应力环境对层面区域水压裂缝扩展的影响

The impact of stress state on the propagation of hydraulic fractures near bedding plane

无论是传统的煤炭、石油、天然气资源开采,还是新兴的非常规天然气开采,控制水压裂缝尽量在指定的资源储层中横向延伸、限制储层外垂向水压裂缝的数目和扩展长度是提高水压致裂效率和保护地层环境的有效途径。层面所处的应力环境是影响水压裂缝扩展的关键因素。采用RFPA2D-Flow,对不同应力环境下,水压裂缝初至层面的扩展行为、沿层面水压裂缝最大开裂长度和水压裂缝的破坏形态进行了模拟。模拟结果表明:1应力环境对水压裂缝初至层面时的扩展行为没有影响;2沿层面水压裂缝扩展的最大长度随主应力比的增加呈双曲线降低;3双向等压时,水压致裂沿层面方向的影响范围最大;4随着主应力比的增加,层面对水压裂缝扩展的影响逐渐减小,应力的作用逐渐增加,水压裂缝沿垂直于最小主应力方向穿层面扩展。

Hydraulic fracturing is widely used in exploiting coal, oil and gas and the emerging unconventional gas. Controlling the hydraulic fractures expand horizontally in specified strata and confining the number and length of fractures outside the specified strata is an effective way to improve the efficiency of hydraulic fracturing and protect the strata environment. The stress state of bedding plane is one key factor affecting the propagation of hydraulic fractures. With using RFPA2D-Flow,crack propagation behavior, such as hydraulic cracks initially meet the bedding plane, the maximum crack length along the bedding plane and the hydraulic crack failure mode are simulated under different stress states. The results show that;①Stress environment has no effect on crack expansion when hydraulic cracks initially meet the bedding plane;②the curve of the maximum hydraulic fracture expansion length along the bedding plane and the principal stress ratio is hyperbola;③when the maximum principle stress equals the minimum principal stress, the influence range along the bedding plane caused by hydraulic fracturing reaches the maximums;④ with the increase of the principal stress ratio, the impact of the bedding plane on hydraulic crack expansion gradually reduces and the hydraulic cracks penetrate the bedding plane perpendicularly to the minimum principle stress.