Chemical Reduces Risk of Stuck Pipeline Cleaning Equipment in Deepwater Subsea Flowlines

Abstract

An oil export pipeline connected to a deepwater production facility in the Gulf of Mexico requires periodic pigging to manage wax deposition on the pipe wall. The facility used in this paper is in the Viosca Knoll Federal lease blocks, located approximately 120 miles SE of New Orleans, LA in a water depth of approximately 3,250 ft. This facility is a Tension Leg Platform (TLP) floating system set on two pontoons which are anchored to the sea floor. Since it was installed in 1999 many modifications have been made to the facility to allow it to serve as a hub to multiple subsea fields, implementing new technologies encompassing enhanced oil recovery techniques and modified process systems to facilitate safe, effective, and environmentally sound exploitation of the asset base. The production facility separates oil and gas, then exports each to shore via separate oil and gas export pipelines. It is important to manage wax deposition on the inner wall of the oil export pipeline, which consists of 22 miles of uninsulated 10-in diameter pipe (Fig. 1). This facility's base wax management strategy for the oil export system consists of periodically launching pipeline cleaning pigs and continuously injecting paraffin inhibitor (PI). The current pipeline routine cleaning frequency, pig type, and PI injection rate have been optimized over time. When the pipeline cleaning pig launcher failed in 2021, a new design needed to be engineered, fabricated, tested, and installed. The expected time required to resume routine pigging for wax management raised concerns regarding excessive wax deposition in the export flowline. Being temporarily without pigging capability triggered mitigation measures such as increased chemical injection concentration, additional scrutiny of pipeline pressure and flow data, and design of a conservative progressive pigging campaign to enable eventual resumption of periodic aggressive maintenance pigging.