Characterizing locality- and scale-dependent heterogeneity in conglomerate core and associated fluid flow using X-ray CT imaging

Abstract

Heterogeneous conglomerates preserving matrix and clasts caused the complex distribution of pore spaces and can eventually influence fluid flow. To evaluate the influence of complex heterogeneous features in conglomerate rock on both pore distribution and fluid flow, two conglomerate cores were analyzed using X-ray computed tomography (X-ray CT). Conglomerate cores (Core I and Core II) characterized by different distributions of matrix and clasts represented highly heterogeneous features; in Core I (clast-supported conglomerate), clasts were evenly distributed through the entire core, but in Core II (matrix-supported conglomerate), large-sized clasts were dominantly positioned at the bottom of core. Such heterogeneous features caused differences in volume of pores (Core I: 7,409.54 mm3 and Core II: 17,525.83 mm3). Based on X-ray CT image analysis, the numerical model (single-phase fluid simulation) was implemented to evaluate the permeability of conglomerate at different scales. Especially, due to inner heterogeneous features (e.g., matrix, clasts, and cracks) in conglomerate cores, permeabilities were changed significantly dependent on the selected location and size of sub-domains representing a few centimeters (kh and kv: 1.18×10-12 to 1.01×10-10m2). This suggests that the effect of small-scale heterogeneity should be evaluated carefully when heterogeneous conglomerate cores were analyzed. Additionally, the measurement scale for X-ray CT analysis should be large enough to capture such heterogeneous features (e.g., the size of clasts).