Summary This paper describes a thermal wellbore model that simulates flow hydraulicsin the wellbore and heat transfer between the wellbore fluid and theoverburden. The thermal wellbore model includes the transient differentialequations for multicomponent three-phase fluid flow in the wellbore and thetransient heat conduction equation in the overburden. Phase behavior of thewellbore fluids is obtained from isenthalpic flash Phase behavior of thewellbore fluids is obtained from isenthalpic flash calculations, which computethe phase splits and compositions at a specified pressure and enthalpy. Thewellbore and overburden equations in the entire discretization domain aresolved simultaneously with a fully implicit Newton's method. The thermalwellbore model was validated with steam-injection and gas-condensate productionfield data. The calculated heat losses and pressure drops compared favorablywith published models. The thermal wellbore model is also used to predict thecritical production rate of methane above which hydrate will not form.
Introduction Steam-injection processes have been very successful in recovering heavy oilfrom hydrocarbon reservoirs and also have been shown to increase oil recoveriesfrom light-oil reservoirs. The increased application of thermal methodsemphasizes the importance of optimal thermal wellbore designs and efficientfield operations for injectors and producers. Wellbore design requires the useof two-phase flow correlations to predict wellbore hydraulics. Depending on theflow pattern, different equations are used to calculate the liquid holdup andfrictional pressure drop. For problems in which the phase behavior of the fluidis temperature-sensitive, a compositional approach to two-phase flow ispreferable to the traditional black-oil method. This paper describes a thermalwellbore model that simulates flow hydraulics in the wellbore and heat transferbetween the wellbore fluid and the overburden. The fluid can flow downward orupward. Fig. 1 shows a temperature profile across a typical wellbore assembly. The thermal wellbore model includes the transient differential equations forthree-phase multicomponent fluid flow in the wellbore and the transient heatconduction equation in the overburden. The phase behavior is obtained from anisenthalpic flash algorithm, which computes the phase splits and compositionsat a specified pressure and enthalpy. The fluid flow honors two-phase flowcorrelations, which are extended to model three-phase flows. The wellbore andoverburden equations in the entire discretization domain are solvedsimultaneously with Newton's method. Because the resulting Jacobian matrix islarge and has a different number of equations for wellbore and overburdenmatrix blocks, an efficient and flexible solution method is used.