the Sichuan Basin and have abundant gas resources. However, the shale lithofacies of the Qiongzhusi Formation are complex due to frequent sea level changes. The reservoir pore structure characteristics and gas content of different shale lithofacies vary significantly, which makes identifying the ‘sweet spot’ a challenging task. In this study, core observation and X-ray diffraction (XRD) were used to analyze the lithofacies types and characteristics of the study area. The pore types of different shale lithofacies were observed using field emission-scanning electron microscopy. Pore structures were studied using low-temperature gas (including N2 and CO2) physisorption, and the pore volume (PV), specific surface area (SSA) and pore structure were systematically characterized. The primary factors influencing pore formation in different types of shale lithofacies were analyzed by combining geochemical experiments and mineral contents. The results indicate that the lithofacies of the Qiongzhusi Formation shale in the study area can be classified into five categories according to mineral compositions: Siliceous argillaceous shale (CM-1), Argillaceous siliceous mixed shale (M-2), Argillaceous siliceous shale (S-3), Siliceous rock (S) and Calcareous siliceous shale (S-2). Pores are abundant in S-3 shale, M-2 shale and CM-1 shale. The S-3 shale is more enriched in organic pores and clay mineral pores compared to other lithofacies shales, and the pore morphology is mainly wedge-shaped and plate-like. M-2 shale and CM-1 shale are rich in clay minerals and mainly develop clay mineral pores and are mainly wedge-shaped and plate-like. The S shale and S-2 shale mainly develop interparticle pores and clay mineral pores, which are mainly slit-like. The results show that TOC, pyrite content, quartz and feldspar mineral content, clay mineral type and content affect the pore structure in the study area. Quartz and feldspar content have a negative effect on micropore and mesopore volumes. TOCs have a weak positive correlation with micropore volume and micropore SSA. Clay mineral content has significant positive effects on the PV and SSA of micropores and mesopores, indicating that clay mineral content is the main factor affecting the pore structure of shale.

Copyright of Multipurpose Utilization of Mineral Resources / Kuangchan Zonghe Liyong is the property of Multipurpose Utilization of Mineral Resources 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.)

Based on the outcrop and drilling data of the Sichuan Basin and its periphery, this paper reveals the concretion development characteristics of the Lower Cambrian Qiongzhusi Formation and its significance to the environment. Three preliminary conclusions are drawn as follows. (1) The exposure layers and lithofacies characteristics of the concretions in the Qiongzhusi Formation are very different from area to area. In the eastern Sichuan-western Hubei-Hunan & Guizhou and southern Sichuan depression areas, the concretionsare developed in the section of SQ1, and are mainly composed of calcareous siliceous mixed shale facies, siliceous shale facies, dolomitic shale facies and dolomite facies. The clay content is generally less than 25% and is significantly less than the surrounding rocks, and the TOC is generally higher in the lower concretion layers and less in the upper concretion layers. In the central Sichuan and northern Sichuan depression areas, the concretions appear in the sections of SQ1 and SQ2, and are dominated by calcareous shale facies and marl facies. The calcic content is obviously higher than that of surrounding rocks, and the clay content is less than that of surrounding rocks, and the TOC is less than 1.50%. Because mineral composition difference is high, most of the GR curves of the concretions show trough response characteristics, reflecting the central region enriched with calcium or siliceous, and the edge enriched with clay and organic matter. (2) The concretion layers generally occur in carbonaceous shale, silty shale and siliceous shale with a TOC over 0.7%, and are especially developed in carbonaceous shale and siliceous shale of SQ1, and occasionally appear in grey silty shale with a TOC over 0.2%, showing that the concretion layers are basically symbiotic with grey shale (especially with high-quality shale). (3) The concretions are a kind of important sedimentary response of rifting activities in Yangtze marine basin. According to the distribution characteristics of concretions and black shale in the Qiongzhusi Formation, the rifting activities of Yangtze marine basin can be divided into three periods including development period (SQ1), adjustment period (SQ2) and abortion period (SQ3). In the period of SQ1, controlled by massive rifting and upwelling ocean currents in Yangtze marine basin, the concretions and organic-rich shale were widely developed in the Lower Qiongzhusi Formation. In the periods of SQ2 and SQ3, while rifting activity of Yangtze marine basin decreased and aborted, and while sea level fell and upwelling ocean currents receded to the southeast, the concretions and organic-rich shale just appeared in the local depression areas in small scale.

