ABSTRACT:

In conventional fully coupled simulation models, it is assumed that the reservoir rock is saturated by a single fluid and therefore tends to inaccurately predict depletion-induced stress changes in unconventional reservoirs because the pore space of the porous rock may have two or more fluids. In field development planning, maximizing infill well potential as well as the economics of parent well is very important. Field observations indicate that infill well propagation path is highly dependent on the stress distribution around the production well. However, the majority of the studies do not account for additional fluid phases. Some of the two-phase models have limited capabilities such as neglecting capillary pressure. In this work, we have developed a fully coupled two-phase 3D finite element model to simulate the stresses and pore pressure fields in porous media with two immiscible fluids. The two-phase model was validated against two problems with known solutions. The proposed model was applied to the simulation of production from a single hydraulic fracture. The results show that considering an additional phase in the reservoir can significantly change the stress and pore pressure distribution field. This simulation approach can shed light on a better understanding of the key parameters affecting depletion-induced stress reorientation/reversal and frac-hits in refracturing of horizontal wells.

1. Introduction

Hydraulic and natural fracture deformation and propagation plays an important role in unconventional petroleum and geothermal reservoirs. The deformation response of the fractures is significantly affected by coupled poroelastic (Cheng, 2016; Zhou and Ghassemi, 2011) and thermo-poroelastic effects (Ghassemi and Zhang, 2006; Ghassemi and Zhou, 2011; Safari and Ghassemi, 2015; Gao and Ghassemi, 2017). These studies have focused on the fracture behavior of single-phase saturated rock. However, often reservoirs are saturated with two or more immiscible fluids and the fracture response and the evolving induced coupled stresses (stress shadow) which can affect refrac considerations (Masouleh et al., 2020; Kumar et al., 2018; Feizi Masouleh, 2020) have not been considered. Numerical simulation of multiphase flow in deforming porous media has been the subject of considerable interest in diverse engineering fields including nuclear waste disposal (Fall et al., 2014), geologic sequestration of CO2 (Rutqvist et al., 2007), groundwater contamination in subsurface systems (Rahman and Lewis, 1999), consolidation analysis of partially saturated soil (Khoei and Mohammadnejad, 2011), wellbore stability and sand production (Wang and Lu, 2001), production induced reservoir compaction and surface subsidence (Schrefler, 2001; Lewis and Sukirman, 1993) and waterflooding (Murad et al., 2013). However, the fundamental response of a fracture in a multi-phase reservoir has not been investigated. Because of the complexity of the field equations, such an effort must rely on numerical tools.

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