Optimization of Cyclic Steam Stimulation (CSS) Under Geomechanics-Dependent Permeability

Abstract

AbstractObjectives/Scope:Since its accidental discovery in Venezuela during a steamflood procedure, and despite the high costs associated with using steam. CSS has been widely used throughout the world in heavy-oil reservoirs, especially in Alberta, California, and Venezuela. It has turned out that it is also important to understand the degree of impact of geomechanics as it is a key parameter in reservoirs with geomechanical response. This makes the optimization process more valuable in terms of the application of crucial operational constraints and parameters, such as injection rate, cycle size, cycle life, and well spacing, not only for the reservoir but also the wellbore, which are important for delivering steam to the subsurface while ensuring minimum heat loss along with reservoir integrity and permeability variation.Methods, Procedures, ProcessThe CSS recovery method is influenced by complex reservoir geologies, where a CSS well can penetrate multiple layers having significantly different properties, including permeability. It is important to have a solid understanding of the impact of multiple layers on recovery when using CSS, not only to help maximize recovery but also net-present value because of the high cost of steam generation. In this study, a commercial full-physics reservoir simulator is used to simulate the effect of multiple layers with varying permeabilities under different operating conditions.Results, Observations, ConclusionsCSS helps to increase recoveries up to 20 to 25% by means of certain mechanisms, including but not limited to viscosity reduction thermal expansion of oil, blocking removal, and gravity drainage. Although it is generally valid that higher steam qualities and shorter soak times provide higher recoveries, the main stages of cyclic steam stimulation (CSS)—injection, soaking, and production—should be carefully optimized because the efficiency of this technique is reduced after the first few cycles. The influence of geomechanics turns out to be a significant parameter in this process.Novel/Additive InformationThe results and sensitivities are compared and discussed in light of a comprehensive literature review of CSS with different process optimization methods, including sequential CSS and cumulative average daily profit methods. The significance of all major parameters are outlined using tornado charts to serve as a practical example for optimization of similar future applications.