Study On The Method Of Evaluating Pore Structure Of Tight Oil Reservoir By The NMR Technique

In recent years,due to the decline of conventional oil and gas production,more and more attention has been paid to unconventional oil and gas resources with great potential.Pore structure characterization is the basis of tight oil reservoir research.On the basis of full investigation of domestic and foreign research methods on the microscopic pore structure of tight oil reservoir rocks,this paper takes the tight oil reservoir in Quan4 member of Changling Sag as the research object,mainly studying the pore structure characterization and fluid occurrence state of tight oil reservoir.For dense oil reservoir pore structure is complex,in the study area with poor physical correlation characteristics,first of all,the use of the casting thin sections and scanning electron microscopic observation method,determining springs of changling sag of four types of the reservoir rock mainly feldspathic lithic sandstone and lithic feldspar sandstone,pore types are mainly the residual intergranular pore,dissolution pore and micro cracks,etc.;Then,according to mercury injection and NMR experimental data,the morphology and pore structure parameters of capillary pressure curve and NMR T₂ spectrum curve were analyzed to qualitatively and quantitatively characterize the microscopic pore structure characteristics of tight sandstone reservoirs in the study area,and a classification method for the pore structure of reservoirs was established.Study fluid occurrence state,in this paper,nuclear magnetic resonance?NMR?method is used to determine the tight sandstone reservoir movable fluid occurrence state,on the basis of a large number of experimental data and previous studies,put forward the nuclear magnetic resonance T₂ spectrum is composed of multiple logarithmic normal distribution spectrum superposition,this study will be tight sandstone T₂ spectrum decomposition for capillary lognormal distribution curve and macropore logarithmic normal distribution curve.The logarithmic normal distribution function and the method of ? and ? value are given.The influencing factors of the occurrence state of the movable fluid were analyzed,and the pore structure of the reservoir was classified according to the T₂ spectrum of the movable fluid.The pressure curve of the pseudocapillary was constructed by using the T₂ spectrum of the movable fluid.