Development Of Retarders For Phosphoaluminate Cement System

The stratum carbon dioxide corrosion on Portland cement sheath has greatly influencedthe production life of oil well. Research suggests that Phosphoaluminate Cement System,which has characteristics of early strength and rapid hardening, is a kind of hydrauliccementing materials with good CO2-resistant performance. For the requairment of applyingPCS in high concentrations CO2oil well-cementing and based on evaluation of oil wellPortland cement retarder effects on PCS, this article has developed a kind of compositeretarder and a type of graft polymer retarder specialize in PCS and analysized the mechanismsof different retarders on PCS.Research suggests that, the phenomenon of hydroxy carboxylic acid, inorganic acid andphosphates not delaying PCS hydration reaction has demonstrated that gelled characteristicsbetween oil-well Portland cement and PCS are different. However, several kinds of inorganicsalts retarders have remarkablely retarding effect on PCS, and the unfavourable result is thatinorganic salts has observably reduced the compression strength. Sodium lignosulphonatewhich could delay hydration reaction of aluminate mineral existing in PCS has attained agood retarding effect, and reduced the apatite mineral content of hydration product leading tothe loss of compression strength.The three-component composites consisting of citric acid, sodium lignosulphonate andboric acid at a certain ratio could achieve the optimal retarding effects. When percentage ofCA: SL: BA is1:20:20, the cement slurry has the favorable behaviors of rheology, shorttransition time from30Bc to100Bc, right-angle-set property and minimal-impact oncompressive strength. According to the independence of components and XRD analysis ofhydration products, the function process of composite retarder can be marked two parts:effective functional groups of SL and BA impacting on PCS particle surface can formadsorbed layer, CA could damage the adsorbed layer and accelerate the formation of apatite.Based on the principle of free-radical polymerization in solution and active mechanismof dominant functional group, AMPS and itaconic acid are optimized as unsaturated monomerwhich are used to grafted onto sodium lignosulphonate, as well as potassium peroxodisulfateis optimized as initiator. According to the influencing factors of aqueous solution polymerization, single factor analysis and orthogonal experiment have been used, leading tothe same result. A certification of graft polymer is done by FT-IR spectra and shows thatAMPS and IA have grafted onto SL. This retarder can apply to high temperature and pressure,what’s more, the relation between thickening times of PCS slurry which has favorablebehaviors of rheology and right-angle-set property and dosages of retarder has beenconfirmed as a linearity curve. The hydration of PCS slurry with a certain dosage of graftpolymer retarder in different ages has been analysed by XRD. Through the micro-analysis andmacro-analysis, the function process of composite retarder can be marked six stages:pre-action stage, initial action stage, enhancing action stage, disguised-failure action stage,transition action stage and failure stage.