The influence of bioturbation on the petrophysical characteristics of the lower cretaceous reservoir rocks of the Northern Caspian

Abstract

The Caspian Sea is one of the most perspective areas for oil and gas exploration. Significant hydrocarbon reserves are contained in the polymictic sand reservoirs of the lower cretaceous (Aptian-Albian) deposits of the North Caspian fields, which are characterized by an irregular distribution of pelitic and silty fractions. This results in high residual water content and low permeability, poor consistency of filtration-volume properties between them. This predetermines high heterogeneity of reservoirs in hydrocarbon reservoirs and unusually low specific electrical resistivities when producing water-free hydrocarbon inflows. As the authors’ studies have shown, the most important reason for the complex structure is the intense bioturbation of deposits virtually throughout the productive section, which actively affects redistribution of clay material in the reservoir rocks and ultimately leads to a decrease in the resistivity of reservoirs to the point where they can be classified as low resistivity.