Research On NMR Experimental Analysis And Logging Evaluation On Low Permeability Reservoirs

Nuclear magnetic resonance logging method can provide many geologic parameters related to reservoir properties and deliverability including porosity,permeability,pore texture,free fluid volume and bound fluid volume and has been widely used.Nuclear magnetic resonance logging method shows unique advantage over other logging methods in reservoirs with low-porosity and low-permeability,thin-bed evaluation,and fluid identification in complex reservoirs,pointing out new thoughts for the solution of complex geologic problems in oilfield exploration and development as an indispensable logging approach.In this study,nuclear magnetic resonance experiments were conducted under the conditions of varying resonance frequencies,fluid properties,and acquisition parameters based on the basic theory of nuclear magnetic resonance,aiming at the cores in regional low-permeability reservoirs.The results showed that the nuclear magnetic resonance spectrum-T2 of cores was influenced by many factors including instrument frequency,echo interval TE,alert time TW,pore fluid property,and different lithologies were affected in different degrees.The acquisition pattern and application condition of nuclear magnetic resonance logging instrument of type P were studied in this research.Design before test was conducted and logging pattern and acquisition parameters were optimized in combination with geologic characteristics of the reservoir and results of core experiments.On the basis of the nuclear magnetic resonance core analysis,the relationship between cutoff value of T2 and characteristic parameters of spectrum-T2 was studied,and a nuclear magnetic resonance log interpretation model based on variable cutoff value of T2 was put forward,thus making up the poor adaptability of single cutoff value of T2 in different hole sections and different lithologies and getting good application results.Starting with the fractal features of pore textures in cores,the relationship between fluid relative permeability and lateral relaxation time was built and the computational method of fluid relative permeability based on fractal and nuclear magnetic resonance of cores was studied in combination with coupling of seepage field and electrical current field and Brooks-Corey/Burdine Model.Applying the distribution of spectrum-T2 in combination with mercury-injection data,the distribution spectrum of relaxation time was transformed using linear and nonlinear method respectively.Through comparison,transformation method was optimized and quantitative analysis of pore texture parameters was conducted.