Pipeline Integrity Monitoring System for Leak Detection, Control, and Optimization of Wet Gas Pipelines

A combined leak-detection, gas-composition-tracking system, PIMS, has been developed, installed and operated for two wet-gas pipelines in the North Sea. One system has been operating for almost 3 years with no false leak indications to date. Thc system is based on a simplified, transient, multiphase, on-line model. The code is small and robust and can run on the same computer as the existing control system. PIMS also tracks gas composition so that the onshore terminal can properly blend low quality gas (high nitrogen content) with richer gases so that the minimum-Wobbe contractual obligations are met. In a field test of this system, the model was able to predict arrival times of packets of low-Wobbe gas to within 1 percent. PIMS also estimates the liquid content of the pipeline and informs the operator when the main trunkline requires pigging to reduce liquid hold-up. The model also provides an estimate of the slug size in front of the pig. Another complementary, on-line model, VO, uses the liquid content estimates. VO controls the flowrate via the wellhead chokes to prevent or minimize ramp-up slugs from forming in infield flowlines. It also controls the flowrate from each well in order to minimize sand production and to keep wells from loading up. Finally, it selects wells and their flow rates in a manner that will control the gas blend to insure that the minimum Wobbe targets are met.