Copyright of Journal of Northeast Petroleum University is the property of Journal of Northeast Petroleum University 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.)

Copyright of Natural Gas Geoscience is the property of Natural Gas Geoscience 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.)

The marine facies highly mature natural gas system with the Lower Cambrian Qiongzhusi Formation as the source rock in the Sichuan Basin is a global model in this field. To deepen the geological understanding of high quality source rocks and the natural gas exploration areas in the Sichuan Basin, taking two hot exploration blocks in the central and northeastern parts of Sichuan Basin as examples, the differential mechanisms of organic matter accumulation in source rocks of the Qiongzhusi Formation were studied, and some gas exploration areas were identified by the means of geochemical methods from three perspectives, including paleoproductivity, redox conditions and input of terristral organic matters. The TOC of source rocks within deep-water shelf in the intracratonic rift sampled from the Gaoshi 17 and Zhongjiang 2 wells in the central Sichuan were higher than that of source rocks within the shallow-water shelf sampled from the Xiaoyangba outcrop, northeastern Sichuan. The organic matter accumulations of both sample sets were mainly controlled by redox condition, but in comparison, the source rocks in the central Sichuan Basin were formed in relative anoxic environment, which was more conducive for the preservation of organic matter than the suboxic environment in northeastern Sichuan Basin. In addition, the dilution effection by terrestrial organic matter input was particularly significant during the formation of source rocks in the northeastern Sichuan Basin, leading to poorer source rock quality. The exploration of natural gas system in the Qiongzhusi Formation still needs to be carried out closely around the intracratonic rift and its surrounding margin in the future, and the deep-water shelf area around the basin also deserves attention. Both conventional and unconventional natural gas resources should be considered.

Methane mainly occurs in the pores of shale in free state and adsorbed state. In this paper, taking the organic-rich shale of the Qiongzhusi Formation in eastern Yunnan as the research object, low-temperature liquid nitrogen adsorption and field emission scanning electron microscopy experiments were used to study the pore structure characteristics of the shale. The results show that the shale pores of the Qiongzhusi Formation in the middle-upper Yangtze area are mainly provided by organic matter and clay minerals, and carbonate minerals have a certain contribution to the development of shale pores. Pores of different pore sizes are developed in shale, and pores below 10 nm contribute the most to adsorption. The total face ratio and porosity of shale show a certain positive correlation. As the total face ratio increases, the porosity increases. The simulation results of heating-hydrocarbon generation history show that the eruption of the Emeishan basalt caused the Qiongzhusi Formation reservoir temperature to rise rapidly, the maximum heating temperature of the formation exceeded 210°C, and the organic matter was mainly converted from oil generation to gas generation. During the hydrocarbon generation evolution, the soluble components in the interlayer fluid formed by the difference of lithofacies are modified, and the petrophysical properties of the reservoir are significantly improved. The research results can be used to guide the evaluation of the occurrence characteristics of shale gas in the Qiongzhusi Formation in the Upper Yangtze area. [ABSTRACT FROM AUTHOR]

Fine characterization of pore systems and heterogeneity of shale reservoirs are significant contents of shale gas reservoir physical property research. The research on micro-control factors of low productivity in the Qiongzhusi Formation (Fm.) is still controversial. The lower Cambrian Qiongzhusi Fm. in the Qujing, Yunnan was taken as the object to investigate the influence of mineral compositions on the physical properties of the reservoir and the heterogeneity of shale, using the algorithm to improve the characterization ability of Atomic Force Microscopy (AFM). The results showed that: (1) The pores are mainly wedge-shaped pores and V-shaped pores. The pore diameter of the main pore segment ranges from 5 to 10 nm. Mesopores are mainly developed in the Qiongzhusi Fm. shale in Well QD1, with the average pore diameter of 6.08 nm. (2) Microscopic pore structure and shale surface properties show strong heterogeneity, which complicates the micro-migration of shale gas and increases the difficulty of identifying high-quality reservoirs. (3) The increase of clay mineral content intensifies the compaction and then destroys the pores. Conversely, brittle minerals can protect pores. The support and protection of brittle minerals to pores space depend on their content, mechanical properties and diagenesis. (4) Compression damage to pores, large microscopic roughness and surface fluctuations and strong pore structure heterogeneity are the reasons for the poor gas storage capacity of the Qiongzhusi Fm., which will lead to poor productivity in the Qiongzhusi Fm.

