Development And Anti - Pollution Mechanism Of High Temperature And High Temperature Isolation Solution In Cementing Engineering

The cementing operation is an extremely important process in well cementation. In order to prevent the contamination phenomenon between cement slurry and drilling fluid, the spacer fluid was injected before the cement slurry. Most of the spacer fluid system existing many defects, such as the poor high temperature resistance and poor compatibility in mixed slurry of drilling fluid-spacer fluid-cement slurry. What’s more, the spacer fluid had been applied in engineering for years, but the study on its anti pollution mechanism is not mature. Therefore, this paper has launched an study on high temperature/high performance PIAS/HS spacer fluid and its anti contamination mechanism.A novel agent for spacer fluid of itaconic acid/acrylamide/sodium styrene sulfonate (IA/AM/SSS, hereinafter referred to as PIAS) was synthesized by free-radical, aqueuous-solution polymerization and characterized by FTIR and TG. The optimum reaction conditions of polymerization were obtained from orthogonal experiments (L33) as follows:the mass ratio of monomers IA/AM/SSS,1:4:3; the reaction temperature,55℃; the amount of initiator,3wt%; the pH of the reaction solution,6-7; the reaction time,5hr. According to the thickening time evaluation of cement slurry with PIAS under180℃×115MPa and early-age compressive strength of set cement, the PIAS made it possible to obtain both a long thickening time and a swift compressive strength development for cement slurry, and therefore the applicable range of bottom hole circulation temperature to the cement slurry has been widened to60-180℃. Moreover, the working mechanism of self-adapting retarder PIAS was found through XRD, SEM, EDS analysis and heating-cooling thickening time test.The flow modifier for spacer fluid of hydroxy ethyl cellulose(HEC)/sodium styrene sulfonate (hereinafter referred to as HS) was synthesized by free-radical, graft copolymerization and characterized by FTIR and TG. By means of the control variables, the synthetic experiment groups of mass ratio, initiator dosage and reaction temperature were designed. With the evaluation index of viscosity, the optimum reaction conditions of polymerization were obtained as flows:the mass ratio of monomers HEC/SSS,1:2; the reaction temperature,50℃; the amount of initiator,0.5wt%; the reaction time,8hr.The suspension stability, the rheology and the compatibility in mixed slurry of spacer fluid were evaluation according to the standard "SY/T5374-2000" after preparation. It had been confirmed that the high temperature/high performance spacer fluid had a good suspension stability under60-180℃, and its density can be adjusted within a certain range of1.2-2.4g/cm3. The rheology of mixed slurry, that is to say the drilling fluid-spacer fluid-cement slurry mixed slurry, was improve significantly. The flocculation and flash set phenomenon of mixed slurry were avoided by the adding of spacer fluid. Furthermore, according to the analysis of SEM and XRD the mechanism of suspension, flush and anti contamination were explained.