Study of fracture propagation uniformity in deep shale reservoir

doi:10.13745/j.esf.sf.2024.7.55

Abstract

Abstract:

The exploration and development of deep shale gas is crucial for achieving the dual-carbon target. To achieve this, multi-clustered hydraulic fracturing is an important method for enhancing production on a large scale. However, when the perforations are densely laid, the propagation of some clusters may be limited. Therefore, it is important to determine a reasonable spacing of fractures to improve reserve recovery and reduce costs. In this study, we established a hydraulic fracturing model for multi-layered reservoirs considering natural fractures. We used the displacement discontinuity method and the P3D model, and introduced Broyden iterative calculation method to propose an efficient solution method for the fluid-solid coupled multi-fracture model. We simulated and analyzed the effects of horizontal stress difference and construction parameters on the morphology of multi-cluster fractures and the uniformity of fracture propagation. The results showed that Broyden iteration is more computationally efficient than Newton iteration. Hydraulic fractures in deep shale reservoirs are difficult to turn under high stress difference conditions (10 MPa). Increasing the cluster spacing to 8m significantly improves the uniformity of each cluster. Additionally, raising the viscosity (>20 mPa·s) and pumping rate (>16 m³/min) of the fracturing fluid is beneficial for dense and uniform fracture propagation. These research results provide theoretical support for optimizing the deep shale fracturing process in China.

Key words: deep shale, fractured reservoirs, multi-cluster fracturing, uniformity of fractures, fracture morphology, numerical simulation

CLC Number:

TE348

HU Jinghong, LIAO Songze, CAI Yidong, LU Jun. Study of fracture propagation uniformity in deep shale reservoir[J]. Earth Science Frontiers, 2025, 32(4): 471-482.

Figures/Tables 19

Fig.1 Fracture propagation model diagram

Table 1 Base parameters of the model

参数类型	地质参数
参数名/ 单位	储层最小水平地应/MPa	储层最大水平地应/MPa	储隔层水平地应力差/MPa	弹性模量/ GPa	泊松比	储层断裂韧性/ (MPa·m^0.5)	隔层断裂韧性/ (MPa·m^0.5)
参数值	65	75	5	20	0.2	1	2
参数名/ 单位	岩石抗拉强度/MPa	储层厚度/m	岩石摩擦系数	天然裂缝长度/m	天然裂缝与水平井筒夹角/(°)	天然裂缝内聚力/MPa
参数值	4.5	30	0.6	5	60	1.5
参数类型	工程参数
参数名/ 单位	压裂液黏度/ (mPa·s)	压裂液密度/ (kg·m^-3)	施工排量/ (m³·min)	射孔数/孔	孔眼直径/ mm	Carter滤失系数/ (m·min^-0.5)	簇间距/ m
参数值	5	1 050	8	12	11	0.000 05	4

Fig.2 Comparison diagram of model calculation efficiency

Fig.3 Comparison of numerical model and PKN model simulation results

Fig.4 Comparison between experimental results and simulation results of natural fracture crossing criteria

Fig.5 Multi-fracture propagation model diagram under the influence of natural fractures

Fig.6 Fracture propagation morphology under high and low stress differences

Fig.7 Fracture propagation morphology under different cluster spacing

Fig.8 Fracture length and height at different cluster space

Fig.9 Injection uniformity coefficient at different cluster space

Fig.10 Fracture propagation morphology at different cluster numbers

Fig.11 Fracture length and height at different cluster numbers

Fig.12 Injection uniformity coefficient at different cluster numbers

Fig.13 Fracture propagation morphology at different viscosities

Fig.14 Fracture length and height at different viscosities

Fig.15 Injection uniformity coefficient at different viscosities

Fig.16 Fracture propagation morphology at different injection

Fig.17 Fracture length and height at different injection

Fig.18 Variation curve of injection uniformity coefficient at different injection

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