The lower Cambrian black rock series in eastern Yunnan province is a high-quality shale gas reservoir with great prospect for oil-gas exploration. However, the depositional conditions and mechanisms of organic matter enrichment are not well understood. In this study, geochemical characteristics of total organic carbon (TOC) and major and trace elements of fourteen black rock series samples from Dahai outcrop in eastern Yunnan province are systematically investigated to analyze the paleoenvironment and their effects on organic matter enrichment and established the accumulation model of organic matter. Results show that TOC contents of the four lithologic units of Qiongzhusi Formation black rock series are 0.70, 0.34, 1.77, and 0.27, respectively, which suggests that TOC content is generally low (mean = 0.51%). The main elements show that P2O5, CaO, and MgO are relatively rich, whereas other elements depleted. The enrichment factors (EFs) of trace elements showed that Pb and Zn are highly enriched in all samples, and Cu, Sr, Ba, U, Mo, V, Be, and Mo are also enriched in different lithofacies units. The elemental anomalies may be related to hydrothermal activities, which may lead to the distortion of some paleoenvironmental indicators to some extent. The Rb/Sr and Sr/Cu values show that the palaeoclimate gradually changed from dry to humid. Al concentrations indicate a gradual increase in terrigenous detritus supply. The hydrodynamic conditions and sedimentation rates implied by Zr/Al and Ti/Al values correspond well with lithology and grain size. Based on the comprehensive analysis of B/Ga and Sr/Ba ratios, it is considered that the black rock series in Qiongzhusi Formation was mainly formed in brachial water. Multiple paleoredox indicators (e.g., Ni/Co, V/Cr, U/Th, and V/(V+Ni) ratios) suggest that the sedimentary environment is mainly oxidized, which is usually considered unfavorable for organic matter preservation, and it also forms carbonaceous shale (unit 3) in a dysoxic environment. The Mo/TOC ratios suggest that the sedimentation during Qiongzhusi Formation period was under restricted conditions. The paleoproductivity indicated by P/Ti, Ni/Al and Babio values decreased gradually from medium level to low level. In summary, relatively high paleoproductivity is a prerequisite for organic matter accumulation and less terrigenous debris supply, and relatively arid climate and reductive conditions are favorable for the preservation of organic matter. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Geoscience is the property of Natural Gas Geoscience 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.)

Sichuan Basin is the only successful basin for shale gas exploration in China. In addition to the main shale in the Lower Silurian Longmaxi formation, the lower Cambrian Qiongzhusi shale is an important potential formation. However, it was once considered that shale gas is difficult to enrich because of its poor sealing conditions and hydrocarbon migration to adjacent reservoirs. With the increasing research on hydrocarbon generation and reservoir in shale of Qiongzhusi Formation in recent years, it has become an important exploration target in Sichuan Basin. The enrichment of oil and gas is closely related to fluid activities. Limited by the degree of exploration, there is little analysis of fluid activities in Qiongzhusi Formation, and there is little analysis of shale gas enrichment potential from the perspective of fluid. The hydrocarbon generated from Qiongzhusi shale in the rift could migrate laterally to the uplift area and form a reservoir in Dengying Formation. The fluid activities from source rock to reservoir are basically the same. Therefore, this paper reconstructed the history of hydrocarbon activities in Dengying reservoirs based on fluid inclusion analysis. Then the fluid activity process in Qiongzhusi shale was studied, and its enrichment conditions of shale gas was discussed. The results show that the hydrocarbon activities of Dengying Formation can be divided into three stages: 1) oil charging stage, 2) oil cracking gas generation stage and 3) gas reservoir adjustment stage. The first stage is under normal pressure, and the second and third stages developed overpressure with pressure coefficients of 1.3 and 1.2, respectively. High pressure coefficient is an important indicator of shale gas enrichment. Because the source rock of Qiongzhusi Formation has always been the main source rock of Dengying Formation, it can supply hydrocarbon to Dengying Formation only with overpressure in gas generation stage. Therefore, overpressure in the last two stages of gas generation indeed existed. As long as the sealing condition of shale itself is not particularly poor, shale gas “sweet points” would be formed. Therefore, the thick shale in Deyang-Anyue rift is the focus of shale gas exploration in Qiongzhusi Formation.

