Method of producing light weight cement for use of cementation of oil and gas wells

Abstract

A cement slurry of low specific density for cementation of oil-and gas wells is produced by mixing oil-well cement with finely divided emission products comprising amorphous silica dust which has been obtained during the electrothermal preparation of ferrosilicon and/or silicon metal, water, and any desirable dispersion components, the emission products being added in an amount in the range of 1-50% of the total weight of dry material. The emission products can either be mixed with the cement while both components are in the dry state whereupon there is added a sufficient quantity of water in order to obtain a desired specific weight of the slurry or first mixed with water and any other desired dispersion components and this slurry is mixed with the oil-well cement.

What is claimed is: 
     
       1. The improved method of cementing the space between the interior wall of a well and the exterior wall of an internal tube therein with a low-density pumpable slurry of cement used in oil and gas well exploration which comprises the steps of: (a) mixing an oil and gas well cement with water and particulate silica formed by precipitating the fumes generated by an electrometallurgical smelting furnace for producing silicon or ferrosilicon, said particulate silica having a surface area from about 18 to about 22 m 2  per gram, the proportion of said particulate silica to cement in said slurry being about one part of silica for each two parts of cement;   (b) adjusting the density of said slurry by adding sufficient water to provide a low density pumpable aqueous slurry of not over about 12.6 pounds per gallon; and   (c) pumping said slurry into the space between said tube and interior wall of the well for cementation thereof.   
     
     
       2. The method of claim 1 wherein the particulate silica and cement are mixed in a dry state followed by addition of water to form the low density slurry. 
     
     
       3. The method of claim 1 wherein dispersion components .[.chosen from the group consisting of bentonite, pozzolan, diatomaceous earth, perlite, water glass and gilsonite.]. are added to vary the density of said slurry from about 11.5 to about 15.5 pounds per gallon. 
     
     
       4. The method of claim 1 wherein an aqueous slurry comprising the said silica and water is formed and thereafter the resulting silica slurry is mixed with said oil and gas well cement. .Iadd. 
     
     
       5.  The improved method of cementing the space between the interior wall of a well and the exterior wall of an internal tube therein with a low-density pumpable slurry of cement used in oil and gas well exploration which comprises the steps of: (a) mixing an oil and gas well cement with water and amorphous particulate silica dust formed by precipitating the fumes generated by an electrometallurgical smelting furnace for producing silicon or ferrosilicon, said amorphous particulate silica dust being about 82 to about 95% silica particulate, said silica particulate having a surface area from about 18 to about 22 m 2  per gram, and a real density of about 2.2 to about 2.25 gram per cm 3 , the proportion of said particulate silica dust to cement in said slurry being from about 1 to about 50% of the total weight of the dry material;   (b) adjusting the density of said slurry by adding sufficient water to provide a low density pumpable aqueous slurry of between about 11.5 and about 15.5 pounds per gallon; and   (c) pumping said slurry into the space between said tube and the interior wall of the well for cementation thereof. .Iaddend. .Iadd.   
     
     
       6.  The improved method of cementing the space between the interior wall of a well and the exterior wall of an internal tube therein with a low density pumpable cement slurry consisting essentially of: oil and gas well cement; water and amorphous particulate silica dust formed by precipitating the fume generated by an electrometallugical smelting furnace for producing silicon or ferrosilicon, said amorphous particulate silica dust having a surface area from about 18 to about 22 m 2  per gram, and a real density of about 2.2 to about 2.25 grams per cm 3  ; said improved method comprising the steps of: (a) mixing said oil and gas well cement with water and said amorphous particulate silica dust, the proportion of said particulate silica dust to cement in said slurry being from about 1 to about 50% of the total weight of dry material;   (b) adjusting the density of said slurry by adding sufficient water to provide a low density, pumpable, aqueous slurry of between about 11.5 and about 15.5 pounds per gallon; and   (c) pumping said slurry into the space between said tube and the interior wall of the well for cementation thereof. .Iaddend. .Iadd.7. The method of claim 6 wherein said amorphous particulate silica dust and cement are mixed in a dry state followed by addition of water to form the low density slurry. .Iaddend. .Iadd.8. The method of claim 6 wherein said amorphous particulate silica dust and water are mixed to form an aqueous slurry and thereafter the resulting aqueous slurry is mixed with said oil and gas well cement. .Iaddend. .Iadd.9. The method of claim 6 wherein a dispersion component is mixed with said oil and gas well cement, water and said amorphous particulate silica dust. .Iaddend.