Differential Deformation Mechanism Of Kelasu Structural Belt In Kuqa Depression: Effects On Oil And Gas Distribution

The Kelasu tectonic zone is an important hydrocarbon accumulation zone in the Kuqa Depression,and the distribution of salt deposits and salt-related structures have an important influence on the extruded saline hydrocarbon basin.The Kelasu tectonic zone is characterized by east-west segmentation and north-south zoning.A systematic analysis of its deformation variability and controlling factors is required to reveal the characteristics and deformation mechanism of the Kelasu tectonic zone,further elucidate the influence of the deformation variability on the hydrocarbon accumulation distribution in the study area,and guide hydrocarbon exploration and development.Based on the tectonic analysis,this thesis uses physical and numerical simulations to analyse the characteristics of differential deformation in the Kelasu tectonic zone,explore its evolutionary process and influencing factors,and reveal the mechanism.Based on this,we analyse the formation process of typical hydrocarbon reservoirs in the Kelasu tectonic zone and elucidate the hydrocarbon effect of differential deformation in the Kelasu tectonic zone.The results show that,(1)differential tectonic deformation in the Kelasu tectonic zone is influenced by basement palaeo-uplift,salt lake thickness,differential loading and extrusion rates.Basement palaeo-uplift affects the depositional distribution characteristics of the salt rocks,which in turn controls the tectonic deposition thickness of the upper salt layer,and variable rate extrusion leads to the formation of recoil faults.During the contraction-extrusion basin phase,the salt rocks flow and deform under the influence of extrusion stresses,and the basement palaeo-uplift simultaneously impedes the lateral flow of the salt rocks.The width of the basal palaeo-uplift becomes progressively wider laterally from west to east in the Kelasu tectonic zone,and as a result,there are differences in the deposition of salt rocks in each section.After extrusion and deformation,the tectonic deformation of the salt rocks is further influenced by the basal palaeo-uplift,resulting in the formation of salt mounds and salt bottom structures,which also lead to different depositional thicknesses of the upper salt layer and rebound faults of the lower salt layer,resulting in different tectonic deformation characteristics.(2)The geometry of the fault-related folds under the influence of the salt layer is clearly asymmetrical,with steep forelimb and gently sloping rear flanks.The high strains are mainly distributed at the fault tip,fault slope,front flank and locally on the back flank of the fault-related folds.The mechanical properties of the rock have a minor influence on the tectonic deformation pattern and strain distribution.The evolution of fault-related folds is mainly influenced by the fault dip,fault friction coefficient,number of faults and fault spacing.(3)There is a paleouplift structure in the Great Northern section of the Kelasu tectonic zone,which limits the deformation space,with strong tectonic deformation,thicker deposition of the supra-salt layer,fault-back-slope controlled reservoir,and better preservation conditions,while the Keshen section is less influenced by the paleo-uplift,with weaker tectonic deformation,thicker deposition of the salt rock layer,thinner deposition of the supra-salt layer as a result,fault-back-slope controlled reservoir,and poorer preservation conditions.Based on imaging logs,natural fracture parameters are measured in different wells to analyse the effect of differential tectonic deformation on the distribution of natural fracture development and accordingly reveal its hydrocarbon effect.The study shows that the high degree of natural fracture development in the forelimb of the fault-related folds is a potential hydrocarbon sweet spot.The thesis has 40 illustrations,15 tables and 143 references.