Copyright of Acta Sedimentologica Sinica is the property of Acta Sedimentologica 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.)

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum 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.)

The black rock series of Lower Cambrian in the Yangtze block in South China is closely related to the formation of various metal nonmetal deposits. In recent years，some breakthroughs have been made in the exploration of the black rock series deposits of the Lower Cambrian Qiongzhusi Formation from Huize area，and there is still great potential. The ore bearing properties were analyzed from the aspects of the enrichment coefficient of ore forming elements (K)，the intensity of late stacking(D) and the coefficient of variation of ore forming elements (CV). The results show that Zn，Pb，B，U，Sn，Li，Cs，Tl，Mo，Rb，Cu，V，and Th are strongly enriched, Sr and Mo are superimposed in the late period, and Mo has a very strong variation. The comprehensive evaluation of the mineralogy of the formation shows that Mo is the most dominant mineral in tBe area，followed by Cu，V，U，Sn and T1, and again Pb and Li，while Sr，Zn，B，Th and Rb also have certain metallogenic capacity. According to R-type cluster analysis, Dre-f(3rming elements can be divided into five groups: Rb, Th,Li,B,Sn,U,Tl；CuPb,Zn；V,Mo；and Sr. Among them,Rb,Th,Li,B and Sn may come from seawater and are related to the adsorption of clay minerals； V and Mo are controlled by the reduced deposition environment； Cu, Pb and Zn are controlled by hot water deposition；Sr and calcite are closely related, This study may be helpful to guide the exploration of the Qiongzhusi Formation black rock series in eastern Yunnan. [ABSTRACT FROM AUTHOR]

Shale gas refers to unconventional natural gas that exists in organic-rich mud shale and its interlayer, with adsorption or free state as the main existence mode. The thesis takes the organic-rich shale in Qiongzhusi, Yunnan Province as the research object. Scanning electron microscopy experiment, low temperature liquid nitrogen experiment and isothermal adsorption experiment were carried out to study the fracture characteristics and methane adsorption characteristics of shale reservoirs in Qiongzhusi Formation. The results show that the lithology of the Qiongzhusi Formation is mainly thin and mediumthick black carbonaceous shale and grayish black calcareous shale with limestone bands, which are weathered like bamboo leaves. The minimum thickness of the developed black shale is 15m. The maximum thickness is greater than 33m. At the same pressure, with the increase of TOC, the maximum methane adsorption capacity increases. The higher the TOC value in the shale of the Qiongzhusi Formation, the greater the maximum gas adsorption capacity of the shale. The pores of shale gas reservoirs are mainly nanopores, and there are certain pores with an amorphous structure. The internal pore structure of mineral particles has parallel plate-shaped slittype pores, and other types of pores also exist. Research on the influencing factors of gas content of shale in Qiongzhusi Formation shows that there is a certain correlation between total gas content and component content and burial depth. [ABSTRACT FROM AUTHOR]

The Lower Cambrian Qiongzhusi Formation contains more than 200 m of marine sediments mainly consisting of mudstone and black shales, which are widely accepted as the most important hydrocarbon source rocks of the Ediacaran–Cambrian giant gas field in the Sichuan Basin. The geochemical compositions of biomarkers and trace elements obtained from black shales at the bottom of the Qiongzhusi Formation were used to reconstruct the palaeoproductivity and palaeoenvironment and to determine the main factors controlling the deposition and preservation of this organic‐rich shales. Based on varieties of steroids and hopanoids compositions, multifarious palaeobios such as pelagophyceae, dinoflagellate, diatom (or its ancestor), sponges, and aerobic/anaerobic bacteria have been proved to evolve in the Early Cambrian in the Sichuan Basin. In addition, a relative high concentration of Cubio compared with modern oceanic palaeoproductivity proxies indicate a moderate to relatively high palaeoproductivity, which is favourable for the organic matter accumulation of this source rocks. Moreover, the evidence from biomarkers and trace element ratios suggest that the Lower Cambrian sediments were deposited under a non‐sulphurized anoxic condition, which provided a favourable preservation condition. The covariation among Porg, Cubio, and TOC shows that the palaeoproductivity is the main controlling factor for the high organic content of the black shales of the Qiongzhusi Formation. [ABSTRACT FROM AUTHOR]

