Method for determining unconventional liquid imbibition in low-permeability materials

A method of determining a rate of fluid imbibition into a low-permeability, hydrocarbon-bearing rock matrix, the method comprising the steps of:

• preparing a sample obtained from the low-permeability, hydrocarbon-bearing rock matrix for a spontaneous imbibition test with a fluid, the fluid operable for use in hydraulic fracturing of the low-permeability, hydrocarbon-bearing rock matrix;
• conducting the spontaneous imbibition test on the sample;
• recording cumulative imbibition of the fluid into the sample over time;
• determining an unconventional flow index, the unconventional flow index representing unconventional flow, and the unconventional flow index determined by a relational assumption where liquid flux into the sample causing the cumulative imbibition is a power function of a pressure gradient of the sample;
• measuring volumetric liquid content spatial distribution along the sample after the spontaneous imbibition test;
• determining a transport parameter of the sample responsive to:
• the volumetric liquid content spatial distribution along the sample after the spontaneous imbibition test;
• an initial liquid content of the sample before the spontaneous imbibition test;
• and the unconventional flow index;
• and
• determining the rate of fluid imbibition into the low-permeability, hydrocarbon-bearing matrix over time responsive to the unconventional flow index and the transport parameter.