Initial ESP designs for the Stag oil field, located on the Australian Northwest Shelf, were based on a low GOR, high viscosity, 19 API, crude oil. However, higher than forecasted gas rates and gas-oil separation in the 3300 ft long horizontal production sections resulted in flow from the reservoir in the form of slugs of gas and oil. Then, with the onset of water production, high volumes of produced sand compounded the problems. These two main issues, plus a rapidly declining reservoir pressure, have combined to present a challenging ESP production environment.
This paper reviews in detail the evolution of the completion design, focusing mainly on the ESP design, which initially ran for only 191 days, but now averages 511 days.
The intent of this paper is to provide advice to be considered when designing ESP completions for new reservoirs, to provide an example of a good completion design for handling fluids with high ratios of gas and sand, and finally, to provide information on new technology developments that have evolved from these learning experiences.