Dynamic optimization of real-time depressurization pathways in hydrate-bearing South Sea clay reservoirs.

Gas permeability and the depressurization path are decisive factors affecting the efficiency of gas hydrate reservoir exploitation. However, there was a lack of quantitative studies on the gas permeability and dynamic optimization of real-time depressurization paths under different in-situ conditions. Therefore, hydrate-bearing cores within the core holder were remolded using South Sea clay under different in-situ conditions. Then, the gas permeability was continuously measured using a constant flow rate. Next, a gas permeability model coupling effective pressure, hydrate saturation, and absolute permeability were established. It was used to predict the gas permeability under different in situ conditions, with deviations mainly in the range of 1–2 %. In addition, the optimum outlet pressure and positive outlet pressure range during depressurization under different in-situ conditions were proposed. The real-time gas flow rate of the optimal depressurization path was larger than other depressurization paths. Also, the logic reasoning process for real-time optimal outlet pressure and positive outlet pressure range was given. Finally, the inlet pressure and the optimum outlet pressure were also accurately predicted. None of the predicted values deviated by more than 4 %. The dynamic optimization of the outlet pressure behavior during depressurization can provide some scientific guidance for hydrate development and utilization. [Display omitted] • Permeability model including hydrate saturation, effective pressure was established. • Optimum outlet pressure and pressure range during depressurization were found. • Real-time inlet pressure of the core was accurately predicted. • Real-time optimal outlet pressure and pressure range were accurately predicted. [ABSTRACT FROM AUTHOR]