Cyclic Steam Reservoir Model for Viscous Oil, Pressure Depleted Gravity Drainage Reservoirs

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract An improved cyclic steam reservoir model has been developed which allows the calculation of steam injection pressure and temperature as well as steam quality. In addition producing rates of oil and water are calculated with consideration given to cumulative effects of changing temperature, fluid levels, relative permeability, fluid viscosities, and fluid saturations. permeability, fluid viscosities, and fluid saturations. A comparison of calculated performance with field results of seven consecutive steam cycles in a well located in the Midway Sunset field in Western Kern County, California is presented. The calculated performance is in excellent agreement with field reports in virtually all areas. The model is presented with simplified mathmatics by subsitituting empiracle equations for rigorous integral equations in several places. places Introduction The literature contains many reports of analytical and numerical reservoir models which may be used to calculate the response of a steam stimulation project. Boberg and Lantz provide a very good method for tracing the temperature history of thermally stimulated wells. However, the method used to predict fluid production is limited to use in reservoirs with relatively light oil and high primary productivity. Kuo, Shain, and Phocas do not address the performance of individual steam stimulation performance of individual steam stimulation cycles. Seba and Perry address gravity drainage but also employ several limiting assumptions. These include constant hot zone radius and temperature and harmonic decline in oil production which may or may not match the decline in areas other than Yorba Linda. Closmann, Ratliff and Truitt studied the effects of changing fluid saturations and crossflow in a cyclic well but simplified the heat loss mechanism and ignored gravity drainage. Williamson, Drake and Chappelear treat the effects of transient relative fluid saturation and viscosity vs temperature in individual wells but the model is designed specifically for use in a numerical isothermal reservoir simulator. In the above abreviated literature survey no provision was found for calculating injection pressure and the associated temperature. pressure and the associated temperature.