压裂中天然裂缝剪切破坏机制研究

 采用理论分析、实验验证和算例分析研究裂缝性储层水力压裂过程中天然裂缝张开和剪切破坏机制。理论分析表明：水平主应力差、逼近角、裂缝面摩擦因数是影响天然裂缝剪切破坏的主要因素，在低应力差、低逼近角或者是摩擦因数较小的条件下，由于水力裂缝的影响，天然裂缝易发生剪切破坏；水平主应力差和近缝面岩石力学特性是影响天然裂缝张开程度的主要因素；试验结果表明，在低水平主应力差或低逼近角情况下，当水力裂缝与天然裂缝干扰后，闭合的天然裂缝张开，易发生剪切破坏；在高水平主应力差和高逼近角情况下，水力裂缝易直接穿过天然裂缝，天然裂缝仅仅被渗透，没有发生剪切破坏。通过算例分析，提出裂缝的张开边界和剪切破坏边界，阐述天然裂缝对流体的极限容量；分析表明逼近角越大，天然裂缝对压裂液的极限容量越小。

MECHANISM STUDY OF SHEARING SLIPPAGE DAMAGE OF NATURAL FRACTURE IN HYDRAULIC FRACTURING

hearing slippage damage and opening mechanism of natural fracture during the process of hydraulic fracturing in naturally fractured reservoir are studied by theoretical analysis，experimental validation and example analysis. theoretical analysis shows that horizontal differential principal stress，approaching angle and coefficient of friction are the main factors that cause fracture shearing slippage damage. In the condition of low horizontal differential principal stress，low approaching angle or low coefficient of friction，shearing slippage damage of natural fracture tend to happen under the influence of hydraulic fracture. The degree of natural fracture opening is determined by horizontal differential principal stress and features of rock mechanics. Experimental results show that after interaction with hydraulic fracture，the previously closed natural fracture opens and the shearing slippage damage happens in the condition of low horizontal differential principal stress or low approaching angle，while in the condition of high horizontal differential principal stress and high approaching angle，the natural fracture is filtered and there is no shearing slippage damage. Fracture opening boundary and shear slippage boundary are given out through example analysis，and the utmost containment of natural fracture is described. The example analysis shows the utmost containment of natural fracture decreases while approaching angle increases.