Microbial-enhanced well cementing and remediation

1. A method of cementing a wellbore comprising:

a) preparing a cement composition comprising a pumpable slurry of cement, water and a healing agent that comprises Bacillus pseudofirmus that is tolerant to pressure of 98 atm (10 MPa) and 20° C.;

b) delivering the cement composition into the wellbore; and

c) allowing the cement composition to set,

wherein the wellbore has a downhole pressure of 1 atm-1000 atm (0.1-100 MPa); and

wherein when the integrity of the set cement composition is breached, activating the Bacillus pseudofirmus in the set cement thereby causing them to grow and replicate at a pressure of at least 98 atm (10 MPa) to thereby restore the integrity of the set cement composition.

2. The method of claim 1 wherein preparing the cement composition comprises introducing the Bacillus pseudofirmus to one or more of the cement, water or cement slurry.

3. The method of claim 2 wherein preparing the cement composition further comprises introducing a nutrient for the Bacillus pseudofirmus to one or more of the cement, water or cement slurry.

4. The method of claim 3 wherein the nutrient is a carboxylic acid calcium salt or calcium lactate.

5. The method of claim 3 wherein the nutrient is encapsulated.

6. The method of claim 1 wherein the Bacillus pseudofirmus is a spore.

7. The method of claim 1 wherein the Bacillus pseudofirmus is encapsulated.

8. The composition claim 1 wherein the Bacillus pseudofirmus is encapsulated for release after the cement is set.

9. The method of claim 1 wherein the Bacillus pseudofirmus is capable of depositing calcium carbonate (CaCO 3 ), lime (Ca(OH) 2 ) or a biopolymer.

10. A method of restoring the integrity of a set cement composition in a wellbore, said method comprising:

a) preparing a pumpable slurry that comprises water, a healing agent that comprises Bacillus pseudofirmus tolerant to pressure of 98 atm (10 MPa) and 20° C., and optionally, cement;

b) pumping the slurry into the wellbore in and around the set cement composition, wherein the wellbore has a downhole pressure of 1 atm-1000 atm (0.1-100 MPa); and

c) allowing the Bacillus pseudofirmus to grow and replicate to thereby restore the integrity of the set cement composition at a pressure of at least 98 atm (10 MPa).

11. The method of claim 10 wherein the Bacillus pseudofirmus is encapsulated.

12. The method of claim 10 wherein the Bacillus pseudofirmus is capable of depositing calcium carbonate (CaCO 3 ), lime (Ca(OH) 2 ) or a biopolymer.

13. The method of claim 10 further comprising introducing a nutrient into the wellbore.

14. The method of claim 13 wherein the nutrient is a carboxylic acid calcium salt or calcium lactate.

15. A method of restoring the integrity of a set cement composition in a wellbore, said method comprising:

a) delivering a healing agent to the set cement in the wellbore, the healing agent comprising Bacillus pseudofirmus tolerant to pressure of 98 atm (10 MPa) and 20° C. and wherein the wellbore has a downhole pressure of 1 atm-1000 atm (0.1-100 MPa);

b) allowing the Bacillus pseudofirmus to grow and replicate within the set cement to thereby restore the integrity of the set cement composition at a pressure of at least 98 atm (10 MPa).

16. The method of claim 15 wherein the delivering step comprises:

a) introducing the Bacillus pseudofirmus to a conveyance fluid; and

b) delivering the conveyance fluid to the set cement composition.

17. The method of claim 15 wherein the introducing step further comprises introducing a nutrient to the conveyance fluid.

18. The method of claim 15 wherein the delivering step comprises:

a) isolating a portion of the wellbore having set cement requiring repair; and

b) delivering the healing agent to the isolated portion of the wellbore.

19. The method claim 15 wherein the delivering step comprises:

a) forming a fluid communication path in the wellbore along a portion of the set cement requiring repair; and

b) introducing the healing agent to the fluid communication path.