Development of a Transient, Multi-Feedzone Geothermal Wellbore Simulator

Abstract

Simulation of the flow in a geothermal wellbore is an important reservoir engineering task, however, most existing geothermal wellbore simulators can only deal with steady-state conditions. This paper discusses the theoretical background and numerical implementation of a transient geothermal wellbore model that is currently under development. The simulator is capable of modelling transient single and two-phase flow in wells with multiple feed-zones. A geothermal wellbore simulator solves the conservation of mass, momentum, and energy equations that govern flow in a geothermal wellbore. These, along with the additional equations required for model closure, are presented. The governing equations are discretized and solved numerically using a fully implicit Newton-Raphson procedure for pressure, temperature (swapped with saturation for two-phase conditions), vapour velocity, and liquid volume flux as primary variables. The implementation of the simulator is tested using analytical solutions for simplified single-phase flow situations. Steady-state validation cases are presented for both single-feed and multi-feed wellbores. Finally, a simulation of the transient behavior of geothermal production well is presented as a test case, and further applications of the simulator are discussed.