Method of cementing gas or oil pipeline and hydraulic cement slurry

Abstract

The present invention relates to a method of cementing a casing of an oil or gas pipeline to a surrounding well wall, where an hydraulic cement slurry is formed and the slurry is deployed in the annulus between the pipeline casing and the surrounding well wall. The cement slurry is formed by mixing together an hydraulic cement 12 to 24% of silica based on the weight of cement, and water; wherein the silica comprises ⅓ to ⅔ microfine silica and ⅔ to ⅓ silica flour. The invention further relates to a cement slurry for use in the method.

1 . A method of cementing a casing of an oil or gas pipeline to a surrounding well wall, which comprises forming an hydraulic cement slurry, deploying the slurry in the annulus between the pipeline casing and the surrounding well wall, and allowing the cement to set; in which the cement slurry is formed by mixing together an hydraulic cement, 12 to 24% of silica based on the weight of cement, and water; wherein the silica comprises ⅓ to ⅔ microfine silica and ⅔ to ⅓ silica flour. 
   
   
       2 . A method as claimed in  claim 1 , in which the silica is in the form of an aqueous suspension of microfine silica and silica flour. 
   
   
       3 . A method as claimed in  claim 1 , in which the microfine silica and silica flour are added separately. 
   
   
       4 . A method as claimed in  claim 1 , in which the microfine silica is microsilica, microfine crystalline silica, colloidal silica or mixtures thereof. 
   
   
       5 . A method as claimed in  claim 4 , in which the microfine crystalline silica has a D50 of maximum 10 μm. 
   
   
       6 . A method as claimed in  claim 1 , in which the silica represents 15 to 20% by weight of cement. 
   
   
       7 . An hydraulic cement slurry for use in the cementation of gas or oil wells having a bottom temperature of between 100 and 150° C., comprising: an hydraulic cement, 12 to 24 of silica based on the weight of cement and water wherein the silica comprises ⅓ to ⅔ microfine silica and ⅔ to ⅓ silica flour. 
   
   
       8 . An hydraulic cement slurry as claimed in  claim 7 , in which the silica comprises an aqueous suspension of microfine silica and silica flour. 
   
   
       9 . An hydraulic cement slurry as claimed in  claim 7 , in which the microfine silica is microsilica, microfine crystalline silica, colloidal silica or mixtures thereof. 
   
   
       10 . An hydraulic cement slurry as claimed in  claim 9 , in which the microfine crystalline silica has a D50 of maximum 10 μm.