The results of sedimentological, mineralogical, geochemical and petrophysical studies on the early Cambrian shale in the Upper Yangtze area are summarized to provide insights on the paleoenvironmental conditions, diagenetic evolution and preservation conditions that give rise to shale gas accumulation. The lower Cambrian organic-rich Qiongzhusi shale is mainly developed in the outer shelf facies of an intracratonic sag [average total organic carbon (TOC): 1.3–2.5%] and in the southeast margin (average TOC: 3.5–5.5%) of the Upper Yangtze area. The thermal maturity values (R eqv) of the Qiongzhusi shale range from 2.19 to 4.23%, while first increasing and then decreasing from the center of the Sichuan Basin outward. The average porosities of the Qiongzhusi shale from the outer shelf facies association (FA5) in the intracratonic rift range from 1.5 to 3.41%, and those from the outer shelf facies association (FA4) in the southeast Sichuan and Guizhou areas range from 1.32 to 2.56%. The organic matter (OM) content and the development degree of OM pores are the main factors that control the porosity and pore structure of the Qiongzhusi shale. For the outer shelf deposits in the intracratonic rift, a quartz (detrital origin) content ranging between 25 and 35% is most favorable for providing an effective support framework for OM pore development due to the mixture of brittle and clay minerals. For the outer shelf deposits in the southeastern margin of the Upper Yangtze area, the high OM content and poor compaction resistance cause a poor development of OM pores, with a smaller average pore diameter than that in the outer shelf shale of the intracratonic rift. In addition, the carbonization of OM in the overmature Qiongzhusi shale change the microstructure and decrease the OM pore volume. Due to poor preservation conditions, the gas content is generally low in the organic-rich shale in the eastern and southeastern parts of the Upper Yangtze region. The Qiongzhusi shale in the interior of the Sichuan Basin, with good preservation conditions, high pressure coefficients, and high gas contents, is a favorable area for shale gas accumulation and potential exploitation. • The organic-rich Qiongzhusi shale mainly developed in outer shelf. • The content of OM and the development degree of OM pores control the pore structure. • A high TOC content leads to a poor development degree of OM pores in siliceous shale. • The Qiongzhusi shale in the interior of the Sichuan Basin is favorable for shale gas accumulation. [ABSTRACT FROM AUTHOR]

Abstract Research on shale pore structures has furthered the understanding of shale oil and gas accumulation. However, understanding of mechanisms of shale lithofacies that affect pore structures remains poor, restricting evaluations of marine shale and accurate estimations of gas content. This study focuses on the over-mature Qiongzhusi marine shales in Lower Cambrian of the Southern Sichuan Basin. A series of laboratory experiments were conducted on core samples, including X-ray diffraction (XRD), scanning electron microscopy (SEM), low-pressure gas adsorption (N 2 and CO 2) and high-pressure mercury intrusion porosimetry (MIP). XRD results show that four main types of shale lithofacies are found in the Qiongzhusi Formation according to the content of siliceous, carbonate and clay minerals, including silica-rich argillaceous shale lithofacies (SAL), argillaceous-rich siliceous shale lithofacies (ASL), carbonate/argillaceous containing siliceous shale lithofacies (C/ASL) and argillaceous/siliceous mixed shale lithofacies (A/SML). SEM images reveal that three kinds of pores within the shale samples (organic matter, intergranular and dissolved pores) with the majority being slit-like and narrow slit-like pores. Silica-rich argillaceous shale lithofacies exhibit the highest pore surface areas and volumes, while other shale lithofacies and carbonate/clay containing siliceous shale lithofacies exhibit relatively lower pore surface areas and volumes. It can be inferred that silica-rich argillaceous shale lithofacies facilitate shale gas storage and flow. Both TOC and clay mineral content are more positively correlated with the microscopic pore structure parameters of micropores than that of mesopores, and thus further interpreted as two dominant factors controlling the development and distribution of micropores. A relatively high quartz content in Qiongzhusi shale of Lower Cambrian are conductive to contribute a large macropore volume, but most importantly, the development of rigid frameworks established by authigenic quartz/pyrite and clay minerals are favorable for the preservation of primary organic matter micropores by providing effective grain supporters. Clay-rich siliceous shale could be deemed as one of the most typical lithofacies types displaying this unique pore-preserving mechanism. Shale lithofacies with different TOC and mineral compositions exhibit distinct differences in pore structures. Highlights • Whole-aperture pore structure characteristics of the Qiongzhusi shale were obtained. • Lithofacies has a stronger effect on micropore structure than mesopore structure. • Protective frames composed of quartz and clay minerals were found in SEM images. [ABSTRACT FROM AUTHOR]

