FEM numerical simulation for hydraulic fracture propagation in shale reservoirs influenced by weak bedding planes

doi:10.3969/j.issn.2096-1693.2025.02.019

Abstract

Abstract:

The Linxing gas field was selected as the research object, where weak bedding planes represent typical features and significantly influence hydraulic fracture propagation. This study provides valuable insights on hydraulic fracture propagation in bedded shale formations and offers guidance for optimizing fracturing techniques. The characteristics of shale featuring bedding planes were examined by utilizing rock mechanics experiments and direct shear tests. Considering the cementation strength and friction properties of bedding planes, a computational subroutine was developed to characterize the contact behavior for bedding planes. A 3D Finite Element Method-Cohesive Zone Model (FEM-CZM) has been established for multi-field coupling analysis of stress-damage-fluid flow, specifically incorporating bedding planes. This model incorporates a contact constitutive relationship that accounts for both friction and cementation strength of the bedding. A comprehensive and systematic quantitative analysis is conducted to investigate the influence of various factors on bedding shear slip and the propagation of hydraulic fractures. These factors include the initial opening of bedding fractures, friction coefficient, cementation strength, number of bedding planes surrounding the wellbore, and fracturing operation parameters. The results indicate that the presence of weakly bonded bedding planes leads to complex fracture propagation patterns involving both tensile and shear fractures. Bedding plane apertures serve as preferential flow pathways for fracturing fluid, significantly inhibiting fracture propagation. When the bedding aperture increases to 300 μm, the fractures are unable to cross bedding planes, which limits the fracture scale. Compared to the bonding strength, the bedding friction coefficient plays a more dominant role in determining whether fractures penetrate. Higher friction coefficients facilitate the penetration, regardless of whether the bedding planes are bonded or not. The penetration probability increases exponentially as the friction coefficient rises. In contrast, with lower friction coefficients and weakly bonded bedding planes, fractures are intercepted, while higher cementation strength allows for effective penetration. Furthermore, with a rise in the number of bedding planes, the shear fractures along these beddings expands considerably, which results in a more intricate fracture pattern. The shear failure of multiple bedding planes restricts the development of tensile-dominated fractures, which reduces the efficiency of reservoir stimulation. Optimizing fracturing fluid injection, increasing high-viscosity fracturing fluid volumes, and raising injection rates can enhance vertical fracture propagation and improve the stimulated reservoir area. Further validation of the influence of bedding planes on fracture propagation is provided by analyzing distributed temperature sensing (DTS) profiles, as well as the post-fracturing performance in Linxing.

Key words: bedding planes, 3D finite element model, hydraulic fracture propagation, frictional slip, stimulation reservoirs area

摘要：

层理弱面是页岩储层水力裂缝扩展的关键控制因素。本文以临兴气区页岩为研究对象，通过室内岩石力学实验明确该区域页岩基质和层理力学特征；建立了含层理弱面的“应力—损伤—渗流”多场耦合三维FEM-CZM模型(Finite Element Method-Cohesive Zone Model)，引入考虑层理界面摩擦及胶结强度的层理接触本构，系统分析层理初始水力开度、摩擦系数、胶结强度、井周层理数目以及压裂施工参数对层理剪切滑移和裂缝扩展的影响。研究结果表明，层理干扰使水力裂缝扩展机制复杂，张拉和剪切裂缝共存。相比胶结强度，层理摩擦系数对裂缝穿层行为起主导作用；高摩擦系数促使裂缝抵抗层理干扰而更早穿层，且层理剪切缝范围减小。低摩擦系数及弱胶结强度时缝高扩展受阻；层理胶结增强会削弱层理滑移，促进裂缝穿层。层理初始水力开度达到300 μm时，压裂液沿层理渗流会导致裂缝无法穿层和改造体积受限。层理缝水力开度越大、摩擦系数越小、胶结强度越低，层理越容易剪切滑移。井周弱层理数目增多导致剪切缝面积增加，但张拉裂缝沟通面积减小。通过优化压裂液泵注程序，增加高黏压裂液用量，提高压裂液泵注排量，可以促进裂缝纵向延伸，提升储层动用程度。现场压裂井的井温监测进一步验证了层理弱面对压裂效果的影响。

关键词: 层理型页岩, 三维有限元, 水力裂缝扩展, 层理剪切滑移, 压裂改造面积

CLC Number:

WANG Fei, LIU Wei, DENG Jingen, LI Donggang, TAN Yawen, FENG Yongcun. FEM numerical simulation for hydraulic fracture propagation in shale reservoirs influenced by weak bedding planes[J]. Petroleum Science Bulletin, 2025, 10(4): 719-735.

