A Comparison of Mass Rate and Steam Quality Reductions To Optimize Steamflood Performance

Abstract

Abstract Most mature steamflood projects have the heat injection rates reduced to minimize fuel costs and extend the economic life of the project. However, there is little industry project. However, there is little industry consensus on whether the heat cuts should take the form of 1) mass rate reductions while maintaining the same high steam quality, or 2) steam quality decreases while keeping the same mass rate. using a commercial three-phase, three-dimensional simulator, oil recovery schedules were generated for several steam mass rate and quality reduction cases under a variety of reservoir and operating conditions. The results indicated that for equivalent heat injection rates, decreasing the steam injection mass rate at a constant high quality will yield more economic oil than reducing the steam quality at a constant mass rate. A sensitivity analysis confirmed this conclusion and demonstrated the importance of the gravity drainage/steam zone expansion mechanism in a low-pressure, heavy oil steamflood with gravity segregation. Furthermore, the impact of discontinuous silts and non-uniform initial temperatures within the steamflood zone was studied, again indicating that a decreasing mass rate injection strategy is a superior operating practice. practice Introduction Heat injection rates are routinely reduced as a steamflood project approaches its economic limit. The major benefit of this practice is to reduce the fuel costs and thus extend the economic life of the project. Furthermore, there is evidence that frequent reductions in the heat injection rate are both theoretically sound and economically advantageous in steamflooding operations. There are two general approaches to accomplishing these reductions:cutting the mass rate of the injected steam while maintaining the same high quality; andreducing the steam quality while keeping the same mass rate. However, there appears to be no industry consensus on which heat reduction process should be applied under a given set process should be applied under a given set of reservoir conditions, and operators will often follow different steam injection rate or quality strategies within the same field. This study examines the recovery consequences of reducing mass rates and steam qualities using a thermal reservoir simulation program. The simulator input was validated for Kern River Field conditions by using the guidelines developed by Johnson, et al. PREVIOUS WORK PREVIOUS WORK Several investigators have studied the effect of varying the heat injection rate with time in thermal recovery projects. Chu and Trimble conducted a reservoir simulation study using a three-dimensional, three-phase numerical model for steam displacement. By using the concept of cumulative discounted net oil (CDNO), they found that the economic performance of a steamflood could be improved performance of a steamflood could be improved over the constant rate injection case by increasing the steam rate in the initial stages and decreasing the steam rate with time. In all cases, the steam quality was held constant at 70%. While they mentioned that further work was needed to determine the optimal variations of steam rates, a hyperbolic decline was superior to a linear variation. P. 449