Pore structure analysis of grain based model of sedimentary rock by means of digital image analysis

Abstract

Three computer models of a sandstone were generated using grain based model. The porosity and the grain radius of the models were made to match the real sample, which is a sandstone obtained from Ngrayong formation. The models were produced using an algorithm to ensure the grains were consolidated. The three models have different grain shapes, which are spherical, ellipsoidal and non-spherical (polygonal). Digital image analysis were performed to the three models in order to characterize the features of the models. The porosity is set on the value ∼21%. Despite the fact that the porosity and grain size (as well as the distribution) of the models are set to have very similar value, the produced models reveal different pore structure features. From the 2D and 3D fractal dimensions, the ellipsoidal model has the highest value among other models (the spherical and polygonal have very similar value) which indicates that the ellipsoidal model has more complex pore structure. This is confirmed by the degree of anisotropy (DA), where the ellipsoidal model has DA of 2.66 while the spherical is of 1.10 and the polygonal is of 1.46. The average of the structure separation of the models, which basically a rough estimate of the pore size reveals that the ellipsoidal model has narrower pore size compared two other models, which have very similar result. The average structure thickness of the models, which basically a rough estimate of the grain size shows that the ellipsoidal model has smallest value compared to the other two models, which once again, have very similar result. Here we conclude that the ellipsoidal model has the most complex and anisotropic pore structure compared to the two other models. Future work are focused on analyzing the effect of the grain size to other physical properties such as permeability, tortuosity and the elastic properties.