Production characteristics and sensitivity analysis on gas hydrate and shallow gas coexistence reservoirs: Focus on gas hydrate formation

The coexistence reservoir of gas hydrate and shallow gas has great production potential. Based on the successful exploitation experience of the Messoyakha gas field, the production method that perforation only in the shallow gas layer has been proposed for the exploitation of the coexistence reservoir. This study conducted production simulation and sensitivity analysis of influence factors on high-quality coexistence reservoirs. The numerical simulation results show that the gas production rate of a coexistence reservoir with a permeability of 680 mD and a gas saturation of 80 % reached 1 × 107 m3/d, but the gas production rate dropped rapidly due to the significant formation of gas hydrates around the wellbore. Sensitivity analysis shows that the production pressure difference, gas saturation, hydrate saturation, and reservoir permeability had a decreasing impact on the gas production of the coexistence reservoir. The formation of gas hydrate around the wellbore, affected by production pressure difference, was the predominant cause of interference with gas production in high permeability and high saturation reservoirs. By controlling the pressure difference within 1 MPa through the method of constant production rate, no gas hydrates formed around the wellbore, and the maximum stable production rate of 5 × 105 m3/d was achieved within 5-year production period. These findings reveal that the production of high permeability and high saturation reservoirs should focus on the formation of hydrates around the wellbore, and demonstrate the feasibility of constant production rate, thereby providing reference for the production of the coexistence reservoir.