Numerical Simulation Investigation And Production Method Study Of Natural Gas Hydrate Reservoir Development

Natural gas hydrates are one of the most important alternative to fossil fuels,with wide distribution,large reserves,and high energy density.The development methods of hydrate reservoirs include depressurization,thermal stimulation,inhibitor injection,gas exchange and combinations thereof.There are large hydrate reserves in China,but the related research in our country is still in the stage of laboratory study and geological investigation.There is a lack of systematic investigation of development simulation.So,it is of great importance to study the development methods of different classes of hydrate reservoirs,to analyze the corresponding production characteristics,and to establish the operation parameter optimization method of gas hydrate reservoirs development,which will be helpful to exploit the hydrate reservoirs efficiently.In this paper,the numerical simulation method of the hydrate reservoir development is investigated first.Considering the underlying mechanisms including phase change,heat transfer,multi-phase flow etc.and the relations between different phases and components are analyzed.After that,the mathematical model is established and the numerical solution method is studied.The result of mathematical model validation shows that the developed model can simulate the hydrate reservoir development effectively.Using numerical simulation technique,depressurization and thermal stimulation combined methods including wellbore heating assisted depressurization,hot water flooding and wellbore heating combined depressurization are adopted to develop Class ?,Class ? and Class ? hydrate reservoirs respectively based on reservoir parameters reported in literatures.The production characteristics are studied and sensitivity analysis of the factors including reservoir parameters and operation parameters are performed.The results show that for Class ? hydrate reservoir,the gas production rate is high in the early stage,while it remains low in later stage.And gas is produced mainly in the early period.For Class ? hydrate reservoir,the gas production rate is relative high in the whole period and gas is produced quickly.For Class ? hydrate reservoir,gas production rate varies periodically due to high hydrate saturation,and the gas accumulates in a stepped way.By the end of simulation,the gas recovery percent and the hydrate dissociation percent of Class ?,Class ? and Class ? hydrate reservoirs decrease in turn;Class ? hydrate reservoir has the highest energy ratio,while the energy ratios of Class ? and Class ? hydrate reservoirs are in a comparatively level;From Class ? to Class ?,the effectiveness of depressurization deceases and thermal stimulation increases.In order to exploit the hydrate reservoirs effectively,using cyclic hot water stimulation with a separated-zone horizontal well,operation parameter optimization method to maximize the net energy is proposed by combining the numerical simulation technique and particle swarm optimization algorithm.As an example,based on the reservoir parameters of the China Shenhu area,optimal operation parameters to develop the heterogeneous hydrate reservoir are investigated.The results show that this method is feasible for recovering heterogeneous hydrate reservoirs: high gas production rate and high energy ratio can be obtained,the reservoir energy is utilized and maintained effectively,the low-permeability areas can be exploited.