Wellbore Behaviour During Saturated Steam Injection

A mathematical model was formulated to describe the injection of saturatedsteam down oilwell tubing under constant inlet conditions. The system was divided into three parts, consisting of the fluid, thewellbore and the formation. Each part was considered to be a separate system, with the heat flux across the boundaries acting as the coupling parameter. Thewellbore consisted of a tubing string enclosed by either one or two casingstrings. The heat transfer in the wellbore was considered as steady state. Theheat transfer in the formation was treated as unsteady-state radial conduction, and the fluid flow was described by a modified two-phase flow correlation. The analysis resulted in three equations, two of them implicit, which weresubsequently solved simultaneously on the 7040 computer. The solution did notpresent any convergence problems. Although a complete verification of themathematical model was not possible, the calculated temperature profiles weresimilar in shape to an observed temperature profile. Introduction With the cost of finding and developing high-grade crude reservescontinually increasing, more attention is being focused on the development ofhigh-viscosity or "heavy" oil reserves. As the oil viscosity is highlydependent on temperature, a small increase in reservoir temperature decreasesthe oil viscosity markedly, facilitating increased production rates andultimate recoveries. One of the more popular means of increasing the reservoirtemperature is steam injection. To evaluate the feasibility of a thermalproject, a reasonably accurate estimate of the heat losses from the well bore, the sandface pressure and the sandface quality of the steam would be desirable, if not necessary. As the injection times are generally quite small, steady-state solutions would not be very representative and unsteady-statesolutions are required.