A Study of Enhanced Heavy Oil Recovery by Two Well Cyclical Steam Assisted Gravity Drainage (TWC-SAGD) in Conventional and Fractured Reservoirs

Abstract

Steam-assisted gravity drainage is one of the most promising strategies to develop huge heavy oil and bitumen accumulations. Like the other thermal processes, this method aims at reducing oil viscosity by increasing the temperature. But in an economical point of view, it requires a great volume of steam for injection. Moreover, early breakthrough of steam and high steam-oil ratio makes it uneconomical, especially in long production time. In this study, a new method, two wells cyclical steam-assisted gravity drainage is compared with a conventional steam-assisted gravity drainage process. Well configuration in two wells cyclical steam-assisted gravity drainage is the same as the steam-assisted gravity drainage process, but injection and production is cyclical with soaking time, like cyclical steam stimulation. Simulation results showed that two wells cyclical steam-assisted gravity drainage has a higher recovery and lower steam-oil ratio. Especially in long production times, two wells cyclical steam-assisted gravity drainage becomes more and more economical. The cyclical nature of this process gives enough time for a high temperature front to spread in the soaking time and much less steam volume is required for injection. The effect of existence of horizontal and vertical fractures, fracture spacing, and fracture density on the two wells cyclical steam-assisted gravity drainage process was investigated. It was found that vertical fractures improve two wells cyclical steam-assisted gravity drainage performance, but horizontal fractures decrease oil recovery. Furthermore, horizontal fractures between injector-producer wells had an insignificant effect on this process.