Abstract:

Atpresent,anumberofgreatesttightsandstonegasfieldshavebeendiscoveredandprovedintheHe8MemberofOrdos Basin.Thetightsandstonereservoirsmainlyconsistofquartzsandstonewithlowfeldspar,lowmatrix,highcompositionalmaturity.Thetypesofreservoirspacearebasedonmultiplesecondaryerosionpores.Inordertostudytheoriginofvuggyporosityofquartz sandstone,acidolysissimulatingexperimentofopensystem,underthehightemperatureandhighpressureconditions,hasbeen conducted.Meanwhile,theanalysisisbasedonnumerouscastingslices,scanningelectronmicroscope,fieldemissionandCTscan. Experimental samples were selected from the Shihezi Formation of Perimian in Ordos Basin, containing green grey mediumcourse-grainedtuffaceousfeldspathicquartzsandstone,greengreymedium-course-grainedtuffaceousfeldspathiclitharenitesandstone, graymedium-course-grainedtuffaceouslithicquartzsandstoneandgraymedium-course-grainedtuffaceousquartzsandstone.In0.5mol/ Lreactionmediator,2ml/minflowrateanddynamiccorrosionfor100hexperimentalconditions,thesecondaryporosityfordifferent typesofsandstoneincreasedsignificantlyandpropertieswereobviouslyimproved.Bythemeansofisotopescanningofdifferent samplesbeforeandafterexperimentanalysis,thefluid-rockinteractionrateanalysisandplasmaemissionspectrumanalyisis,the authorsindicatethatthemainoriginofthesecondaryporesarethecorrosionoftuffaceous,calcareousandfeldsparmineraletc.The tuffaceous,calcareousoccurerosionundertheconditionoflowtemperature,andfeldsparcorrosionoccurunderhightemperature conditions.Thedevelopmentmechanismoftheerosionoftuffaceous,calcareousandfeldsparmineraletc,poreformationandnew mineralshasbeenrevealed.Combinedwiththeanalysisofburialhistoryandthermalhistory,thediageneticsequencesandporosity evolutionmodeloftightsandstoneofHe8Memberwasputforward.Allthestudiesmakethegenesisofsecondaryporesofquartz sandstoneclearly.

Key words: :reservoiroftightsandstone;acidcorrosionsimulationexperiment;secondaryporositygenesis;poreevolvementmodel;the eighthmemberofShiheziFormation;OrdosBasin