Sensitivity analysis on the interaction between hydraulic and natural fractures based on an explicitly coupled hydro-geomechanical model in PFC2D
Sensitivity analysis on the interaction between hydraulic and natural fractures based on an explicitly coupled hydro-geomechanical model in PFC2D
复制标题
基于 PFC2D 中显式耦合水文地质力学模型的水力裂缝和天然裂缝之间相互作用的敏感性分析
DOI：
10.1016/j.petrol.2018.04.046
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发表时间：
2018
影响因子：
--
通讯作者：
Han Zhenhua
中科院分区：
文献类型：
--
作者：
Zhang Luqing;Zhou Jian;Braun Anika;Han Zhenhua
流体诱导裂缝成核、扩展及其与天然裂缝的相互作用是理解非常规储层水力压裂过程的关键问题。本文采用二维颗粒流程序（PFC2D）中的显式耦合水力-地质力学模型，研究了水力裂缝（HFs）与天然裂缝（NFs）之间的相互作用，并通过分析结果对数值格式进行了验证。目前正在研究和讨论影响诱导裂缝与纳米颗粒相互作用的几个因素。仿真结果表明：(1)直接通行、(2)偏置通行和(3)无通行（拦阻）三种基本通行情景均能得到较好的再现，且通行类型在Blanton准则评价中具有较好的一致性。敏感性分析表明，水力裂缝在低进近角时倾向于被天然裂缝阻挡，而在高地应力差状态下倾向于越过天然裂缝。对于摩擦系数较低、渗透率较高的NFs，可能会阻碍其通过。此外，较低的压裂液注入量和较低的流体粘度都是NF再激活的有利条件，并倾向于阻止HF。此外，上述因素对高通量和低通量相互作用的影响机理可以通过预存在界面上的法向应力演化来解释，这是正确模拟水力压裂的关键问题。与解析模型相比，该模型更能反映裂缝性储层的动态应力演化过程，为裂缝性储层水力压裂优化设计提供了有益的工具。
Fluid-induced fracture nucleation, propagation and interaction with natural fractures are the crucial issues for well understanding the process of hydraulic fracturing in unconventional reservoirs. In this paper, an explicitly coupled hydro-geomechanical model in two-dimensional Particle Flow Code (PFC2D) is employed to investigate the interaction between hydraulic fractures (HFs) and natural fractures (NFs), and the numerical scheme is validated by using analytical results. Several factors affecting the interactions between induced-fractures and NFs are being investigated and discussed. The simulation results show that three fundamental crossing scenarios can be well reproduced: (I)Direct Crossing, (II)Offset Crossingand (III)No Crossing(Arrested), and the crossing types agree well in the evaluation by Blanton's criterion. A sensitivity analysis shows that hydraulic fracture (HF) tend to be arrested by a natural fracture (HF) under low approach angles and prefer to cross the NF under higher in-situ differential stress states. Crossing is likely to be impeded for NFs with lower frictional coefficient and higher permeability. Additionally, lower fracturing fluid injection rates and lower fluid viscosities both are advantageous conditions for NF reactivation, and tend to arrest the HF. Moreover, the mechanism of the interaction of HFs and NFs influenced by the aforementioned factors can be well explained by the evolution of normal stress on the pre-existing interface, which is the key issue for correct simulation of hydraulic fracturing. Compared with the analytical model, the model in this study can reflect the dynamic stress evolution process, which will be a useful tool for optimizing the design of hydraulic fracturing in fractured reservoirs.