一种页岩体积压裂复杂裂缝的量化表征

Quantitative characterization of complex fractures after volume fracturing in shale

基于典型页岩压裂复杂裂缝分布形态,在考虑裂缝复杂程度、裂缝分布和裂缝对产量贡献的基础上,建立了复杂裂缝表征方法,提出了裂缝潜能指数的概念,作为定量对比复杂裂缝优劣的参数之一。使用上述裂缝表征方法计算裂缝在距离改造点不同位置处的分布密度,以判断裂缝系统的增产有效性。根据4种典型裂缝分布形态的表征结果,相对于裂缝分布曲线先缓慢上升后急剧增加的内疏外密裂缝系统,分布曲线先急剧增加后缓慢上升的内密外疏的裂缝增产效果更好。开展了页岩水力压裂物理模拟实验,进行了裂缝形态表征对比。结果表明,与高水平地应力差条件相比,低水平地应力差下形成的裂缝网络的潜能指数和单位复杂程度对应的潜能都明显较大,说明低水平地应力差下的裂缝网络具有较大的提高产量潜力。研究结果显示,建立的裂缝表征方法综合体现了裂缝复杂程度、裂缝分布特征和裂缝对产量的贡献,可用于评价和描述页岩压裂复杂裂缝的增产有效性。

According to the typical geometry of complex hydraulic fractures of shale,a new method which takes the fracture complexity,the fracture distribution and the attribution of fracture to production into consideration was proposed to describe complex fractures.Moreover,the concept of fracture potential index was put forward,and it can be used as one of the parameters for quantitative evaluation of the complex fractures.The density of fractures with different distances from the stimulation location was estimated with the method for determining the effectiveness of the fracture network.Compared with the fracture network with the characteristics of being dense inside but sparse outside,the fracture network being sparse outside but dense inside is more effective in enhancing production according to the description results.Hydraulic fracturing experiments were conducted and the geometries of hydraulic fractures in the shale were described with the application of the method.Results show that the potential index of fracture network formed under low horizontal geostress difference is greater than that of fractures formed under high horizontal geostress difference.It reflects that the fracture network formed under low horizontal geostress difference has higher potential for enhancing production.The above results indicate that the method established for describing complex fractures can comprehensively reflect the fracture complexity,fracture distribution and attribution to production.It provides a mean for evaluating the effectiveness of complex hydraulic fracture network.