Structural Analysis And Analogue Modeling Of Salt Structures In The Salt-bearing Sedimentary Basin

The Kuqa depression in the southern edge of Tianshan, the Precaspian basin in the central Asia and the Red Sea basin in the central Africa are foreland, cratonic and rift salt-bearing sedimentary basin, respectively. Very thick Paleogene-Eocene Kumugeliemu group (E1-2km) (the west part), Lower Permian Konggu group (P1kg) and Miocene Dungunab group rock salt were deposited with abundant salt-related structures occurred in these three basins. Moreover, oil and gas exploration indicated that the hydrocarbon accumulation is closely related with the salt-related structures. Therefore, it has very important guiding significance on oil and gas exploration by understanding the salt structural styles, geometric features, the deformation mechanism and the controlling factors in these three basins.After the literature research of salt structures in the global salt-bearing basins, and on the basis of field works, the structural interpretation of seismic profiles and analogue experiments, this thesis analyzed and discussed the features of the salt-related structures and their deformation mechanism and controlling factors in these three basins mentioned above. Some important research results were achieved as following:1. The Kuqa depression is a salt-bearing foreland basin. The main salt structures include salt diapir, salt anticline, salt nappe (allochthonous salt sheet) and salt weld. Salt structural characteristic in this basin is typical compressional deformation. The differential structural deformation is also represented by structural differentiation in different levels, latitudinal zonation and longitudinal sections. Field geological investigation, geophysical profiles and analogue experiments shown that the features and mechanisms of salt structural deformation was controlled by the compression stress, the variable depositional width of the salt basin, the pre-existing diapir, the subsalt basement ramp, the gravity loading and the syn-kinematic sedimentary rate together:(1) The compression stress from the north only caused the uplifting of the north flank in the broad salt basin (Baicheng sag), while uplifting the whole salt basin (Awate sag) associated with a very thin deposition strata in the narrow salt basin; (2) Talake fault, a dextral strike-slip fault, was formed in the western boundary of Awate sag, where salt is pinch-out, in the western Kuqa depression. This strike-slip fault influenced the structural formation and evolution of the salt related folds in Awate sag; (3) Pre-existing passive salt diapirs in Qiulitage thrust-and fold belt could be evolved into salt related thrust structures under the compression stress; (4) the subsalt basement ramp and the gravity loading from the Baicheng sag, which caused the salt converging and upwelling together, influenced the structural formation and evolution of the salt related structures above the basement ramp, such as the formation of the Misikantake anticline, south Qiulitage anticline in the Quele area and the Baozidun salt diapir between the Baicheng sag and Awate sag; (5) syn-kinematic sedimentary rate controlled the thrust direction of the pre-existing salt diapir during the propagation of the compressional stress. The differential sedimentary rate made the differential deformation in the middle and western Qiulitage structural belt.2. The Precaspian basin is a cratonic salt-bearing basin. The salt structures mainly include salt wall, salt diapir, salt roll, salt pillow (or salt dome), salt weld, Flip-flop salt structure, intrasalt withdrawal minibasin and crestal sag basin. Salt structural characteristic in this basin is presented by typical thin-skinned extensional deformation. Regional geophysical profiles and analogue experiments shown that the features and mechanisms of salt structural deformation was controlled by progradation, the gravity spreading and the distribution of the the subsalt uplift basement:(1) progradation induced the differential deposition loading and controlled the formation and evolution of the salt diapir at the location of the progradation front; (2) the gravity spreading induced the extension in the overburden and controlled the formation and evolution of the reactive triangle salt diapir; (3) the subsalt basement palaeohigh has an important controlling influence on the development of the salt structures. The salt diapirs could be easily induced at the location of the juncture between the margin of the subsalt basement palaeohigh and the slope.3. Sudanese Red Sea basin is a rift salt-bearing basin. The salt-related structural styles mainly include salt roll, salt diapir and salt related drape structure. Salt structural characteristic in this basin is presented by typical thick-skinned extensional deformation. Regional geophysical profiles and analogue experiments shown that the main the features and formation mechanism of these salt structures was controlled by the movement of basement faults, syn-rift deposition and the initial thickness of the salt layer:(1) The movement of basement faults improved the strata rotation and induced the normal fault occurring in the overburden, which controlled the development of the salt structures in the overburden; (2) The syn-rift deposition caused the differential gravity loading, which made the salt flowing and converging at the location of the lower gravity potential; (3) The initial thickness of the salt layer influenced the salt-related structural styles in the overburden; (4) According to the distribution of these syn-rift salt structures, the structural traps in the overburden could be classified into salt-related barrier trap, rolling anticline trap and draping structural trap, while in the basement mainly include basement fault-related structural trap, such as fault-related anticline.