The optimum pressure drawdown for production from a shale gas reservoir: A numerical study with a coupled geomechanics and reservoir model

摘要

Pressure drawdown in a production well is a key parameter to control and optimize hydrocarbon production from the reservoirs. During production process in a stress-sensitive unconventional reservoir, there exist two competing mechanisms that are related to the pressure drawdown and impact the production: pressure gradient between the reservoir and production well and stress dependency of permeability. The combination of the two mechanisms results in the potential existence of the optimum pressure drawdown beyond which the production rate decreases with further increasing pressure drawdown for a given reservoir. This study investigates the factors impacting the optimum drawdown based on a coupled geomechanics and reservoir model. Specifically, we employed a reservoir simulator (TOUGH2) coupled with a geomechanics simulator (FLAC3D) to model the reservoir gas production under stress effects on porosity and permeability. The reservoir matrix permeability is exponentially related to the change in effective stress through the stress sensitivity factor. Simulation results show that the optimum pressure drawdown exists only for stress-sensitive shale reservoirs and mainly depends on the stress sensitivity factor, rather than the initial reservoir matrix permeability. This provides a simple guideline for the pressure drawdown management; the pressure drawdown should not exceed the optimum pressure drawdown in the field operations.