Fault dislocations as fluid barriers of hydrocarbon deposits near salt domes in the Dnipro-Donets Depression, Ukraine

Within the Dnipro-Donets aulacogen, Devonian salt stocks (diapirs) are widely developed. The suprastock, interstock, and nearstock areas associated with these diapirs have consistently drawn the interest of researchers in the Dnipro-Donets Depression for hydrocarbon exploration. Uprastock and interstock areas, primarily associated with anticlinal structures, have been the primary targets for exploration. Numerous significant hydrocarbon accumulations, including large and unique deposits, have been discovered in these structures. These deposits are classified as bedded, massive-bedded, and dome-shaped, with lithological or tectonic confinement. Sealing rocks are the Permian chemogenic sedimentary succession or clay-rich roks at various stratigraphic levels of the overlying rocks. Modern seismic methods effectively identify, outline, refine, and prepare such structures for drilling, with a geological success rate of approximately 0.6. Nearstock areas encompass parts of salt-dome structures with unique characteristics resulting from salt diapirism. These areas often feature hydrocarbon traps only a few hundred meters wide, characterized by low seismic reliability due to salt-induced wavefield distortions and complex structures. The geological success rate for hydrocarbon exploration in these challenging conditions is approximately 0.12. Four main types of hydrocarbon traps are identified in nearstock areas: reefal deposits in the Upper Pennsylvanian Araukarytova Formation and the Early Permian Slovians’k Formation; dikes in the Upper Pennsylvanian and Lower Permian sedimentary rocks; tectonic satellite blocks including Serpukhovian, Bashkirian, and Upper Pennsylvanian rocks; and carbonate banks in the Lower Permian deposits. Nearstock traps are confined by salt stocks or by radial faults and salt filling radial fractures. Caps include salt diapir overhangs and Lower Permian chemogenic rocks. In the absence of robust fluid seals, nearstock traps often prove empty, likely due to poor sealing properties at the salt diapir-collector contact. Despite this, nearstock hydrocarbon sedimentary rocks with pre-Cenozoic salt formation are found in various Dnipro-Donets Depression regions.