Study On The Depressurization Exploitation Of Natural Gas Hydrate Based On Formation Stability

Natural gas hydrate is considered as the most promising new strategic energy.In the process of exploitation,hydrate decomposition reduces the formation strength,which will lead to formation subsidence,and even a series of engineering disasters.In this thesis,the multi-phase seepage and formation stability during hydrate exploitation were taken as the core issues,and the depressurization process of hydrate was studied by combining theoretical analysis with numerical simulation.The main innovative work are as follows:1?Based on the existing mathematical model of multi-phase seepage of hydrate,the variation law of main parameters with time and space was analyzed,and the production law of depressurization under seepage model was obtained.2?For hydrate reservoir with different saturation,the applicability of constitutive model was evaluated.Based on this,geomechanics and seepage coupling model of hydrate reservoir with different saturation was established,and the influence mechanism and law of formation deformation on hydrate decomposition are obtained.Through analyzing the sensitivity of formation subsidence to different parameters,the parameters that need to be optimized for safe and stable production were determined.3?Based on the mechanism and law of formation failure,the judgement basis and critical condition of formation failure were determined,and the optimal production pressure for safe and stable exploitation was obtained for hydrate reservoirs of contact cementation,particle-wrapping and particle-supporting mode.4?For the exploitation of hydrate reservoir with underlying water layers,DWS method was proposed for the first time,and the feasibility of this method to control water coning and increase the production was verified by simulation.This method is helpful to further increase the production of depressurization based on formation stability.The above innovative work and corresponding conclusions have important guiding significance for hydrate exploitation and have laid a certain foundation for further theoretical and experimental research.