地应力差对煤层水力压裂的影响
Influence of Ground Stress Deviation on Coal Seam Hydraulic Fracturing
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摘要: 为进一步揭示地应力的大小和方向对煤层水力裂缝破裂压力和裂缝几何形态及延伸的影响，从而指导水力压裂设计、施工，提高压裂抽采效果，采用RFPA数值模拟软件对不同地应力差下破裂压力和裂缝延伸的变化规律进行研究。结果表明：煤层的水力压裂过程可分为裂前、微裂和破裂3个阶段，破裂阶段初始时的注水压力即为破裂压力；破裂压力随地应力差增大而线性减小；地应力差大于4 MPa时，最大地应力方向主导裂缝延伸方向；地应力差小于2 MPa时，裂缝形态趋于复杂；地应力差越大，裂缝形态越单一，方向性越显著，主裂缝延伸范围越大，越有利于煤层的增透和瓦斯的抽采，工程应用结果与数值模拟结果一致。Abstract: In order to reveal the influence of magnitude and direction of ground stress on hydraulic fracture pressure, fracture geometric shape and fracture extension and guide the design and operation of hydraulic fracture to improving gas extraction effect, we simulated and studied the changing behavior of fracture pressure and fracture extension under different ground stress deviations by using software RFPA. The results showed that the hydraulic fracturing process had 3 stages which were prior cracking, initial cracking and cracking and the pressure during cracking was considered the fracture pressure. The fracture pressure decreased linearly with the ground stress deviation increasing. The direction of cracks were determined by the max stress when the ground stress deviation was more than 4 MPa and the directions were complex when the ground stress deviation was less than 2 MPa. With the ground stress deviation increasing, the directions would become single and the extension would become bigger and it was good for gas extraction. The application results were in accordance with the simulated results.
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Keywords:
- coal seam /
- hydraulic fracturing /
- ground stress deviation /
- numerical simulation /
- gas extraction
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