ABSTRACT:

Numerical simulation of hydraulic fracturing plays a critical role in optimal development of unconventionals. Several tools have been developed over the past decade by academia and industry to address this requirement. The complexity of non-linear governing equations combined with fracture propagation at field length scales drive the necessity to simplify the problem. The simplifying assumptions in governing equations and/or numerical scheme significantly limit the fidelity of the tool. In this work, we present a numerical simulator that solves the governing equations of hydraulic fracturing mechanism in poro-elastic rock with finite element displacement and finite volume pressure discretization. Fracturing fluids pumped from the wellhead are modeled using compressible pipe flow with frictional pressure loss. Wellbore is connected to fractures through orifice perforations. Fluid flow in fractures is governed by plane Poiseuille flow and is followed by leak-off and proppant transport. The coupled system of equations is solved simultaneously using an iterative solver, leveraging high performance computing. We present numerical case studies involving multiple clusters, stages and wells to demonstrate the scalability and features of the simulator. This distinguishing capability to solve full multi-physics governing equations on large field scale problems provides significant insights into complex subsurface interactions in Unconventionals.

1. Introduction

Hydraulic fracturing plays a pivotal role in the economics of unconventional oil and gas assets. The characteristics of these assets such as large areal expanse, thin stacked pay zones, and low permeability require novel and innovative engineering techniques for cost-effective development. Due to the vast uncertainty in the subsurface, modeling and simulation tools are an integral part of development planning decisions. Typical questions that one would pose to these simulation tools would be landing depth sensitivity, optimal well and stage spacing, cluster spacing, fluid and proppant pumping volumes, inter stage and inter well pressure communication, etc. The key components necessary to simulate these problems include (i) rock porous flow and mechanical response with fracture propagation (ii) fluid flow in fracture with leak-off into rock, (iii) flow through perforations, and (iv) flow in wellbore. The flow in fracture and perforations, along with fracture propagation result in nonlinear coupled governing equations. There have been many methods proposed in literature from both academia and industry to solve the corresponding governing equations. The approaches proposed include semi-analytical, finite volume, finite element, extended finite element, boundary element, displacement discontinuity, to name a few. The choice of approach is often driven by the desired accuracy, flexibility of the simulator and the model size of interest. It is very challenging to balance the accuracy and flexibility to enable large field scale calculations within practical runtimes. The underlying assumptions for each of the proposed methods in literature emphasize one of these aspects while ignoring the rest.

This content is only available via PDF.
You can access this article if you purchase or spend a download.