Well cementing process and gasified cements useful therein

A process for primary cementing in the annulus between a well casing and a bore hole comprising:

• placing in the annulus a column of cement slurry containing a stable volume of at least 0.1 SCF of gas per cubic foot of cement slurry at a time prior to the initial set of the slurry, wherein the gas is formed in situ by mixing particulate aluminum in an amount of from about 0.02 to about 5.0 percent by weight of dry cement in the slurry prior to placement of the slurry in the annulus;
• and
• maintaining sufficient gas in the slurry to prevent substantial reduction in the pressure in the slurry column during transition of the slurry to a solid state.

A process for primary cementing in the annulus between a well casing and a bore hole comprising:

• placing in the annulus a column of cement slurry containing a stable volume of at least 0.1 SCF of gas per cubic foot of cement slurry at a time prior to the initial set of the slurry, wherein the gas is formed in situ by dispersing in the slurry prior to placement about 0.02-5.0 percent by weight of the dry cement a material selected from the group consisting of CaCl.sub.2, ZrOCl.sub.2, ZrCl.sub.4, Ca.sub.3 N.sub.2, KBH.sub.4, metals which release hydrogen from an aqueous alkaline solution in accordance with the EMF series, and mixtures thereof;
• and
• maintaining sufficient gas in the slurry to prevent substantial reduction in the pressure in the slurry column during transition of the slurry to a solid state.

A process for primary cementing in the annulus between a well casing and a bore hole comprising:

• placing in the annulus a column of cement slurry containing a stable volume of at least 0.1 SCF of gas per cubic foot of cement slurry at a time prior to the initial set of the slurry, wherein the gas is formed in situ by dispersing in the slurry prior to placement an effective amount of a metal selected from the group consisting of Al, Ca, Zn, Mg and mixtures thereof;
• and
• maintaining sufficient gas in the slurry to prevent substantial reduction in the pressure in the slurry column during transition of the slurry to a solid state.

The method of preventing gas leakage into the annulus between the casing and bore hole of an oil well from an adjacent gas-bearing formation comprising:

• placing a cement slurry in the annulus across the face of the gas-bearing formation;
• and generating a gas in the slurry in an amount and at a rate, by incorporating in the slurry with mixing about 0.02-5.0 weight percent of particulate aluminum based on the weight of dry cement, such that prior to the time the slurry sets to a hardened state, the decrease in the downhole pore pressure of the cement slurry is less than the difference between the initial hydrostatic pressure and the reservoir pressure of said gas-bearing formation at a point adjacent to said gas-bearing formation prior to the time the slurry sets to a hardened state.

In a process for placing hydraulic cement slurry in a subterranean zone and allowing the cement slurry to set, wherein a portion of the zone is exposed to gas pressure in the earth adjacent the zone, the process characterized by incorporating in said cement slurry a means for pressurizing said slurry by adding a means for generating gas including a gas generating agent which reacts in the cement slurry to produce gas to maintain sufficient gas in the slurry to prevent substantial reduction in pressure in the slurry and to offset the gas pressure adjacent said zone during the transition of the slurry to a solid state.