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Physical Analogue Experiment Of Shuangyushi Area In Northwestern Sichuan And Its Implications For Hydrocarbon Accumulation

Posted on:2021-03-10Degree:MasterType:Thesis
Country:ChinaCandidate:Q LuoFull Text:PDF
GTID:2370330647963167Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
The Shuangyushi structural belt is typically concealed beneath the piedmont belt of the northwestern Longmenshan-Sichuan fold-and-thrust belt and Sichuan foreland basin,located in the Jiange area of Mianyang,Sichuan Province.It is roughly parallel to the Longmenshan thrust belt,NE-SW distributed.Hidden faults and traps are well developed in this area.In recent years,many exploration wells in Shuangyushi area have drilled high-yield gas flow in Permian strata,indicating Shuangyushi area becomes the hot spot of exploration in western Sichuan.This paper focuses on the study of the geological and geophysical interpretation from the surface to the hinterland of Shuangyushi structural belt and its adjacent areas in northwestern Sichuan,and its sandbox physical analogue.The main conclusions are as follows:(1)Based on the field survey of three typical profiles and study of the Kuangshanliang-Tianjingshan structural characteristics,which are respectively the Zhaohua-Shuimogou section,the Ximiao-Fengshunchang section and the Zhangming-Yangjiagou section,we conclude that 3 main faults control the strong tendency and zonation characteristics of northwestern Sichuan(Nanba-Beichuan Fault,Majiaoba Fault and Guangyuan-Xiangshui concealed fault).The deformation and metamorphism are weakened along the structural tendency from northwest to southeast,with involved layers being shallower and the strata newer.The intensity of deformation and erosion of the northwestern Sichuan along the structural trend varies from northeast to southwest.(2)The geophysical data of the Shuangyushi area show that the deformation characteristics of the deep Paleozoic concealed structural belt are obviously different from those of the shallow continental facies system,which is bounded by the middle-lower Triassic detachment layer.In the shallower piedmont belt,passive tilting deformation occurs,and the deformation weakens to the basin until the strata is nearly horizontally distributed;But in the deeper part,there are a large number of concealed faults and associated fault noses,fault anticlines and pop-up structures trap types mainly developed in the Permian strata.Based on the geological structure model of Shuangyushi structural belt,the concealed structural belt has obvious segmented characteristics.The north,middle and south segments respectively develop foreland thrust structures,pop-up structure and hinterland thrust structure,which reveals the propagation deformation strength of the concealed structural belt gradually weakens from north to south.(3)The strata scaled model experiment(I)and the ramp-flat structure model experiment(II)reveal the layered deformation characteristics of the northwestern Sichuan.The evolution process can be divided into two stages: foreland propagation deformation and duplex structure propagation deformation.In the stage of foreland propagation deformation,the deep and shallow materials develop same thrust deformation.With the continuous compression,the shallow quartz sand in the stage of duplex propagation deformation firstly slipped and extended to the front along the silica gel detachment layer,and formed a shallow propagating fault at the front edge.At this time,the sandbox material showed a ramp-flat structure,which is that the deeper old fault,silica gel detachment layer and shallower new fault respectively represented the lower slope,the middle flat and the upper slope.Then,the material in the front of the deep downhill is thrusting.With this process repeated,a typical duplex structure under the silica gel is forming.In addition,experiment II reveals the control of the basement ramp-flat structure on the Paleozoic concealed structure in northwestern Sichuan,and the Shuangyushi structural belt developed in late Cenozoic caused by the extension deformation of Longmenshan thrusting.The experiment results can be divided into the hinterland imbricated thrust belt,the internal duplex structural deformation belt and the frontal propagation deformation belt along the direction of compression and shortening,which can be well compared with the typical section of northwestern Sichuan.(4)The tectonic erosion-sedimentation experiment reveals the differential deformation characteristics along the structural strike of northwestern Sichuan resulted from the process of surface differential erosion and sedimentation.During the experiment,the sandbox materials in the non-eroded and non-sedimentary area(III-1 area)were thrusting forward in an orderly sequence,and the materials under the silica gel detachment layer were thrusting to form a corrugated or bumpy roof duplex structure and imbricated structure,with a large width of material deformation zone.In the erosion-sedimentary area(III-3 area),affected by the surface structure denudation and deposition process,faults in hinterland area were exposed with multi-stage reactivation.The activity of frontal faults is restrained by the sedimentary.As a result,the faults are characterized by disordered thrusting in III-3 area.Breaching duplex structures developed in its deep part,with a narrow width of material deformation zone,and the space between faults is small.The erosion with non-sedimentary area(III-2 area)acts as a transition zone,forming oblique faults to coordinate the asymmetric deformation on its both sides in the evolution process.The difference of structural deformation strength and fault lateral distribution revealed by the experimental results is consistent with the actual conditions of the Shuangyushi structural belt in northwestern Sichuan.Along the structural strike,the structural deformation strength gradually weakens from northeast to southwest,and faults gradually converge or merge.(5)The structural deformation characteristics of Shuangyushi area is controlled by multiple sets of detachment layers,the lower ramp-flat structure and surface erosion and sedimentary process.The structural traps in the Shuangyushi structural belt formed in late Cenozoic were associated with the concealed faults,indicating the great importance of late adjustment and accumulation of oil and gas.There are multi-layer source rocks and high-quality Paleozoic dolomite reservoirs in northwestern Sichuan.The effective source reservoir transport system is the main controlling factor for the late hydrocarbon accumulation in the Shuangyushi structural belt.
Keywords/Search Tags:Northwestern Longmenshan fold-and-thrust belt and Sichuan foreland basin, Shuangyushi structural belt, Structural style, Tectonic physical anologue experiment, Hydrocarbon accumulation
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