Abstract
Natural gas hydrate is an ice-like crystal formed by methane and water, which is a new type of strategic energy with huge reserves. The exploitation of deep-sea hydrate will cause a large amount of decomposition of hydrate, which will decrease the sediment strength. In this paper, production models of different types of hydrate reservoirs under different BHP (bottom hole pressure) were established. Then, sensitivity analysis was conducted to determine parameters which have the most significant influence on formation subsidence. After that, hydrate formation failure was discussed using two different criteria: formation subsidence and stress-strain curve. Then, critical production pressure was determined. Through comparison, it was found that the criterion of formation subsidence is more suitable. Finally, based on this criterion, the optimal production pressure of different types of hydrate reservoir was determined. The work of this paper will provide a certain reference value for the efficient and safe production of hydrate in the future.
Highlights
Natural gas hydrate (NGH) is considered as the most promising new strategic energy [1]
Decreasing BHP can accelerate hydrate decomposition, but when pressure difference between BHP and formation pressure is too large, a great amount of gas will be produced from hydrate, which will lead to a sharp increase in effective stress of the formation and formation failure
We use two ways to determine the critical condition of formation failure, that is, method based on formation subsidence and method based on stress-strain curve
Summary
Natural gas hydrate (NGH) is considered as the most promising new strategic energy [1]. Solid gas hydrate is usually a cemented component of the reservoir, and its decomposition will cause a series of changes in reservoir physical parameters, mechanical properties, and pore pressure [2]. A large number of experimental and numerical simulation studies have shown that hydrate decomposition leads to a significant increase in the physical parameters such as reservoir porosity and permeability, and the mechanical parameters such as elastic modulus and cohesion are significantly reduced. Research on hydrate production mainly focuses on the effect of production parameters on gas production and decomposition rate. The results showed that with the same production pressure, combined method increased the gas production by 1.8 times compared with simple depressurization [5]
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