Subsea Application of Viscosity Reducers Improves Operational Efficiencies and Increases Oil Production

Abstract Crude oil emulsions can be challenging to produce due to high fluid viscosities causing increased frictional forces in the tubing and flowlines, resulting in slug flow, production deferment and poor oil / water separation. Through the application of an Emulsion Viscosity Reducer (EVR) chemical some of these challenges can be overcome, while additional benefits can be achieved. This paper will present examples of EVR applications offshore in the North Sea that enabled increased oil production. The Emulsion Viscosity Reducer was injected via subsea umbilical to a flowline or through the gas lift system into the production tubing downhole. Various parameters such as produced fluid viscosity, bottom hole pressure, well and flowline slugging, and oil production were monitored. The chemical injection rate was optimised based on the monitored parameters. Trials were performed with the chemical injection stopped and re-started so that the effect of the emulsion viscosity reducer is confirmed against numerous baseline data sets. In one of the examples, the performance of a newly developed combination EVR-wax inhibitor product is detailed. Injection of EVR resulted in reduced viscosity fluids being produced and as such various positive effects were observed including reduced bottom hole pressure, mitigation of slugging, choke opening being enabled, increased oil production, improved oil / water separation in the process and reduced flaring. Significant increases in oil production were observed. In the example where the combination EVR wax inhibitor was injected, evidence of improved wax inhibition efficiency compared to the wax inhibitor chemistry alone was observed. The combination of a slight increase in fluids temperature due to shorter transit time as a result of increased and more consistent flow, and the surface-active nature of the EVR chemistry led to the observed improvement. Through this work production parameters which indicate if a well or flowline may be suitable for an EVR application were identified and the benefits of such an application may be quantified. We also introduce the concept of a tool which can estimate the potential uplift in oil production given specific well and production parameters, resulting in methods for other oil and gas production facilities to re-produce similar operations and increase production efficiency.