A brief communication on the effect of seawater on water flow in offshore wells at supercritical state

Abstract

At present, the study of supercritical water (SCW) flow in wellbores is at the starting stage. In this paper, a simple but useful model is developed to study the effect of seawater on the thermophysical properties of SCW in offshore vertical wellbores. Firstly, based on the momentum and energy balance equations, a flow model describing SCW flow in a tube is established. Then, coupled with transient heat transfer model in seawater and formation, and thermophysical parameters of SCW, a comprehensive mathematical model is established. In order to solve the model, the governing equations are expressed in the form of difference equations. The straight forward numerical method is adopted to solve the model from wellhead to well-bottom. In the process of solving, iterative technique is used to control the calculation accuracy. Finally, type curves of SCW flow in offshore wellbores and sensitivity analysis are discussed. Results show that (a) the flow of seawater results in a rapid decline in the temperature/enthalpy of SCW in wellbores. (b) Heat loss is the dominant factor of physical parameter distribution in wellbores when the injection rate is relatively small. (c) Heat loss has an obvious influence on temperature drop when SCW is sparse in volume. (d) The SCW pressure decreases with increasing of injection temperature. KeywordsHeavy oil recovery • Wellbore modeling • Supercritical water • Effect of seawater • Heat loss rate • Injection parameters List of symbols w SCW The mass flow rate of SCW in offshore wells (kg/s) r ai The inner radius of the inner tubing (m) SCW The density of SCW (kg/m 3 ) v SCW The flow velocity of SHS (m/s) zThe well depth (m) Q SCW The heat transfer rate from SCW to seawater/formation (J/s) h SCW The specific enthalpy of SCW (J/kg) gThe gravitational acceleration (m/s 2 ) The well angle from vertical (rad) fThe shear force in the vertical wellbores (N)