煤层水力压裂应力与裂隙演化的细观规律

李全贵; 邓羿泽; 胡千庭; 张跃兵; 宋明洋; 刘继川; 石佳林

doi:10.12363/issn.1001-1986.21.10.0603

煤层水力压裂应力与裂隙演化的细观规律

doi: 10.12363/issn.1001-1986.21.10.0603

李全贵^{1, 2,},
邓羿泽^{1, 2},
胡千庭^{1, 2},
张跃兵^{1, 2},
宋明洋^{1, 2},
刘继川^{1, 2},
石佳林^{1, 2}

基金项目: 国家自然科学基金项目(52074049)

详细信息

第一作者:
李全贵，1986年生，男，河南民权人，博士，副教授，从事煤矿瓦斯防治、煤层气开发. E-mail：liqg@cqu.edu.cn

中图分类号: TD163；TE377
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- 被引次数: 0
出版历程
- 收稿日期: 2021-11-01
- 修回日期: 2022-01-13
- 发布日期: 2022-06-25
- 网络出版日期: 2022-05-30

Mesoscopic law of stress and fracture evolution of coal seams hydraulic fracturing

LI Quangui^{1, 2
,},
DENG Yize^{1, 2},
HU Qianting^{1, 2},
ZHANG Yuebing^{1, 2},
SONG Mingyang^{1, 2},
LIU Jichuan^{1, 2},
SHI Jialin^{1, 2}

摘要

摘要: 水力压裂作为煤层强化增透技术的一种，其应力演化特征及裂隙形态与扩展范围的判断尤为重要。采用离散元数值方法，以导向压裂为背景，建立水力压裂流固耦合模型；通过应力路径、裂纹热点图等手段，探究水力压裂过程中压裂排量、泊松比、天然裂隙密度对应力演化和裂隙演化的影响及其细观规律。结果表明：不同压裂排量下的应力演化方向及最终应力路径曲线形状有着明显的不同，低排量下裂隙附近的应力比值逐渐增大，而在高排量下先增大后减小；煤层泊松比越大，平均压裂半径越低，但对起裂时间及裂隙的扩展形态影响不明显；天然裂隙的发育情况对水力裂隙的扩展起着关键性作用，高裂隙发育煤层水力裂隙扩展的方向性无法预测，应力演化方向会出现反转现象；压裂过程中不同区域的应力演化特征能够反映出裂隙的扩展状态，现场可通过监测压裂区域附近应力变化，判断水力压裂缝网的扩展范围。
- 水力压裂 /
- 应力演化 /
- 裂隙演化 /
- 细观规律 /
- 离散元
Abstract: Hydraulic fracturing is a technology to increase coal seam permeability, and its stress evolution characteristics and the judgment of fracture morphology and propagation range are particularly important. In this paper, based on directional fracturing, a fluid-structure coupling model of hydraulic fracturing is established by using the discrete element numerical method. The effects of fracturing flow, Poisson’s ratio, natural fracture density on stress evolution and fracture evolution, and their mesoscopic laws are investigated by means of the stress path and crack hot spot diagram. The results show that the stress evolution direction and the final stress path curve shape are obviously different at different fracturing rates. The stress ratio near the crack increases gradually at a low fracturing rate, but increases first and then decreases at a high fracturing rate. The larger the Poisson’s ratio, the smaller the fracture radius, but its influence on fracture initiation time and fracture propagation morphology is not obvious. The development of natural fractures plays a key role in the propagation of hydraulic fractures, and the direction of fracture propagation is more random in coal seams with high natural fracture development, and the direction of stress evolution is reversed. The stress evolution characteristics of different regions can reflect the propagation state of fractures in the fracturing process, the propagation range of the hydraulic fracture network can be determined by monitoring the triaxial stress of several fixed positions near the fracture zone.
- hydraulic fracturing /
- stress evolution /
- crack evolution /
- mesoscopic law /
- discrete element

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图 1 单轴压缩标定结果

Fig. 1 Calibration results of uniaxial compression

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图 2 巴西劈裂标定结果

Fig. 2 Calibration results of Brazilian split

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图 3 管域模型

Fig. 3 Pipe-domain model

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图 4 水力压裂模型

Fig. 4 Hydraulic fracturing model

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图 5 微裂隙扩展形态

Fig. 5 Schematic diagram of microcrack propagation

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图 6 不同排量下水力压裂应力与裂隙细观演化特征

Fig. 6 Mesoscopic evolution of hydraulic fracturing stress and fracture at different flow rates

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图 7 不同泊松比下水力压裂应力与裂隙细观演化特征

Fig. 7 Mesoscopic evolution of hydraulic fracturing stress and fracture under different Poisson’s ratios

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图 8 不同天然裂隙密度下水力压裂应力与裂隙细观演化特征

Fig. 8 Mesoscopic evolution of hydraulic fracturing stress and fracture under different natural fracture density

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表 1 试样宏观参数与模型宏观参数的比较

Table 1 Comparison between sample macro parameters and model macro parameters

宏观力学参数	实际值	PFC^2D 计算值	误差/%
单轴抗压强度σ_c/MPa	32.22	32.04	−0.5
弹性模量E/GPa	1.81	1.82	0.5
泊松比ν		0.25
本体抗拉强度σ_t/MPa	2.83	2.96	4.6

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表 2 模型细观参数

Table 2 Model mesoscopic parameters

参数类别	细观参数	数值
颗粒	颗粒最小半径R_min/mm	0.30
	最大最小粒径比R_max/R_min	1.66
	颗粒密度ρ/(kg∙m⁻³)	1 280
	孔隙率/%	9
	阻尼β/(Ns∙m⁻¹)	0.50
接触模型	细观弹性模量E_c/GPa	1.00
	刚度比k_n/k_s	2.30
	摩擦因数μ	0.50
	细观抗拉强度σ_c/MPa	11
	黏聚力c/MPa	20
	摩擦角φ/(°)	37.50
	法向临界阻尼比β_n	0.57

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表 3 水力压裂模拟方案设计

Table 3 Scheme design of hydraulic fracturing simulation

序号	天然裂隙密度	煤体泊松比	压裂排量Q/(mL∙min⁻¹)
1	无	0.25	20
2	无	0.25	40
3	无	0.25	60
4	无	0.16	40
5	无	0.35	40
6	低	0.25	40
7	中	0.25	40
8	高	0.25	40
注：低、中、高泊松比分别代表ν = 0.16、ν = 0.25、ν = 0.35；低、中、高压裂排量分别代表Q = 20、Q = 40、Q = 60 mL/min；低、中、高天然裂隙密度分别代表与参考线相交的裂隙数量为5、10、20个。

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