One of the most serious challenges in deepwater operations occurs when the reservoir pressure drops too low to support production by the normal operation techniques. To overcome the low pressure challenge during a restart, a gasified dead oil stream can be used as a technique for continuously unloading the production risers. The technique needs to be evaluated and optimized by simulating the unloading process in a transient manner. As the first step, the simulation accuracy is evaluated in the paper for the future oil gasification simulations and for optimizing the operation procedures for oil gasification. Simulations of the sequence actually performed in the dead oil gasification field trial were performed and the simulation results were benchmarked with the field data. The gas/oil ration (GOR), gas rates and gas ramp-up rates with the surface constraints were optimized to obtain the lowest riser base pressure. The results showed using a gasified dead oil stream can successfully unload the production risers before the restart of production wells. The OLGA model with CompTracking matches well with dead oil gasification field data except with slightly larger fluctuations when the system gets close to slugging region as the gas and oil rates decrease. It can capture the gas absorption and breakout during dead oil gasification, showing better results compared with standard OLGA.
In deepwater operations, hydrocarbon fluid is often replaced with dead oil when the system needs a long shut-in to reduce flow assurance risks due to the system cool-down. The lengths of riser A and B are approximately 15000 ft, the length of flowline A is approximately 9000 ft and that of flowine B is approximately 10500 ft. The manifold pressure, riser A topsides pressure, flow rates at riser B are closely monitored during the process.