ESP Performance Enhancement Using Multiphase Ejector to Reduce and Recover Casing Pressure as Sales Gas

Abstrak

The major issue of mature offshore facilities along ESP well operations, atmospheric casing venting has been performed as a quick guideline to prevent gas lock occurrence. Considered as field rule of thumb, this practice is able to optimize well production substantially by maintaining the desirable fluid level above submersible pump intake. In order to overcome both operational and environmental excellence, this paper deliver the extensive design, selection, sizing, and application of multiphase ejector to address: casing pressure reduction, ESP performance enhancement without loss flow phenomenon due to gas lock, and emission reduction by recovering casing gas as sales gas.

Energy-efficient solution of multiphase ejector for ESP is developed using fluid dynamic modelling. Transient mode of “k-epsilon” approach is being applied during the computational process to accommodate fully turbulent flow phenomenon whereas occurred along mixing chamber between high pressure motive fluids attracting low pressure casing gas. The eddy viscosity formulation is used to account the transport effect of the turbulent shear stress inside multiphase ejector. Once computational fluid dynamic complete, field fabrication and workshop test is being conducted prior to field commissioning to obtain the best ejector performance. Benefit from tree cap of ESP wells, high pressure motive fluid is being used to generate vacuum effect inside ejector, attract low pressure casing gas, and displace the flow to medium pressure destination of pipeline network.

In general, gas lock phenomenon occurred in several ESP well along baturaja carbonate reservoir with depth± 2500-2700ft TVDS and sand thickness ± 40ftTVD. Based on data shown in this paper, multiphase ejector is designed to attract the accumulated casing gas using heavy (18API) and viscous (35cp) motive fluid. The customized “Y-type” ejector succeded in lowering casing pressure of ESP-G6 well up to 15 psig followed by a wider ESP operability in terms of frequency, higher pump discharge, and a  table motor temperature. This solution reliable to deliver an instant rate of 61 MCFD of casing gas without any further atmospheric casing venting application preventing further occurrence of gas lock phenomenon and better ESP operability shown by the intermittent flowing patterns.Success story of the “Y-type” ejector is the unique ventury entrance of motive fluid to disperse heavy fluid delivering suitable choke condition and vaccuum effect inside the mixing chamber of ejector. Therefore A stable ejector operations is important to be maintained as a assurance of the continuous vaccuum effect.