An important discovery in Well Luntan-1 of the Tarim Basin, China, and its significance for ultra-deep oil and gas exploration
(2.PetroChina Exploration & Production Company)
(3.PetroChina Research Institute of Petroleum Exploration & Development)
(4.CNPC Bureau of Geophysical Prospecting INC.)
【Abstract】In January 2020, light crude oil was obtained from Lower Cambrian dolomite with burial depth greater than 8,200 m in Well Luntan-1, which was located in the Lunnan low bulge in the Tabei uplift, indicating a major breakthrough in ultra-deep oil and gas exploration in old craton of Tarim Basin. This paper describes the background of well Luntan-1 discovery and analyzes the exploration history of the ultra-deep Cambrian pre-salt oil reserves, aiming to provide experience and reference for the exploration of new zones, new strata, and new types in other similar areas. According to the drilling results, Well Luntan-1 penetrated a set of high-quality source rocks in Cambrian Yuertusi Formation and 2 sets of reservoir-cap assemblages, which are evaporite gypsum cap rocks in the Awatage Formation and dolomite reservoir in the Shayilike-Wusonggeer Formations, and mudstone cap in the Yuertusi Formation and dolomite weathering crust reservoir in the Sinian Qigebulake Formation. The production layer in well Luntan-1 is the Wusonggeer Formation with volatile oil at normal temperature and pressure systems. In addition, trace natural gas was obtained from the weathering crust of the Sinian Qigebulake Formation. The exploration of the platform-basin area in the Tarim Basin has experienced 2 strategic shifts from clastic rocks to carbonate rocks, and then to pre-salt dolomite. Well Luntan-1 is an important sign of the second strategic shift, which is of milestone significance. The favorable oil accumulation conditions of well Luntan-1 are the successive development of stable paleo-uplift and the high-quality source-reservoir-cap assemblages. By analogy, this paper analyzes the exploration prospect of the Cambrian pre-salt dolomite in Tarim Basin and points out that the Tazhong-Gucheng area, the south slope of the Tabei area and the northern Maigaiti slope-Keping area are the favorable and key zones for further exploration.
【Keywords】 Tarim Basin; Well Luntan-1; ultra-deep exploration; great breakthrough; pre-salt dolomite;
 He Zhiliang, Mao Hongbin, Zhou Xiaofen, Gong Ming, Yu Xiaoyu. Complex petroleum system and multicycle basin in Tarim [J]. Oil & Gas Geology, 2000, 21 (3): 207–213 (in Chinese).
 Sun Longde, Li Yuejun, Jiang Tongwen, Yang Haijun. The central Tarim lower uplift: a composite hydrocarbon accumulation play in the Tarim Basin, NW China [J]. Chinese Journal of Geology, 2007, 42 (3): 602–620 (in Chinese).
 Yang Haijun, Han Jianfa. The composite hydrocarbon accumulation characteristics and major controlling elements on Lunnan lower uplift, Tarim Basin [J]. Science in China Series D: Earth Sciences, 2007, 37 (S2): 53–62 (in Chinese).
 Yang Xuewen, Wang Zhaoming, He Wenyuan, Tian Jun. Super-depth exploration practice and innovation in Tarim Basin [M]. Beijing: Petroleum Industry Press, 2019 (in Chinese).
 Sun Longde, Jiang Tongwen, Xu Hanlin, Shan Jiazeng, Lian Zhanggui. Unsteady reservoir in Hadson oilfield, Tarim Basin [J]. Petroleum Exploration and Development, 2009, 36 (1): 62–67 (in Chinese).
 Yang Haijun, Han Jianfa, Sun Chonghao, Wang Fuhuan, Zheng Yan, Ji Yungang. A development model and petroleum exploration of karst reservoirs of Ordovician Yingshan Formation in the northern slope of Tazhong palaeouplift [J]. Acta Petrolei Sinica, 2011, 32 (3): 199–205 (in Chinese).
 Zheng Duoming, Li Zhihua, Zhao Kuanzhi, Shen Feng, Dang Qingning, Gao Lianhua. Quantitative seismic characterization of Ordovician fracture-cavity carbonate reservoirs in Tarim oilfield [J]. China Petroleum Exploration, 2011, 16 (5): 57–62 (in Chinese).
 Zhang Lijuan, Ma Qing, Fan Qiuhai, Zhu Yongfeng, Gao Chunhai, Cai Quan, et al. Paleokarst reservoir recognition and geology modeling of Ordovician carbonate of block Ha 6 in Tarim Basin [J]. China Petroleum Exploration, 2012, 17 (2): 1–7 (in Chinese).
