Shale Gas Reservoirs Micromechanics Balance And Its Application

Microscopic mechanism of shale gas is an important part of theoretical research,shale porosity is nano-scale,it is necessary to study shale gas forming mechanism from the nanometer level.In this paper,shale gas accumulation mechanism is researched through microscopic nano-scale mechanical theory.The microscopic mechanism of adsorption of shale gas,the balance forces of methane molecules,the interaction potential between the methane molecule,three nanoscale reservoir model and the application of microscopic mechanical balance in shale gas evaluation.Through systemic research,main achievements are obtained as follows:(1)Shale gas nano transmission mechanism includes a portion of free gas and a portion of adsorbed gas.The portion of free gas is based on the bulk diffusion,including continuous flow,slip flow and Knudsen diffusion.The portion of adsorbed gas is based on surface diffusion.The respective gas transmission quantity corresponding to different transmission mechanism consists of the total amount of the gas transmission.(2)Based on the micromechanics balance analysis in shale gases,the state transition condition is given that in the microscopic pores micromechanics are the dominant forces.Shale gas methane molecule cannot reach saturation adsorption and are in adsorbed state.In the mesoporous molecular methane reach adsorption saturation.Free gas increase.Shale gases coexist in adsorbed and free state.In the macropores macromechanics are the dominant forces.Methane molecule s transport and storage in the communication hole and are in adsorbed state.(3)The total intermolecular interaction potential including dispersion,near-field repulsion,orientation and induction is proposed.An intermolecular interaction is proposed that is suitable for shale gas methane molecules,including dispersion between the non-polar methane molecules,induction between the polar organic molecules and non-polar methane molecules and near-field repulsion,while eliminating the orientation between polar organic molecules.(4)Thermodynamic equilibrium conditions are obtained.The effects of changes from temperature,pressure and chemical potential to thermodynamic equilibrium are analysed.The thermal equilibrium condition requires that in the various parts of the system temperature is equal.The mechanical equilibrium condition requires that in the various parts pressure is equal.The chemical equilibrium condition requires that in each part chemical potential is equal.(5)The shale porosity models are classified into closed pores,open pores and semi-enclosed holes by closure.Three models are affected by pressure,temperature and chemical potential respectively in adsorbed state and free state.(6)A new understanding of the calculation method for the free shale gas content is proposed.An adsorption coefficient was introduced to reduce the error that occurs in the calculation of the free shale gas content.The calculation method of the proportion of free gases and absorbed gases were improved.The theoretical maximum number of layers that shale gas absorbed in the surface of mesoporous is caculated.