Progress, challenge, and prospect for exploration and development of continental shale gas in Yanchang exploration area in Ordos Basin
(2.Shaanxi Key Laboratory of Continental Shale Gas Accumulation and Exploitation)
(3.National Engineering Research Center of Continental Shale Gas of Petroleum and Chemical Industry)
【Abstract】As a large superimposed basin with rich oil and gas, the Ordos basin develops multiple sets of Permian and Triassic continental shale strata and is abundant in continental shale gas resources. Compared with the marine shale, the continental shale is more complicated. There are many challenges during the exploration and development of continental shale, which restrict its economic exploitation. In this paper, in terms of the geological characteristics, resources background, and technologies of exploration and development, the achievements in the practice of the exploration and development of continental shale gas in the Ordos basin were summarized. In addition, the current technical difficulties of continental shale gas were analyzed to effectively utilize opportunities and timely approach challenges in the development process. According to comprehensive analyses, the shale gas parameters in the Yanchang exploration area, such as the continental shale thickness, total organic carbon content, maturity, and gas content, have reached above the lower limit of favorable intervals of shale gas stipulated by national standards. Therefore, it meets the geological conditions for accumulation of shale gas. Under the control factors of macro and micro heterogeneous, the continental shale gas has different enrichment characteristics in terms of phase state and scale. There are two types of accumulation modes, which are adsorption accumulation and adsorption + free composite accumulation. The understanding of different accumulation mechanisms guides the selection of the favorable zone and the production from continental shale gas wells. A number of key supporting technologies have been formed during the exploration practice of continental shale gas. Logging evaluation methods suitable for strong heterogeneous continental shale have been established. The water-based drilling fluid system and a series of supporting equipment for drilling and completion have been developed. The CO2 fracturing technology system and the recovery-utilization technology of wellsite waste fluid have been formed. Meanwhile, there are still many challenges in terms of precise prediction of “sweet spot”, improvement of drilling rate and efficiency, environmental protection and efficiency improvement of fracturing, and cost reduction. At present, the exploration and development of continental shale gas in China is still in an early stage, with high costs and low initial production. It is still necessary to carry out pilot tests for the exploration and development of continental shale gas to achieve scientific and technological breakthroughs. Besides, it can form a resource replacement and promote the continental shale gas industry to obtain economic benefits.
【Keywords】 Ordos Basin; Yanchang exploration area; continental shale gas; progress in exploration and development; challenge; prospect;
 Wang Xiangzeng. Mesozoic out crop in southeastern of Ordos Basin (Atlas) and its geological interpretation [M]. Xi’an: Northwestern University Press, 2012 (in Chinese).
 Wang Xiangzeng. Advances and prospects in oil and gas exploration and development of Shanxi Yanchang Petroleum (Group) Co., Ltd [J]. China Petroleum Exploration, 2018, 23(1): 36–42 (in Chinese).
 Wang Xiangzeng. Advance in unconventional gas exploration and development of Yanchang Petroleum Group [J]. Acta Petrolei Sinica, 2016, 37(1): 137–145 (in Chinese).
 Wang Xiangzeng. Lacustrine shale gas [M]. Beijing: Petroleum Industry Press, 2014 (in Chinese).
 Zou Caineng, Tao Shizhen, Bai Bin, Yang Zhi, Zhu Rukai, Hou Lianhua, et al. Differences and relations between unconventional and conventional oil and gas [J]. China Petroleum Exploration, 2015, 20(1): 1–16 (in Chinese).
 Wang Xiangzeng, Zhang Jinchuan, Cao Jinzhou, Zhang Lixia, Tang Xuan, Lin Lamei, et al. A preliminary discussion on evaluation of continental shale gas resources: a case study of Chang 7 of Mesozoic Yanchang Formation in Zhiluo-Xiasiwan area of Yanchang [J]. Earth Science Frontiers, 2012, 19(2): 192–197 (in Chinese).
 Wang Xiangzeng, Gao Shengli, Gao Chao. Geological features of Mesozoic continental shale gas in south of Ordos Basin [J]. Petroleum Exploration and Development, 2014, 41(3): 294–304 (in Chinese).
