Multi-segmented non-isothermal compositional liquid gas well model for geothermal processes

TL;DR

This work develops a numerical framework for simulating transient, two-phase, non-isothermal geothermal wellbore flows with phase transitions and multi-branch wells, coupled to reservoir models. It combines a Coats-type compositional formulation with a drift-flux hydrodynamic model and NPW momentum balance, and employs a fully implicit, staggered finite-volume discretization. A key contribution is the monotone two-point flux for phase superficial velocities, paired with phase-based upwind transport of molar fractions, density and enthalpy, enabling stable coupling across present phases. The solver eliminates hydrodynamic and thermodynamic closures to reuse reservoir primary unknowns, and the method is validated on stand-alone well tests and fully coupled well-reservoir simulations, including cross-flow scenarios. The approach provides robust, scalable geothermal simulations with realistic well geometries and strong reservoir coupling.

Abstract

We consider a non-isothermal compositional gas liquid model for the simulation of well operations in geothermal processes. The model accounts for phase transitions assumed to be at thermodynamical equilibrium and is based on an hydrodynamical Drift Flux Model (DFM) combined with a No Pressure Wave approximation of the momentum equation. The focus of this work is on the design of a robust discretization accounting for slanted and multibranch wells with the ability to simulate both transient behavior such as well opening as well as coupled simulations at the time scale of the reservoir. It is based on a staggered finite volume scheme in space combined with a fully implicit Euler time integration. The construction of consistent and stable numerical fluxes is a key feature for a robust numerical method. It is achieved by combining a monotone flux approximation for the phase superficial velocities with an upwind approximation of the phase molar fractions, density and enthalpy. In order to facilitate the coupling of the well and reservoir models, the Newton linearization accounts for the elimination of the hydrodynamical unknowns leading to Jacobian systems using the same primary unknowns than those of the reservoir model. The efficiency of our approach is investigated on both stand alone well test cases without and with cross flow, and on a fully coupled well-reservoir simulation.