The Selection of Reasonable Pore-Throat Cutting Factor for Shrinkage Pore Network Extraction in Sandy Conglomerate Reservoir

Abstract

The sandy conglomerate reservoir exhibits substantial vertical extent and considerable thickness, which provides significant capacity for CO₂ storage. Meanwhile, the shrinkage pores are developed in the tuff-filled material of sand conglomerate reservoir, which is not only the oil/gas storage space, but also the ideal fluid flow channel of CO₂. It is particularly important to select a reasonable pore throat cutting factor and accurately describe the structural and physical characteristics of the shrinkage pores for the evaluation of sand conglomerate reservoir. In this paper, the shrinkage pore developed sample is scanned with micro-computed tomography (CT) to obtain the 3D gray image. The shrinkage pore 3D digital rock is segmented, and the corresponding pore network model is extracted. Then, based on the 3D shrinkage pore network model, a different pore-throat cutting factor is selected to construct the shrinkage pore network models with different pore-throat spaces and calculate the physical/structural parameters. It can be found that, with the increase of pore-throat cutting factor, the number of pore-throat and porosity remain unchanged, and the permeability decreases, the pore volume distribution shifts to the left, the throat volume and throat length shifts to the right, and shape factor continuously shifted to the right. The increase of pore-throat cutting factor causes the interface between pore and throat to be more inclined to the pore side; the pore volume thus decreases, and the throat volume increases. Given the close agreement between laboratory-measured permeability (36.3 mD) and Lattice Boltzmann simulation results (38 mD) for the original shrinkage pore digital rock model, a pore-throat truncation factor of 0.3 ± 0.1 (range: 0.2–0.4) is validated for sandy conglomerate reservoir characterization. When α < 0.2, it causes overestimation of pore volumes and underestimation of flow resistance; when α > 0.4, it induces excessive throat length and misrepresents real pore-throat morphology. This provides a basic platform for the accurate characterization of the shrinkage pores in sand conglomerate reservoirs.