ABSTRACT

Digital Rock Physics (DRP) has been practiced for decades and is continuously improving with advancements of high-resolution imaging, faster-computing, and improved understanding of fluid flow in porous media. Traditional DRP applications have been predicting rock properties in challenging conditions such as unconsolidated samples, tight rocks, and irregular-shaped samples that are difficult to measure. In this study, DRP was used to better understand physical measurements and their interpretations and to reconcile different core analysis data for more complete formation evaluation. Carbonate core samples were mounted in a specially designed high pressure MicroCT core-holder as such stress can be applied to the imaged core to simulate reservoir conditions. High resolution microCT was used to scan the samples at different stresses to monitor the effect of stress on pore structure. Based on the high-resolution images, DRP was used to extract rock capillary pressure (Pc) at different stresses, which allowed to evaluate the effect of stress on rock properties. To complement and calibrate petrophysical properties derived from DRP, rock characterization was carried out including X ray diffraction, thin section, scanning electron microscopy, porosity and permeability, followed by measurements of Pc using centrifuge and porous plate methods at different stresses. Results from this study of integrating DRP and physical measurements show that Pc obtained by different methods agree well at ambient conditions. With increasing in stresses, differences in Pc have been observed, which allowed to provide correlations between applied stress and differences in changes in rock properties, which can then be used in integrated reservoir studies. In summary, DRP helps to explain physical measurements and interpreted results to gain insights of complex relationships between rock properties and test conditions of core analysis.

INTRODUCTION

Capillary pressure (Pc) is the difference in pressure at the interface between two immiscible fluids. It is caused by the curvature of the interface and is defined as the product of fluids interfacial tension (IFT) and the interface curvature (Ma and Morrow, 1993). Capillary pressure is an important factor in determining fluids distribution in and flow through a reservoir (Brown, 1951; Ma et al., 1996; Harrison and Jing, 2001; Masalmeh and Jing, 2006; Lang et al., 2018). At equilibrium in an oil reservoir, Pc may be calculated based on the following equation:

(equation)

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