Paraffin Cleanout in a Single Subsea Flowline Environment: Glycol to Blame?

Abstract Paraffin deposition was found in the RedHawk #2 subsea flowline and was successfully removed using a xylene slug swept by produced gas from the well. Testing indicated that the problem resulted from the interaction between glycol and produced condensate. Overtreatment with glycol and low produced water volumes contributed to the precipitation of paraffin and eventual plugging of the flowline. The objective of this procedure was to clear the restriction by pumping a slug of xylene into the flowline and producing the well to carry the solids to surface. Glycol can react negatively with the condensate in some dry gas wells, resulting in paraffin precipitation. When there is sufficient water present to mix with the glycol the problem does not occur, however a lack of water causes the glycol to react with the condensate and form paraffin. Clearing the restriction would eliminate a pressure drop in the flowline, thus allowing the well to produce at optimal rate and prolonging the well's life. All work was performed from the host spar facility using temporary separation equipment and platform methanol pumps. The RedHawk flowline restriction was successfully removed using two 25 bbl xylene slugs which were swept from the flowline with produced gas from the well. With the restriction removed, 982 psi of frictional loss was regained and the well was returned to optimal production. The deposition appears to be reoccurring, although at a much slower rate than before. However, any further reduction in glycol usage would not guarantee effective hydrate inhibition. Changing hydrate inhibitors is impractical due to platform equipment and annual cleanouts are a more cost effective option. It is quickly becoming critical to develop means of cleaning single flowline systems with highly efficient and low cost methods. By understanding new problems that arise and putting new solutions into practice operators can extend the life of some wells and avoid significant downtime and workover costs. Introduction RedHawk is an Anadarko Petroleum Corporation operated cell spar located in 5300' of water in Garden Banks Block 876, about 177 miles southeast of Cameron, LA in the Gulf of Mexico. Devon Energy Corporation is a 50% working interest partner in the RedHawk field. The platform consists of two dry gas subsea tie-back wells, shown in figure 1, that are treated with recycled MEG via RedHawk's Glycol Reclamation Unit (GRU) for hydrate inhibition. As the GB 877 #2 well's chokes were opened to maintain the target rate of 75 MMCFD, it became apparent that the chokes were no longer controlling the flow from the well but rather some other restriction in the flowline (see figure 2). Modeling and testing showed that there was a restriction in the flowline causing a pressure loss and limiting the production rate of the well. The restriction was initially thought to be the result of fluids from the initial completion cleanup or from a preexisting blockage that occurred during installation of the flowline.

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