A New Method for Characterizing the Pore Size Distribution of Rock by Combing Nuclear Magnetic Resonance and Multistage Centrifuge

Pore structure characterization plays key role in efficient development of petroleum, natural gas and shale gas, and it also holds important place in the evaluation of gas outburst and rock weathering damage. In this paper, a high-precision, nondestructive, and repeatable method for characterizing pore size distribution of rock is proposed. By taking sandstone, marble, granite, and rock-like samples as object, capillary pressure curves derived from the transverse relaxation time and centrifugal results are acquired based on the nuclear magnetic resonance test and centrifugation test. The pore size conversion coefficients are obtained through capillary pressure curves fitting, and they are compared with the value gained by the other two methods. Results show that the pore size conversion coefficients of sandstone, marble, granite, and rock-like specimens calculated by the proposed method are 0.483 μm/ms, 0.583 μm/ms, 0.253 μm/ms, and 0.077 μm/ms, respectively. These pore size distribution curves obtained by the proposed method are quite close to curves obtained by the other two methods. One defect of this method is that it cannot obtain complete capillary pressure curves. Overall, it provides a new idea and path for characterizing pore structure accurately and repeatedly.