Abstract
A series of qualitative descriptions and quantitative analyses was used to determine the lithofacies characteristics and recognize the favorable shale intervals of Dawuba Formation in the Ziyun area of South Qian Depression. The qualitative descriptions include core description and scanning electron microscope (SEM) observation. The quantitative analyses include X-ray diffraction, total organic content analysis, vitrinite reflectance, maceral composition, porosity, and permeability, as well as gas and element composition. The Dawuba Formation could be divided into four members. In general, the shale in the first and third members showed similarly high organic matter content with most samples in range of 2–2.5% and higher brittle mineral content with a content of quartz 40.53% and 33.21%, respectively, compared with the other two members, as well as high gas content. However, the first member shale samples exhibited much higher porosity and permeability than the third member shale samples. Furthermore, the shale gas in the first member was chiefly composed of methane (average: 83.63%), while that in the third member mainly consisted of nitrogen (average: 79.92%). Hence, the first member should be regarded as the most favorable target.
Highlights
In recent years, the success of shale oil and gas exploration and development in North America, such as the Barnett shale with tremendous cumulative gas production, has driven and promoted the development of shale oil and gas industry in China [1,2,3,4,5,6,7,8]
The shale intervals of the Dawuba Formation in Ziyun area of South Qian Depression were evaluated through mineral composition, organic matter character, pores, porosity, and permeability, as well as gas-containing property
(1) The Dawuba Formation had a stable distribution in Ziyun area and was mainly composed of platform and basin facies deposits
Summary
The success of shale oil and gas exploration and development in North America, such as the Barnett shale with tremendous cumulative gas production, has driven and promoted the development of shale oil and gas industry in China [1,2,3,4,5,6,7,8]. The industrial breakthroughs of shale gas exploration and development in China were achieved mainly in the Ordovician Wufeng and Silurian Longmaxi Formation marine shale reservoirs in Weiyuan, Zhaotong, and Jiaoshiba areas in the southern Sichuan Basin, where the shale gas output reached 10 billion cubic meters in 2019 [9,10,11,12,13,14]. Shale oil exploration in the 2nd member of the Kondian Formation in Cangdong Sag of Bohai Bay Basin has made great breakthroughs, and industrial oil flows have been obtained in several wells such as KN9 and GD6 × 1 [23]
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