Determination of Specific Surface of Rock Grains by 2D Imaging

Specific surface is an important parameter for predicting permeability of porous rocks. Many digital methods have been invented to extract the rock properties via imaging such as Micro-CT. With utilizing 3D volume data, this helps in precise investigation; however, it is neither economically efficient nor can be applied for different situations. In this study, a new approach is developed to estimate rock specific surface using 2D thin section images with micron resolution. One specific conclusion of this study is that there is specific ratio between the specific perimeter of 2D images and the specific surface in the 3D real rock structure. To further investigate this ratio several 3D blocks of rock volume data have been virtually cut in every possible angle and the value of specific perimeter calculated for each obtained 2D thin section. Finally, the predicted value of specific surface for 6 rock types is compared with the real values calculated from the original 3D data. Result indicates acceptable precision of this approach for sandstone rocks whereas not applicable for carbonate rocks. 1. Introduction Specific surface area of a porous material is defined as the interstitial surface area of pores per unit of bulk volume or solid volume of the porous material. Specific surface is critical parameter considering fluid permeability of a porous material [1–3]. Since specific surface is the ratio of area to volume, it has dimension of . The specific surface of porous granular media is defined as follows [3]: Several methods for estimating specific surface of porous materials have been discussed in the literature until now. Collins [1] is one of the first pioneers of using these methods for specific surface measurement. Collins categorized the methods of specific surface determination into three main groups as follows: (A) adsorption measurement of specific chemicals into pore walls, (B) measuring the fluid flow through medium [4], and (C) statistical methods such as stereological, optical, and NMR analysis. In the adsorption based methods, Methylene Blue Dye, as well as gas adsorption, has been used to determine the surface area of clay minerals for several decades [5]. Dogan et al. [6] measured the specific surface of clay minerals by the Brunauer, Emmett, and Teller (BET) method of adsorption of nitrogen gas. Fluid flow methods which are basically an application of Kozeny-Carman equation are widely treated in the literature. This equation is the most famous permeability-porosity relation, which is widely used in the field of flow in porous media and is