Numerical simulation of hydraulic fracturing process in a naturally fractured reservoir based on a discrete fracture network model

摘要

This research presents a simulation of hydraulic fracturing process in a naturally fractured reservoir based on a discrete fracture network (DFN) model coupling different kinds of pre-existing discontinuities. Natural fractures and bedding planes obtained from outcrops and downhole camera in the Ordos Basin of China are used to build a three-dimensional DFN model. The propagation of hydraulic fractures in the layered and naturally-fractured reservoir, and the complex interactions between hydraulic fractures, natural fractures and bedding planes are simulated using the displacement discontinuity method. The results show that strong interactions between hydraulic fractures and pre-existing discontinuities occur during fluid injection, causing complex fracture geometry. When the injection rate is 0.01 m3/min, only one major hydraulic fracture is induced, and crack growth along bedding interface does not occur since the fluid pressure is not high enough. With increasing injection rate (0.1 m3/min and 1.0 m3/min), natural fracture and bedding planes are activated, inducing multiple major hydraulic fractures and reticulated fractures. For each injection scheme, fracture geometry in the horizontal and vertical directions becomes more complex with the injection of fracturing fluid. However, fracture complexity in the horizontal direction is smaller than that in the vertical direction when the injection rate varies from 0.01 m3/ min to 1.0 m3/min. Besides, the results show that injection rate has a strong positive influence on the increment of fracture complexity.