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Correlation and Integration of Seismic Velocities, Rock Properties, and Pore Structure in from Outcrop of Wasia Group Rocks in the U.a.E
(1) Petroleum Geosciences, The Petroleum Institute, Abu Dhabi, United Arab Emirates.
(2) Geology, University of Miami, Miami, OH.
An earlier geological and petrophysical investigation of the Lower Cretaceous, Wasia Group in the UAE found potential correlations between seismic velocities (Vp and Vs) and fracture density, except for a group of rock samples that deviates from the general trends. The aim of this study is to better understand the previous results to improve characterization and correlation of the geology and rock properties of the exposed rock.
Rock properties of 17 samples from various outcrop locations are related to different geological parameters observed at different scales, from thin sections over core plugs to outcrop dimensions. In order to achieve this correlation, we combine the following methodologies: a) examination of 30 thin sections under the microscope trying to group samples and to find any common features that can explain any correlation with the rock properties; b) digital image analysis (DIA) to determine quantitative DIA parameters for the description and characterization of the pore space; 3) comparison of DIA analysis and core plugs, using crossplots to investigate any other possible correlations, and d) correlation of a shallow fully processed and migrated 2-D seismic reflection profile from the study area, outcrop stratigraphy, and rock properties.
The results show a general trend in seismic velocity-fracture density but an outliner group of samples deviates from this trend. The type of porosity seems to cause the deviation of outlier samples from the general trend. We find that all samples belonging to the outliner group have intraparticle porosity that is randomly distributed. In contrast, the porosity in the other samples is associated with fractures and/or stylolites. Moreover, quantitative DIA analysis confirms that the effect of pore spaces can be the cause of different trends of the different groups. The crossplots from the quantitative DIA analysis corroborate results of the previous work that correlated rock properties with velocities. In addition, the results display that the complexity of pore space, is related to the velocities, which decrease generally as pore spaces get more complex in terms of shape and dimensions. The quantitative DIA also shows that the more complex the pore system, the higher the fracture density. Finally, we use these results to process and interpret a 2-D seismic reflection profile to better understand the seismic response in the highly fractured exposed rocks of Wasia Group.