Abstract
Abstract Previous study, of a geological and petrophysical investigation from an outcrop in the UAE, found a potential correlation between acoustic velocities and fracture density. However, it was not clear what could be the effect of this correlation in the seismic response. The aim of this paper is to extend this previous study to better understand its results and to investigate their significance in the seismic response. To achieve this purpose, we correlated geological and geophysical parameters at four different scales: outcrop, seismic, core plugs and thin sections. We acquired a seismic line on the top of an outcrop. From the same outcrop we examined 17 core plugs and 30 thin sections along different locations. We found that acoustic velocities, measured in the lab, decrease with increase in fracture density. This result was supported by the outcomes of the outcrop-seismic correlation where changes in fracture density were found to be an important factor that affects the seismic response in carbonate rocks. Such correlation can lead to better understanding of the seismic response which can result in an improvement in seismic interpretation of areas with similar geological conditions. Introduction Correlations between seismic and rock properties in carbonates are not well understood yet. An earlier geological and petrophysical investigation of an outcrop, from 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 (Al Menhali et al., 2008). However, it is not clear what could be the effect of this correlation in the seismic response. The aim of this paper is to extend this previous study to better understand its results and to investigate their significance in the seismic response. It particularly aims to find a potential reason behind the acoustic velocities-fracture density relation and to investigate why an outliner group deviated from the general trend. It also aims to study the significance of acoustic velocities-fracture density relation on seismic response, as well as to investigate factors that affect seismic response in the study area by correlating outcrop, seismic and lab measurements from core plugs. The outcome of such correlation can lead to an improvement in seismic interpretation of areas with similar geological conditions. To achieve the purpose of our study, we correlated geological and geophysical parameters at four different scales: outcrop, seismic, core plugs and thin sections. We combined the following methodologies: a) describing the exposed rocks in the outcrop in terms of texture, bed thickness and stratigraphy; b) measuring fracture density, acoustic velocities (compressional, Vp, and shear, Vs), density, porosity and permeability of 17 core plugs taken from various locations along the outcrop and using cross plots to investigate any possible correlations, c) examining 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; d) performing digital image analysis (DIA) to determine quantitative DIA parameters for the description and characterization of the pore space; e) acquiring a shallow (around 30 m of penetration) seismic line over the outcrop, which has a flat top surface; f) processing and interpreting the seismic profile; and g) integrating the results of the previous methodologies to correlate the outcrop, seismic and rock properties measured in the lab.