Pre-stressed annular sealant and method of creating a durable seal in a well bore annulus
View Patent ↗A pre-stressed annular sealant and method of creating a durable seal in a well bore annulus which is based on hydraulic cement that is designed to be easily pumped and placed into a casing-wellbore annulus, to set into a hardened mass, and to then undergo post-set crystal growth and phase changes in the crystalline matrix to combat inherent volumetric shrinkage and to create internally-generated compressive stress in the cement matrix. This internally-generated compressive pre-stressing compensates for tensile stress induced by well operations. The tensile stress must be greater in magnitude than the magnitude of the compressive pre-stress plus the magnitude of the cement's tensile strength before the cement sheath will fail in tension. This expansion and pre-stressing also creates significantly higher shear bond strengths than those developed with ordinary hydraulic cement.
1. A pre-stressed annular sealant, comprising:
a. a quantity of hydraulic cement;
b. deadburned magnesium oxide added to the cement in concentrations of greater than 25% by weight of cement to provide a hydraulic cement matrix with post-set crystalline growth needed for pre-stressing;
c. microfine cement, crystalline silica added to the formulation to stabilize the hydraulic cement matrix at high temperature;
d. fluid loss control additive;
e. a set retarder;
f. a cement dispersant; and
g. a quantity of water added to the formulation to required density for placement of the formulation in a well.
2. A method of creating a durable seal in a well bore annulus, comprising the following steps:
a. providing a quantity of hydraulic cement;
b. adding deadburned magnesium oxide to the cement in concentrations of no less than 25% by weight of cement to provide post-set crystalline growth needed for pre-stressing;
c. adding microfine cement, crystalline silica to the cement formulation to stabilize the hydraulic cement matrix at high temperature; and
d. adding quantity of water to the formulation to required density for placement of the formulation in a well.
3. A cementing formulation comprising hydraulic cement, microfine cement, crystalline silica and greater than equal to and no less than 25% MgO pumped and placed into a casing-wellbore annulus, to set into a hardened mass, to then undergo post-set crystal growth and phase changes in the crystalline matrix to combat inherent volumetric shrinkage and to create internally-generated compressive stress in the cement matrix.
4. The formulation in claim 3 , wherein the internally-generated compressive pre-stressing compensates for tensile stress induced by well operations.
5. The formulation in claim 3 , wherein the tensile stress must be greater in magnitude than the magnitude of the compressive pre-stress plus the magnitude of the cement's tensile strength before the cement sheath will fail in tension.
6. The formulation in claim 5 , wherein the expansion and pre-stressing also creates significantly higher shear bond strengths than those developed with ordinary hydraulic cement.
7. A pre-stressed annular sealant, comprising:
a. a quantity of hydraulic cement;
b. deadburned magnesium oxide added to the cement in concentrations of greater than 25% by weight of cement to provide a hydraulic cement matrix with post-set crystalline growth needed for pre-stressing;
c. microfine cement, crystalline silica added to the formulation to stabilize the hydraulic cement matrix at high temperature;
d. fluid loss control additive;
e. a set retarder; and
f. a cement dispersant.
8. The annular sealant in claim 7 , further comprising a quantity of water added to the formulation to required density for placement of the formulation in a well.
9. A method of creating a durable seal in a well bore annulus, comprising the following steps:
a. providing a quantity of hydraulic cement;
b. adding deadburned magnesium oxide to the cement in concentrations of no less than 25% by weight of cement to provide post-set crystalline growth needed for pre-stressing; and
c. adding microfine cement, crystalline silica to the cement formulation to stabilize the hydraulic cement matrix at high temperature.
10. The method in claim 9 , further comprising the step of adding quantity of water to the formulation to required density for placement of the formulation in a well.
11. The method in claim 9 , wherein the concentration of deadburned magnesium oxide added to the cement would comprise no greater than 40% by weight of cement.