Theoretical Analysis of Gravity-Controlled Waterfloods

Abstract

The concept of dumpflooding is to flow water from a high pressure aquifer zone to a low pressure oil producing zone by natural force of gravity through a well connecting the two zones to enhance oil sweep into a producing well. The research described is aimed to find solutions to one of the flaws in dumpflooding that is, the inability to quantify the rate of water injection from a high pressure aquifer zone to a low pressure oil producing zone. Theoretical dumpflood equations were developed for evaluating the rate of water injection from an aquifer into various types of oil reservoirs. Two cases were considered in the development of the rate of injection equations, which were; water from a finite aquifer injecting into a finite oil reservoir and water from an infinite aquifer injecting into a finite oil reservoir. In each case, the theory is applied to undersaturated oil reservoir as well as oil reservoir with a gas cap. A simple single-well model was built using Excel Spreadsheet to solve the rate of injection equations by Bisection iteration technique. Graphical sensitivity analysis ascertained in both cases that, the rate of water injection increases as productivity index increases at constant time interval, however, there is a decline in rate of injection for constant productivity index as time increases. In conclusion, the rate of water injection recorded in both cases higher values in the finite oil reservoir with gas cap compared to the finite undersaturated oil reservoir because, large amount of water goes into compressing the gas cap gas. The boundary pressure in the finite aquifer zone depletes much faster compared to the infinite aquifer zone.