Successful Pipeline Clean Out—Lessons Learned From Cleaning Paraffin Blockage From a Deepwater Pipeline

Abstract

This paper presents a case history of inspecting, cleaning and re-establishing communication in a deepwater pipeline that had plugged because of paraffin deposition over an extended period. Early mitigation attempts did not remove the solid mass causing the blockage but, rather, compounded the problem. A chemical capable of dispersing the wax mass was applied to the plugged pipeline through a snubbing unit. Access to the pipeline and the wax plug was gained by disconnecting the line at the subsea site, lifting the pipeline to a work rig, installing the snubbing unit and applying the chemical solution in sea water at a prescribed dilution ratio. One critical step in dispersing and removing the solid wax mass was selecting the dispersant package. In addition, after the correct chemistry was identified, its application required a complex operation. A snubbing unit inside the pipeline jetted the chemical dispersant and drilled through the wax mass. The dispersed fluid was then returned to the working rig where the paraffins were disposed. The operation was successful and the pipeline was placed back into production. However, it was complicated by the ocean floor topography: The deepwater environment adds a degree of difficulty that is not experienced in shelf waters or on land. The exercise taught several lessons, the most significant being that a slow and consistent effort is ideal. Once the mass is dispersed it is best to continuously remove this fluid. Stop-and-start operations allow the solubilized mass to re-solidify as the solvent drains away from the mass under static conditions. Although operators would like for all operations to proceed according to plan, unforeseen and undesirable situations arise. In the case of a plugged pipeline, several causes need to be investigated in order to prevent future occurrences. Operators need to know that operational experience combined with application chemistry exists to help unplug a deepwater pipeline. Introduction: This paper is about a pipeline plugging problem. The problems were technical, mechanical and chemical. The focus of the paper is selection and application of the correct paraffin dispersant chemistry that was then combined with the right mechanical application to solve the technical problem. Solving problems in the oil field is always a challenge. Solving problems of an unknown or uncertain type complicate the challenge. In this case history a deepwater operator found himself with a pipeline plugging problem. It was not possible to identify the type of plug or its location in the pipeline. For that reason the operator went through a series of fixes using the method most probable to prioritize the sequence of solution operations. This was complicated in that a solution that does not remediate the problem may make a second attempt more complex. We surmise that in the first attempt to fix this particular problem, methanol was added to a hydrocarbon matrix and precipitated a hard wax. In the end, the quick fix approaches served to teach to people what would not work and led them to the right solution. In hindsight, it would be easy to second-guess the unsuccessful steps that were taken. However, it is best to appreciate this effort as a complicated process of elimination. In that type of process, it is best when the negative outcome can be used to better define an improved process that more efficiently results in the desired outcome.

Flow Assurance Technologies for Mitigating Wax Deposition in Subsea Petroleum Production System

“…14와 같이 무극성인 왁스와 상호간 공 유결합을 이루어 왁스의 용해도를 높인다 (Dobbs, 1999;Wylde and Slayer, 2012). 용매제의 분자길이가 길어질 수록 왁스를 용해시킬 수 있는 성능이 더 증가한다 (Poole et al, 2008). (Frenier et al, 2010).…”

Successful Application of LDHI and Paraffin Inhibitor Provides a Step Change in Flow Assurance Management in a Subsea Network in the Gulf of Mexico

“…Macrocrystalline paraffin has a low solubility in polar solvents whereas microcrystalline paraffin is soluble to an appreciable extent in non-polar solvents (7) . The lower the melting point of paraffin the greater the solubility in a given solvent.…”

Fluid-fluid and fluid-solid phase equilibria in carbon dioxide + waxy systems 1. CO + n-C

“…The deposition and buildup of solid waxes on the inner surface of the cold pipe wall decreases the pipeline cross-sectional area and increases the surface roughness of pipes causing a restriction of oil flow and ultimately plugs the production equipments. Mitigation and remediation of waxy solid requires use of various techniques which includes mechanical cleaning (pigging) [2], chemical injection (inhibitors, dispersants or solvent) [3], thermal method (insulation, heating) [4,5] and surface treatment (anti-wax coating) [6]. Most of these techniques are costly and must be expanded in right place upon in an adequate manner.…”