王菲, 刘伟, 邓金根, 李东刚, 谭雅文, 冯永存. 基于有限元方法的层理弱面对页岩水力裂缝扩展影响规律[J]. 石油科学通报, 2025, 10(4): 719-735.

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URL: https://sykxtb.cup.edu.cn/EN/10.3969/j.issn.2096-1693.2025.02.019

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Figures/Tables 24

Fig. 1 Electric imaging logging and rock samples of the Taiyuan formation Linxing

Table 1 The mechanics tests results for shale cores of Taiyuan formation in Linxing-Shenfu

力学参数	参数范围	参数平均值
单轴抗压强度/MPa	37.23~76.73	58.39
弹性模量/GPa	15.16~27.56	20.92
泊松比	0.16~0.32	0.25
抗拉强度/MPa	6.70~8.90	7.11
断裂韧性/(MPa·m^-1/2)	0.40~1.90	1.40

Fig. 2 Stress-strain curve characteristics and post-failure behavior of Linxing Taiyuan Formation shale under triaxial compression (10 MPa confining pressure)

Fig. 3 Test apparatus and schematic diagram of the direct shear tests

Fig. 4 Direct Shear test curves of laminated shale along the bedding direction under different normal stresses

Fig. 5 Friction coefficient testing curves for fracture surfaces of shale along the bedding planes

Fig. 6 Schematic diagram of the bedding slip during hydraulic fracture propagation

Fig. 7 3D FEM-CZM of hydraulic fractures propagation in laminated shale formations with weak bedding planes

Table 2 Basic parameters of FEM-CZM

类型	模型参数	参数取值
基质单元	基质岩石杨氏模量/GPa	21.0
	基质岩石泊松比	0.25
	基质岩石渗透率/mD	2.0
Cohesive 单元	页岩、层理抗拉强度/MPa	7.0、2.0
	页岩、层理断裂能/(J·m^-2)	2000、150
	页岩、层理滤失系数/(m·Pa^-1·s^-1)	1×10^-12 1×10^-12
层理	层理摩擦系数	0.75
层理	层理剪切刚度/(GPa·m^-1)	25.0
压裂液	压裂液密度/(kg·m^-3)	980
	压裂液黏度/(mPa·s)	10.0
	压裂液排量/(m³·min^-1)	4.0
地应力条件	上覆岩层应力/MPa	43.0
	最大水平地应力/MPa	34.0
	最小水平地应力/MPa	28.2

Fig. 8 Comparison of fracture trajectories from numerical calculation and experimental observations

Fig. 9 Comparison of HF morphology under the influence of bedding interfaces with initial aperture

Fig. 10 Pore pressure evolution at bedding plane A in hydrau-lic fracturing with varying initial apertures of bedding-parallel fractures

Fig. 11 Variation of bedding plane shear slippage displacement under different initial hydraulic apertures and bedding-parallel fractures

Fig. 12 Schematic diagram of critical conditions for shear slip activation along bedding planes

Fig. 13 The influence of bedding interface friction coefficients on hydraulic fracture propagation

Fig. 14 Time-dependent bedding-plane slip displacement under different friction coefficients

Fig. 15 Fracture damage maps for different bedding cementation strengths at the friction coefficient of 0.6

Fig. 16 The bedding shear slip for different bedding cementation strengths at the friction coefficient of 0.6

Fig. 17 Impact of friction coefficient and bedding joint strength on fracture geometry parameters

Fig. 18 Simulation results of fracture morphology for different bedding numbers

Fig. 19 Relationship between fracture propagation and bedding numbers

Fig. 20 The influence of fracturing fluid parameters on fracture propagation in layered formations

Fig. 21 Results of fracture morphology characteristics with variations in fracturing fluid injection parameters

Fig. 22 Well temperature curves before and after fracturing of LX-A and LX-B wells

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