Gas-bearing characteristics and major controlling factors of shallow marine shale: a case study of the Lower Silurian Longmaxi Formation in Taiyang block of Zhaotong area

Abstract

The exploration and development of shallow shale gas has the advantages of low cost and fast production reduction, so it has attracted wide attention. The shale gas in the Lower Silurian Longmaxi Formation (S1l) in Taiyang block of Zhaotong National Shale Gas Demonstration Zone has the characteristics of shallow burial depth and high gas content, showing good exploration potential. However, the gas-bearing distribution and major controlling factors of shallow shale gas in this research area are rarely studied previously. In order to enrich the research in this field, this paper analyzes the gas-bearing characteristics and the major controlling factors of the shale samples of Long-1 subsection (S1l1) in the Taiyang block. The results show that the total gas content of S1l11-1 is the highest in the study area, the gas content gradually decreases from bottom to top, and areas with high shale gas content in S1l1 appear in the north and south of the study area on the plane. Organic matter content, mineral components, reservoir properties and external preservation conditions have a certain role in controlling the gas properties of shallow shale in S1l11 subsection of the study area. Organic matter is the primitivesubstance that generates shale gas, at the same time, the organic matter hole formed by hydrocarbon cracking sprovides a lot of storage pace for shale gas, while the content of organic matter is the major controlling factor of the total gas content. The high content of silicoide is conducive to later fracturing development. The adjacent rock strata of S1l11 subsection in the study area are compact in lithology, with good sealing property, showing the characteristics of slight overpressure and overpressure, which effectively prevents the escape of shale gas, and has broad exploration prospects.

Keywords

• shallow shale gas
• longmaxi formation
• gas-bearing characteristics
• controlling factors
• zhaotong area