Pore-scale Characterization of Carbonate Rock Heterogeneity and Prediction of Petrophysical Properties

Carbonate reservoirs, accounting for majority of the world’s hydrocarbon reserves, are well known for their heterogeneity and multiscale pore characteristics. The pore sizes in carbonate rock can vary over orders of magnitudes, the geometry and topology parameters of pores at different scales have a great impact on flow properties. A relatively simple way to integrate a set of digital pore space images of different resolutions is to superpose these images into one single large image by matching the resolutions of the individual images. In this paper, a series of 2D thin section carbonate images with different resolutions are collected with scanning-electron microscopy (SEM). The lower resolution image shows macro pore properties, while the higher resolution shows micro pore properties. With two different scale resolution images, a Markov Chain Monte Carlo (MCMC) method is used to construct 3D macro pore and micro pore digital rocks respectively. Basing on the macro pore and micro pore digital rocks, superposition method is introduced to construct multiscale digital rock. Then, pore analysis tools (PATs) are used to generate macro pore, micro pore and superposition network respectively; and flow calculation is performed on a pore-network model extracted from the combined image. At last, geometry-topology and flow properties are compared among the three different scale networks. Results show that, the superposition network could capture the important pore scale properties of both macro pore network and micro pore network. More importantly, different contributions to flow properties of certain scale pore structures are recognized, in particular, the potential impact of the micro porosity on the pore connectivity and the interconnectivity between different scale porosities is investigated and highlighted, which could describe the carbonates in a better way and has a dramatic effect on permeability and higher recoveries.