Debottlenecking Through Produced-Water Partial Processing Unlocks Production

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 187109, “Partial Processing: Produced-Water Debottlenecking Unlocks Production on Offshore Thailand MOPU Platform,” by C.H. Rawlins, SPE, eProcess Technologies, prepared for the 2017 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, 9–11 October. The paper has not been peer reviewed. An operator in the western Gulf of Thailand installed two water-management partial-processing systems on its mobile offshore production units (MOPUs) to increase oil production. Water removed at the production manifold is treated and transferred directly to the injection system, thus bypassing primary separation, transfer piping, fluid heating, and floating storage facilities. Water debottlenecking increased oil production by 80% and reduced the in-field transfer volume by 62%. Introduction In mature oil basins, the ability to sustain oil production depends on managing an increasing volume of produced water. The partial-processing method seeks bulk (not complete) removal of a throughput-constraining phase from oil and gas production using compact processing equipment. Partial-processing technology normally is installed on facilities that have space or weight constraints, where traditional separation technologies will not fit. Fitting within or around existing process equipment, partial-processing equipment maximizes the capability of an existing facility footprint. The constraining phase may be gas or water, and specific technologies are available to address each. The application detailed in this paper addresses produced-water debottlenecking. Removal of the water constraint unlocks production potential from mature or marginal fields and has been shown to increase hydrocarbon production. Design Stages and Setup For water-constrained systems, the most significant benefit comes from the removal of bulk water as far upstream as possible. High-water-cut wells are combined into a discrete manifold that may handle part or all of the field production. The partial-processing system is on this manifold, upstream from the existing process equipment. Debottlenecking at this point opens capacity in the flow lines, transfer piping, and processing facilities. The partial-processing skid can be installed on unmanned platforms with limited utilities and space and weight constraints. Bulk water removal and treatment may have two or three stages. The first stage, preseparation, involves bulk water removal from the multiphase-flow stream. A specially designed liquid/liquid hydrocyclone (preseparator) removes a bulk portion (60–95%) of the water from the flow stream. Next, the removed bulk water passes to the deoiler hydrocyclone, which operates in a standard produced-water-treating mode. For example, the preseparator will reduce oil content from 10 to 0.2%. The deoiler will take the 2,000-ppm oil down to or near discharge quality (20–50 ppm), depending on oil properties, pressure drop, and temperature. A tertiary treatment stage is optional and is used for difficult separation (e.g., cold fluids with heavy oil) or very stringent disposal requirements (e.g., low oil-in-water levels for enhanced-oil- recovery injection). This stage uses a compact flotation unit (CFU) for both degassing and oil polishing. The CFU removes gas effervescing from solution after the deoiler (which can be 5–10% of the gas void fraction) and uses that gas to float the fine oil droplets.