Surfactants may be one of the best options to improve recovery from geologically challenging reservoirs. For over forty years, concepts and results of surfactant applications have been published. During recent years, depressed oil prices have limited surfactant consideration. However, surfactant recovery can be economically attractive for reservoirs where recovery is dominated by gravity and imbibition processes. Massive and/or fractured formations of moderate 30-50% recovery may warrant consideration for surfactant processing. Applications must meet laboratory performance hurdles for high incremental recovery at relatively low surfactant concentrations (quantified wettability and bond number). Placement of chemical in the reservoir at optimum concentration is the next challenge. This paper presents analytical and simulation assessment of chemical placement within a massive fractured carbonate formation undergoing surfactant EOR field testing. Placement methods can range from continuous injection to interrupted "huff-n-puff' application. The gravity stabilized reservoir management process currently being applied in the reservoir avoids some of the chemical flood conformance challenges of classic applications.

Oil mobilization by surfactant huff-n-puff in a naturally fractured reservoir is a complex process. The success of the application depends not only on surfactant chemical and physical properties and surfactant concentration injected, but also on fracture surface area treated by chemical solution and penetration depth of surfactant into matrix rock. In order to optimize the design of a dilute surfactant treatment in the Yates Field, an analytical model was developed to investigate effects of various parameters on the fracture surface area treated and penetration depth of surfactant solution into matrix block. These parameters include surfactant injection rate, injection volume, chemical diffusion, convection and fracture properties. Results of the analytical application are compared to simulator solutions. Laboratory testing, formation target screening, and field application are also discussed.

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