LBM For Adsorption-desorption Simulation Of Shale Gas And NMR Experiment

With the demand of shale gas and oil exploration and development and the related technology,the microscopic mechanism and macroscopic characterization of fluid occurrence,adsorption and desorption are becoming more and more important.Shale gas is present in the micro-pore system by adsorption and free-state,and its output process is related to desorption.Adsorption and desorption is one of the key core issues in shale gas development,which runs through the entire development process.In this paper,lattice Boltzmann method?LBM?simulation and nuclear magnetic resonance?NMR?experiments of shale gas adsorption-desorption are mainly divided into three parts:?1?theory and physical description of adsorption and desorption of porous media;?2?digital core image acquisition and processing,nano-pore extraction and gas-bearing shale adsorption and desorption of the lattice Boltzmann simulation;?3?nuclear magnetic resonance observation of adsorption and desorption.The modeling and image processing methods of gas-bearing shale pores at mainland and abroad are analyzed and compared.Focus Ion Beam Scanning Electron Microscopes?FIB-SEM?and Transmission Electron Microscope?TEM?are used to obtain high-resolution micro-pore images.The Compressive Sensing?CS?reconstruction with sub-nanometer resolution provides a feasible method for the establishment of a shale pore structure model,which is a basis for subsequent numerical simulation and calculation.Using the above model,then,it is carried on that the numerical simulation to the shale gas reservoir.The adsorption characteristics of methane in shale are described by Ono-Kondo model equation and Peng-Robinson gas equation of state.The numerical simulation of gas adsorption and multi-scale integration is carried out by LBM.The research on the adsorption process and the multi-scale interface includes:?1?the expansion of the basic theory of multi-scale Shan-Chen adsorption LBM;?2?the experiment and the comparison of the adsorption curve with the multi-scale LBM simulation based on Molecular Dynamics?MD?.The correctness of this new type of LBM is ensured by validating and comparing large-scale MD and various types of empirical adsorption curves.Finally,the kinetic behavior of adsorption molecules on the walls of kerogen,single wall and multiwalled carbon nanotubes was simulated by MD-LBM.The corresponding NMR signals were obtained by using the obtained molecular motion and rotation.The distribution of high T₁/T₂ ratio peak phenomenon is interpreted.An NMR method for the analysis of the structure and kinetic information of adsorbed fluid molecules in nanoscale pores is proposed.The physical experiment verification problem of LBM adsorption model is solved by this method.LBM has been rapidly developed and applied in a variety of interdisciplinary disciplines.The advantages of this algorithm are taken into account:the programming efficiency is high,the program is concise and has very intuitive physical meaning,and a numerical simulation tool and modeling method based on LBM adsorption and desorption are designed.The method has great advantages in programming efficiency,and has the advantages of high parallelism and good code reusability.Its physical meaning is intuitive:density and pressure are extracted directly from the node information.These significant usability makes it suitable for large-scale high-resolution digital core simulation,and its application to the actual shale gas adsorption and desorption simulation has broad research prospects.LBM simulation and NMR experiments of shale gas adsorption-desorption are studied,which enrich the numerical analysis and physical experimental method of shale gas content.