 Wang Xiangzeng, Zhang Lixia, Gao Chao. The heterogeneity of shale gas reservoir in Yanchang Formation, Xiasiwan area, Ordos Basin [J]. Earth Science Frontiers, 2016, 23(1): 134–145 (in Chinese).
 Yang Zhi, Fu Jinhua, Guo Qiulin, Lin Senhu, Chen Ningsheng, Pan Songqi, et al. Discovery characteristics and resource potential of continental tight oil in Triassic Yanchang Formation, Ordos Basin [J]. China Petroleum Exploration, 2017, 22(6): 9–15 (in Chinese).
 Fu Jinhua, Yu Jian, Xu Liming, Niu Xiaobing, Feng Shengbin, Wang Xiujuan, et al. New progress in exploration and development of tight oil in Ordos Basin and main controlling factors of large-scale enrichment and exploitable capacity [J]. China Petroleum Exploration, 2015, 20(5): 9–19 (in Chinese).
 Du Yan, Yu Bo, Xu Min. Geochemical characteristics of shale from Yanchang Formation in southeastern Yishan Slope [J]. Journal of Xi’an University of Science and Technology, 2015, 35(1): 63–71 (in Chinese).
 Sun Jianbo, Sun Binghua, Zhao Qianping, Jiang Chengfu, Liu Gang, Yin Jintao, et al. Geological characteristics and exploration potential evaluation of Chang 7 lacustrine shale oil in Yanchang Formation, Fuxian area, Ordos Basin [J]. China Petroleum Exploration, 2018, 23(6): 29–37 (in Chinese).
 Jiang Chengfu, Wang Xiangzeng, Zhang Lixia, Wan Yongping, Lei Yuhong, Sun Jianbo, et al. Geological characteristics of shale and exploration potential of continental shale gas in 7th member of Yanchang Formation, southeast Ordos Basin [J]. Geology in China, 2013, 40(6): 1880–1888 (in Chinese).
 Qi Panwen, Jiang Chengfu, Liu Gang, Shi Peng, Zhao Qianping, Wan Yongping. Shale gas content and its occurrence state of the Triassic lacustrine shale, Ordos Basin, China [J]. Journal of Northeast Petroleum University, 2016, 40(2): 11–18 (in Chinese).
 Liu Gang, Zhao Qianping, Gao Chao, Jiang Lei, Sun Jianbo, Liu Chao. A critical desorption time method to improve the calculation accuracy of gas loss in shale gas content testing [J]. Natural Gas Industry, 2019, 39(2): 71–75 (in Chinese).
 Zhao Qianping, Zhang Lixia, Yin Jintao, Yu Yuxi, Jiang Chengfu, Wang Hui, et al. Pore structure and physical characteristics of shale reservoir interbedded with silty layers: an example from Zhangjiatan lacustrine shale [J]. Journal of Jilin University: Earth Science Edition, 2018, 48(4): 1018–1029 (in Chinese).
 Wang Xiangzeng, Zhang Lixia, Li Zongtian, Fu Haijiao. Pore type classification scheme for continental Yanchang shale in Ordos Basin and its geological significance [J]. Oil & Gas Geology, 2016, 37(1): 1–7 (in Chinese).
 Yang Hua, Fu Jinhua, Liu Xinshe, Meng Peilong. Accumulation conditions and exploration and development of tight gas in the Upper Paleozoic of the Ordos Basin [J]. Petroleum Exploration and Development, 2012, 39(3): 295–303 (in Chinese).
 Fu Jinhua, Duan Xiaowen, Jiang Yingkun. Geological features and exploration methods of natural gas reservoir formation in the Upper Paleozoic in the Ordos Basin [J]. China Petroleum Exploration, 2001, 6(4): 68–75 (in Chinese).
 Zhang Lixia, Jiang Chengfu, Guo Chao. Exploration potential of Upper Paleozoic shale gas in the eastern Ordos Basin [J]. Journal of Xi’an Shiyou University: Natural Science Edition, 2012, 27(1): 23–26 (in Chinese).
 Dou Weitan, Hou Mingcai, Dong Guiyu. Provenance analysis of the Upper Paleozoic Shanxi to Lower Shihezi Formations in north Ordos Basin [J]. Natural Gas Industry, 2009, 29(3): 25–28 (in Chinese).
