ABSTRACT:
In this study, a 3D DEM lattice simulator is utilized to model the simultaneous growth and mechanical interference among members of an array of hydraulic fractures along a horizontal well. The deformation and fracturing of the rock matrix are simulated by the lattice. Fluid flow is implemented within the fractures and fully coupled with the mechanical deformation. Simulation results demonstrate non-planar fracture propagation behaviors induced by the stress shadowing effect in a full 3D setting without restriction on the fracture trajectory. Indeed, the simulation shows one fracture can be dominant in growth due to local heterogeneity and take in most of the fluid flow. The simulation also captures complex fracture front segmentation and asymmetric growth both in length and height under the combined impact of stress shadowing effect and perforation/in-situ stress misalignment, which could not be explicitly considered in previous pseudo-3D or parallel-planar 3D models.
1. INTRODUCTION
Multi-stage hydraulic fracturing is the preferred method for effective reservoir stimulation in unconventional hydrocarbon reservoirs (e.g. King 2010). Within each stage, multiple hydraulic fractures are placed and promoted to propagate simultaneously in an array distribution along consecutive sections of wellbores. However, research from field data analysis and numerical simulation both indicate that a significant proportion of fractures from perforation clusters within a fracturing stage can be largely suppressed (Fisher et al. 2004; Miller et al. 2011; Bunger and Peirce 2014). Evaluation of production logs shows that almost one-third of perforation clusters from 100 horizontal shale wells in multiple basins are not contributing to production (Miller et al. 2011). One main factor is the geomechanical interactions (stress shadowing effect) between growing fractures and the resulting disturbance on local stress field. Hydraulic fractures may grow asymmetrically, with some fractures becoming dominant while the others are suppressed and hence do not contribute to the stimulation effect.
There are several recent investigations that aim generally at reducing the negative impact of stress shadowing and thereby optimizing multistage completions. Less stress shadowing effect would generally be expected for uniformly distributed clusters with larger cluster spacing. For closely-spaced hydraulic fractures, the dynamics of geomechanical interactions between fractures can be substantially changed by perturbing the locations of perforation clusters away from the uniform distribution, which may potentially promote uniform distributions of fractured surface (Germanovich and Astakhov 2004; Bunger and Peirce 2014; Lecampion and Desroches 2015; Peirce and Bunger 2015; Wu et al. 2016). It has been shown numerically that an approximately 50 to 75% increase in hydrocarbon recovery, if scaled with the fractured area, is possible by specially choose the locations of the interference fractures (Peirce and Bunger 2015).
