孔隙水压力梯度对煤层导向压裂控制影响

基于孔隙水压力梯度对孔壁及裂缝尖端应力作用,提出了煤层导向压裂扩展方法.通过研究有效应力变化,建立了导向压裂起裂压力及裂缝扩展压力计算模型.采用RFPA~(3D)-Flow流固耦合软件建立了孔隙压力梯度场下的导向压裂数值模型.对7组不同数值模型计算分析,研究了导向孔的布置方式、距离、控制水压三个主要因素对导向压裂作用效果.研究结果表明:孔隙压力梯度能有效降低压裂孔起裂压力及裂缝扩展压力.起裂压力及裂缝扩展压力降低幅度与导向孔控制水压呈正相关关系,与导向孔距离呈负相关关系.数值计算得到的起裂压力变化规律与理论计算预测相符合,论证了导向压裂起裂压力计算模型的正确性以及导向压裂裂缝控制方法的可行性.

Influence of Pore Water Pressure Gradient on Guiding Hydraulic Fracturing in Underground Coal Mine

Based on the influence of pore water pressure gradient on the stress of hole wall and crack tip， a new crack-guiding method with guiding drilling is proposed. According to research on changing of the effective stress， the calculation model of the fracturing pressure and fracture propagation pressure is established. By using RFPA^3D-Flow fluid solid coupling software， the numerical model of oriented fracturing under pore water pressure gradient field is established. 7 groups of different guiding drilling models are calculated to study the guide fracturing effect of three main factors， viz. arrangement of guide borehole， distance， and water pressure. The results show that the pore pressure gradient can effectively reduce the crack initiation pressure and crack propagation pressure. The pressure of initiation and crack propagation is positively correlated with the control pressure of the guiding hole and inverse correlation between the distance from the guide hole. The variation law of the initial crack pressure calculated by the numerical calculation is consistent with the theoretical prediction. The study demonstrates that the guiding fracturing pressure calculation model is correct and the control method of the fracture orientation is feasible.