Structural Features Of Late Paleozoic Paleo-uplift And Its Controls On Large Natural Gas Accumulation In Wensu-Luntai Area,Tarim Basin

The paleo-uplift is a bulging structure in the formation and evolution of the basin during a certain geological history,and is an key window for understanding the evolution and tectonic deformation of the basin.The Paleo-uplift is one of the most important oil and gas exploration fields.Its geometric shape,geological structure,evolution process and its relationship with sedimentation and hydrocarbon accumulation are the joint research directions of basin dynamics and petroleum geology.The Kuqa foreland basin is superior in petroleum geology and rich in oil and gas resources,so it is the main source of gas for the "West-East Gas Transmission Project".The study during the "Twelfth Five-Year Plan" showed that the Paleozoic paleo-uplifts developed in the area played a very important role as the bond on the sedimentary system of the Mesozoic,the distribution of the Paleogene gypsum salt rock,and the formation of the Late Himalayan thrust belt.Therefore,the study on the tectonic features of the Late Paleozoic paleo-uplift and its control of large-scale natural gas accumulation in the Wensu-Luntai area in the southern Kuqa depression is of great importance at solving the geological problems faced by oil and gas exploration and production,guiding the optimization and regional evaluation of oil and gas exploration in the southern margin of Kuqa and promoting the study of the geological structure of the Kuqa foreland basin.Based on the full use of geological outcrops,seismic and non-seismic data in Wensu-Luntai region,this study aims to carry out the research on the geological structure and tectonic evolution of the Late Paleozoic paleo-uplift andthe research on the control of hydrocarbon accumulation conditions such as source rocks,reservoirs,and trapsthrough comprehensive interpretation,structural modeling,structural balance profiles,and paleo-structural restoration,etc.This will guide oil and gas exploration in the area and provide a basis for improving the tectonic evolution process in the northern Tarim Basin.Through the research of the thesis,the following results have been achieved:(1)Through the regional seismic section,non-seismic data interpretation and structural modeling,the geological structure characteristics of the Kuqa foreland basin and the Tabei uplift transition zone are established,and it is found that there is a large paleo-uplift belt(Wensu-LuntaiPaleo-uplift)on the southern margin of the Kuqa foreland thrust belt.The uplift belt can be divided into WensuSub-uplift,XiqiuSub-uplift,XinheSub-uplift and YahaSub-uplift from west to east,and has a geese-type distribution feature on the plane;(2)Through the regional tectonic evolution analysis and the restoration of the balanced profile,it is determined that the paleo-uplift of the Wensu-Luntai area experienced the tectonic evolution of the Paleozoic,Mesozoic and Cenozoic phases.When the Permian South Tianshan Ocean gradually closed,the Kuqa area experienced compressional structural deformation and the Wensu-Luntai area became the structural pivot zone of the extrusion structure front,forming the paleo-uplift belt.The Triassic Kuqa foreland basin was characterized by the foreland load intrusion caused by the uplift of the South Tianshan Mountains.The Wensu-Luntai paleo-uplift forms a narrow east-west long bulge,which is affected by tectonic activities.The basement fracture is developed in the paleo-uplift belt.In the Jurassic-Cretaceous period,the Kuqa areawas characterized by an active period of the depression basin,and the gradually weakened activity of Wensu-Luntai paleo-uplift.In the middle to late Cenozoic,the southern Tianshan Mountains were once again uplifted.Due to the strong orogeny,the paleo-uplifts in the Wensu-Luntai area were re-activated.Large-scale salt diapir structure were formed in the salt-rock formation due to the effect of the vertical uplift of the paleo-uplift;(3)Through the study of the formation mechanism of paleo-uplifts,we conclude that the basement fault is an important factor in the formation of zoning during the evolution of the paleo-uplift;the difference of stratigraphic dryness caused by the interbedded deposition of brittle and plastic strata plays an important controlling role on the layered deformation of the overlying strata;(4)Through the study of the oil and gas accumulation control of the Kuqa foreland basin by the Late Paleozoic paleo-uplift in the Wensu-Luntai area,we postulate that the paleo-uplift plays a significant role in constraining the thrust range,controlling the distribution of the reservoir-caprock combination and promoting oil and gas migration and accumulation.The foreland thrust belt in the late Himalayan period is mainly developed north of the paleo-uplift,forming a large-area anticline and an anticline trap under the salt;The Mesozoic clastic rocks overburdened from the paleo-uplift,forming a reservoir-caprock combination of the Jurassic and Triassic hydrocarbon source rocks and the Cretaceous,Paleogene and Paleogene caprocks to the north of the Paleo-uplift.In the late Himalayan Movement,the paleo-uplift and its southern part showed that oil and gas migrated along the Mesozoic thick sandstone or unconformity surface in a wide range,and vertically transported into the reservoir in a short distance along the fault zone(collectively referred to as "large lateral,small vertical").In contrast,the natural gas of the Krassu tectonic belt in the north is characterized by vertical and short-distance transport along the fault(referred to as "small lateral,small vertical").