A Comprehensive Simulation Study of Steamflooding Light-Oil Reservoirs After Waterflood

Abstract

Summary Steamflooding, the most successful among enhanced recovery methods, has been applied mainly to heavy-oil reservoirs. This paper presents a comprehensive simulation study on the use of steamflooding after waterflood in light-oil reservoirs. Some important observations are made on this new application of the process. Guidelines are developed not only for selecting reservoir candidates for steamflooding, but also for designing and operating steamfloods in watered-out reservoirs. Relative importance of key mechanisms to oil recovery is also discussed. Introduction The use of steamflooding as a tertiary recovery method for light-oil reservoirs after waterflood has been of interest in recent years. Although steamflooding applied to heavy-oil reservoirs has been a fully proven method, the technology of applying it to light-oil reservoirs, especially those that have been watered out, is still in its infancy. This paper will answer the following questions that remain about steamflooding.Can watered-out light-oil reservoirs perform as well as heavy-oil reservoirs under steamflooding?What kind of reservoirs will be suitable for steamflooding after waterflood?How would one design and operate a steamflood once a reservoir is chosen?What are the main recovery mechanisms in this process? Several authors have made simulation studies on steamflooding light-oil reservoirs. Aydellote and Ramesh studied steamflooding economics with variations in oil composition, permeability, depth, pattern type, well spacing, and steam injection rate. A uniform fluid saturation was used at the start of the steamflood. Hanzlik improved on this work by preceding the steamflood with a waterflood that generates a nonuniform fluid saturation before steamflood starts. Both waterflood and steamflood were considered to take place in the same 5-acre [2.0-ha] five-spot patterns. He studied the effects of oil composition, reservoir thickness, and steamflood timing on steamflood performance. Hongs studied steamflooding the light-oil reservoir at Buena Vista field, CA, using a uniform fluid saturation at the start. This work starts with a 40-acre [16.2-ha] waterflood that is later converted to steamfloods with smaller patterns. A three-dimensional multiphase thermal recovery simulator with nine-point finite-difference formulation was used so that the grid orientation effect was greatly reduced in the simulation of steamfloods in five- and nine-spot patterns. A large number of reservoir oil and rock properties and also a large number of steamflood design and operating variables were considered. The following were developed: general observations on the process, guidelines for selecting candidates for steamflooding after waterflood, guidelines for designing and operating steamfloods, and relative importance of the various key mechanisms to oil recovery.