Successful Sand Blockage Removal from Sealine Using an Innovative Plastic Coiled Tubing

Abstract

Sand accumulation occurs in subsea infrastructure and pipelines, also called sealines, when the fluid carrying capacity isn't sufficient. Once this situation degenerates, the maximum achievable production rate decreases till complete stop: a sand blockage is formed and production lost. The first worldwide subsea application for a plastic coiled tubing for sand removal demonstrates the opportunity to think for alternatives and use an innovative technology to avoid expensive pipeline replacement and to restore the production in a quicker and cheaper way. With space upon FPSO units inherently limited, a complex engineering solution involving workover rig or intervention vessel is typically required to support the removal of sand plug or line section replacement. Those options, are inherently expensive, and could shut down the production for a long period and generate additional HSE risks. A preliminary analysis is necessary to identify the sand plug dimension and plan the proper remedial job. In 2014, Operator decides to think for alternatives and performed a smart intervention using an innovative Plastic Coiled Tubing directly from FPSO, washing down the riser and the subsea flowline till complete sand blockage removal. The use of a standard coiled tubing unit isn't an applicable solution for severe limitations in transport and rig/up operations; so the decision is to select and develop a customized ultra-lightweight, highly flexible pipe compared to conventional coiled tubing. On board of the FPSO unit, a continuous improvement process is necessary to optimize equipment layout and configuration. Adjustments in operative procedures and some troubleshooting actions maintain higher the efficiency during the washing and cleaning job through riser and subsea flowline. The final result is the complete sand blockage removal and the hydraulic continuity re-establishment inside the pipeline. The overall process successfully validates the so performed analysis, screening and equipment selection, demonstrating that plastic coiled tubing is a valid and innovative tool for sealines washing and production restoration in a quicker way.