New Vibroseis data and interpretations from the Shebsh oil and gas field, southwestern Russia

The Kuban Basin is one of two foredeeps in the northern Caucasus region, southwestern Russia, and has been a significant source of oil and gas in Russia for the past century. In October 2001, The University of Tennessee and Kuban State University acquired new vibroseis data in the Shebsh oil field of the Kuban Basin with the goals of (1) imaging a thrust fault and deeper structures thought to underlie the anticline in the Shebsh field, (2) determining the particular type of fault-related folding that was important during the formation of the anticline, (3) determining the timing of tectonic activity both within the Shebsh oil and gas field and, by inference, elsewhere within the Kuban Basin, and (4) locating prospective hydrocarbon reservoirs within the anticline. An existing interpretation of the structure, based in part on well data and several vintages of older seismic data, depicted it as either a fault-bend or fault-arrest fold with up to 1 km of displacement along a ramp underlying the anticline. The new seismic sections reveal that detachment folding accommodated a major portion of the tectonic shortening. A decollement formed in mechanically weak Paleocene strata that thickened above steeply dipping Cretaceous rocks, which possibly had a buttressing effect during thrusting. Additional tectonic shortening may have been accommodated by the displacement of Paleocene and younger strata up a ramp in fault-arrest folding. Seismic reflector geometries reveal sedimentary thickening on the northeast limb of the anticline, leading to an interpretation that a significant episode of thrusting occurred coeval with sedimentation between ~16 and 7 Ma. The new seismic sections also contain bright spots and high amplitude reflectors that correlate with interpreted sandstone and limestone layers, and may lead to new drilling targets and increased hydrocarbon production in Eocene, Middle Miocene, and Upper Miocene age strata.