Development and Application of a Rock Physics Model to Infer Pore-Geometry and Clay-Distribution in Argillaceous Sandstone

Due to its favorable pore-permeability characteristics, sandstone serves a crucial role in applications such as oil and gas production, freshwater extraction, and underground CO₂ storage. As the primary reservoir space and migration pathway for hydrocarbons, accurate porosity data are essential for seismic exploration and reservoir development. In unconventional reservoirs, establishing an appropriate tight sandstone rock physics model is key to understanding how petrophysical parameters influence porosity and permeability. However, conventional models often fail to dequately represent both the three-dimensional irregularity of pore geometries and the spatial distribution of clay minerals.

To address these limitations, this study develops a novel rock physics model that incorporates superspherical pores and clay distribution to characterize argillaceous sandstone. Clay is categorized into structural clay (within the matrix) and dispersed clay (within pores). Following a sequential approach that reflects natural sandstone grain stacking, the proposed model is constructed by employing Voigt-Reuss-Hill averaging methods to incorporate structural clay, coupling the superspherical pores model, and applying solid substitution equations to determine the saturated rock modulus, which contains dispersed clay. This framework allows quantitative analysis of how pore geometry and clay occurrence states affect rock elastic properties.

However, in practical settings, the high cost of well logging often prevents direct measurement of these parameters. Therefore, a simulated annealing algorithm is employed to inversely determine pore characteristics and clay content in different occurrence states at each sampling point along the wellbore.

The validity and practical applicability of the proposed model are demonstrated through comprehensive sensitivity analyses and real-data applications.