| Keshen-A borefield Kelasu gas field,located in the northern Kuqa Depression,is multi-phase tectonic superimposed,complex in geological conditions,and has a Higher difficulty for exploration,Cretaceous Bashijiqike formation in this area as a tight sandstone reservoirs,has a good show of gas.A borefield is the favorable range of oil and gas exploration area,this paper hope to use the research on the sedimentary phase,reservoir characteristics,diagenesis,diagenetic evolution sequences,etc of Cretaceous Bashijiqike in A borefield to grading and evaluating the reservoir,analysing the factors influencing reservoir development,and providing the foundation for the development of the favorable range of oil and gas exploration area.research shows:(1)The first and the second member of Cretaceous Bashijiqike group in Keshen-A borefield developed braideddelta front subfacies,mainly develop underwater distributary channe and channel mouth bar microfacies.(2)The rock type of reservoir interval mainly are lithic arkose,lithology mainly medium-fine sandstone with thin mudstone and silty mud interbed inside and siltstone;high interstitial material with an average of 17.1%,in which matrix is brown mudstone dominated,with an average of 6.1%.Cement type include dolomite,calcite,kiesel,albite,anhydrite,with an average of 11%;heavy minerals include the medium stable and heavy part of magnet and titanium dioxide,the type of clay minerals mainly illite,illite/smectite-based;compositional maturity moderate-poor,and medium-poor textural maturity.(3)reservoir interval matrix porosity mainly range from the 3.0%to 5.0%,an average of 3.9%,permeability mainly range from 0.003×10-3?m2 to 0.014×10-3?m,an average of 0.009×10-3?m2,The second member is slightly better than the first one on the whole,belong to ultra-low porosity and ultra-low permeability reservoir;fractures mainly with high angles and reticulate fractures dip angle:60°?90°,opening degree:0.1?3.0mm,density range from 0.065 to 1.45 bar/m,mainly filled-half filled-unfilled,fracture are mainly filled with gypsum,calcite,dolomite and other minerals,which formed earlier is completely filled,fractures in the second member developed better than the first one.The first member continuity slightly worse,almost fault,fractures always grow structural high.(4)The region of interest generally belongs to standard of classification ???according to "the Ministry of Petroleum Industry",of which the main type is porous fractured,and the porosity and permeability are positively correlated,while the correlation is bad which is also influenced by the fracture greatly,with dual media features.Pore type mainly intergranular dissolved pore and intragranular dissolved pore,less residual primary intergranular pores,showing the feature of fine-micro pore throat in general,the connectivity of pore throat is poor.(5)The main types of diagenesis are compaction(pressolution),cementation,dissolution,tectonic disruption and metasomatism.with the tectonic uplift and erosion effect,the region of interest reservoir reached the diagenetic B stage.Compaction greatly reduces the primary porosity,The sedimentary facies with coarser grain holds a better accumulation ablity.sedimentary microfacies are the main factors influencing reservoir development.The fractures formed after the fast anadiagenesis at late period and tectonic compression contribute a lot to raising the filtration capacity,hydrocarbons-charging saving the pore,slower the compaction by forming high pressure,Promoting the dissolution with the ideal gypsum cover saving the underlie reservoir pore,and forming secondary porosity. |
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