Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Abstract

Influences of the characteristics of organic matters and mineral compositions on the development of shale microscopic pores were discussed through performing low-temperature nitrogen adsorption, whole-rock "X" diffraction, and field emission scanning electron microscope on black organic-rich shale samples of Longmaxi Formation in the Dingshan area, southeastern Sichuan Basin, in combination with the characteristics of shale organic matters. The shale in the Dingshan area has complex mineral composition, which is mainly quartz and clay minerals. Both contents range from 23% to 72% and 36% to 70%, respectively. The vertical variation is obvious, and there are few feldspar and carbonate rocks; the pyrite content is more than 2%. The bottom shale has high brittleness and gradually decreases in the vertical direction. The brittleness index is between 0.481 and 0.627 and is concentrated above 0.5. It shows strong compressibility and is easy to form a complex network system in hydraulic fracturing. Quartz and feldspar mainly provide secondary dissolved pores, intercrystalline mineral pores, and nanoedge gaps in contact with organic matter. They have no obvious correlation with the specific surface area of shale but have a weak correlation with pore volume. They mainly control the development of macropores. Organic matter develops many hydrocarbon-generating pores, which strongly correlate with the specific surface area and a weak correlation with pore volume. It mainly controls the development of micromesopores. Clay minerals mainly provide a large number of interlaminar pores and interlayer fractures in the clay. The intergranular pores of clay and clay have a weak correlation with pore volume and specific surfaces. They contribute to the development of shale micropores, mesopores, and macropores. Pyrite mainly provides intercrystalline pores and mold pores. By restricting the interaction with organic matter, the development of shale pores is promoted within a certain content range. When the content exceeds this range, the development of micropores is inhibited. The conversion threshold in the Dingshan area is 5.0%.

Geological Characteristics of Deep Shale Gas in the Silurian Longmaxi Formation in the Southern Sichuan Basin, China

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“…An increasing number of countries have been engaged in the exploration of shale gas. Additionally, the subsequent technological innovation has fueled the efficient development of shale gas, and the supporting fundamental geological surveys and development techniques have been advanced (Fan et al, 2020a;Fan et al, 2020b;Hou et al, 2020;Wang H et al, 2020;He et al, 2021). Nevertheless, the commercial development of shale gas has been rarely achieved despite some countries acquiring shale gas via exploration (He et al, 2018).…”

Development Characteristics and Finite Element Simulation of Fractures in Tight Oil Sandstone Reservoirs of Yanchang Formation in Western Ordos Basin

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Deformation Differences in Complex Structural Areas in the Southern Sichuan Basin and Its Influence on Shale Gas Preservation: A Case Study of Changning and Luzhou Areas

“…The contradiction between oil and gas demand growth and insufficient supply stimulates oil and gas exploration to enter deeper and wider fields (Jarvie et al, 2007;Ambrose et al, 2010;Fan et al, 2020;Zhang et al, 2020;Chen et al, 2021;He et al, 2021). As an important replacement area for unconventional oil and gas tools , commercial oil and gas reservoirs have been discovered in tight sandstone gas, super-heavy oil, coalbed methane, and other fields, which relieved the pressure on energy and adjusted the energy structure.…”