A 350 ℃ High Temperature Silicate Cement Slurry Used in Cementing Heavy Oil Thermal Production Wells

Conventional cement slurries with sand have loose structures and low compressive capacity at high temperatures such as 350℃ in heavy oil thermal production wells. Aluminate cement and phosphoaluminate cement are expensive, while silicate cement always cause contamination to the reservoir formations. Based on the understanding of high temperature strengthening mechanism, some special strengthening additives were developed. These additives, plus some silicate additives, were used to formulate a cement slurry that is resistant to 350℃ high temperature to deal with the problems as said above. The general performance of the cement slurry was tested, the composition of the crystal phase of the cement was analyzed with XRD, and the morphology of the crystal phase was analyzed with SEM. It was found that the high temperature (HT) silicate cement slurry had top and bottom density difference of less than 0.02 g/cm³, zero free water, API filtration rate of less than 50 mL, and mobility of greater than 20 cm. The 24 h compressive strength of the set cement of the HT silicate cement slurry at 70℃ was greater than 14 MPa, and the compressive strength of the set cement in three rounds of test was greater than 40 MPa, indicating that the HT cement slurry has stable long-term strength development, and therefore satisfies the requirement of heavy oil thermal production. Silicate cement slurry used in previous ultra-high temperature operations had low strength, to have high strength, expensive aluminate cement or phosphoaluminate cement had to be used. With the development of the high temperature silicate cement, all these difficulties have diminished, and progress in ultra-high cement slurry technology has been made.