The albitization of K-feldspar is a common diagenetic process that has thus far received little attention and is not fully understood in fine-grained sedimentary rocks. To better understand the albitization of K-feldspar, studies in organic- and silt-rich fine-grained rocks of the lower Cambrian Qiongzhusi Formation in the southwestern Upper Yangtze region, China, were carried out via X-ray diffractometry (XRD) and field emission scanning electron microscopy (FE-SEM). The results show that five types of albitized K-feldspar textures have developed: microcrystal albite replacement, irregular blocky replacement along margins, cleavage planes or microcracks of K-feldspars, complete pseudomorphic replacement, albite overgrowth, and albite pore filling. Organic- and silt-rich fine-grained rocks differ from sandstones and mudstones in terms of the rock structure and mineral assemblage, which results in differences in the textures and degree of albitization of K-feldspar. Illitization of clay has an impact on the albitization of K-feldspar. In provenance analyses using feldspar, fine-grained rocks, especially those that underwent mesogenesis, should be treated with caution because detrital feldspars have been destroyed. Theoretically, the albitization of K-feldspar could increase the porosity of reservoirs, although, from our observations, most of the related secondary pores are cancelled out or became isolated pores due to other diagenetic processes (compaction, cementation, etc.) in organic- and silt-rich fine-grained rocks.

The Lower Cambrian Qiongzhusi shale is the main producing layer of shale gas in the northern Sichuan Basin. Natural fractures are considered an important factor that influences the exploration and development of shale gas. In this study, outcrops, drill cores, thin sections, fluid inclusions and rare earth element (REE) were analyzed to determine the characteristics, changes in fluid chemistry, and fluid source of different types of fractures and then reveal their effects on the accumulation and preservation of shale gas. Natural fractures of Qiongzhusi shale are mainly composed of non-strata-bounded fractures (NSBFs), strata-bounded fractures (SBFs), and bed-parallel fractures (BPFs). NSBFs span multiple layers, which can significantly enhance the vertical connectivity of shale reservoirs. There are three dominant orientations of NSBFs, as N-S, NNE-SSW, and E-W trends. The E-W trending fractures, which intersect with the maximum principal stress (NWW-SEE) at a small angle, have larger permeability and control the vertical leakage of shale gas. SBFs are confined to individual layers. Homogenization temperatures of aqueous inclusions in SBF veins vary from 149.7 to 172.3 °C. Calcite veins exhibit positive Eu anomalies (δEu = 11.71, 27.9). Analysis of fluid inclusions and rare earth elements indicated that SBF vein-precipitating fluids were derived from the surrounding wall rock. The development of SBFs contributes to shale gas enrichment. BPFs are parallel to bedding planes or intersect at a low angle (<20°). Microstructural analysis suggests that cemented BPFs form from the multiple crack-seal processes. The temperature of fluid during mineral precipitation exceeds 200 °C. REE concentrations vary significantly across the BPF veins (δEu = 2.31–119.37), donating that fluid characteristics episodically changed during vein growth. The methane inclusions trapped in cements and mixing externally sourced fluids indicate that BPFs are the preferential fluid-flow pathway of shale gas and controls the lateral migration of shale gas. • The types and development characteristics of natural fractures in Qiongzhusi shale. • Microchemical characteristics of different types of natural fractures in shale. • Effects of different types of fractures on shale gas preservation. [ABSTRACT FROM AUTHOR]

