Oil and Gas Traps
Related to Salt Tectonics in the
Stovba, Sergiy M.1, Dmitriy B. Vengrovitch2, Randell A. Stephenson3 (1) Scientific Research Institute of Oil and Gas Industry (Naukanaftogaz) of National Joint-Stock Company “Naftogaz of Ukraine”, Kyiv, Ukraine (2) Institute of Geophysics, National Academy of Science, Kyiv, Ukraine (3) Vrije Universiteit, Amsterdam, Netherlands
Hundreds of oil-and-gas traps formed due to salt tectonics host the most important hydrocarbon reserves in the Dniepr-Donets Basin (DDB). As most of concordant salt structures were studied by drilling, the main significance for future exploration has traps nearby salt diapirs. Some salt diapirs formed as a salt plug pushing ahead of it a faulted column of country rocks with vertical displacement more than 1 km. In the early growth history of such structures, simple arching and erosion of sedimentary overburden was the primary process. Bedding can be vertical in the direct vicinity of salt diapirs that are more than 5 km high. Diapirism caused blocks on the top of a previously concordant salt structure to rotate upward and outward.
Rheology of natural materials was applied to model quantitatively the mechanism of trap and salt structure formation. The dynamic model of overburden is characterised by the presence of internal block structure. The overburden can be separated or crushed by external load. Thus, the salt overburden is a brittle-elastic medium that is frequently used on physical simulation of salt tectonics. The modelling results show that buoyancy, erosion, and differential loading all play a role in driving halokinesis once tectonic forces have pushed the salt-overburden system into disequilibrium; among these factors, erosion of overburden above growing salt structures acted as a key self-renewing force. The results are in accordance with peculiarities of salt diapirsm in the DDB. The modelling approach gives a possibility to predict oil/gas traps in overburden nearby salt structures.