 Wang Zhaoming, Xie Huiwen, Chen Yongquan, Qi Yingmin, Zhang Ke. Discovery and exploration of Cambrian subsalt dolomite original hydrocarbon reservoir at Zhongshen-1 well in Tarim Basin [J]. China Petroleum Exploration, 2014, 19 (2): 1–13 (in Chinese).
 Zhang Jizhi, Wang Zhaoming, Yang Haijun, Xu Zhiming, Xiao Zhongyao, Li Zhongxuan. Origin and differential accumulation of hydrocarbons in Cambrian sub-salt dolomite reservoirs in Zhongshen area, Tarim Basin, NW China [J]. Petroleum Exploration and Development, 2017, 44 (1): 40–47 (in Chinese).
 Tian Jun. Petroleum exploration achievements and future targets of Tarim Basin [J]. Xinjiang Petroleum Geology, 2019, 40 (1): 1–11 (in Chinese).
 Lv Xiuxiang, Bai Zhongkai, Fu Hui. Probe into exploration prospect of Cambrian subsalt carbonate rocks in Tarim Basin from east Siberia basin [J]. Xinjiang Petroleum Geology, 2009, 30 (2): 157–162 (in Chinese).
 Wu Lin, Guan Shuwei, Yang Haijun, Ren Rong, Zhu Guangyou, Jin Jiuqiang, et al. The paleogeographic framework and hydrocarbon exploration potential of Neoproterozoic rift basin in northern Tarim Basin [J]. Acta Petrolei Sinica, 2017, 38 (4): 375–385 (in Chinese).
 Ren Rong, Guan Shuwei, Wu Lin, Zhu Guangyou. The north-south differentiation characteristic and its enlightenment on oil-gas exploration of the Neoproterozoic rift basin, Tarim Basin [J]. Acta Petrolei Sinica, 2017, 38 (3): 255–266 (in Chinese).
 Zhu Guangyou, Cao Yinghui, Yan Lei, Yang Haijun, Sun Chonghao, Zhang Zhiyao, et al. Petroleum exploration potential and favorable areas of ultra-deep marine strata deeper than 8000 meters in Tarim Basin [J]. Natural Gas Geoscience, 2018, 29 (6): 755–772 (in Chinese).
 Zhu Guangyou, Du Dedao, Chen Weiyan, Sun Qisen, Li Tingting, Zhang Zhiyao, et al. The discovery and exploration significance of the old thick black mudstones in the southwest margin of Tarim Basin [J]. Acta Petrolei Sinica, 2017, 3 8(12): 1335–1342 (in Chinese).
 Yan Wei, Zheng Jianfeng, Chen Yongquan, Huang Lili, Zhou Peng, Zhu Yongjin. Characteristics and genesis of dolomite reservoir in the lower Cambrian Xiaoerblak Formation, Tarim Basin [J]. Marine Origin Petroleum Geology, 2017, 22 (4): 35–43 (in Chinese).
 Ni Xinfeng, Shen Anjiang, Chen Yongquan, Guan Baozhu, Yu Guang, Yan Wei, et al. Cambrian carbonate platform types, platform margin segmentation characteristics and exploration enlightenment in Tarim Basin [J]. Natural Gas Geoscience, 2015, 26 (7): 1245–1255 (in Chinese).
 Chen Yongquan, Guan Baozhu, Xiong Yixue, Kang Qian. Compound cap rocks and slide faults controlling mechanism on reservoir and reserves: an example on lower Ordovician dolostones exploration in Manxi-Gucheng area, Tarim Basin [J]. Natural Gas Geoscience, 2015, 26 (7): 1268–1276 (in Chinese).
 Du Jinhu, Pan Wenqing. Accumulation conditions and play targets of oil and gas in the Cambrian subsalt dolomite, Tarim Basin, NW China [J]. Petroleum Exploration and Development, 2016, 43 (3): 327–339 (in Chinese).
 Yi Shiwei, Du Jinhu, Yang Haijun, Li Jun, Li Yong. Controlling factors and exploration idea about reservoir formation of Lower Palaeozoic, Tarim Basin [J]. China Petroleum Exploration, 2012, 17 (3): 1–8 (in Chinese).
 Zou Caineng, Du Jinhu, Xu Chunchun, Wang Zecheng, Zhang Baomin, Wei Guoqi, et al. Formation, distribution, resource potential and discovery of the Sinian-Cambrian giant gas field, Sichuan Basin, SW China [J]. Petroleum Exploration and Development, 2014, 41 (3): 278–293 (in Chinese).
 Chen Yongquan, Yan Wei, Han Changwei, Yan Lei, Ran Qigui, Kang Qian, et al. Structural and sedimentary basin transformation at the Cambrian/Neoproterozoic interval in Tarim Basin: implication to subsalt dolostone exploration [J]. Natural Gas Geoscience, 2019, 30 (1): 39–50 (in Chinese).