Nano Self Assembly Material Pore Structure And Permeability NMR Characterization Methods Study

With the increase of unconventional shale oil production,shale oil and gas exploration and development has become one of the researches focuses in the industry.The main pores of shale are nano pores,the final production of shale oil is closely related to the oil and gas molecular migration in pore channels,most of which are nano scale channels after fracturing.Therefore,this paper selects nano self-assembly material?-Al₂O₃ as the substitution model of shale after fracturing.Nano self-assembly material and its precursor is used to establish a one dimensional and two-dimensional NMR microscopic pore structure characterization method and to establish a theoretical research model of permeability.This theory is beneficial to improve shale oil recovery and pore characterization less than 100 nm in catalytic industry.The research in this paper includes three parts:pore structure,pore connectivity and permeability model theoretical experimental research,which are interrelated and progressive.1.In nuclear magnetic resonance characterization of pore structure,nano self-assembly material?-Al₂O₃ is used as sample to determine the surface relaxation rate of the material and NMR pore size distribution by one-dimensional NMR experiment and an error function method.The surface relaxivity are 0.525?0.45?0.4?m?s^-1,the main pore distribution of small pores is 5?9 nm,and that of large pores is29?47 nm.Compared to the pore size distribution obtained from BET and mercury injection experiment,the characterization of NMR pore size distribution is more accurate and comprehensive.NMR can comprehensive reflect 2.8-315nm pore system.Moreover,the surface relaxation rate and pore size distribution from random walk numerical simulation agrees with the NMR experimental results.For fluid-filled nanoscale self-assembled precursor samples,it can be simplified as a model with small pore saturated water and big pore saturated hydrocarbon.Deviation function method is improved and a novel mothod,which is named double-C method,is introduced.The surface relaxation rates of different liquids in small and big pores were determined separately by double-C method.The surface relaxivity of small pores is 0.85?m?s^-1?0.65?m?s^-1,and that for large pores is 0.55?m?s^-1.The surface relaxation of small pores saturated with water is greater than that of big pores saturated with hydrocarbon,indicating that pore walls of inorganic substance has a stronger force with water molecules than hydrocarbons.2.Capillary pressure curve is an important means to reflect the connected pore characteristics.In the process of oilfield development,it is difficult to obtain the measured capillary pressure curve,as a result,a lot of new method for obtaining pseudo-capillary pressure curves from NMR measurements are developed,with a large error in small pores.A new method combined with hyperbolic model and RBF is introduced,the predicted NMR capillary pressure curve is almost coincided with the measured mercury injection and ejection capillary pressure curve in pores larger than9nm.Channel connectivity is analyzed according to the throat to pore ratio and ejection efficency,it is found that pores from 9-77nm has a better connectivity,the conditions for macromolecular migration are satisfied and the corresponding migration mechanism is given.Finally,it was verified by polymer extraction experiment.3.According to Darcy's law and Poiseuille's equation,considering the effect of aperture variation,NMR permeability model is improved through theoretical deducing.The improved permeability model maintains the ratio of movable fluid to irreducible fluid item,new parameters of definite physical significance such as throat to pore ratio,film thickness and tortuosity are added.Materials before and after polymer extraction are used as samples,and one-dimensional and two-dimensional NMR experiments are performed.Combined with infrared spectrum,gel chromatography and microscopic observation,fluid analysis is performed to determine the permeability of the material.The one dimensional NMR improved permeability model results are 7.39m D,6.02m D,5.27m D,6.25m D,nearly the same with mercury permeability 5.10m D,4.73m D,5.82m D,5.56m D and Darcy permeability 4.1m D,5.19m D.The results agree with the permeability obtained from mercury injection experiment and Darcy's law.Considered sometimes it is difficult to calculate the film thickness and ratio of movable fluid to irreducible fluid,the improved permeability model can be transformed into another useful form including surface relaxivity and T_2LM.D-T₂ spectrum is obtained by two-dimensional NMR measurement,and the functional relationship between diffusion coefficient and transverse relaxation time T₂ is established through DCLM method.Acquiring the surface relaxivity and tortuosity.The permeability obtained from new model are 6.04m D?6.39m D?5.96m D agrees with that from the improved model before transformation,as well as the results from classical Kozeny-Carman permeability formula.