Pumice containing compositions for cementing a well
A cement composition comprises fine pumice particles, for use in cementing subterranean wells, and oil and gas wells in particular. The pumice containing cement blends feature enhanced compressive strength, and favorable compressive strength to Young's Modulus ratios. Lightweight cement blends containing pumice, and their use in cementing oil and gas wells are also described.
1. A cement composition for use in the manufacture of a subterranean well, the cement composition comprising:
(a) about 5-100% (wt) of ground or crushed amorphous reactive pozzolan, of which the particle size has a range which falls into a normal distribution, screened to have a maximum particle size of about 200 μm such that the ground or crushed amorphous reactive pozzolan has particle sizes up to and including about 200 μm; and
(b) about 0-95% (wt) of a mixture of American Petroleum Institute (API) Class A or Class G Portland cement and fly ash in a ratio of about 100:0 to about 50:50.
2. The cement composition of claim 1 wherein the amorphous reactive pozzolan comprises pumice.
3. The cement composition of claim 2 wherein the cement has a density of less than about 1400 kg/m 3 .
4. The cement composition of claim 3 wherein the cement has a density of less than about 1300 kg/m 3 .
5. The cement composition of claim 4 wherein the cement has a density of less than about 1200 kg/m 3 .
6. The cement composition of claim 5 wherein the cement has a density of less than about 1100 kg/m 3 .
7. The cement composition of claim 2 wherein the cement has a transition time of less than about 15 minutes.
8. The cement composition of claim 7 wherein the cement has a transition time of less than about 12 minutes.
9. The cement composition of claim 1 or 2 wherein the Portland cement comprises American Petroleum Institute (API) Class A cement.
10. The cement composition of claim 1 or 2 wherein the Portland cement comprises API Class G cement.
11. The cement composition of claim 2 wherein the cement has a compressive strength to Young's Modulus ratio of greater than about 5.0×10 −3 , with a compressive strength of greater than about 3.5 MPa.
12. The cement composition of claim 2 wherein the ground or crushed pumice has a particle size range having a normal distribution up to and including about 120 μm.
13. The cement composition of claim 2 wherein the ground or crushed pumice has a particle size range having a normal distribution up to and including about 100 μm.
14. The cement composition of claim 2 wherein the ground or crushed pumice has a particle size range having a normal distribution up to and including about 80 μm.
15. The cement composition of claim 2 wherein the ground or crushed pumice has a particle size range having a normal distribution up to and including about 70 μm.
16. A method of cementing a subterranean well, comprising the steps of preparing the cement composition of claim 1 , placing the cement composition in the well, allowing the cement composition to set.
17. The cement composition of claim 2 , 12 , 13 , 14 or 15 , wherein the cement composition comprises 10% to about 30% ground or crushed pumice.