“Three-Gas-One-Oil” drilling findings and reservoir formation geological conditions in the lower Yangtze area: Exemplified by Gang Di 1 well in South Anhui
SHI Gang;XU Zhenyu;ZHENG Hongjun;YIN Qichun;TENG Long;ZHOU Daorong;FANG Chaogang;SHAO Wei;WANG Jialong;HUANG Zhengqing;Nanjing Geological Survey Center,China Geological Survey;
In the lower Yangtze region, the tectonic movement is complicated and the geological conditions are complex, which has a great impact on the conditions of oil and gas accumulation and preservation. The shale has the characteristics of generating gas and storing gas. The requirements for preservation conditions are relatively lower than those for conventional oil and gas, which makes it possible to form a large oil and gas reservoir in lower Yangtze region. Through drilling the Gang Di 1 well, the authors revealed"Three-Gas-One-Oil"feature that includes shale oil, shale gas, coalbed gas and tight sandstone gas in Permian Dalong Formation and Longtan Formation in lower Yangtze region. It is different from conventional oil and gas storage in which gas is in the upper part and oil is in the lower part; therefore, the feature revealed by the authors is an unconventional oil and gas reservoir mode. It is observed that organic shale thickness is about 70 m, and formation dip is about 10 o～25 oin the core of GD1. The in situ desorption data show that methane content is about 80%. Experimental data show TOC is 1.9%～2.3%, about 2.0% on average; Rois about1% ～1.25%, about 1.2% on average in the core of GD1. Based on GD 1 drilling discovery, the authors hold that the "small and whole" depression or basin has the geological conditions for forming shale oil and gas reservoirs with weak tectonic movement,small basin and good preservation conditions in the lower Yangtze region.