 Qi Panwen, Xue Pei, Zhao Qianping, Shi Peng, Sun Xining. Characteristics and evaluation of shale gas reservoirs in Shanxi Formation in Xiasiwan area, Ordos Basin [J]. Unconventional Oil & Gas, 2019, 6(4): 10–17 (in Chinese).
 Zhao Qianping, Gao Chao, Yin Jintao, Zhang Lixia, Cao Cheng, Liu Gang, et al. Hydrocarbon generation characteristics of source rocks in Shanxi Formation of Xiasiwan Area, Ordos Basin [J]. Journal of Xi’an University of Science and Technology, 2018, 38(1): 108–117 (in Chinese).
 Standardization Administration of the People’s Republic of China. GB/T 31483-2015 Shale gas geological evaluation method [S]. Beijing: China Standard Press, 2015 (in Chinese).
 Qi Panwen, Jiang Chengfu, Zhao Qianping, Shi Peng, Sun Derui. Evaluation method of continental shale gas logging [J].Unconventional Oil & Gas, 2017, 4(6): 116–122 (in Chinese).
 He Yufei, Wan Jinbin, Yu Xiaolong, Cheng Daojie, Ni Jun, Chen Yulin. Quantitative evaluation of shale gas content based on logging data [J]. Well Logging Technology, 2018, 42(6): 667–671 (in Chinese).
 Wang Xiangzeng, Gao Ruimin, Wu Jinqiao, Wen Fenggang, Li Wei. Optimization of drilling fluid of natural gas exploration wells in Yanchang Oilfield [J]. Applied Chemical Industry, 2010, 39(3): 373–376 (in Chinese).
 Ma Zhenfeng, Yu Xiaolong, Yang Quanzhi, Yang Xianlun, Li Hongmei, Zhao Yi. The technology of improving rate of penetration in continental shale gas horizontal well [J]. Unconventional Oil & Gas, 2017, 4(4): 88–92 (in Chinese).
 Mu Jingfu. Anisotropic investigation of the mechanical property of shale [J]. Unconventional Oil & Gas, 2016, 3(5): 114–120 (in Chinese).
 Wan Xin, Wu Jinqiao, Yang Chao, Wang Hongjuan. Study of safe drilling mud weight window for shale gas horizontal well in Yanchang Oilfield [J]. Unconventional Oil & Gas, 2016(5): 121–126 (in Chinese).
 Li Wei, Wang Tao, Wang Xiuling, Li Shekun, Zhou Zhanyun, Li Yan. Cementing technology for horizontal wells of terrestrial shale gas: a case study of the Yanan national terrestrial shale gas E&P pilot area [J]. Natural Gas Industry, 2014, 34(12): 106–112 (in Chinese).
 Wang Xiangzeng, Wu Jinqiao, Zhang Juntao. Application of CO2 fracturing technology for terrestrial shale gas reservoirs [J]. Natural Gas Industry, 2014, 34(1): 64–67 (in Chinese).
 Wang Xiangzeng, Sun Xiao, Luo pan, Mu Jingfu. Progress and application of CO2 fracturing technology for unconventional oil and gas [J]. Lithologic Reservoirs, 2019, 31(2): 1–7 (in Chinese).
 Gao Zhiliang, Duan Yuxiu, Wu Jinqiao, Qiao Hongjun, Guo Qing, Nan Beibei. Selection and performance study of foaming agent of CO2 acidic crosslinking foam fracturing liquid [J]. Drilling Fluid and Completion Fluid, 2013, 30(5): 79–81 (in Chinese).
 Guo Qing, Shen Feng, Qiao Hongjun. Discussion on stimulation technology of shale gas reservoir in Yanchang Formation, Ordos Basin [J]. Petroleum Geology and Engineering, 2012, 26(2): 96–98 (in Chinese).
 Lv Lei, Wang Zimin, Yang Zhigang. Problem and solving countermeasures on recycling technology for fracturing flowback fluid of shale gas [J]. Chinese Journal of Environmental Engineering, 2017, 11(2): 965–969 (in Chinese).