裂缝性页岩储层多级水力裂缝扩展规律研究

水力裂缝监测技术显示页岩储层中水力裂缝形态复杂,与传统的砂岩储层有本质区别,传统的裂缝扩展模型难以描述和解释页岩地层裂缝扩展的复杂性。基于线弹性断裂力学理论,针对页岩地层裂缝发育的特征,采用位移不连续法建立了一种多裂缝扩展二维数值模型,模拟了页岩地层中水力裂缝在随机分布的天然裂缝干扰下扩展的复杂形态。数值模拟显示,当相对净压力较大、天然裂缝与初始水力裂缝最优扩展方向夹角较大时,更倾向于形成复杂形态裂缝;水平应力差较大时,水力裂缝分叉的几率越小,通过对页岩露头的真三轴水力压裂物理模拟试验研究进一步验证了数值模拟方法的合理性,龙马溪组页岩地层的微地震监测解释结果与本数值模拟结果吻合良好。

Propagation of multiple hydraulic fractures in fractured shale reservoir

The monitoring of hydraulic fracture shows that the morphology of hydraulic fracture in shale reservoirs is complex, and is essentially different from that in the traditional sandstone reservoirs. The traditional models for fracture propagation are difficult to describe and explain the complexity of fracture propagation in shale formation. Based on the theory of linear elastic fracture mechanics, in accordance with fracture development characteristics in shale formation, a 2D numerical model for multi-fracture propagation is established by adopting the displacement discontinuity method. This model simulates the complex morphology of hydraulic fracture propagation under the interference of randomly distributed natural fractures in shale formation. Numerical simulations show that when the relative net pressure is high, the angle between natural fracture and optimized propagation direction of the initial hydraulic fracture is large, and it is more liable to create complicated fractures. And when horizontal stress difference is larger, it is less liable for hydraulic fractures to branch. The true tri-axial hydraulic fracturing tests on shale outcrops further validate the reasonability of this numerical simulation method. The results of micro seismic monitoring interpretation of Longmaxi shale formation agree well with the numerical results in this paper.