<p>Calcite veins, as weak structural planes in shale reservoirs, jointly influence hydraulic fracturing behavior along with the significant in-situ stress differences in northern Guizhou. Based on CT scanning and numerical simulation, this study constructs a three-dimensional heterogeneous model to elucidate the coupling mechanism between the horizontal stress differential coefficient (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">$K_{h}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>K</mi> <mi>h</mi> </msub> </math></EquationSource> </InlineEquation>) and the inclination angle that calcite veins have on the propagation of fluid fractures. The results indicate that, due to the angular effect of the principal stress and the failure axis, the failure stress of shales shows a tendency to initially increase and then decrease with the increase in calcite vein inclination. Meanwhile, the weak-plane effect of calcite veins determines the initial fracture propagation direction, allowing hydraulic fractures to preferentially extend along the vein strike before branching and diffusing into the shale matrix. A significant negative correlation is observed between <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$K_{h}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>K</mi> <mi>h</mi> </msub> </math></EquationSource> </InlineEquation> and the fracture complexity index (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">$F_{CI}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>F</mi> <mrow> <mi mathvariant="italic">CI</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>) during hydraulic fracturing: as <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$K_{h}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>K</mi> <mi>h</mi> </msub> </math></EquationSource> </InlineEquation> increases, <InlineEquation ID="IEq5"> <EquationSource Format="TEX">$F_{CI}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>F</mi> <mrow> <mi mathvariant="italic">CI</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> decreases, leading to a more simplified fracture morphology. Furthermore, the dynamic evolution of the acoustic emission b-value demonstrates the link between magnitude distribution and hydraulic fracture complexity, with bigger b-value peaks corresponding to lower fracture complexity. This study looks at the coupling effect of geological weak planes and the in-situ stress field on hydraulic fracturing, giving theoretical support for fracture design and complex fracture network optimization in northern Guizhou shale reservoirs.</p>

Study on the Evolution Characteristics of Hydraulic Fracturing Cracks in Shale with Calcite Veins Under Different Horizontal Stress Differences

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发表日期：

2025年9月23日

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Ronghua Zhang,
Zhonghu Wu,
Guoqing He,
Xianchao Yang,
Jintao Zhou,
Yao Wang

摘要

Calcite veins, as weak structural planes in shale reservoirs, jointly influence hydraulic fracturing behavior along with the significant in-situ stress differences in northern Guizhou. Based on CT scanning and numerical simulation, this study constructs a three-dimensional heterogeneous model to elucidate the coupling mechanism between the horizontal stress differential coefficient ( $K_{h}$ $K_{h}$ ) and the inclination angle that calcite veins have on the propagation of fluid fractures. The results indicate that, due to the angular effect of the principal stress and the failure axis, the failure stress of shales shows a tendency to initially increase and then decrease with the increase in calcite vein inclination. Meanwhile, the weak-plane effect of calcite veins determines the initial fracture propagation direction, allowing hydraulic fractures to preferentially extend along the vein strike before branching and diffusing into the shale matrix. A significant negative correlation is observed between $K_{h}$ $K_{h}$ and the fracture complexity index ( $F_{CI}$ $F_{CI}$ ) during hydraulic fracturing: as $K_{h}$ $K_{h}$ increases, $F_{CI}$ $F_{CI}$ decreases, leading to a more simplified fracture morphology. Furthermore, the dynamic evolution of the acoustic emission b-value demonstrates the link between magnitude distribution and hydraulic fracture complexity, with bigger b-value peaks corresponding to lower fracture complexity. This study looks at the coupling effect of geological weak planes and the in-situ stress field on hydraulic fracturing, giving theoretical support for fracture design and complex fracture network optimization in northern Guizhou shale reservoirs.