Abstract

Hydraulic fracturing (hydrofrac) is a very successful method that has been used to extract oil and gas from highly carbonate rocks like shale for a number of decades. However, there are still many aspects related to hydrofrac operations and how they affect the hydrocarbon’s recovery levels that remain poorly understood. At Los Alamos National Laboratory (LANL), the combined finite-discrete element (FDEM) modeling team is working in conjunction with an experimental team to improve the understanding of fracture initiation and propagation in shale rocks. In this paper, in order to address the effects of the fluid pressure, a pseudo fluid solver has been implemented in LANL’s in-house FDEM code. The pseudo fluid solver calculates the pressure in the fluid domain as a function of both the time and the distance from the fluid source. During the hydrofrac simulation, the pressure calculated from the pseudo solver is applied to the original free faces as well as the faces created by fracturing. After that, the sensitivity of the obtained fracture patterns related to uncertainties and/or changes in the boundary conditions is demonstrated using FDEM. Simulation results compared to triaxial core flooding experiments are presented. FDEM numerical simulations were able to replicate the main features of the fracturing processes while showing the importance of fluid penetration into fractures as well as layering in determining final fracture patterns.

1. INTRODUCTION

Hydraulic fracturing (hydrofrac) is a successful method used to extract oil and gas from highly carbonate rocks like shale and it has been used by industry since the mid- 50s [1-4]. However, there are many things that are still not clear regarding the mechanisms governing the hydraulic fracturing. To better understand how to improve hydrofrac recovery efficiencies and to lower its costs, LANL recently funded the Laboratory Directed Research and Development (LDRD) project: "Discovery Science of Hydraulic Fracturing: Innovative Working Fluids and Their Interactions with Rocks, Fractures, and Hydrocarbons". Under the support of this project, the LDRD modeling team is working in collaboration with the experimental team to improve the understanding of fracture initiation and propagation in shale rocks.

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