缝洞型碳酸盐岩储层水力裂缝扩展机理

Mechanism of hydraulic fracture propagation in fracture-cavity carbonate reservoirs

应用损伤力学的方法,建立了缝洞型碳酸盐岩储层水力裂缝扩展的物理模型和数学模型,探讨了在渗流场、应力场和温度场共同作用下水力裂缝受到天然裂缝和缝洞体干扰后其走向的影响因素,研究了不同条件下裂缝的形态,分析了缝内压力的变化趋势。模拟结果表明,水力裂缝遇到天然裂缝和缝洞体后,一部分水力载荷损失在非水力裂缝路径上,但迂曲一段距离后仍会沿着平行于最大水平主应力方向延伸。水力裂缝迂曲转向的临界条件随天然裂缝与最大水平主应力方向夹角以及天然裂缝和缝洞体规模的不同而发生改变。由于迂曲转向引起的摩阻增加,使得缝内压力下降明显。

The physical and mathematical model of hydraulic fracture propagation in fracture-cavity carbonate reservoirs were established on the basis of the damaging mechanics. The influences of natural fracture and cavern on the hydraulic.fracture were studied under the coordination of the filtering flow, stress and temperature fields. The fracture shapes under different conditions and the curve of pressure variation in the hydraulic fracture were analyzed. The results of numerical simulation indicated that some hydraulic load would be loss in the deviating way of the fractures propagation if the hydraulic fracture encountered natural fracture. Then hydraulic fracture extended along the direction parallel to the maximum horizontal stress after deviating a distance. The critical turning condition of the hydraulic fracture was sensitive to some factors such as the angle of natural fracture with the maximum horizontal stress and the scale of nature fractures and caverns. The pressure in the hydraulic fracture dropped obviously due to the increasing friction during the fracture turning.