A Method for Predicting Oil Recovery by Steamflooding Including the Effects of Distillation and Gravity Override

Abstract

Abstract This paper describes a semianalytical method for calculating oil recovery by steamflooding. It accounts for effects of steam distillation and gravity overlay of steam. First, the equations for the heat balance and the configuration of the steam/liquid interface are solved simultaneously to predict the volume of the overall heated zone and the volume and shape of the steam zone. Second, the approximate enthalpy and material balances are combined with the thermodynamics of differential vaporization to derive a fully compositional method for calculating the volume and composition of steam-distilled hydrocarbons. Finally, the results of the foregoing are combined with a fluid flow model, similar to Higgins and Leighton's cell model for waterflood analysis to calculate oil recovery.This semianalytical method can account for almost all the important recovery mechanisms involved in steamflooding with relatively small computation time. Good agreement has been obtained between available experimental data and calculations carried out in accord with this analysis. Introduction Significant gravity override of steam has been observed by various investigators in both laboratory experiments and field operations. This layover phenomenon, however, has not been considered in previous analytical methods for calculating steam and hot condensate zone growth. Marx and Langenheim's method, for example, assumes that the condensation front is perpendicular to the reservoir bedding plane, and Mandi and Volek's analysis restricts the shape of the front that can be specified. Although multidimensional numerical simulators have been used for the prediction of such layover phenomena, a relatively simple semianalytical method, acceptable for engineering purposes, was sought to reduce the operating costs purposes, was sought to reduce the operating costs for such analysis.Van Lookeren was able to estimate the approximate shape of the steam/liquid interface by employing the segregated flow principles but did not extend his work to development of a complete prediction model. In this work, a method has been prediction model. In this work, a method has been developed for calculating the shape and growth of the steam and hot condensate zones by taking into account the gravity override of steam on a semianalytical basis.A fully compositional method for calculating hydrocarbon distillation in steamflooding also is addressed in this work. Steam distillation contributes to the recovery of crude oil in steam-drive operations - all the more so as the gravity of the crude increases. Willman et al. and Volek and Pryor attributed the low residual oil saturations (2 to 8%) they encountered in laboratory experiments and field tests to steam distillation, and Wu and Browns also reported the effectiveness of steam distillation in laboratory experiments. Recently, Konopnicki et al. 10 reported that a steam-drive pilot resulted in a residual oil saturation of less than 5% .Johnson et al. presented a method for calculating the amount of hydrocarbon distilled and condensed at the leading edge of the steam zone. But their method did not permit calculation of the composition of the distilled hydrocarbon, which is a factor affecting the solvent displacement mechanism. Ferrer and Farouq Ali reported a compositional thermal simulator, and Coats presented a steamflooding simulation that included distillation and solution gas. Coats considered the crude to be a three-component system in order to reduce the required computation time. SPEJ P. 249