Abstract

Multistage hydraulic fracturing is commonly applied to enhance gas productivity in unconventional reservoirs. Since the multiple fractures are created and propagated simultaneously or in a sequential manner from perforation clusters, the induced stress interference is a predominant reservoir geomechanical consideration in multi-stage hydraulic fracturing design. This paper presents a numerical model for multiple fracture propagation and induced stress analysis in multi-stage horizontal wells. The reservoir rock is assumed linear elastic, homogenous and isotropic. The influences of original stress condition, perforation numbers, wellbore inclination angles and some critical parameters on the feasibility of complex fracture network generation are investigated. The results demonstrate that the stress interference of the simultaneous initiation of fractures in simultaneous perforation manner is greater than conventional sequential perforation manner in one stage, which is beneficial for complex fracture network complexity. Under sequential fracturing manner, the induced stress increases with the increased length of the pressurized fracture. Moreover, the perforation orientations and original horizontal stress difference controls the stress interference simultaneously and then affect complex fracture network generation. In particular, if the horizontal stress difference is great, it's hard to create complex fracture network under current hydraulic fracturing stimulation technology.

1. Introduction

In recent years, unconventional reservoirs like shale gas and tight gas are expected to account for vast gas supply all over the world. Permeability for unconventional reservoir formations generally range from 1md down to 1μd or less, thus the novel stimulation technology is necessary to substantially improve the quality of unconventional reservoirs and required for increased final gas recovery. The horizontal well with multiple transverse fractures has proven to be an effective strategy for commercial shale gas reservoir exploitation. The aim of multi-stage hydraulic fracturing is to create complex fracture network or stimulated reservoir volume (SRV), which can be identified by microseismic mapping (Warpinski et al. 2009; Soliman and Augustine, 2010).

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