Boscan Field_Highly Deviated Wells to Avoid Water Production in a Heavy-Oil Reservoir Influenced by an Active Aquifer

Abstract

The Boscán field is a giant heavy oil reservoir (10° API) located in western Venezuela. The field is operated by the Empresa Mixta PetroBoscán. OOIP is estimated as high as 35 billion barrels. For over 60 years of production history, only ~5% of the OOIP has been recovered thereby considerable development opportunities remain at Boscán to increase recovery. Drilling highly deviated completions has proven to be a successful strategy to maximize oil recovery and mitigate ever increasing water production. The southern part of the reservoir is in contact with an active aquifer where a high contrast in fluid viscosity is present between formation water and heavy oil (0.7 vs. 350 cP) generating large differences in the mobility ratio. This causes premature water breakthrough and sharp increases in water cuts over short periods of time. Water production during the last 10 years has exceeded the handling, separation and injection capabilities at Boscán leading to a significant number of wells being prematurely shut-in. In the past, in order to control water production, shorter vertical wells were drilled and bottom water shut-off jobs were performed. However, these strategies have proven unattractive since overall net pay was reduced and coning tendencies were high. A new strategy was introduced of drilling highly deviated wells to maximize the reservoir exposed and mitigate water production by reducing pressure drawdown in the near wellbore region. Recently, a ~5.5 million upscaled grid-block reservoir simulation model was developed and is being utilized to understand the aquifer impact and for optimal field development. Initial simulation results confirmed that highly deviated wells perform better and delay water conning. This paper focuses on a deviated well strategy to increase recovery per well from a heavy oil reservoir with a strong aquifer influx. It shows how multi-disciplinary teamwork is being utilized to develop and execute the strategy and how Boscán may be used as an analogy for other fields having similar reservoir conditions.