A Study On The Controlling Factors Of Favorable Reservoir In Upper Paleozoic Of Dongsheng Gas Field

Targeting on the reservoir in upper Paleozoic in Dongsheng gas field of the Ordos basin,integrated utilizing the identification and quantitative statistics of rock thin sections under the microscope,electron scan microscope(ESM),and the other analytical techniques,combined with the result of clay mineral analysis,mineral analysis of the whole rock,mercury intrusion porosimetry(MIP),and the other test result,this research detailed describes the petrologic feature,pore and throat texture and physical characteristics of the reservoir in upper Paleozoic,analyses diagenesis type and diagenesis evolution,studies the influential factors on reservoir properties,and finally clears up the controlling factors of physical properties.Based on the identification of thin sections under the microscope,combined with analysis and test results,this study defines the reservoir characteristics of each layer.Taiyuan formation and Shan-1 formation have the characteristics that the lithology of the reservoir are sub lithic sandstone with high content of quartz,and the main type of the pore are residual original intergranular pore.Shan-2 formation and lower Shihezi formation have the features that the lithology of the reservoir are lithic sandstone,sub lithic sandstone and feldspathic litharenite with high content of feldspar,lithic and kaolinite,and the main type of the pore are secondary porosity and intercrystal porosity.In the Shan-2 formation and lower Shihezi formation,north of the fault has higher feldspar and kaolinite content.The rate of porosity are mainly from 4% to 18%,and the rate of permeability are mainly from 0.1×10-3?m2 to 10×10-3?m2.The physical properties of reservoir shows higher physical properties in the north of the fault.The diagenesis types mainly include compaction,cementation and metasomatic alteration of carbonates contending iron,metasomatic alteration of silicic and clay minerals,dissolution and so on.The diagenetics stages in north of fault is A1 of late diagenetic stage with higher content of the kaolinite and more serious chemical erosion.However,in the south of the fault,the diagenetics stages is B of late diagenetic stage with stronger compaction and quartz overgrowth.The phenomenon that the content of kaolinite and feldspar is higher in the north of fault,maybe come from the reaction that kaolinite reacts with feldspar to form illite in the south of the fault.This research analyses the controlling factors of physical properties.Compaction in the main controlling factors of Taiyuan formation and Shan-1 formation,which shows up as the granularity are correlated with physical properties,and coarse sandstone and coarse sandstone contending gravel have good physical properties.In Shan-2 formation and lower Shihezi formation,braided channel and underwater distributary channel have batter physical properties.For the controlling factors of physical properties,granularity is the main controlling factors of the south of fault which have batter physical properties in coarse sandstone,while in the north of fault,diagenesis is the main controlling factors with higher physical properties in the region that develops dissolution.Synthesizing physical properties,pore and throat texture,diagenesis and lithology of the reservoir,this study divide the reservoir into 4 type,of which,I and II is favorable reservoir.The lower Shihezi formation have relatively larger region of favorable reservoir.Taiyuan formation and Shan-1 formation mainly have favorable reservoir II.In the Shan-2 formation and lower Shihezi formation,favorable reservoir I mainly develops in the north of the fault,and only develops in regional area in the south of the fault.