Subsea Demulsifier Injection to Reduce Emulsion Viscosity and Enhance Crude Oil Production

Abstract

Abstract Water-in-oil (w/o) emulsions are formed during the simultaneous flow of oil and co-produced water through the well and production pipelines. The viscosity increment due to stable w/o emulsion formation may lead to important production losses as friction pressure drop increases. The emulsion viscosity is affected by a number of factors, such as water content, oil viscosity, temperature, droplet size and the presence of solids. Rheological evaluations using synthesized emulsions of different Brazilian crude oils at different water contents showed the viscosity of a w/o emulsion at 50% water cut is about 5 to 9 times that of the oil and about 6 to 90 times at 70% of water cut. The experimental works presented here shows that emulsion breaker treatment is a good alternative to reduce crude oil emulsion overall viscosity and, consequently, improve production. This paper investigates this effect in two wells from Campos Basin, offshore Brazil. For these two wells, field implementation of subsea demulsifier treatment resulted in a 47% additional oil production uplift, an increase of 3,000 bbl/d for the Company. Besides, these subsea chemical injections also promoted flow stabilization which allowed the opening of the production choke, restrained due to slug flow limitations at the top side treatment unit. Despite the good results, further investigation was conducted to understand differences in oil production increment from each well. Thus, new laboratory tests (bench and flow loop) and multiphase flow simulations were performed based on field data in order to evaluate the difference in demulsifiers performance considering the fluid and flow characteristics. The results have shown that higher oil production is observed in wells that produce stable emulsions above 30% water cut, flowing with Reynolds number lower than 105. The additional oil production obtained in the field and confirmed by multiphase flow simulations at steady-state and transient regimes occurred primarily by the reduction of the frictional pressure drop. Secondary effects included flow stabilization, which allowed the choke opening and the consequent top side pressure reduction. As crude oil emulsions are formed in most all oil production systems in its lifetime, the emulsion breaker’s subsea injection implementation is a concealed production uplift opportunity. The novelty of this study is in the discussion of the ability to define a criterion to select chemicals and wells to improve crude oil production in offshore systems.