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1、CementAdditivesAlmostallcementusedinoilandgaswellsisPortlandcement.However,neatcementisseldomusedthroughoutajobsincevariousadditivesareusuallynecessarytomodifythepropertiesofeitherslurryorsetcement.Withbasiccements(APIClassGorH)andtheuseofadditives,cementslurriescanbe
2、tailoredforanyspecificrequirement.Mostadditivesincurrentusearefree-flowingpowdersthataredry-blendedwiththecementpriortoitstransportationtothewell.Whennecessary,somepowderedadditivescanbedispersedinmixingwateratthesite.Liquidadditivesaremorecommonlyusedoffshoreandinrem
3、otelandlocationswheredrycementblendingandstorageareaproblem.Propertiesthataremodifiedbyadditivesareshownbelow:Fortheslurry:·thickeningtime(acceleration,retardation)·density(extenders,weightincrease/reduction)·frictionduringpumping·fluidloss(byfiltrate)·lost-circulatio
4、nresistance(wholeslurryloss)Forsetcement:·compressivestrength·strengthretrogression(losswithtime)·expansion/contraction AcceleratorsCement-settingtimeisacceleratedtoreduceWOCtimeandtoincreaseearlystrength.Thisisdesirableforsurfacepipe,inshallow(cooler)wells,andforsett
5、ingplugs.Generalpressurerecommendationsareasfollows:�pipesupportandzonalisolation—100psi(690kPa)�drillingout—500psi(3450kPa)�perforating —bullets—500psi(3450kPa)—hollowcarrierorexpendablejets—2000psi(13,800kPa)�whipstockplug—2500psi(17,200kPa)orgreater(orharderthanfor
6、mation)Themostcommonacceleratorsarecalciumchloride,sodiumsilicate,sodiumchloride(lowconcentrations),seawater,hemihydrateformsofgypsum,andammoniumchloride.Table1showstypicalamountsusedpersack. TypeAmountusedpersack(%byweight)Accelerators CalciumChloride(CaCl2)(flake,po
7、wder,anhydrous)2–4SodiumChloride(NaCl) 3-10(water) 1.5-5(cement)Hemihydrateformsof20-100Gypsum(plasterofParis) SodiumSilicate(Na2SiO3)w1-7.5Cementswithdispersantsandreducedwater0.5-1.0SeaWater Retarders Calcium-SodiumLignosulfonate0.1-1.0CalciumLignosulfonate0.1to1.0
8、CalciumLignosulfonate0.1to2.5plusorganicacid CMHEC0.1to1.5SaturatedSalt15to17lb/skTable1.Commonlyusedacceleratorsandretarder
