煤岩裂隙形态对渗流能力影响数值模拟研究

doi:10.13809/j.cnki.cn32-1825/te.2023.04.003

Abstract

Abstract:

The fracture network developed in coal rock serves as the primary channel for gas migration, significantly influencing the seepage capacity of coal reservoir. The geometric characteristics of fracture plays a crucial role on determining the flow characteristics of coal-bed methane. To study this, a two-dimensional fracture network model of coal rock was established using COMSOL Multiphysics simulation software, focusing on the coal samples of Baode block as the research subject. The effects of fracture length, density, opening degree and angle on production were investigated, providing valuable theoretical guidance for enhancing coal-bed methane production. The results indicate that fracture length, density, and opening degree have a positive correlation with the seepage capacity of coal rock, while the angle with the flow direction negatively impacts it. However, with the increase of length, density and opening degree, the improvement in flow rate slows down, and the effect of increasing single factor to improve coal-bed methane mining can be neglected, making it difficult to control the cost-benefit ratio. Among the factors influencing outlet, angle and density exert a more significant effect than length and opening degree. Considering the surface directional well plus the high pressure hydraulic cutting method, we can enhance the efficiency of coalbed methane development. This approach connects the natural fracture system using directional borehole and hydraulic slot, fully utilizing the permeability advantage of parallel surface cutting direction. The high-pressure hydraulic cutting process induces cracks in the coal seam, increasing the number and connectivity of diversion channels, thereby bolstering the production of coal-bed methane.

Key words: coal-bed methane, fracture morphology, numerical stimulation, seepage capacity, COMSOL Multiphysics simulation software

CLC Number:

TE37

SHI Leiting, ZHAO Qiming, REN Zhenyu, ZHU Shijie, ZHU Shanshan. Numerical simulation study on the influence of coal rock fracture morphology on seepage capacity[J].Petroleum Reservoir Evaluation and Development, 2023, 13(4): 424-432.

Figures/Tables 16

Fig. 1

Table 1

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Table 2

Parameter collection"

参数	符号	初始值	保德区块煤样特征
储层温度/K	T	304.6
基质孔隙度	φ_m	0.047	煤孔隙度介于2.86 %~6.52 %，平均为4.69 %
裂隙孔隙度	φ_f	0.005
气相摩尔质量/ （g/mol）	M_g	0.016
普适气体常数/ [J/(K·mol)]	R	8.314
气相黏度/（mPa·s）	$μ$ _g	0.022
平行裂隙开度/mm	d_px	1	微裂隙开度约介于 0.5~1.5 mm
垂直裂隙开度/mm	d_cz	1	微裂隙开度约介于 0.5~1.5 mm
标准情况下气相密度/（kg/m³）	$ρ$ _ga	0.714
兰氏压力/MPa	p_L	5.29
兰氏体积/m³	V_L	2.47×10^-3
煤层密度/（kg/m³）	$ρ$ _c	2.6×10³
气体偏差因子	Z	1.032
井底流压/MPa	p_w	5
初始压力/MPa	p₀	12	储层压力介于 2.56~12.00 MPa

Table 2

Fig. 5

Table 3

Fig. 6

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测试内容	样品编号	样品尺寸	来源	裂隙方向
不同轴压加载	cz-8	?25 mm×L70 mm	8+9号煤层	垂直裂隙
不同轴压加载	px-8	?25 mm×L70 mm	8+9号煤层	平行裂隙
不同围压加载	cz-9	?25 mm×L70 mm	8+9号煤层	垂直裂隙
不同围压加载	px-9	?25 mm×L70 mm	8+9号煤层	平行裂隙

Numerical simulation study on the influence of coal rock fracture morphology on seepage capacity

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References 23

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长度/cm	密度/（条/4 cm）	开度/mm	角度/（°）
2	1	0.5	0
4	3	1.0	45
6	5	1.5	90