Coupled Wellbore-Reservoir-Geomechanical Modelling of Uneven Depletion and Induced Stress Responses in Shale Oil Reservoirs with Heterogeneous Hydraulic Fractures

ABSTRACT: The production in horizontal wells with multi-stage hydraulic fractures causes pressure drop and depletion-induced in-situ stress state changes at both near-well and far-field locations. Multi-stage hydraulic fractures are usually heterogeneous with various widths, heights, half-lengths, and conductivities. The pipe flow in wellbores is also affected by multi-stage fractures connected through perforations. This study proposes a numerical model that simultaneously considers the coupled behaviors of pipe flow, depletion in heterogeneous fractures and reservoirs, and induced in-situ stress state evolutions. In this numerical model, the three physical fields mentioned above are modeled and fully coupled. Heterogeneous hydraulic fractures are assigned with uneven fracture widths, fracture half-lengths, and fracture conductivities. Simulation results indicate that dominant flow paths are observed and they are usually associated with hydraulic fractures with greater sizes and better conductivities. Within the reservoir, dominant fractures lead to greater and faster depletion and stress reorientation, while inferior fractures result in slower and insignificant stress responses. Another observation captured by the coupled wellbore-reservoir-geomechanical simulation is the effect of productivity competition between superior and inferior hydraulic fractures during production. Fractures with greater sizes and higher productivities draw fluids from adjacent fractures and intensify uneven flow distribution and induced stress changes. Increasing cluster spacing can help to obtain more uniform stress state changes during horizontal well production and to avoid excessive local stress reversals around dominant fractures. The study helps to improve the representation of wellbore-reservoir interaction in the simulation of horizontal well depletion-induced reservoir stress responses. It also provides a numerical modeling reference to the optimization of hydraulic fracturing design and production schedules. 1. INTRODUCTION During the development of shale oil reservoirs, horizontal wells and hydraulic fracturing techniques are widely used. In certain scenarios, re-fracturing and infill well fracturing techniques are involved due to the limited recovery efficiencies of hydraulically fractured legacy wells (Gupta et al., 2013). To optimize hydraulic fracturing parameters and fracturing timings in these scenarios, it is very important to understand depletion-induced stress evolutions in the reservoirs (Morales et al., 2016; Jacobs, 2017). Due to this effect, local stress magnitudes and stress orientations can be different from the original in-situ stress state prior to any shale oil production (Roussel et al., 2013; Chen et al., 2021; Zhi et al., 2021). In such complex and heterogenous stress fields, the propagation behaviors of new hydraulic fractures caused by infill well fracturing and re-fracturing can be hard to predict.