Variable Dimension Fractal-Based Conversion Method Between The Nuclear Magnetic Resonance T-2 Spectrum And Capillary Pressure Curve

Pore structure is the primary control factor of pore fluid distribution and flow capacity. It is an important content in reservoir evaluation. The capillary pressure curve is a major method to obtaining pore structure characteristics. The NMR T-2 spectrum reflects pore size distribution. Both of them have a connection. Investigating methods of converting the NMR T-2 spectrum into a capillary pressure curve is the key step to use nuclear magnetic resonance (NMR) logging data to quantitatively characterize the pore structure. The pore throat size distribution obtained by the NMR T-2 spectrum and capillary pressure curve has fractal features. However, studies about the relationship between the capillary pressure curve and NMR T-2 spectrum by the fractal characteristic have not been reported. This paper studies the relationship between the capillary pressure curve and NMR T-2 spectrum by the fractal characteristic and proposes a method of converting the NMR T-2 spectrum to the capillary pressure curve. To fully consider the influence of the pore structure, the dimension coefficient is set to be a variable that is related to the pore structure. The proposed model is verified by 20 rock samples in Nanpu sag, China by comparing the new method of calculate capillary pressure curves and experimental capillary pressure curves. Results show that the new method improves the accuracy of the conversion method between the NMR T-2 spectrum and capillary pressure curve in the complex pore structure reservoirs. This research provides a new way to enrich pore structure characteristic parameters for high-precision reservoir evaluation and has certain guidance and reference significance for the research work of petrophysics, reservoir evaluation, and NMR logging data application.