Halite scaling has a dreadful impact on production pipelines. Produced water from Nubia formation in "E" field has high level of total dissolved solids (TDS) concentration. Halite scale causes complete blockage of the flow paths, integrity complications and periodic production interruption. Pipeline pigging and flushing with fresh water were performed frequently to eliminate blockage and restore production.
An offshore platform with six online gas lifted wells; two high rate wells are producing from Nubia formation through the production pipeline and the remaining low rate wells are producing from other formations with a lower TDS through the test pipeline. High saline water flows through the production pipeline and cools down to seabed temperature resulting in halite precipitation, which regularly blocks the pipeline and requires repetitive fresh water flushing and pigging operations. Laboratory water analysis and scale tendency were conducted in conjunction with a pipeline network model to predict the halite precipitation temperature, actual friction coefficient and optimum fluid mixing and dilution strategy.
The combination of complete water analysis, scale tendency, real time remote monitoring system and pipeline network modeling showed that halite scaling started inside the subsea pipeline nearby the platform. The model matching revealed a high friction coefficient, which indicated partial plugging of the production pipeline. The model sensitivity analysis predicted that diluting the supersaturated water by mixing it with other wells’ lower salinity waters – into the same pipeline, would drop the mixture salinity with no halite scaling along the pipeline. As a result, the strategy of mixing was selected and optimized based on the modeling results and water compatibility tests to reduce losses due to back pressure and to minimize the risk of hard scale deposition. For more than a year, no halite has precipitated, which resulted in an uninterrupted production and allowed well testing of the remaining wells discretely through the test pipeline.
This paper demonstrates a comprehensive case in which halite scaling issues were predicted and mitigated through an integrated scale management system. The operating expenditures of pipeline flushing and pigging operations and oil losses were decreased due to interrupted production.