Modeling of multiphase flow in marine gas hydrate production system and its application to control the production pressure difference

Abstract

The accuracy control of the production pressure difference is of great importance to the efficient development of marine gas hydrates through depressurization. But from the field trial production, the existing control method of bottom hole pressure is difficult to achieve the expected depressurization target. To this end, a transient gas-liquid two-phase flow model in marine gas hydrate production system was established, which considers the coupling interactions of the wellbore, the formation and the downhole electric submersible pump (ESP). Besides, an automatic control method of production pressure differential was proposed through real-time optimization of the pump displacement. Using the model, a series of numerical simulations were performed to study the multiphase flow rules in the production well. The results indicated the depressurization process could be divided into four stages based on the characteristics of gas-liquid flow in different pipelines. During the depressurization, the liquid level in the well exhibited a trend of first falling and then rising, and may eventually reach the wellhead for continuous drainage. In addition, sensitivity analysis showed that the smaller the pipe diameter, the higher the gas-liquid separation efficiency, and the greater the possibility of continuous drainage from the gas production pipeline. As the result, it was verified that the proposed model and method can achieve the expected depressurization well, which will provide useful references for the production design during the development of marine natural gas hydrate resources.