Utilizing drilling fluid in well cementing operations

A method of cementing a subterranean zone penetrated by a well bore comprising the steps of:

• forming a pumpable set-activated cementing composition comprised of water, particulate condensed silica fume consisting of particles having diameters less than about 1 micrometer and having an average particle diameter of about 0.1 micrometer suspended in said water in a weight ratio of condensed silica fume to water in the range of from about 1:2 to about 1.5:1, a dispersing agent comprised of the condensation polymer product of acetone, formaldehyde and sodium sulfite, a set-activator comprised of calcium hydroxide present in said cementing composition in an amount whereby the weight ratio of condensed silica fume to calcium hydroxide is in the range of from about 1:1.5 to about 3:1, a set delaying additive comprised of calcium lignosulfonate and drilling fluid used to drill said well bore in an amount whereby the weight ratio of said drilling fluid to the other components of said cementing composition is in the range of from about 1:10 to about 1:3;
• pumping said cementing composition into said zone by way of said well bore;
• and
• allowing said cementing composition to set in said zone.

A method of cementing a string of pipe in a well bore containing drilling fluid comprising:

• placing said string of pipe in said well bore;
• circulating said drilling fluid by pumping it downwardly through the interior of said pipe and upwardly through the annulus between the exterior of said pipe and the walls of said well bore while conditioning said drilling fluid by removing drilling solids and gas therefrom;
• combining a portion of said conditioned drilling fluid with a set activated cementing slurry in an amount whereby the weight ratio of said drilling fluid to the other components of said set-activated cementing slurry is in the range of from about 1:10 to about 1:3 to form a set-activated cementing composition containing drilling fluid, said set-activated cementing slurry comprising water, particulate condensed silica fume consisting of particles having diameters less than about 1 micrometer suspended in said water in a weight ratio of condensed silica fume to water in the range of from about 1:2 to about 1.5:1, a dispersing agent for facilitating the dispersal of said silica fume particles in said water and maintaining said particles in suspension therein, a set-activator selected from the group consisting of calcium hydroxide, magnesium oxide and mixtures thereof, and a set delaying additive for increasing the time in which said composition sets after said set-activator is combined therewith;
• pumping said set-activated cementing composition containing drilling fluid into said annulus by way of the interior of said pipe while displacing drilling fluid from said annulus therewith;
• and
• allowing said cementing composition containing drilling fluid to set into a hard mass in said annulus.

A method of cementing a string of pipe in a wellbore containing drilling fluid comprising:

• placing said string of pipe in said wellbore;
• circulating said drilling fluid by pumping it downwardly through the interior of said pipe and upwardly through the annulus between the exterior of said pipe and the walls of said wellbore while conditioning said drilling fluid by removing drilling solids and gas therefrom;
• combining a portion of said conditioned drilling fluid with a concentrated aqueous slurry of a particulate condensed silica fume having a weight ratio of silica fume solids to water in the range of from about 1:2 to about 1.5:1, additional water, and preformed aqueous solutions of a dispersing agent and a set delaying additive to thereby form a pumpable non-activated cementing slurry;
• combining an aqueous solution of a set-activator with said non-activated cementing slurry to thereby form a set activated cementing composition;
• immediately thereafter pumping said set-activated cementing composition into a zone of said wellbore;
• and
• allowing said set-activated cementing composition containing drilling fluid to set into a hard mass in said zone;
• wherein the weight ratio of said drilling fluid to the other components of said set-activated cementing composition is in the range of from about 1:10 to about 1:3;
• said particulate condensed silica fume consists of particles having diameters less than about 1 micrometer suspended in said water;
• and
• said set-activator is selected from the group consisting of calcium hydroxide, magnesium oxide and mixtures thereof.