A method for measuring the in-situ porosity of shale

Abstract

The present invention provides a method for measuring the in-situ porosity of shale, comprising the following measurement steps: S1. Acquisition of basic experimental data: Prepare shale plunger samples, measure their geometric volume, determine total porosity using a helium porosimeter, and obtain nitrogen adsorption–desorption isotherms through an automatic gas adsorption analyzer. In the present invention, a dual-porosity cooperative characterization and fractal-permeability coupled system for measuring shale porosity and permeability is constructed, overcoming the limitations of a single-pore model. Based on the nitrogen adsorption–desorption isotherms, the non-negative least squares method is employed to simultaneously fit pore size distribution models of plate-shaped and cylindrical pores, accurately separating the structural characteristics of these two typical pore types. Subsequently, pore volume is normalized to connect the measured total porosity with the theoretically calculated values, and dedicated flow models are applied for different pore morphologies. Finally, the dual-pore system permeability is coupled in parallel with porosity as the weighting factor, thereby addressing the problem of incomplete characterization of the multi-morphology pore structure in shale.