Abstract

Many challenges are encountered when separating oil and water in onshore and offshore production trains. The challenges include presence of stable emulsions, increased water cuts, small water droplets due to high shear or pressure drops, and/or high crude viscosities. These issues can have a significant negative impact on the separation efficiency if not addressed properly. The conventional way of addressing these issues usually involves a combination of high process temperatures, high chemical dosages, large vessels and/or increased number of separation stages. Conventional solutions often demand increased energy consumption, higher material costs, larger operating costs, more weight and/or larger space requirement for the production facility. Furthermore, conventional solutions are not always practically feasible, due to restricted energy availability or space restrictions.

Early stage implementation of electrocoalescence through VIEC (Vessel Internal Electrostatic Coalescer) technology allows for a much more efficient and cost effective means of resolving the challenges in the separation train. The VIEC technology was the OTC “Spotlight on new Technology” award winner in 2004 and has since then been implemented in several major projects.

The VIEC technology applies high voltage electrical fields to promote droplet-droplet coalesce, thus greatly speeding up and enhancing separation efficiency. VIEC technology combines fully insulated electrodes with a low voltage feed and distribution inside the separator shell. Due to these characteristic features, the VIEC technology can tolerate any water cut and presence of gas, as opposed to conventional electrocoalescers. Consequently, the technology enables use of the powerful mechanism of electrocoalescence in any three-phase separator to speed up separation efficiency and resolve emulsion problems.

VIEC Technology will reduce the BS&W out of a given separator, increase capacity of an existing separator or enable a more compact separation solution for a given throughput of crude. Additional benefits include production at higher viscosities and at lower temperatures and improved level control due to reduced emulsions layers. Furthermore, consumption of demulsifier is often seen to be reduce significantly, when electrocoalescence is applied compared to conventional separation.

The paper will give a detailed presentation of the mechanism of electrocoalescence and how it is implemented in the VIEC technology. The paper will focus on how to predict electrostatically enhanced separation performance by combining laboratory testing with separation modelling, to give representative predictions of separation benefits and allow for designing solutions custom-fitted to specific separation challenges. A specific case from the Gulf of Mexico will be presented, where an existing TLP was retrofitted with VIEC technology to increase its capacity and enable a tie back from a nearby reservoir.

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