Online Journal for E&P Geoscientists

Vega, Sandra ^*1; Jouini, Mohamed S.¹; Mokhtar, El Amin ¹
(1) The Petroleum Institute, Abu Dhabi, United Arab Emirates.

Heterogeneity seems to highly affect acoustic response in carbonate rocks. Some studies suggest that different pore space can be one of the major factors to have different acoustic responses. On the other hand, pore space soils and rocks often behaves as multifractals. Some of the parameters obtained from multifractal analysis, such as the range of singularity exponent (alpha) and the width (w) of the multifractal spectrum, can measure the degree of heterogeneity. However, all those previous works have been done mainly in soils and carbonates with clay content, and no correlation between heterogeneity and acoustic parameters have been calculated yet.

In this paper, we present a preliminary study that examine (1) if it is feasible to use multifractal analysis to scale rock properties from SEM images to core plugs in carbonate rocks free of clay, and (2) how acoustic measurements are affected by heterogeneity in these rocks. To accomplish our objectives, we perform a multifractal analysis using 2D SEM images from 3D carbonate core plug samples of a Middle East reservoir, which contains mainly calcite and dolomite and no clay minerals. We have found that most of the pore space captured in SEM images present multifractal behavior, and some of them are either in their upper or lower fractal limit. When studying if there is any correlation between porosity and the range of alpha, we find that the higher the porosity in the image, the higher the heterogeneity. On the contrary, when comparing the porosity from the corresponding 3D samples and the range of alpha, the relation is inverse. This difference is also reflected in an inverse correlation between porosity from the images and porosity from the core plugs. In addition, when comparing the porosity of the images, porosity of the core plugs, Vp and w, no clear correlations are revealed. Finally, to find a potential correlation between acoustic velocity and heterogeneity in carbonates, we compare Vp measured in core plugs and the range of alpha from images. We find an exponential correlation between Vp and the range of alpha. Then, our preliminary results imply that it might be possible to quantify the heterogeneity of the images, and correlate it with Vp. However, further studies need to be done adding more samples with same porosity and different pore space. Future work will also include thin-section images to complete a larger range of scales and magnifications.