Abstract

Many natural gas reservoirs are characterized by large networks of pre-existing natural fractures. To design hydraulic fracturing treatments in these systems, models are needed that can account for the complex interaction of hydraulic fractures with natural fracture networks. This work presents a new method for modeling hydraulic fracturing in these reservoirs using an algorithm based on the discontinuous deformation analysis (DDA). To demonstrate the method’s capabilities, hydraulic fracturing is simulated in two theoretical pre-fractured reservoirs subjected to different levels of background stress. The results of this work demonstrate that principal stress will be one of the primary factors determining the direction of fracture propagation within a naturally fractured system. In addition, the orientation of the natural fracture networks will also influence the direction of fracture propagation, particularly when the difference between the maximum and minimum principal stress is minimal. Finally, the results demonstrate that fluid viscosity and injection rate will have a direct impact on the extent to which fracturing fluid will invade a pre-existing network of natural fractures, but only a minimal impact on the direction taken by propagating hydraulic fractures.

1. INTRODUCTION

In the field, natural gas reservoirs are frequently characterized by large networks of pre-existing natural fractures. Hydraulic fracturing treatments for these reservoirs are often designed using bi-wing or radial fracturing models, both of which are based on strict assumptions for the geometry of the propagating fracture [1, 2]. The presence of pre-existing natural fractures, however, can lead to the formation of complex fracture networks which are not well characterized by these models [3]. In addition, natural fractures can cause the flow and production properties of a targeted reservoir to deviate greatly from those predicted by bi-wing or radial fracture models. Given the potential impact of natural fractures on hydraulic fracture propagation and reservoir production, the study of fracturing in naturally fractured reservoirs deserves further attention.

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