Characteristics of Multi-Scale Pore-Fracture Structure of Deep Coal Rocks in the Daning-Jixian Block

doi:10.3969/j.issn.1006-6535.2022.05.013

Abstract

Abstract: In response to the problem that it is difficult to quantitatively characterize the complex multi-scale pore-fracture structure of deep coal rock reservoirs in the Daning-Jixian Block with a single technical method, a multi-scale digital core technology is adopted to scan and analyze coal and rock samples based on full-diameter CT scanning, micro-CT scanning, FIB-SEM scanning, and argon ion polishing field emission scanning electron microscopy and other experimental methods. The result shows: The multi-scale pore-fracture systems develop in the deep coal rocks in the Daning-Jixian Block. The nano-scale development is dominated by stomatal and tissue pores, the micro-scale development is dominated by micro-fractures and mineral dissolved pores, and the millimeter-scale development is high-angle fractures and cleat assemblages. The full-diameter CT scanning technology can effectively identify millimeter-scale fractures, cleats and dissolved pores. The core hole-fracture model of the coal section of Well D20 is established, and the calculated fracture porosity is 1.55%, the fracture density is 22.5 pieces/m, and the average opening of fractures is 1.1mm; the average radius of micro-pores is 2.99-4.15 μm, the average radius of micro-throat is 1.16-1.80μm; the average opening of micro-fractures is 3.75-4.84 μm; the average radius of nano-pores is 51.21-80.65 nm, the average radius of the nano-throat is 19.44-32.06 nm; the multi-scale distribution characteristics are obtained through the splicing of micro- and nano-pore data. The number of micro-pores is the largest, with the average surface area accounting for 63.68%, while the number of macro-pores (greater than 103 nm) is small but contributes a large amount of pore volume. The research results can provide technical support for the exploration and development of deep coalbed methane.

Key words: deep coal rock, multi-scale pore-fracture structure, digital core technology, coalbed methane fracturing and seam selection, Daning-Jixian Block

CLC Number:

TE135

Yang Xiuchun, Song Bairong, Chen Guohui, He Rui, Zhao Haoyang, Yang Xiao. Characteristics of Multi-Scale Pore-Fracture Structure of Deep Coal Rocks in the Daning-Jixian Block[J]. Special Oil & Gas Reservoirs, 2022, 29(5): 94-100.

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