Study On The Theory And Model Of Adsorption Of Shale Gas

Shale gas is a multicomponent natural gas which mainly exits in the shale rocks and congregates in the forms of adsorbed gas phase and desorbed free gas phase.Shale gas reservoirs are significantly different from conventional gas reservoirs in terms of hydrocarbon accumulation,reservoir physical properties,storage characteristics and fluid flow mechanisms,thus,the development method of shale gas reservoirs would be different.As the exploration and development of shale gas reservoirs in our country is in the early stage,many limitations including the insufficient knowledge and technology of adsorption theory,phase behavior theory,reservoir properties and fluid flow mechanism would restrict the scientific development of the shale gas reservoirs.Therefore,it is of great theoretical and practical importance to study the complicated adsorption and desorption mechanisms of shale gas reservoirs as well as to further study the theory of fluid flow,production capacity,numerical simulation,reserve evaluation and reservoir development technology of shale gas reservoirs.In the multi-component shale gas reservoir,the adsorption and desorption of each gas component is different.There always exists competitive adsorption – desorption equilibrium in this system.In this paper,according to the thermodynamics equilibrium theory,the adsorption and desorption mechanisms of multi-component shale gas are studied based on the adsorption characteristics of shale gas during the migration process.The main achievements of this research are as follows:(1)The literature review of the domestic and abroad researches related to the experiment,analysis,model and practical application of adsorption has been done.Among those,the most advanced model of the adsorption considering the effect of porous media has been studied.(2)Based on the Polanyi potential theory,the adsorption isotherms of all components of the gas system in the same pore media at any temperature could be estimated by applying the limited adsorption experiment data of a certain component at the lab temperature.In this way,the adsorption isotherm of the untested gas components in the shale gas reservoir could be obtained without adsorption test.(3)According to the characteristics of the multi-component shale gas system,the porous medium and the multi-component fluid are regarded as a unified system of interaction.The multi-component adsorption thermodynamic equilibrium model is established on the basis of the vacancy solution theory and equation of state.(4)The regression of the measured core adsorption isotherm is carried out.Meanwhile,based on the reservoir core characteristics and the basic test data,representative numerical core samples to study the adsorption are established.The properties of those numerical core samples including the porosity,permeability,density and specific surface,etc.are determined and the adsorption isotherm of each component at the reservoir condition is obtained.(5)The constant volume depletion simulations are carried out by applying the numerical core samples and the saturations of the adsorbed gas phase and free gas phase in the cores are studied during the simulation.(6)The numerical simulation model of the single well is established.The reserve parameters of the shale gas reservoir,development dynamics performance of the shale gas reservoir blocks are determined.