Characteristics of carbonate and terrigenous subsalt formations of the Caspian Depression and formation of hydrocarbon traps within them
KT-II carbonate and terrigenous sequence is a main petroleum producing object in the eastern shoulder of the Caspian Syneclise. Oil production in the large oil and gas fields is associated with these formations. At the same time, in a number of fields in the eastern shoulder of the Caspian Depression the producing petroleum reservoirs are associated with terrigenous formations. In the fields, where reservoirs are represented by carbonate rocks, terrigenous formations play a role of seal. The detailed studies of sedimentation settings and tectonic conditions of carbonate and terrigenous rocks formation is an important task when geological exploration planning and conduction, and selection of exploration well sites. The paper presents substantiation of mechanism of hydrocarbon accumulations formation in КТ-I and КТ-II series of Zharkamyssky and Temirsky massifs owing to oil and gas vertical migration from underlying formations, presumably, КТ-III. The authors propose a scale for evaluation of traps potential in КТ-I and КТ-II series on the basis of folding and faulting criteria; and also criteria for petroleum potential assessment in the traps of КТ-III series. Phase state of hydrocarbons in a trap of КТ-III formation is predicted.