Abstract

Hydraulic fracturing in tight gas reservoirs is a complex physical process with interactions between fracking fluid flow in a confined channel, fracture propagation in reaction to an initial and evolving stress state, proppant transport inside an advancing fracture and finally gas production over the life-time of the well. This paper outlines the modelling methodology of a combined Finite Element (FE) and Discrete Element (DE) technology which is used in the software package ELFEN to simulate hydraulic fracturing. Current FE/DE technologies require a fine mesh in the region of the advancing tip to satisfactorily capture stress concentrations. The developments are centred on the capability to simulate fracture propagation within a geometry fracture insertion rather than element splitting framework. A local remeshing scheme is adopted instead of a traditional global remeshing procedure in which a fine mesh is maintained only adjacent to fracture tips to readily cut down on computational cost. The newly developed technology is demonstrated on simulating fluid driven fractures in single and multiple stimulated wells.

1. INTRODUCTION

In light of the recent commercial interest in the hydraulic stimulation of unconventional reservoirs, the key processes involved have received much attention in the scientific community. The hydraulic fracturing process has been employed to enhance the production of oil and gas from underground reservoirs [1]. Hydraulic stimulation is a particularly energy and resource intensive operation. A typical frack pump will be rated from 700 to 2700 hydraulic horsepower [2]. A single stage hydraulic fracturing treatment can consist of 4.2 million gallons of slickwater [3]. The injected proppant amount varies from about 36,000 to over 140,000 kg per stage [4]. With these enormous numbers it is imperative to enhance the hydraulic stimulation process to reduce both the amount of energy and resources used. Modelling approaches tied closer to a better understanding of the physical processes offer a robust framework in which to move forward.

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