Semianalytical thermal model for linear steam drive.

摘要

Thermal recovery by steam injection has proven to be an effective means of recovering heavy oil. Forecasts of reservoir response to the application of steam are necessary before starting a steam drive project. A semianalytical model (SAM) has been developed for one-dimensional linear systems and two-dimensional linear cross-sectional systems. Wells are located at both ends of the reservoir. At the injection well, wet steam is injected at a constant rate and enthalpy. The production well produces at a constant flowing bottomhole pressure. The SAM includes formation dip, compressible formation, water, and oil, and thermal expansion of the formation,water, and oil. The model automatically calculates the steam zone steam saturation and includes the water front and overburden heat losses. The two-dimensional model also includes gravity override of steam. The system of equations is solved by iterating on the injection well pressure. For each iteration, the lengths of the steam, water, and oil zones are determined. The pressure drop is calculated for each of these zones and at each well to compute the production well pressure. This value is compared to the production well boundary condition, and iteration continues until convergence is achieved, usually in five iterations. In the process, front locations, temperatures, pressures, and phase saturations are determined for each of the zones. Since the temperatures and pressures are computed, the compressibility and thermal expansion of the rock, oil, and water can be considered. Oil and water production rates are calculated by material balance. In the two-dimensional model, a new empirical method is presented which determines the shape of the steam front, and an extension of an existing water flooding correlation is used to determine the volumetric sweep efficiency for the reservoir. 56 refs., 72 figs., 15 tabs.