Abstract

Recent studies reveal that unconventional reservoirs contain complex natural fracture networks. Thus, in stimulating hydraulic fractures, it is important to study the interactions between natural fractures and hydraulic fractures. The goal of this work is to describe practical aspects of recent advances in the domain of geomechanical and discrete fracture network coupling, stimulation modeling, treating large number of fractures, adaptive mesh refinement methods, and overall fracture management within an unconventional setting. The computational framework is developed as an in-house code named IPACS (Integrated Phasefield Advanced Crack Propagation Simulator). Here, we describe a diffusive adaptive finite element phase field approach for modeling natural and hydraulic fractures. High fidelity finite element methods are employed to model multiphase flow with local mass conservation and dynamic mesh adaptivity. Geomechanics approximated by a continuous Galerkin finite element method is coupled to multiphase flow approximated by an enriched Galerkin finite element method by applying an iteratively coupled scheme.

Introduction

Through extended field experimentation recent field observations have shown that current stimulation models fall short in predicting hydraulic fracture geometries, proppant placement and transport, flowback, and the effects of stress shadowing and parent/child fracture parents. Moreover, most current simulators are unable to treat fracture propagation and production of flow and mechanics in a seamless fashion. Effects in including geochemistry are generally ignored except in very simple models. Thus, there is a need to demonstrate recent research efforts that can assist in predicting and modelling realistic stimulation processes. Consequently, engineering stimulated reservoir volume including proppant placement and/or acid fracturing treatments, can be achieved within computationally realistic frameworks, which can be used for reservoir management studies. In these research fields, the Center for Subsurface Modeling (CSM) in collaboration with other international institutes, has been contributing numerous studies. The emphasis has been on rigorous mathematical modeling, physics based discretizations, and numerical simulations. A robust and efficient computational framework for reservoir fracture modeling was developed resulting in IPACS - an integrated phase-field advanced crack propagation simulator. In this paper we describe and illustrate the main features of IPACS [1].

In this presentation we focus on a phase field approach for fracture stimulation. The phase-field methodology is a powerful tool for modeling the evolution of microstructures and their interactions of defects in a wide range of materials and physical models. The accurate simulation of fracture evolution in solids is a major challenge for computational algorithms, in large part due to crack paths that are generally unknown a priori. In this regard, phase-field approaches have shown great potential with their ability to automatically determine the direction of crack propagation through minimization of an energy functional. The phase-field framework naturally handles the emergence of phenomena such as crack nucleation and branching without the need to introduce additional criteria. In particular, formulations derived from variational theory have received a lot of attention from the applied mechanics community due to its strong ties to Griffith’s theory [2] for brittle fracture.

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