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

油气藏评价与开发 ›› 2023, Vol. 13 ›› Issue (4): 424-432.doi: 10.13809/j.cnki.cn32-1825/te.2023.04.003

煤岩裂隙形态对渗流能力影响数值模拟研究

施雷庭¹(),赵启明^1,²(),任镇宇³,朱诗杰⁴,朱珊珊¹

1.西南石油大学油气藏地质及开发工程国家重点实验室，四川成都 610500
2.重庆能源职业学院，重庆 402260
3.中联煤层气有限责任公司，北京 100016
4.重庆科技学院石油与天然气工程学院，重庆 401331

收稿日期:2023-03-31 发布日期:2023-09-01 出版日期:2023-08-26
通讯作者: 赵启明（1994—），男，硕士，讲师，从事提高采收率技术与教学研究。地址：重庆市江津区双福新区福星大道2号，邮政编码：402260。E-mail：zhaoqm.eor@qq.com
作者简介:施雷庭（1976—），男，博士，教授，从事提高采收率技术与教学研究。地址：四川省成都市新都区新都大道8号西南石油大学，邮政编码：610500。E-mail: slting@swpu.edu.cn
基金资助:
重庆市教育委员会科学技术研究项目“煤岩裂隙形态对渗流能力影响机理及模型构建”(KJQN202305603);重庆市教育委员会科学技术研究项目“近井地带对入井工作液的剪切机制及数学模型构建”(KJQN202301518)

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

SHI Leiting¹(),ZHAO Qiming^1,²(),REN Zhenyu³,ZHU Shijie⁴,ZHU Shanshan¹

1. State Key Laboratory of Oil and Gas Reservoir Geology and Development Engineering, Southwest Petroleum University, Chengdu, Sichuan 610500, China
2. Chongqing Energy College, Chongqing 402260, China
3. China United Coalbed Methane Corp. Ltd., Beijing 100016, China
4. School of Petroleum Engineering, Chongqing University of Science & Technology, Chongqing 401331, China

Received:2023-03-31 Online:2023-09-01 Published:2023-08-26

摘要/Abstract

摘要：

煤岩内发育的裂隙网络是气体运移的主要通道，影响煤储层的渗流能力，裂隙网络的几何特征对煤层气流动特性具有重要影响。以保德区块煤样为研究对象，利用COMSOL Multiphysics模拟软件，建立了煤岩二维裂隙网络模型，研究裂隙长度、密度、开度和角度等因素对产量影响，为提高煤层气产量提供理论指导。研究结果表明：裂隙形态因素影响关系为长度、密度、开度越大，与流动方向夹角越小，煤岩渗流能力越强。但随着长度、密度与开度的增加，流量增幅变缓，继续增加单一因素提高煤层气开采效果不显著且成本难以控制。各因素的增长对出口流量的影响程度中，角度、密度影响效果大于长度和开度。考虑地面定向井+高压水力切割方法提高煤层气开发效率。利用定向井眼和水力缝槽沟通天然裂缝系统，充分利用平行面割理方向渗透率优势；高压水力切割过程中诱导煤层产生裂隙，增加导流通道数量与连通性，有助于提高煤层气产量。

关键词: 煤层气, 裂隙形态, 数值模拟, 渗流能力, COMSOL Multiphysics模拟软件

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

中图分类号:

TE37

施雷庭,赵启明,任镇宇等. 煤岩裂隙形态对渗流能力影响数值模拟研究[J]. 油气藏评价与开发, 2023, 13(4): 424-432.

Leiting SHI,Qiming ZHAO,Zhenyu REN, et al. 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.

图/表 16

图1

表1

图2

图3

图4

表2

参数采集"

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

表2

图5

表3

图6

图7

图8

图9

图10

图11

图12

图13

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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

煤岩裂隙形态对渗流能力影响数值模拟研究

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

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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