Method for establishing mathematical model of relationship between spontaneous imbibition volume and time of porous medium

A method for establishing mathematical model of relationship between spontaneous imbibition volume and time of porous medium in a spontaneous imbibition process, comprising following steps:

• step 100, selecting two parallel rock core plug samples for pretreatment, cleaning and drying the two parallel rock core plug samples, evacuating a first rock core plug sample and then injecting the first rock core plug sample with water to obtain a fully-saturated sample;
• then centrifuging the first rock core plug sample and recording changes of weight and nuclear magnetic resonance (NMR) T2 distributions to obtain water distribution characteristics of the fully-saturated sample in pores, wherein the selecting two parallel rock core plug samples for pretreatment, cleaning and drying the two parallel rock core plug samples comprising:
• drilling the two parallel core plug samples from the rock vertical to its bedding direction, cleaning and drying the two parallel core plug samples at 105° C. for 48 hours until mass remained unchanged, and the evacuating a first rock core plug sample and then injecting the first rock core plug sample with water to obtain a fully-saturated sample comprising:
• put the first rock core plug sample into a vacuum pump and vacuum for 8 hours, then injecting 3% KCl solution into the pump and pressurize to 30 MPa, and maintaining the pressure for 24 hours, and the centrifuging the first rock core plug sample and recording changes of weight and nuclear magnetic resonance (NMR) T2 distributions comprising:
• centrifugating the fully-saturated sample under centrifugal pressure and recording a mass of the sample before and after centrifugation;
• step 200, conducting spontaneous imbibition experiment on a second rock core plug sample, conducting NMR analysis on a result of the spontaneous imbibition experiment to obtain a T2 distribution of the second rock core plug sample;
• step 300, plotting cumulative volume distributions of the first rock core plug sample under fully-saturated and imbibition saturated states, to obtain a T2 value (T2c) when a cumulative volume in fully-saturated distribution equals to a total volume of a centrifuged sample and to obtain a centrifugal radius and surface relaxivity through T2c then calculating imbibition permeability and average pore pressure through porosity of the first rock core plug, saturation, and the T2 distribution of the second rock core plug sample under the fully-saturated state;
• and
• step 400, obtaining a mathematical model for the spontaneous imbibition process of porous media based on NMR by using the imbibition permeability, the average pore pressure, and the surface relaxivity based on a classical Handy relationship to substitute for corresponding parameters therewith.