Hydrate Reformation Characteristics in Offshore Natural Gas Hydrate Reservoir Using the Horizontal Well Depressurization Production

Abstract During depressurization production of natural gas hydrate, the reformation of hydrate is likely to occur in the reservoir, hindering the efficient development of hydrate. Previous studies on the reformation of hydrate in the process of natural gas hydrate production were mainly focused on experimental research and numerical simulation under experimental conditions. In this work, a multi-field coupling flow model considering the effect of hydrate reformation during depressurization production of hydrate reservoir was established, and the accuracy of the model was verified by the field measured data. Meanwhile, the reformation characteristics of hydrate in the reservoir using the horizontal well depressurization production were simulated and investigated. The results show that the reformation of hydrate in the reservoir mainly occurs in the upper part and middle boundary of the hydrate decomposition zone during the depressurization production. Moreover, the smaller the pressure drop extent, absolute permeability and initial hydrate saturation, and the deeper the horizontal well, the larger the hydrate secondary formation zone in the reservoir, the faster the rate of hydrate reformation, and the greater the hydrate saturation caused by hydrate reformation would be, which would make the risk of flow blockage by reformed hydrate in the reservoir rise. The results of this study can provide theoretical support for the safe and efficient development of offshore natural gas hydrate.