ROCK TYPING AND PETROPHYSICAL PROPERTY ESTIMATION VIA DIRECT ANALYSIS ON MICROTOMOGRAPHIC IMAGES

ABSTRACT Correlations for petrophysical parameters and saturation dependent transport properties are usually grouped by "rock type". This is a broad classification including quantitative measures such as porosity, permeability, pore and throat size distributions, pore connectivity and qualitative descriptions of rock fabric and texture. Rock typing is based on conventional core analysis data (porosimetry, permeametry, mercury injection capillary pressure (MICP)), special core analysis (SCAL), wireline logs (electrofacies), description of cuttings and depositional environment, and thin-section analysis. The broad nature of this classification has obvious limitations and fails to fully capture the complex dependence between pore space geometry and topology (rock micro-structure) and petrophysical properties. We propose an alternate classification for rocks based on high resolution X-ray computed microtomography which is complementary to the conventional approach and allows the establishment of a more direct relationship between rock micro-structure and petrophysical properties. Petrophysical properties are computed directly from 3D microtomographic images of clastic and carbonate cores drawn from a wide range of reservoirs. The computed petrophysical properties are used to test empirical correlations between permeability and other important petrophysical parameters (e.g., hydraulic radius, drainage capillary pressure, NMR response, grain size and sorting) for various rock types. We find that the most universally robust correlations are based on the critical pore radius determined from drainage capillary pressure data. The results clearly demonstrate the potential for digital imaging and computations on 3D images to develop improved correlations for petrophysical properties