portable pig launcher, Kuparuk, pigging
Many oil fields on the North Slope were built without pig launchers and receivers in production gathering lines. Maintenance cleaning and smart pigging of selected lines have become necessary as the field matures. This paper discusses the field background, design considerations, and test strategy for a portable pig launcher designed to ease the task of pigging multiple lines with a single facility
The Kuparuk oil field is located on the North Slope of Alaska, approximately 40 miles west of Prudhoe Bay. The reservoir produces approximately 300,000 barrels of crude oil each day (47,690 kLOPD) and 353,000 BWPD (56,102 kLWPD). The extremely cold temperatures can make even comparatively simple operations complex.
The Kuparuk crude oil is produced from 42 drill sites throughout the field, Oil produced at individual wells are manifolded at each drill site into a single gathering line, These lines flow cross country and join the flows from multiple drill sites in larger diameter gathering lines, which then flow to the Central Processing Facilities (CPFS) for separation of the oil, water, and gas. The piping arrangement is a trunk-and-lateral design. Eight-inch (203 mm) to sixteen- inch (406 mm) nominal diameter piping from an individual drill site flows into twenty-four inch (61O mm) cross - country gathering lines. Thus, production from drill sites closer to the CPFS are merged with production from drill sites farther from the CPFS. The lines that carry the crude were constructed in different expansions. Therefore the pipeline layout is somewhat disorderly. They branch, interconnect, and change size as they flow crude from the production sites to the processing facilities.
The original piping design called for pig launchers and receivers, but these were omitted from the as-built facilities due to shipping and delivery time constraints. As such, it was not possible to run cleaning pigs through the production lines. Likewise, it was not possible to run inspection vehicles through the pipelines. Kuparuk cross-country pipelines run above ground on steel vertical support members (VSMS). The pipe runs incorporate road crossings and Caribou crossings, where the piping passes below ground through steel casings. These areas cannot be inspected by conventional means unless they are excavated. Smart pigging is a method which would allow complete inspection of the internal and external condition of the piping without excavation.
The trunk-and-lateral layout of the pipelines means that capital costs for conventional pigging facilities would be exorbitant. A field survey indicated that 116 sites would be required to pig only those lines that exceed 1 mile in length. Corrosion studies indicate that the primary mode of corrosion in these lines involves an under-deposit corrosion mechanism and so pigging must be evaluated as a method of corrosion control.
FACILITY DESIGN CONSIDERATIONS
A decision was made to pig two of the lines as a pilot test. Both of the lines in question showed elevated coupon rates, and spot inspection with ultrasonic and radiographic methods confirmed these lines as good candidates for pigging and corrosion mitigation tests. The prc}gram is investigating solids accumulation and composition, the application of corrosion inhibitors in conjunction with maintenance cleaning of the lines, the efficiency of corrosion inhibitor injection without pigging, and the internal and external condition of both the lines with several types of instrumented pigs.
Because of the high capital cost of conventional facilities, portable pigging facilities were considered a practical approach to the problem. How