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| 1 | Geological and Geochemical Characteristics and Exploration Prospect of Coal-Derived Tight Sandstone Gas in China: Case Study of the Ordos, Sichuan, and Tarim Basins显示文摘This work extensively investigated global tight sandstone gas, and geologically and geochemically analyzed the tight sandstone gas in China's Ordos, Sichuan, and Tarim basins. We compared typical tight sandstone gas in China with that in North America. We proposed six conditions for the formation of China's tight sandstone gas, and illustrated the geological characteristics of tight sandstone gas. In China, gas-bearing tight sandstones were mainly deposited in continental lake deltas and marine-terrigenous facies basin environments, associated with coal-measure strata, and were mostly buried deeper than 2000 m under a formation pressure of 20–30 MPa, with pressure coefficients varying from overpressure to negative pressure. In other countries, tight gas bearing sandstones were dominantly deposited in marine to marine-terrigenous facies environments, occurred in coal-measure strata, and were mostly buried shallower than 2000 m in low-pressure systems. We systematically analyzed tight sandstone gas in the Ordos, Sichuan, and Tarim basins in terms of chemical compositions, geochemical characteristics of carbon isotopes, origins, and sources. Tight sandstone gas in China usually has a hydrocarbon content of >95%, with CH4 content >90%, and a generally higher dry coefficient. In the three above-mentioned large tight sandstone gas regions, δ13 C1 and δ13 C2 mainly ranges from-42‰ to-28‰ and from-28‰ to-21‰, respectively. Type III coal-measure source rocks that closely coexist with tight reservoirs are developed extensively in these gas regions. The organic petrology of source rocks and the carbon isotope compositions of gas indicate that tight sandstone gas in China is dominantly coal-derived gas generated by coal-measure strata. Our analysis of carbon isotope series shows that local isotope reversals are mainly caused by the mixing of gases of different maturities and that were generated at different stages. With increasing maturity, the reversal tendency becomes more apparent. Moreover, natural gas with medium-low maturity(e.g., Xujiahe Formation natural gas in the Sichuan Basin) presents an apparent reversal at a low-maturity stage, a normal series at a medium-maturity stage, and a reversal tendency again at a high-maturity stage. Finally, we proposed four conditions for preferred tight sandstone gas 'sweep spots,' and illustrated the recoverable reserves, proven reserves, production, and exploration prospects of tight sandstone gas. The geological and geochemical characteristics, origins, sources, and exploration potential of tight sandstone gas in China from our research will be instructive for the future evaluation, prediction, and exploration of tight sandstone gas in China and abroad. | ZOU Caineng TAO Shizhen HAN Wenxue ZHAO Zhenyu MA Weijiao LI Changwei BAI Bin GAO Xiaohui | 2018 | Acta Geologica Sinica(English Edition)2018，92，4： | 11 |
| 2 | 莱州湾凹陷北洼沙河街组三段砂岩储层孔隙定量演化模式显示文摘莱州湾凹陷位于渤海湾盆地南部,是一个'小而肥'的富烃凹陷,其储层成岩作用的研究程度较低。铸体薄片、扫描电镜、X射线衍射和阴极发光等多种技术手段的分析结果显示,莱州湾凹陷沙河街组三段中—深层储层的岩性主要为中粒—细粒岩屑长石砂岩,其成分成熟度和结构成熟度为中等偏好,属于中孔、中—低渗储层类型,储集性能良好,成岩作用处于中成岩阶段A1期。地层埋藏史、热演化史、烃源岩生烃史和成岩演化史的综合分析指示,储层孔隙空间的演化主要经历了机械压实减孔、早期胶结减孔、酸性溶蚀增孔和晚期胶结减孔4个阶段,其孔隙度的变化量分别为7.73%、4.61%、5.99%和2.54%,由此可建立储层孔隙定量演化的综合模式。受长期浅埋环境和成岩演化阶段影响,莱州湾凹陷沙河街组三段在古成藏期的储层孔隙度约为25%,油气充注情况良好。现今的孔隙类型仍以原生粒间孔为主,油气保存情况较好,勘探潜力较大。这一认识可为研究区的进一步勘探开发提供理论支持。 | 王彤 朱筱敏 张自力 刘宇 郭诚 李卓 | 2020 | 石油学报2020，41，6： | 8 |
| 3 | A Volumetric Model for Evaluating Tight Sandstone Gas Reserves in the Permian Sulige Gas Field,Ordos Basin,Central China显示文摘To accurately measure and evaluate reserves is critical for ensuring successful production of unconventional oil and gas. This work proposes a volumetric model to evaluate the tight sandstone gas reserves of the Permian Sulige gas field in the Ordos Basin. The reserves can be determined by four major parameters of reservoir cutoffs, net pay, gas-bearing area and compression factor Z, which are controlled by reservoir characteristics and sedimentation. Well logging, seismic analysis, core analysis and gas testing, as well as thin section identification and SEM analysis were used to analyze the pore evolution and pore-throat structure. The porosity and permeability cutoffs are determined by distribution function curve,empirical statistics and intersection plot. Net pay and gas-bearing area are determined based on the cutoffs, gas testing and sand body distribution, and the compression factor Z is obtained by gas component. The results demonstrate that the reservoir in the Sulige gas field is characterized by ultralow porosity and permeability, and the cutoffs of porosity and permeability are 5% and 0.15×10^(–3) μm^2, respectively. The net pay and gas-bearing area are mainly affected by the sedimentary facies, sand body types and distribution. The gas component is dominated by methane which accounts for more than 90%, and the compression factor Z of H_8(P_2h_8) and S_1(P_1s_1) are 0.98 and 0.985, respectively. The distributary channels stacked and overlapped, forming a wide and thick sand body with good developed intergranular pores and intercrystalline pores. The upper part of channel sand with good porosity and permeability can be sweet spot for gas exploration. The complete set of calculation systems proposed for tight gas reserve calculation has proved to be effective based on application and feedback. This model provides a new concept and consideration for reserve prediction and calculation in other areas. | CUI Mingming FAN Aiping WANG Zongxiu GAO Wanli LI Jinbu LI Yijun | 2019 | Acta Geologica Sinica(English Edition)2019，93，2： | 4 |
