S. T. Khusanov, Sh. S. Khusanova, Sh. T. Nizamov

Geological structure of the Upper Jurassic carbonate formation in the Bukhara–Khiva oil and gas province (South-West Uzbekistan)

Abstract. The paper examines the formation conditions and specifies the geological structure of the Upper Jurassic carbonate formation in the Bukhara–Khiva oil and gas region as one of key areas of hydrocarbon reserves concentration within the Central Asian oil and gas province. The paper summarizes and organizes materials from long-term geological exploration, lithofacies, paleontological, and stratigraphic studies, as well as utilizes data from deep drilling and regional tectonic analysis. The focus is on characteristics of sub-reef horizons XVI and XV, in addition to the Upper Oxfordian–Kimmeridgian reef and supra-reef deposits formed under conditions of the area's active tectonic evolution. The authors examine pre-reef deep-water, barrier-reef, and back-reef lagoon facies, their material composition, spatial vari- ability, and relationship with paleorelief morphology. Reef buildups and related accumulative structures prove to be critical for the most capacious and permeable carbonate reservoir formation and are confined to zones of tectonic bends, flex- ures, and faults in the Paleozoic basement. The balance between the tectonic basin floor subsidence rate, sea level, and high biological productivity of reef-building organisms controlled the growth and spatial position of barrier and isolated reefs. There are grounds for activation of fault structures contributing to the formation of relative uplift areas where bioherm and reef buildups with improved reservoir properties developed, as well as zones of back-reef aprons and carbonate shoals. The applied facies analysis methods, lithological and petrographic, and paleontological studies refined the formation model of the Upper Jurassic carbonate formation in the Bukhara–Khiva oil and gas region.

Keywords: Upper Jurassic deposits, carbonate rocks, reef buildups, fault tectonics, Paleozoic basement, facies analysis, reservoir properties, Central Asian province