A novel apparatus for modeling the geological responses of reservoir and fluid-solid production behaviors during hydrate production

Gas hydrate is a promising alternative energy resource that undergoes complex phase changes and coupled geological responses during hydrate production. Insufficient knowledge of those coupled behaviors still challenge safe and efficient gas production from hydrate. Here, a novel experimental apparatus was developed to simulate the gas-water-sand production and to evaluate the related multifield and multiphase processes. The experimental apparatus is equipped with displacement, ultrasonic, and electrical resistivity sensors and gas/water flowmeters, and this apparatus can work up to a maximum loading stress of 25 MPa and a maximum pore pressure of 20 MPa over a temperature range from -20 to 50 degrees C. The hydrate production and sand production case were performed on a synthetic specimen with hydrate saturation of 12.8% by using multi-step depressurization. The pressure-temperature conditions, settlement, ultrasonic propagation, electrical resistivity, and permeability of hydrate reservoirs during production were simultaneously monitored to evaluate the geological characteristics and heat and mass transfer characteristics of the hydrate reservoir. The results indicated that the gas/water production mainly occurred during the first third of each depressurization period, and their production rates were low at the beginning. Flowing water mobilized the sand particles, and the addition of gas exacerbated the sand-particle migration. Interpretation of the coupled behaviors supported that the reservoir could maintain a temporary stable structure even when losing a certain amount of sand particles with no sand control methods; however, necessary sand-prevention approaches are wise to support long-term reservoir production operations. These laboratory insights would contribute to optimizing the field strategies for economical gas production from hydrate.

Automated summary

This study developed a novel experimental apparatus to simulate gas-water-sand production and evaluate the associated multifold and multiphase processes. The results showed that gas/water production primarily occurred during the first third of each depressurization period, with low production rates initially. Flowing water mobilized sand particles, and the addition of gas exacerbated their migration. The study also revealed that the reservoir could maintain a temporary stable structure even when losing a certain amount of sand particles, but sand prevention approaches are advisable for long-term reservoir production.