Pore-scale analysis of coal structure and mechanical properties evolution through liquid nitrogen thermal shock

被引：0

作者：

Yang R. ^{[1
,2
]}

Cong R. ^{[1
,2
]}

Liu H. ^{[3
]}

Huang Z. ^{[1
,2
]}

Wen H. ^{[1
,2
]}

Hong C. ^{[1
,2
]}

机构：

[1] State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing

[2] CBM Research Center, China University of Petroleum, Beijing

[3] Engineering & Design Institute of CPOE, CNPC Offshore Engineering Company Limited, Beijing

来源：

Natural Gas Industry | 2021年 / 41卷 / 07期

关键词：

Atomic force microscope (AFM); Coalbed methane; CT scanning; Digital core; Liquid nitrogen fracturing; Mechanical property; Micro-nano scale; Pore throat connectivity; Reservoir stimulation efficiency;

D O I：

10.3787/j.issn.1000-0976.2021.07.009

中图分类号：

学科分类号：

摘要：

Liquid nitrogen fracturing is one of the potential feasible technologies for improving the stimulation efficiency of coalbed methane (CBM) reservoirs. At present, the visualization of pore-throat connectivity and microscopic seepage characteristics in coal rocks under liquid nitrogen thermal shock is still lack of studying. In order to provide theoretical basis for the stimulation behavior of liquid nitrogen fracturing in coal beds, the change of micro-nano pore structure and mechanical property of coal rocks before and after liquid nitrogen were investigated using CT scanning and atomic force microscope (AFM). The influence of liquid nitrogen thermal shock on the seepage routes of coal rock was examined. The number and scales of pores in the coal increased after liquid nitrogen thermal shock. In the experiment, porosity increased by 200%, micro fracture is dominant and its volume ratio increased to 90% from 7.7% before liquid nitrogen treatment. The three-dimensional pore structure reconstruction model obtained by CT showed that after the liquid nitrogen treatment, the number, total length, and total volume of throats in the coal rock increased by 170%, 140%, and 130% and the pore connectivity improved significantly. The absolute permeability of coal after liquid nitrogen treatment is 77 times higher than that before liquid nitrogen cooling. The micro fracture induced by thermal stress is the main percolation routes in coal after liquid nitrogen cooling. Pores and fractures were newly formed on both matrix and mineral domains, and the surface roughness increased. The elastic modulus in matrix and mineral domains of coal drops, and the average elastic modulus dropped by 81% and 91%, respectively.

引用

页码：82 / 92

页数：10

共 35 条

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