Seismic lithology and geological implications of pre-salt jurassic carbonate rocks in the Amu Darya Right Bank

Abstract

The formation and evolution of oil and gas reservoirs are typically related to the environment where sedimentary facies occur and regional sedimentary facies are distributed. The accurate characterization of reef–shoal complexes is one of the important tasks for exploring oil and gas in carbonate reservoirs. However, most traditional methods for characterizing sedimentary facies are based on high-density drilling data, core data, and thin-section data, often making them less suitable in areas with few drilled wells or sparse well networks. Hence, they often cannot characterize sedimentary facies accurately, severely hindering the oil and gas exploration success rate. This study seeks to characterize sedimentary facies using limited amount of data from drilled wells. An innovative model representing the relationship between lithofacies and seismic attributes was established by comprehensively analyzing the relationship among lithologic associations, principal component analysis, and regression analysis based on seismic lithology and data from various sources. The sedimentary facies of the Upper Jurassic (Oxfordian) formation in the eastern region of the Amu Darya Right Bank were accurately characterized using Red-Green-Blue (RGB) fusion. These analyses indicate that the relationship among micrite, bioclastic micrite, and bioclastic limestone can effectively represent the developmental pattern of sedimentary facies in the study area. The planar distribution of sedimentary facies based on the relationship between the lithologic associations identified through seismic interpretation revealed the relationship between sedimentary facies and the paleomorphology of the region. Results show that the paleo-landform in the study area's western zone is low-lying, where shoals are poorly developed; the paleo-landform in the central zone is high, with high-energy water and well-developed and widely distributed thick shoals; and the eastern zone is far from the open sea and affected by the central-zone landform, with low-energy water and low-quality reef–shoal complexes. Controlled by the unique landforms of the study area, the western reservoirs are thin and have low quality, central reservoirs are thick with good petrophysical properties, and eastern reservoirs have differing thickness and petrophysical properties.