Edward J. Grave

Performance Testing of an In-Line Electrocoalescer Device with Medium and Heavy Crudes

Introduction Dehydration plays a fundamental role in the production and processing of crude oil. The removal of water from heavy crude is a challenge for many oil-processing facilities, even when only topside applications are considered (Moraes et al. 2013). It can also pose a big challenge for processing medium crudes, and in general for any highly emulsified hydrocarbon liquids, such as those obtained from high-pressure applications and enhanced-oil-recovery (EOR) processes. Besides using mechanical means to separate water from oil, other common methods of enhanced dehydration include heating, use of chemical demulsifiers, and electrostatic treatment (Silset 2008). Other possible techniques are pH adjustment, filtration, and membrane separation (Eow et al. 2001). Heat treatment can effectively destabilize water-in-oil (WIO) emulsions; however, it is also energy intensive and typically results in a larger system footprint. Capital and operational expenditure can be considerable in conventional applications (Pruneda et al. 2005), and the use of heat treatment is either economically unattractive or impractical in subsea, Arctic, remote, or marginal field applications. Further, the solubility of water in oil increases with temperature. As the oil cools during transportation, free water drops out in the pipeline, which could cause flow-assurance issues. Besides this, heat treatment causes volatile hydrocarbons to flash out of the liquid phase, which can result in appreciable volume shrinkage and API-gravity reduction in the heated crude oil (Manning and Thompson 1995). This means that there is a practical and economical limit in the amount of water that can be removed from crude oil through the use of heat treatment alone. For this reason, a combination of heat treatment and demulsifiers is by far the most-common method of enhanced dehydration because many crude-oil emulsions become unstable when treated with the right type and concentration of demulsifier (Arnold and Stewart 1998; Caird 2008; Kelland 2009) at high temperature. While chemical treatment requires a relatively lower capital investment and less energy than heat treatment, it can bear a considerable operating cost, and ensuring an uninterrupted supply of chemicals to the production site can be challenging. While the supply of chemicals to any production facility can be expensive and sensitive to changes in weather conditions, market availability, or political factors, the supply of chemicals to subsea, Arctic, remote, or marginal field applications is a far greater logistical and economical challenge. Electrostatic treatment can be effective at breaking WIO emulsions. It is also one of the most energy-efficient methods used for destabilization of WIO emulsions (Eow et al. 2001), and is considered an enabling technology for the subsea separation of produced water from heavy oil in deepwater developments (Euphemio et al. 2007). When it is used in combination with chemical and/or heat treatment, it can improve the economics of the production facility by reducing the overall energy consumption, by reducing the use of chemical demulsifier, or both. The electrical field produced by an electrostatic coalescer affects the morphology of WIO emulsions because of the polarization of dispersed water droplets in the oil Copyright