Fractal dimension and morphological heterogeneity of pore in carbonate rocks: implications for production differences between adjacent wells

This work investigates the morphological heterogeneity of pore systems in the carbonate rocks of the Canglangpu Formation, Sichuan Basin, aiming to explain the significant gas production disparity between two adjacent wells. An integrated methodology combining scanning electron microscopy (SEM) with digital image analysis was employed to classify pore morphologies and calculate fractal dimensions for 132 and 153 SEM images from Wells P7 and P9, respectively. The results demonstrate that Well P7 exhibits a more heterogeneous and intricate pore network, characterized by a higher median D value and a broader distribution, dominated by sub-circle pores across a wide complexity spectrum. In contrast, Well P9 possesses a more homogeneous pore structure with a lower, more clustered D value distribution. This morphological difference provides a mechanistic explanation for the production data, where the complex pore architecture of P7 likely impedes fluid flow, resulting in minimal production, while the more uniform system of P9 suggests better matrix connectivity. This matrix characteristic, combined with a more developed natural fracture network (the primary driver for high flow rates in such tight rock), correlates with its high daily gas output. In contrast, the complex pore architecture of P7 likely impedes matrix flow, contributing to its minimal production. The findings underscore that quantitative pore-scale characterization is critical for accurately assessing reservoir quality and predicting productivity in heterogeneous carbonate reservoirs, with direct implications for optimizing exploration and development strategies.