Abstract
Currently, one-third of the heavy oil production in Trinidad and Tobago comes from the land areas; where steam- flooding has been the preferred method of oil recovery. Guapo Thermal Scheme is such a heavy oil reservoir. However even after thirty [30] years of steaming oil recovery is only about twenty (20) percent as a result of low sweep efficiency, steam override, by-passed oil and low reservoir energy.
A well-known analytical model for thermal oil recovery processes, which determined the volume of the steamed zone, was used previously for predictions but this was upgraded to a fully explicit three dimensional model, which tracked the movement of reservoir fluids over time from inception of the steam-flood. This dynamic model was efficiently prepared using modern, state-of-the-art computers and modern simulation software. The simulated results showed that oil, water and steam banks developed and these propagated through the system in 3 dimensions. This paper shows how reservoir simulation led to the determination of the location of remaining oil and successful drilling in the Guapo Thermal Scheme, Trinidad.
Guapo Thermal Area is situated along the south west coast of Trinidad, West Indies. See Fig. 1. Steam flooding commenced in 1980. Wells were "huff and puff" initially. In 1990, the wells in the area of focus of this paper, Fault block F15BK5, experienced problems of: low steam injection, damaged casing, low fluid levels damaged liner and plugged perforations and coupled with low oil prices at that time resulted in steam injection being discontinued. Past production figures and response maps showed that the former injectors were not in communication with some off-takes suggesting an alternate faulting system. This fact was supported by a new 2D seismic / geological interpretation by C. Bhagirath and T. Andrews 2006. The study showed that the area lies within a composite incised-valley system with predominant prograding clinoforms that are elongated in a NE-direction. Reservoir simulation of this complex area led to the determination of location of remaining oil in Fault Block, F15BK5. The simulation results, which showed present day oil saturations were used in the selection, prediction and successful drilling of two [2] wells in the Guapo Thermal Scheme, Trinidad.
