Evaluation of the Rock Properties in Structurally Deformed Areas Based on Outcrop Analogues for Offshore Fields in Azerbaijan

Abstract

Deformation bands have been evidenced from both outcrop observations and subsurface data worldwide. These features form in variety of tectonic settings and are known to influence the rock properties in various ways. The aim of this study is to quantify the impact of deformation bands and their kinematics on reservoir properties for a wide range of rock types based on the field measurements in the outcrops of Yasamal Valley located in the western part of the South Caspian Basin. The study reveals deterioration of rock properties through deformation bands depending on several structural, lithological and petrophysical factors. An integrated approach was put together to understand the impact of these factors including the measurements of natural gamma radioactivity, permeability, dip and strike across the range of facies and distribution of deformation bands using portable tools. Additionally, Routine and Special Core Analyses were performed on the outcrop plugs with and without bands to estimate the alteration of the rock properties at the micro-level supported by petrographical description, SEM, XRD and CT scan tests. Interpretation of data shows that no bands occur in the rocks with shale volume greater than 32% as determined from the field gamma ray measurements. Moreover, the probability function of the band occurrence for a range of clay content was determined. High amount of calcite cement observed in the field appears to increase the number of deformation bands and significantly reduce porosity and permeability of the host rock. A petrographic analysis of the collected samples allowed to determine the impact of the mineralogical composition on degradation of rock properties. Laboratory results from the collected outcrop samples containing single deformation band show 33% and 3% decrease in permeability and porosity, respectively, in comparison with the adjacent host rock plug without a deformation band. No obvious correlation between bed dip and strike with concentration of deformation bands could be identified. The occurrence of bands and their subsequent influence on rock properties is a complex function of several factors that either counteract or enhance each other. Nevertheless, clay content is amongst the dominating parameters affecting the occurrence, concentration and the type of deformation bands.