Investigation of Surfactant-SAGD Process in Fractured Carbonate Reservoirs

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Abstract

Abstract SAGD is a very promising recovery process to produce heavy oils and bitumen resources. The method ensures both a stable displacement of steam and economical rates by using gravity as the driving force and a pair of horizontal wells for injection/production. Surfactant injection for improving conformance and increasing oil recovery has been successfully employed in a number of steam injection operations. Successful application of foaming surfactants to control injection profiles in steam processes has been reported and their use to limit steam flow through depleted zones of the reservoir during steam process has been proposed. This study was carried out to develop a methodology for SAGD studies and provide some understanding of the performance of foam forming surfactants in the SAGD process applied to fractured carbonate reservoirs. A total of 6 experiments were performed to study the effects of fractures and surfactant on SAGD process in a 3-D model using 18 ? API gravity crude oil. 30 cm × 30 cm × 10 cm rectangular box shaped model was used with horizontal injection-horizontal production well pair configuration. Temperature distributions, the rise and growth of the initial steam chamber were observed by using 25 thermocouples. Clean crushed limestone was mixed homogeneously with water to provide the conditions of waterwet system. Viscous crude oil was introduced to yield the desired fluid saturations and the mixture was packed into the model. The effect of fracture orientation (vertical or horizontal) and surfactant concentration on steam-oil ratio (SOR) and oil recovery was studied using horizontal well pair scheme. In Surfactant-SAGD process, maximum oil recovery was observed using horizontal injection-horizontal production well scheme with fractures due to favorable steam chamber. The fractures gave significantly higher steam-oil ratios than those observed in the uniform reservoir model. The injection of surfactant from injector was attractive for mobile heavy oil by strong foaming and flooding functions at the initial stage when pre-heating effects were not enough. Surfactant-SAGD process was shortened the lead time and enhanced oil production rate after steam breakthrough. Introduction Steam-assisted gravity drainage (SAGD) is a very promising recovery process to produce heavy oils and bitumen resources. The method ensures both a stable displacement of steam and economical rates by using gravity as the driving force and a pair of horizontal wells for injection/production. In the SAGD process, this is achieved by drilling a pair of horizontal wells. Typically, the two horizontal wells are located at a short distance one above the other. Steam is injected into the upper well and hot fluids are produced from the lower well. This progressively creates a steam chamber, which develops by condensing steam at the chamber boundary and giving latent energy to the surrounding reservoir. Heated oil and water are drained by gravity along the chamber walls towards the production well 1,2,3,4. Figure 1 shows a vertical section through a rising steam chamber for conventional SAGD and surfactant-SAGD processes. During the rise period, the oil production rate increases steadily until the steam chamber reaches the top of the reservoir.

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