Abstract: According to the latest drilling data, the geologic survey of surrounding outcrops and the laboratory test results of rock samples, this paper studies the regional distribution, geochemical and reservoir characteristics and gas concentration of organic-rich shales to reveal the shale gas generation and potential of the Lower Cambrian Qiongzhusi Formation of the Southern Sichuan Basin. The study area features high organic content (with TOC between 0.55% and 25.7%, average of more than 2%), great net shale thickness (of 60–300 m), high brittle mineral content (over 40%), abundant micro- and nanometer-sized pores and micro-fractures, and high gas content (0.27–6.02 m3/t, average of 1.90 m3/t), which is in favor of the generation and accumulation of shale gas. The Lower Cambrian Qiongzhusi Formation is one of the most favorable strata which has frequent gas show and industrialization breakthrough during drilling, and the Weiyuan and Xunyong-Junlian areas are two most realistic and favorable targets for shale gas exploration and development. [Copyright &y& Elsevier]

[Display omitted] • AFM is a powerful tool to characterize shale gas reservoir physical properties. • Reasons for the poor gas storage capacity and productivity of the reservoir are revealed. • Microscopic roughness and surface fluctuations lead to strong pore structure heterogeneity. Fine characterization of pore systems and heterogeneity of shale reservoirs are significant contents of shale gas reservoir physical property research. The research on micro-control factors of low productivity in the Qiongzhusi Formation (Fm.) is still controversial. The lower Cambrian Qiongzhusi Fm. in the Qujing, Yunnan was taken as the object to investigate the influence of mineral compositions on the physical properties of the reservoir and the heterogeneity of shale, using the algorithm to improve the characterization ability of Atomic Force Microscopy (AFM). The results showed that: (1) The pores are mainly wedge-shaped pores and V-shaped pores. The pore diameter of the main pore segment ranges from 5 to 10 nm. Mesopores are mainly developed in the Qiongzhusi Fm. shale in Well QD1, with the average pore diameter of 6.08 nm. (2) Microscopic pore structure and shale surface properties show strong heterogeneity, which complicates the micro-migration of shale gas and increases the difficulty of identifying high-quality reservoirs. (3) The increase of clay mineral content intensifies the compaction and then destroys the pores. Conversely, brittle minerals can protect pores. The support and protection of brittle minerals to pores space depend on their content, mechanical properties and diagenesis. (4) Compression damage to pores, large microscopic roughness and surface fluctuations and strong pore structure heterogeneity are the reasons for the poor gas storage capacity of the Qiongzhusi Fm., which will lead to poor productivity in the Qiongzhusi Fm. [ABSTRACT FROM AUTHOR]

The albitization of K-feldspar is a common diagenetic process that has thus far received little attention and is not fully understood in fine-grained sedimentary rocks. To better understand the albitization of K-feldspar, studies in organic- and silt-rich fine-grained rocks of the lower Cambrian Qiongzhusi Formation in the southwestern Upper Yangtze region, China, were carried out via X-ray diffractometry (XRD) and field emission scanning electron microscopy (FE-SEM). The results show that five types of albitized K-feldspar textures have developed: microcrystal albite replacement, irregular blocky replacement along margins, cleavage planes or microcracks of K-feldspars, complete pseudomorphic replacement, albite overgrowth, and albite pore filling. Organic- and silt-rich fine-grained rocks differ from sandstones and mudstones in terms of the rock structure and mineral assemblage, which results in differences in the textures and degree of albitization of K-feldspar. Illitization of clay has an impact on the albitization of K-feldspar. In provenance analyses using feldspar, fine-grained rocks, especially those that underwent mesogenesis, should be treated with caution because detrital feldspars have been destroyed. Theoretically, the albitization of K-feldspar could increase the porosity of reservoirs, although, from our observations, most of the related secondary pores are cancelled out or became isolated pores due to other diagenetic processes (compaction, cementation, etc.) in organic- and silt-rich fine-grained rocks. [ABSTRACT FROM AUTHOR]