考虑水力压裂缝和天然裂缝动态闭合的三维离散缝网数值模拟

doi:10.19596/j.cnki.1001-246x.8435

摘要/Abstract

摘要：

基于嵌入式离散裂缝模型, 提出一种可在三维空间中考虑应力状态影响的裂缝动态闭合表征方法。将任意方向裂缝的开度和渗透率考虑为作用在裂缝平面法向有效应力的函数, 同时用裂缝传导率变化表征支撑剂充填的水力压裂缝与被开启的天然裂缝由于油藏开发过程中地层流体压力下降而发生的动态闭合行为。研究表明: 致密油藏开发以缝控储量为主。对压裂水平井进行产能评价时, 裂缝动态闭合会导致产能的部分损失, 其影响不可忽略; 水力压裂缝的支撑剂材料属性及天然裂缝的刚度是其中的主控因素。因此需要增大支撑剂的浓度、粒径大小并改善支撑剂的性质, 在最大程度上降低裂缝闭合对生产的不利影响。

关键词: 致密油藏, 嵌入式离散裂缝模型, 裂缝闭合, 数值模拟, 三维裂缝可视化

Abstract:

A characterization method for fracture dynamic closure considering influence of stress state in three-dimensional space is proposed based on an embedded discrete fracture model. Aperture and permeability of fractures in any direction are considered as functions of normal effective stress acting on the fracture surface. Meanwhile, the change of fracture conductivity is used to characterize dynamic closing behavior of proppant-filled hydraulic fractures and opened natural fractures due to the decrease of formation fluid pressure during reservoir development. It shows that the development of tight oil reservoirs is dominated by "fracture-controlled reserves". In evaluating productivity of fractured horizontal wells, the dynamic closure of fractures lead to a partial loss of production, and its influence can not be ignored. Proppant material properties of hydraulic fractures, and stiffness of natural fractures are the main controlling factors. To minimize adverse impact of fracture closure on production it is necessary to increase the concentration and particle size of proppant and improve proppant properties.

Key words: tight oil reservoir, embedded discrete fracture model, fracture closure, numerical simulation, three-dimensional fracture visualization

杜旭林, 程林松, 牛烺昱, 陈玉明, 曹仁义, 谢永红. 考虑水力压裂缝和天然裂缝动态闭合的三维离散缝网数值模拟[J]. 计算物理, 2022, 39(4): 453-464.

Xu-lin DU, Lin-song CHENG, Lang-yu NIU, Yu-ming CHEN, Ren-yi CAO, Yong-hong XIE. Numerical Simulation of 3D Discrete Fracture Networks Considering Dynamic Closure of Hydraulic Fractures and Natural Fractures[J]. Chinese Journal of Computational Physics, 2022, 39(4): 453-464.

图/表 18

图1 天然裂缝与水力压裂缝表面的受力分析(a) 天然裂缝；(b) 水力压裂缝；(c) 支撑剂颗粒的嵌入

Fig.1 Surface stress analysis of natural fracture and hydraulic fracture (a) natural fractures; (b) hydraulic fractures; (c) embedment of proppant particles

表1 不同支撑剂种类的Barree模型回归系数[10]

Table 1 Regression coefficients in Barree model for different proppants[10]

	k₁	m₁	m₂	m₃	m₄	s₁	w₁
棕砂	0.000 089	2.34	2 550	2.23 × 10^-6	0	22 000	0.116 9
白砂	0.000 15	2.28	3 150	1.4 × 10^-7	0.5	27 000	0.116 4
高密度陶粒	0.000 021	2.6	3 800	3 × 10^-6	0	45 000	0.098

图2 传导率模型的验证

Fig.2 Verification of conductivity model

图3 压裂水平井基本模型

Fig.3 Basic model of fractured horizontal well

表2 模型验证基本参数

Table 2 Basic parameters in model verification

物理量	参数	物理量	参数
原油标况密度/(kg·m^-3)	820	原油黏度/(mPa·s)	2
基质孔隙度	0.13	基质渗透率/mD	0.1
水力压裂缝孔隙度	0.4	水力压裂缝初始渗透率/mD	20 000
水力压裂缝长度/m	200	水力压裂缝初始开度/m	0.01
水力压裂缝间距/m	200	束缚水饱和度	0.3
原始油藏压力/MPa	20	井底流压/MPa	10

图4 用于验证的局部网格加密模型

Fig.4 Local grid refinement model for verification

表3 水力压裂缝的传导率变化

Table 3 Conductivity change of hydraulic fracture

地层压力/MPa	水力压裂缝传导率/(mD·m)
20	86.14
18	79.95
16	74.05
14	68.48
12	63.24
11	60.74

图5 静态缝与动态缝的产能结果

Fig.5 Production results of static and dynamic fractures

图6 支撑剂类型与颗粒直径的影响

Fig.6 Influence of proppant types and particle size

图7 支撑剂类型与浓度的影响

Fig.7 Influence of proppant types and proppant concentration

图8 支撑剂颗粒嵌入对裂缝开度减小量的影响

Fig.8 Influence of proppant particle embedding on fracture aperture reduction

表4 不同的模拟方案

Table 4 Conductivity change of hydraulic fracture

	支撑剂浓度/(g·cm^-2)	支撑剂颗粒的中值直径/μm	支撑剂类型
方案一	0.5	300	棕砂
方案二	2	300	棕砂
方案三	0.5	450	棕砂
方案四	0.5	300	高密度陶粒

图9 压裂水平井压力分布(a) 30天；(b) 100天；(c) 300天；(d) 1000天

Fig.9 Pressure distributions of fractured horizontal well at (a) 30 days; (b) 100 days; (c) 300 days; (d) 1000 days

图10 压裂水平井产能曲线

Fig.10 Production curves of fractured horizontal well

图11 复杂裂缝网络基本模型

Fig.11 Basic model of complex fracture networks

图12 静态缝网(左)与动态缝网(右)不同时期压力分布(a) 30天；(b) 100天；(c) 300天；(d) 1000天

Fig.12 Pressure distributions of static fracture networks (left) and dynamic fracture networks (right) in different periods(a) 30 days; (b) 100 days; (c) 300 days; (d) 1000 days

图13 静态缝网与动态缝网的产量曲线(a) 日产油量；(b) 累积产油量

Fig.13 Production curves of static fracture networks and dynamic fracture networks (a) daily oil production; (b) cumulative oil production

图14 天然裂缝不同初始法向刚度的地层压力和产量(a) 地层压力；(b) 累积产油量

Fig.14 Formation pressure and production of natural fractures with different initial normal stiffness (a) formation pressure; (b) cumulative oil production

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