ABSTRACT:

Hydraulic fracture modeling in naturally fractured reservoirs is an emerging field. Methods to study this problem include Discrete Fracture Network Model, Discrete Element Method and Extended Finite Element Method. Each method has received some success and has its merits and drawbacks. In this paper, we target this problem with Discontinuous Deformation Analysis (DDA). Based on the original DDA code developed by Dr. Gen-hua Shi, we add a fluid network model. With the new code, we can simulate how hydraulic fractures initiate and propagate with the fluid injection.

1. INTRODUCTION

Recent development of unconventional gas stimulates research on naturally fractured reservoir. Hydraulic fracture diagnostic data suggest complex hydraulic fracture geometry is a common occurrence in developing unconventional reservoirs [1-4]. However, hydraulic fracture models used in the industry today can only simulate a bi-wing planar fracture (for example, [5]). Hence, developing a complex fracture model which can explain how complex fractures are formed and optimize hydraulic fracture designs for engineers is in great demand. There have been some attempts to tackle this problem. Discrete Element Method (DEM) was invented by Dr. Peter Cundall and several commercial software packages have been developed over the years by Itasca Consulting Inc. These software packages include UDEC, 3DEC, PFC2D and PFC3D and were used by several research groups to study hydraulic fracturing in fractured rocks. Last and Harper were probably the first one to study the response of fractured rock subjected to fluid injection with discrete element method [6-8]. McLennan et al. [9] used 3DEC and Discrete Fracture Network to model fluid invasion and hydraulic fracture propagation in naturally fractured rock in three dimension. Zhao and Young use PFC to study seismicity induced by hydraulic fracturing in naturally fractured reservoirs. Recently, Dahi-Taleghani studied the interactions between natural and induced fractures with Extend Finite Element Method.

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