Micro-pore structure and fractal characteristics of terrestrial shales: A case study of Shahezi Formation in Xujiaweizi Fault Depression

Authors

LIN Zizhi, School of Geoscience, China University of Petroleum(East China), Qingdao 266580, ChinaFollow
LU Shuangfang, School of Geoscience, China University of Petroleum(East China), Qingdao 266580, China
CHANG Xiangchun, College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China
LI Junqian, School of Geoscience, China University of Petroleum(East China), Qingdao 266580, China
ZHANG Pengfei, College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China
ZHOU Nengwu, School of Geoscience, China University of Petroleum(East China), Qingdao 266580, China
ZHANG Yu, School of Geoscience, China University of Petroleum(East China), Qingdao 266580, China
WANG Junjie, School of Geoscience, China University of Petroleum(East China), Qingdao 266580, China
HUANG Hongsheng, School of Geoscience, China University of Petroleum(East China), Qingdao 266580, China

Abstract

The pore structure and fractal characteristics of shale are analyzed, and their impacting factors are also revealed using the low temperature nitrogen adsorption-desorption method, combined with scanning electron microscopy, C-S analysis and XRD. The results showed that the mineral compositions of Shahezi Formation continental shales were dominated by clay minerals, quartz and feldspar. The pore types in shales were mainly clay mineral intragranular pores, feldspar dissolution pores and grain edge pore, while the organic pores were not developed. The adsorption isotherms of shales belonged to the type Ⅳ isotherm according to the IUPAC, which develop two types of hysteresis loop, H2 and H3. The type H3 shales are characterized by a lower specific surface area, a larger average pore size, and a higher macro-pore content. Meso- and macro-pores mainly contribute to the total pore volume, while the meso-pores mainly contribute to the specific surface area. The pore size distribution was bimodal, characterized by a left peak at about 2.7 nm and the right peak at 20-70 nm. The shales showed two stages of fractal characteristics and the pore structures of type H3 shales were more homogeneous and simpler. The pore structures of Shahezi Formation shales were mainly controlled by the mineral composition rather than TOC. The higher the micropore content and the specific surface area value, the higher the macropore content and the average pore size, the more complex the shale pore structure, which is not conducive to the migration and production of shale gas. The differences between marine and terrestrial shale reservoirs are constrained by the differential sedimentary environments and the organic matter types, which fundamentally affected their pore structures and shale gas enrichment.

Keywords

terrestrial shales, pore structure, fractal dimension, low temperature nitrogen adsorption-desorption, Shahezi Formation, Xujiaweizi Fault Depression

DOI

10.3969/j.issn.1001-1986.2021.01.016

Recommended Citation

LIN Zizhi, LU Shuangfang, CHANG Xiangchun, et al. (2021) "Micro-pore structure and fractal characteristics of terrestrial shales: A case study of Shahezi Formation in Xujiaweizi Fault Depression," Coal Geology & Exploration: Vol. 49: Iss. 1, Article 17.
DOI: 10.3969/j.issn.1001-1986.2021.01.016
Available at: https://cge.researchcommons.org/journal/vol49/iss1/17

Reference

[1] 邹才能,杨智,朱如凯,等. 中国非常规油气勘探开发与理论技术进展[J]. 地质学报,2015,89(6):979-1007. ZOU Caineng,YANG Zhi,ZHU Rukai,et al. Progress in China's unconventional oil & gas exploration and development and theoretical technologies[J]. Acta Geologica Sinica,2015,89(6):979-1007.

[2] 邹才能,董大忠,王玉满,等. 中国页岩气特征、挑战及前景(一)[J]. 石油勘探与开发,2015,42(6):689-701. ZOU Caineng,DONG Dazhong,WANG Yuman,et al. Shale gas in China:Characteristics,challenges and prospects(I)[J]. Petroleum Exploration and Development,2015,42(6):689-701.

[3] 邹才能,杨智,张国生,等. 非常规油气地质学建立及实践[J]. 地质学报,2019,93(1):12-23. ZOU Caineng,YANG Zhi,ZHANG Guosheng,et al. Establishment and practice of unconventional oil and gas geology[J]. Acta Geologica Sinica,2019,93(1):12-23.

[4] 扈金刚,黄勇,熊涛,等. 湘鄂西地区龙马溪组黑色页岩孔隙结构及分形特征[J]. 中国煤炭地质,2018,30(12):5-14. HU Jingang,HUANG Yong,XIONG Tao,et al. Pore structure and fractal features of black shale in Longmaxi Formation,western Hunan and Hubei[J]. Coal Geology of China,2018,30(12):5-14.

[5] 王思远,李俊乾,卢双舫,等. 渝东南地区海相页岩有机质孔隙发育特征[J]. 地球科学与环境学报,2019,41(6):721-733. WANG Siyuan,LI Junqian,LU Shuangfang,et al. Development characteristics of organic matter pores of marine shale in the southeastern Chongqing,China[J]. Journal of Earth Science and Environment,2019,41(6):721-733.

[6] SHI Miao,YU Bingsong,XUE Zhipeng,et al. Pore characteristics of organic-rich shales with high thermal maturity:A case study of the Longmaxi gas shale reservoirs from well Yuye-1 in southeastern Chongqing,China[J]. Journal of Natural Gas Science and Engineering,2015,26:948-959.

