The salt structure characteristics and formation mechanism of Early Permian Kungurian in Pre-Caspian Basin

The Pre-Caspian Basin is a large superimposed salt-bearing basin, which is also one of the largest sedimentary basins with the richest oil and gas resources in the world. The Kungurian Stage salt-bearing strata are distributed throughout the basin. The salt beds are very thick and widely developed in salt structural units. There are many structural types and different influencing factors. Due to the nature of salt rock itself and the particularity of deformation, the factors affecting structural deformation are diverse and complex. To study the influencing factors on the deformation of the huge thick salt structures in the basin, we scrutinized the evolution process of the basin from the perspective of the whole basin and analyzed the characteristics of the salt structure in the whole basin by using 2D seismic profile data and regional geological data. The formation and evolution of salt structure in the basin and its triggering mechanism are discussed through the restoration of balanced profile. Results show that the deformation degree of salt rock decreases from the center of the basin to the edge of the basin, showing zoning characteristics. The compressional action of preexisting slope and basin margin is the factor of initial deformation of salt rock, and the differential loading of overlying strata is the dominant factor of structural deformation of salt rock. The strata beneath salt beds have good continuity and weak deformation duo to the existence of salt rock, while the upper salt layer is poorly continuous and severely deformed. Therefore, the continuous and extremely thick salt bed in the Pre-Caspian Basin is a natural cap rock, and the reservoir under the salt is good, which should be the focus of oil and gas exploration in the future.