The Reservoir Diagenesis And Its Influence On Reservoir Quality In Gaotaizi Formation Of QiJia-GuLong Depression

Diagenesis is a core element to determine reservoir quality, nearly half a century,scholars had achieved lots of achievements on the study of diagenesis, thetransformation of diagenesis on reservoir is one of the research hotspots currently.Songliao Basin is a large complex Cenozoic sedimentary basins in eastern China,is the largest oil and gas producing basins in China. Qijia-Gulong Depression is animportant exploration in the north of Songliao Basin, has about fifty years ofexploration history so far, Gaotaizi reservoir is typically tight reservoir, the study ofthe effects of diagenesis on reservoir properties are conducive to further explorationdevelopment.Statisticsl framework clastic composition, particle size and it’s distribution todetermine rock types and structures; identify the main authigenic mineral types andformation time, define the paragenesis; make sure the diagenetic stage based onorganic geochemical data; combine the description of the pore types and structurewith the porosity and permeability data to determine reservoir space and reservoirproperties.The rock types of reservoir stondstone are mainly lithic arkose and feldspathiclitharenite, mainly fine-grained, moderate-well sorted, based on the microscopicidentification ofa large number of thin sections and references of the identified iresultscollected.Observations of polarization microscope and cathodoluminescence show that theparagenesis in the target stratum is listed as follows：clay(illite/chlorite),micro-calcite, micro-quartz and overgrowth quartz, oil and gas charging/feldspardissolution,autogenic illite,coarse crystalline calcite/calcite vein.Based on organic geochemical data analysis, combined with the microscopicidentification,we find clear reservoir diagenesis belong to middle diagenesis, the claymineral assemblages are mainly: illite+kaolinite+chlorite+illite/smectite mixedlayer (I+K+Ch+I/S) and illite+chlorite+illite/smectite mixed layers (I+Ch+I/S).The observe with polarizing microscope and image analysis system showde thepore types of target stratum are mainly intergranular dissolved pores,and intragranulardissolved pores of feldspar, intragranular dissolved pores of rock fragments, primaryintergranular pores,residual intergranular dissolved pores。Qijia-Gulong Gaotaizi reservoirs mainly ultrafine pores-micro pores, followedby mesopore and a small number of large pores, medium pore connectivity, mainlyorphaned development.Gaotaizi reservoir in Qijia-Gulong belong to the tight reservoir Ⅰ, followed bytight reservoir Ⅱ, containing a small amount of tight reservoir Ⅲ, low porosity andlow permeability reservoir.The influences of diagenesis acting upon reservoir physical property are threeways: mechanical compaction, the deposit of calcite cementation, authigenic quartzand filaments illite and the inject of oil and gas destory the reservoir porosity;Thechlorite cladding protects the reservoir; dissolution du to oragnic acid improvingreservoir properties by the formation of secondary porosity to increase reservoirspace.