Correlations for Predicting Oil Recovery by Steamflood

Abstract

Reservoir simulation was used to develop a set of correlation charts for predicting steamflood oil recovery and oil/steam ratio as functions of predicting steamflood oil recovery and oil/steam ratio as functions of reservoir characteristics and operating conditions. The correlations emphasize the effects of steam quality, mobile oil saturation, reservoir thickness, and net/gross ratio. Introduction Heavy-oil properties that classify as candidates for steamflooding often need to be screened for priority ranking due to budget, manpower development and permitting limitations. Also, sensitivity studies often permitting limitations. Also, sensitivity studies often are run on steamflood projects to determine the effects of various operating strategies on project performance and economic feasibility. Steamflood performance and economic feasibility. Steamflood performance predictions required in such screening performance predictions required in such screening and sensitivity studies certainly can be made using one or more of the analytical and empirical models available in the literature. Numerical reservoir models that simulate the process of steamflooding also can be used to make the required predictions. While these analytical and/or numerical models could suffice, they generally require somewhat lengthy computations and necessitate the use of a computer. There is a need for a simplified easy-to-use method for predicting steamflood performance. This paper describes the development of such a method and its basis, procedures, and limitations of applicability. Basic Concept and Assumptions The basic concept of the method is to define the minimum set of parameters that have the most influence on steamflood oil recovery and are easy to determine for any given project. Oil recovery then is determined as a function of these parameters using field data and/or numerical simulation. Generalized correlations or charts are prepared from these results and used for prediction purposes. In a steamflood, oil recovery should be dependent on (1) rock properties such as permeability, porosity, compressibility, relative permeability, capillary pressure, and net/gross ratio; (2) fluid properties pressure, and net/gross ratio; (2) fluid properties such as specific gravity, viscosity, compressibility, and PVT relationships; (3) flood geometry such as pattern shape, spacing, and sand thickness; (4) pattern shape, spacing, and sand thickness; (4) thermal properties such as thermal conductivity, heat capacity, and thermal expansion; (5) reservoir conditions such as initial oil saturation, temperature, pressure, and residual oil saturation after pressure, and residual oil saturation after steamflood; and (6) injection conditions such as rate, pressure, and steam quality. pressure, and steam quality.Because most steamflood applications are focused on shallow heavy-oil-bearing sands, typical unconsolidated sand characteristics were used in this work. This meant that parameters such as absolute permeability, capillary pressure, compressibility, permeability, capillary pressure, compressibility, thermal properties, and fluid properties were not considered as variables in the development of these correlations. Instead, these parameters were fixed at acceptable typical values. In most projects, reservoir temperature and pressure prior to steamflooding generally are low. pressure prior to steamflooding generally are low. JPT P. 325