The Impact of Gas Hydrate Critical Shear Stress, Deposition, and Sloughing on Multiphase Flow Pressure Drop: Simulating Field Experiments with a Transient Hydrate Kinetics and Transportability Model

Efforts to model gas hydrate kinetics and transportability in transient multiphase flow scenarios aim to provide information about the risk of forming a gas hydrate obstruction in pipeline systems used to transport oil, natural gas, and CO2. An increased risk of forming gas hydrate obstructions during transient flow operations can arise from a lack of warm fluids supplied during a restart operation or the cessation of thermodynamic inhibitor (e.g., methanol) injection. A variety of previous models have been developed to calculate gas hydrate kinetics and transportability, showing fair agreement between the predicted gas hydrate volume fraction as a function of time with flowloop experiments. However, there is a general limitation in the simulations with these models providing limited or no field observable (i.e., pressure drop, which is an indicator of resistance to flow) transient data responses to gas hydrate phenomena, instead offering only qualitative plug/no plug predictions. These transient data responses, which are directly observable in the field through data acquisition systems, offer an opportunity to detect the onset of gas hydrate obstructions before they become a complete blockage. This work applies a new transient gas hydrate kinetics and transportability model to simulate the phenomena of gas hydrate crystal growth, deposition, sloughing, and plugging in a uniquely controlled field experiment. The transient model is coupled with a transient multiphase flow simulator and considers an expanded set of kinetics and transportability phenomena, including the impact of intermittent flow patterns on the gas hydrate formation rate, bedding/deposition, and sloughing under fluid supplied shear stress. The transient model was able to predict the sloughing behavior with similar timing to the field data. The pressure drop trend profile of the simulated system and the final time to reach a full blockage predicted by the transient model agreed with the field data. The model may be useful to provide operators with insight into how measured pressure drop data in the field can serve as an early warning for gas hydrate plugging.