Research On The Basic Characteristics And Controlling Factors Of The Fourth Member Of The Sinian Dengying Formation In Longnüsi, Central Sichuan

The Graduation thesis based on the fundamental state of sedimentary facies,stratigraphic classification and distribution in the Longnvsi region in the center of Sichuan basin.Focus on thin section identification,physical property data analysis,cathodoluminescence analysis,element analysis and so on as the means.The systematic research on the lithologic characteristic,physical characteristics,types of reservoir space,reservoir types and the reservoir distribution of the fourth section of Sinian Dengying Formation in research area is carried out.Studies have shown that the fourth section of Sinian Dengying reservoir has the following main features:?the fourth section of Sinian Dengying Formation in research area is restricted carbonate platform sedimentary facies with various types of reservoir rock mainly for the fine-microtek dolostone,grain dolostone and algae dolostone,the main rock types constituted the algal mound,grain beach and platform plateau subfacies.On the longitudinal,it shows the polycyclic evolution characteristics.?the fourth section of Sinian Dengying reservoir matrix property belongs to the type of low permeability reservoirs as a whole.Karst cave development zone total porosity can show the characteristics of the middle pore.Most porosity are between 2.0%?2.0%,then 4%?6%,some could reach 6?10%.?The formation types of reservoir space are various and uneven developed.the reserving space with cavern,intercrystalline pore,stromatolite algal crystal pore,stromatolite algal geode developed well.Tectonic fissures are the most,sometimes developed diagenetic fissures,fissure has the feature of many times,and most fissures are Karst fissures by the corrosion;And the reservoir type is fissure-pore reservoir.Research shows that reservoir development is controlled by multi-factor composite superposition.Multi-phase polygenetic cementation is an important factor to reduce pore.Polygenetic dissolution(dissolved)is the key to the formation of reservoir.?Grain bank,algal mound is favourable for the development of reservoir sedimentary subfacies.Primary intergranular pore and pores dissolved inside the particles or hexagonal pores of algae fold layers formed by dissolution in the near-surface environment.As preserved,it provides an important channel for late diagenetic fluid migration and good for reservoir development.?Tong Wan movement which happened in the late deposition of Dengying Formation made the formation lifted to surface and then be denuded.Hypergene karstification Formed a karst reservoir,By mechanical sediments,more times after chemical sediment filling many pores reduced,but the late hydrothermal modification still remain part of the solution pores.?Multiphase strong tectonic movements could form a large number of propped fracture and improve the seepage condition,or provide the channel for acidity and hydrothermal filling and transformation.On the one hand,tectonic hydrothermal dolomitization transform the micrite matrix formed a nonselective solution pores.On the other hand,the saddle backed dolomite directly deposited from the thermal fluid and other hydrothermal minerals filled dissolution pores and,reduced the reservoir space.Organic acid dissolution is the another important factor for the formation of the secondary reservoir space.But the asphalt of hydrocarbon fissureing has an obvious reduction to the pores,holes and fissures by filled them.Through the research,we established the forming model of the Sinian Dengying Formation in research area.That is:In penecontemporaneous period,metrical water dissolution form intragranular pore,algal laminated pore and cementing plug pore;The formation of supergene karst dissolved pore in Tong Wan period,Hydrothermal mineral filling and preservation of the remaining karst holes which is reduced by grape lace cementation;Tectonic hydrothermal solution increases the hole and hydrothermal mineral filling;Burial stage dissolved organic acid increase hole and asphalt reduce hole;The late tectonic movement make fissures,building complex fissure and hole net.