Switch from spheres to pipeline pig improves gas-gathering efficiency

Removing accumulated line liquids with pigging rather than conventional sphere-launching methods has improved natural-gas flow efficiencies to more than 90% from 15% in 200 miles of a high-pressure gathering system in western Oklahoma. The first phase of the project involved determining the flow efficiencies of more than 200 miles of high-pressure gathering lines. The procedure consisted of determining the pressure drop along the gathering lines at intervals of approximately 5 miles. Marketing a sphere revealed that one of the two launched spheres was being left in the canyon section of the discharge line and that subsequent launched spheres would only displace the stationary sphere. Subsequent launching of the 12-in. pig improved efficiencies to more than 95% along the 55-mile portion of this line. The Bucher Canyon area pressure drop was reduced to about 5--10 psig from 100 psig. The pig, because of its greater sealing ability within the line, was able to dislodge the stuck spheres. The increased efficiencies allowed GPM to shift 5 MMcfd of gas from the Cimarron plant to the more efficient Okarche plant. Currently, three pigs per week are required to maintain the 95% efficiency.