Digital carbonate rock physics

Abstract

Abstract. Modern estimation of rock properties combines imaging with advanced numerical simulations, an approach known as digital rock physics (DRP). In this paper we suggest a specific segmentation procedure of X-ray microcomputed tomography data with two different resolutions in the µm range for two sets of carbonate rock samples. These carbonates were already characterized in detail in a previous laboratory study which we complement with nanoindentation experiments (for local elastic properties). In a first step a non-local mean filter is applied to the raw image data. We then apply different thresholds to identify pores and solid phases. Because of a non-neglectable amount of unresolved microporosity (micritic phase) we also define intermediate threshold values for distinct phases. Based on this segmentation we determine porosity-dependent values for effective P -and S-wave velocities as well as for the intrinsic permeability. For effective velocities we confirm an observed twophase trend reported in another study using a different carbonate data set. As an upscaling approach we use this twophase trend as an effective medium approach to estimate the porosity-dependent elastic properties of the micritic phase for the low-resolution images. The porosity measured in the laboratory is then used to predict the effective rock properties from the observed trends for a comparison with experimental data. The two-phase trend can be regarded as an upper bound for elastic properties; the use of the two-phase trend for low-resolution images led to a good estimate for a lower bound of effective elastic properties. Anisotropy is observed for some of the considered subvolumes, but seems to be insignificant for the analysed rocks at the DRP scale. Because of the complexity of carbonates we suggest using DRP as a complementary tool for rock characterization in addition to classical experimental methods.

Digital Carbonate Rock Physics

“…This porosity-velocity trend is exactly the same as has been observed for a carbonate data set from a different location used in Saenger et al (2014). In their paper this trend has been observed for three different resolutions (65 nm, 1 and 4 µm).…”

“…This data-driven upper bound is much stricter than the bound given by Hashin-Shtrikman (see Fig. 8) and is now confirmed for several carbonates using several resolutions (this study and Saenger et al, 2014). Only for the low-resolution images we observe a slightly different trend for P waves (Eq.…”

“…4 and 5), which is supported by two observations. First, this trend was already observed by Saenger et al (2014) on different scales on a different carbonate data set. Second, there is an observed self-similarity for carbonates (Jouini et al, 2015).…”

EPCI: A new tool for predicting absolute permeability from computed tomography images

“…Numerical simulations can then be performed on the digital rock sample (resulting digital rock model) to quantify the available pore space, fluid transport properties (e.g. absolute permeability) and other rock properties such as elastic modulus, and the formation resistivity factor (Saenger et al, 2016).…”

Quantifying Rock Weakening Due to Decreasing Calcite Mineral Content by Numerical Simulations

“…Moreover, the same rock sample can be examined under varying testing conditions or mineral composition, which can be virtually varied [ 48 ]. Present numerical models employ calculation techniques to determine static [ 49 , 50 , 51 ] and dynamic moduli [ 52 ] mainly for reservoir rocks such as sandstones [ 53 , 54 ] and carbonates [ 55 , 56 ], but also for shales [ 57 ]. However, there is still a discrepancy between the achieved numerical estimates of mechanical properties derived from micro-CT images and laboratory data, where, regardless of the numerical approach, the simulated moduli are systematically higher [ 58 , 59 ].…”