Abstract:

Block Sagizski (Block S) is located in the Southeast of Pre-Caspian basin, which is abundant in hydrocarbon enrichment. But the prospection has no big breakthrough in recent years, because the study of the mechanism of hydrocarbon accumulation locality is weak, especially when there is no unified understanding about salt layer effect on hydrocarbon accumulation. The authors aim at the salt layer characteristics and its effect on hydrocarbon accumulation by means of geological analysis, seismic interpretation and typical oil/gas pool dissection. Based on studies, the characteristics of the salt thereby is described as follows: As a whole, the mode of salt’s formation belongs to the deep-basin and shallow-water salifying pattern; The forming mode of the salt-dome in Block S is mostly differential loading, partly consequent flow determined by faults; Salt structure movement took place many times over the Mesozoic and Cenozoic; The salt bed trends southeastwards thin and northwestwards thick in Block S, namely it tends to be thicker from the margin to the center of the basin; Salt windows well developed herein, the area of the salt window in south (close to the margin of the basin) is bigger than that in west (close to the center of the basin) generally. The effects of salt on the hydrocarbon accumulation within post-salt strata (including the strata over and between salt domes) in Block S can be concluded as follows: trap types and its distribution of the post-salt strata are well controlled by the salt. The scale of salty window influences the accumulation degree of oil pool nearby. Overall, there are three periods of hydrocarbon accumulation within the post-salt strata, and they are the period from Later Triassic to the end of Early Jurassic, the end of the Late Jurassic as well as the period from Late Cretaceous to Eocene respectively.

Key words: salt layer, strata over , salt domes, hydrocarbon accumulation, Kungurian Stage of Early Permian, block Sagizski, petroleum gas, Pre-Caspian basin