A Molecular Simulation Study On Adsorption And Flow Characteristics Of Tight Oil

As an important and unconventional oil and gas resource,tight oil has become a new hot spot in the global oil and gas exploration and development.In order to develop the dense oil efficiently,the microscopic characteristics of adsorption and flow of dense oil need to be deeply understood.As tight oil reservoirs are low porosity and low permeability reservoirs,most of the reservoir pores are in the nano scale.Therefore,the traditional research methods are difficult to describe the adsorption and flow characteristics of tight oil.In this paper,the molecular simulation method is used to study the adsorption and flow characteristics of tight oil from the microscopic point of view.We according to the lithological parameters of tight oil reservoir and pore structure characteristics,construct the micro pore model of tight oil reservoir in nano scale.The skeleton of pore were quartz and dolomite,oil molecules in pores are n-pentane,octane and n-dodecane.Study adsorption characteristics of alkane molecule in micro nano pore in the Monte Carlo and molecular dynamics methods,discussed the influence of tight oil adsorption by pressure,temperature,pore width of alkanes and components on of alkane.From the research we find that(1)alkanes in micro nano pore density distribution is not uniform,showing a cyclical fluctuations,and the occurrence of multilayer adsorption in the pores,the thickness of adsorption layer is about 0.475nm;(2)under the same conditions,the pressure of alkanes in the adsorption effects of the pore is not obvious,while the temperature has a greater effects;(3)alkanes in the pores of the adsorption layers increased with the increase of pore width and ultimately achieve stability,the adsorption capacity and the number of adsorption layers are influenced by the number of carbon atoms,the adsorption capacity of heavy components in micro nano pore is better;(4)the adsorption capacity of dolomite is stronger the quartz.Using non-equilibrium molecular dynamics method,by simulating the flow of pores of quartz and dolomite in alkanes,discussed how driving force and pore width influences the flow of alkane.From the study we found that(1)The velocity profile of alkanes in quartz and dolomite pores is paraboloid,and the velocity of alkanes in pores increases with the increase of driving force and pore width;(2)pentane occurred slip phenomenon in quartz pore,the slip length increases with the increasing of driving force,with the increase of pore width,it decreases and then tends to be stable,but the slip phenomenon is not found in the dolomite pores;(3)the flow rate of n-pentane in two kinds of pores increases nonlinearly with the change of pressure gradient,which is no longer consistent with the description of Darcy law of convection flow.The results of the study on the adsorption and flow characteristics of dense oil in micro pores can provide some theoretical support for the exploration and development of dense oil.