Modeling Dynamic Behaviors of Complex Fractures in Conventional Reservoir Simulators

Xu, Yifei (The University of Texas at Austin) | Yu, Wei (Texas A&M University) | Sepehrnoori, Kamy (The University of Texas at Austin)

OnePetro 

Abstract

Field data has shown the decline of fracture conductivity during reservoir depletion. In addition, recently, refracturing and infill drilling have gained much attention as efficient methods to enhance recovery in shale reservoirs. However, current approaches present difficulties in efficiently and accurately simulating such processes, especially for large-scale cases with complex hydraulic and natural fractures.

In this study, a general numerical method compatible with existing simulators is developed to model dynamic behaviors of complex fractures. The method is an extension of an embedded discrete fracture model (EDFM). With a new set of EDFM formulations, the non-neighboring connections (NNCs) in the EDFM are treated as regular connections in traditional simulators, and the NNC transmissibility factors are linked with gridblock permeabilities. Hence, manipulating block permeabilities in simulators can conveniently control the fluid flow through fractures. Complex dynamic behaviors of hydraulic fractures and natural fractures can be investigated using this method.

The proposed methodology is implemented in a commercial reservoir simulator in a non-intrusive manner. We first present a case study in a shale-oil reservoir to verify the model accuracy. Subsequently, four field-scale case studies with complex fractures in both 2D and 3D are presented to illustrate the applicability of the method. These studies involve vertical and horizontal well refracturing in tight reservoirs, infill drilling, and fracture activation in a naturally fractured reservoir. The proposed approach is combined with empirical correlations and geomechanical criteria to model stress-dependent fracture conductivity and natural fracture activation. It also shows convenience in dynamically adding new fractures or extending existing fractures during simulation. Results of these studies further confirm the significance of dynamic fracture behaviors and fracture complexity in the analysis and optimization of well performance.

Introduction

Hydraulic fracturing has been a successful technology in the oil and gas industry for several decades. Recently, techniques such as horizontal drilling and multi-stage hydraulic fracturing have made it possible to economically develop shale reservoirs with extremely low permeability.