| 4 | Numerical Simulation of the Influence of Pore Structure on Resistivity, Formation Factor and Cementation Index in Tight Sandstone显示文摘Tight sandstone,with severe diagenesis and complex pore structure,differs greatly from conventional sandstone in terms of rock electrical parameters.In subsurface rock electrical experiments,various electrical parameters are confounded and can only be analyzed qualitatively.The lack of quantitative analysis for each individual electrical parameter presents a challenge for the evaluation of oil and gas saturation in tight sandstone.Based on the 2D pore-throat model and the features of pore structure in the tight sandstone of the Penglaizhen and Shaximiao Formations in the upper and middle Jurassic of the Western Sichuan Depression,this paper presents 3D micro pore-throat models for three types of tight sandstone.It proposes a finite element-based rock electrical simulation method to analyze the influence of pore structure parameters,such as throat radius and throat tortuosity,on electrical parameters such as resistivity,formation factor,and cementation index quantitatively.The research revealed the following results:(1)Throats of tight sandstone usually have lamellar or curved lamellar shapes that are slender and narrow.The lamellar throat used in the proposed porethroat model is more consistent with the features of tight sandstone than the tubular throat used in the original model.(2)The throat determines the conductivity of tight sandstone.The throat parallel to the electric potential has the greatest influence on conductivity,and the throat perpendicular to the potential has the least influence.(3)In tight sandstone grades I to III,as the porosity decreases,the formation factor increases and the cementation index decreases.(4)The results of the rock electrical simulation are consistent with the results of the rock electrical experiment,which indicates that the proposed rock electrical simulation method of tight sandstone is effective and accurate. | WU Feng WEN Zhu YAO Cong WANG Xianhu XI Yanping CONG Linlin | 2020 | Acta Geologica Sinica(English Edition)2020，94，2： | 0 |
| 5 | Geological Controls on High Production of Tight Sandstone Gas in Linxing Block, Eastern Ordos Basin, China显示文摘Tight sandstone gas in the Linxing Block, eastern Ordos Basin, has been successfully exploited. The high performance is mainly a result of the special geological conditions. The key geological controls for high production have been discussed on the basis of seismic data, field observation, sample features, mercury porosimetry, mechanical properties, and basin modeling. Firstly, the coal measures have good gas generation potential, not only because of the existence of coalbeds and organic-rich shales, but also because coal laminae and microbial mats in the shales significantly increase their total organic carbon(TOC) contents. Secondly, except for the uplifted zone of the Zijinshan complex and the eastern fault zone, rare large faults develop in the Carboniferous–Permian sequence, ensuing the sealing capacity of cap rock. Small fractures generally concentrated in the sandstones rather than the mudstones. Thirdly, gas accumulation in the Linxing Block was controlled by the tectonic, burial and thermal histories. Gas accumulation in the Linxing Block started in the Late Triassic, followed by three short pauses of thermal maturation caused by relatively small uplifts;the maximum hydrocarbon generation period is the Early Cetaceous as a combined result of regional and magmatic thermal metamorphisms. Field profiles show abundant fractures in sandstone beds but rare fractures in mudstone beds. Mechanical properties, determined by lithostratigraphy, confine the fractures in the sandstones, increasing the permeability of sandstone reservoirs and retaining the sealing capacity of the mudstone cap rocks. The modern ground stress conditions favor the opening of predominant natural fractures in the NNW-SSE and N-S directions. These conclusions are useful for exploring the potential tight sandstone gas field. | QI Yu JU Yiwen MENG Shangzhi YU Kun LI Wuyang JIA Tianrang WU Jianguang CHEN Wangang LUO long | 2020 | Acta Geologica Sinica(English Edition)2020，94，2： | 0 |
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