[7] 张慧,林伯伟,卞建玲,等. 富有机质海相与陆相页岩的对比研究:以南方早古生代和华北石炭-二叠纪页岩为例[J]. 煤田地质与勘探,2018,46(6):88-95. ZHANG Hui,LIN Bowei,BIAN Jianling,et al. Comparative study on organic-rich marine and continental shale:The case of Lower Paleozoic in south China and Carboniferous-Permain shale in North China[J]. Coal Geology & Exploration,2018,46(6):88-95.

[8] HU Jingang,TANG Shuheng,ZHANG Songhang. Investigation of pore structure and fractal characteristics of the Lower Silurian Longmaxi shales in western Hunan and Hubei Provinces in China[J]. Journal of Natural Gas Science and Engineering,2016,28:522-535.

[9] 李文镖,卢双舫,李俊乾,等. 南方海相页岩物质组成与孔隙微观结构耦合关系[J]. 天然气地球科学,2019,30(1):27-38. LI Wenbiao,LU Shuangfang,LI Junqian,et al. The coupling relationship between material composition and pore microstructure of southern China marine shale[J]. Natural Gas Geoscience,2019,30(1):27-38.

[10] 郭思祺,肖佃师,卢双舫,等. 徐家围子断陷沙河子组致密储层孔径分布定量表征[J]. 中南大学学报(自然科学版),2016,47(11):3742-3751. GUO Siqi,XIAO Dianshi,LU Shuangfang,et al. Quantificational characterization of tight reservoir pore size distribution of Shahezi Formation in Xujiaweizi Fault Depression[J]. Journal of Central South University(Science and Technology),2016,47(11):3742-3751.

[11] 张大智. 利用氮气吸附实验分析致密砂岩储层微观孔隙结构特征:以松辽盆地徐家围子断陷沙河子组为例[J]. 天然气地球科学,2017,28(6):898-908. ZHANG Dazhi. Characterization of microscopic pore structure of tight sandstone reservoirs through nitrogen adsorption experiment:Case study of Shahezi Formation in Xujiaweizi Fault Depression,Songliao Basin,China[J]. Natural Gas Geoscience,2017,28(6):898-908.

[12] 卢双舫,谷美维,张飞飞,等. 徐家围子断陷沙河子组致密砂砾岩气藏的成藏期次及类型划分[J]. 天然气工业,2017,37(6):12-21. LU Shuangfang,GU Meiwei,ZHANG Feifei,et al. Hydrocarbon accumulation stages and type division of Shahezi Fm tight glutenite gas reservoirs in the Xujiaweizi Fault Depression,Songliao Basin[J]. Natural Gas Industry,2017,37(6):12-21.

[13] 刘超. 徐家围子断陷沙河子组致密气生储盖条件及成藏特征研究[D]. 大庆:东北石油大学,2015. LIU Chao. Research on the source-reservoir-cap conditions and tight gas accumulation rule in Shahezi group of Xujiaweizi Fault depression[D]. Daqing:Northeast Petroleum University,2015.

[14] 王民,孙业峰,王文广,等. 松辽盆地北部徐家围子断陷深层烃源岩生气特征及天然气资源潜力[J]. 天然气地球科学,2014,25(7):1011-1018. WANG Min,SONG Yefeng,WANG Wenguang,et al. Gas generation characteristics and resource potential of the deep source rock in Xujiaweizi Fault depression,northern Songliao Basin[J]. Natural Gas Geoscience,2014,25(7):1011-1018.

[15] LI Ang,DING Wenlong,HE Jianhua,et al. Investigation of pore structure and fractal characteristics of organic-rich shale reservoirs:A case study of Lower Cambrian Qiongzhusi Formation in Malong Block of eastern Yunnan Province,South China[J]. Marine and Petroleum Geology,2016,70:46-57.

[16] WANG Xixin,HOU Jiagen,LI Shaohua,et al. Insight into the nanoscale pore structure of organic-rich shales in the Bakken Formation,USA[J]. Journal of Petroleum Science and Engineering,2020,191:107182.

[17] LOUCKS R G,REED R M,RUPPEL S C,et al. Spectrum of pore types and networks in mud rocks and a descriptive classification for matrix-related mud rock pores[J]. AAPG Bulletin,2012,96(6):1071-1098.

[18] SING Kenneth S W. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity(Recommendations 1984)[J]. Pure and Applied Chemistry,1985,57(4):603-619.

[19] YAO Yanbin,LIU Dameng,TANG Dazhen,et al. Fractal characterization of adsorption-pores of coals from North China:An investigation on CH₄ adsorption capacity of coals[J]. International Journal of Coal Geology,2008,73(1):27-42.

[20] 宋岩,高凤琳,唐相路,等. 海相与陆相页岩储层孔隙结构差异的影响因素[J]. 石油学报,2020,41(12):1501-1512. SONG Yan,GAO Fenglin,TANG Xianglu,et al. Influencing factors of pore structure differences between marine and terrestrial shale reservoirs[J]. Acta Petrolei Sinica,2020,41(12):1501-1512.