Method of well treatment and construction

1. A method of well construction or treatment which comprises introducing a setable cement composition down a borehole, characterized in that said composition contains pulverulent aplite.

2. The method as claimed in claim 1 wherein said cement is a cement composition comprising at least 30% by weight of cement (bwoc) pulverulent aplite on a dry solids basis.

3. The method as claimed in claim 1 wherein said setable cement is a non-self-setable cement and wherein an activator is introduced into said borehole separately from said setable cement.

4. The method as claimed in claim 1 wherein said cement is a cement composition containing at least 100% bwoc of pulverulent aplite on a dry solids basis.

5. The method as claimed in claim 1 wherein said cement is a cement composition containing aplite having a particle size of less than 200 μm.

6. The method as claimed in claim 1 wherein said cement is a cement composition containing at least 100% bwoc of pulverulent aplite on a dry solids basis and containing aplite having a particle size of less than 200 μm.

7. The method as claimed in claim 1 wherein the silicon content of said aplite is at least 68 wt %, expressed as oxide content.

8. The method as claimed in claim 1 further containing a non-aplite silicate wherein the weight ratio of non-aplite silicate to aplite is in the range 2:98 to 70:30.

9. The method as claimed in claim 1 wherein said cement comprises a cement base comprising portland cement.

10. The method as claimed in claim 1 , wherein the composition further contains carbon fibres.

11. The method as claimed in claim 10 , wherein said composition is a non-self-settable composition and wherein an activator is introduced into said borehole separately from said composition.

12. A cement composition comprising from at least 30% by weight to 400% of cement (bwoc) pulverulent aplite on a dry solids basis.

13. A cement composition as claimed in claim 12 containing at least 100% bwoc of pulverulent aplite on a dry solids basis.

14. A cement composition as claimed in claim 12 containing aplite having a particle size of less than 200 μm.

15. A cement composition as claimed in claim 12 containing aplite having a particle size of less than 100 μm.

16. A cement composition as claimed in claim 12 comprising a cement base comprising portland cement.

17. A cement composition, as claimed in claim 12 , further comprising blast furnace slag and pulverulent aplite.

18. A cement composition as claimed in claim 12 wherein the silicon content of said aplite is at least 68 wt %, expressed as oxide content.

19. A cement composition as claimed in claim 12 further containing a non-aplite silicate wherein the weight ratio of non-aplite silicate to aplite is in the range 2:98 to 70:30.

20. A cement composition as claimed in claim 12 wherein said set cement composition has a shrinkage on setting of less than 3% by volume.

21. A set cement formed from a cement composition as claimed in claim 12 wherein said set cement has a permeability of no more than 0.0005 mD at a density of 1.9 SG.

22. A set cement formed from a cement composition as claimed in claim 12 wherein said set cement has a permeability of no more than 0.0003 mD at a density of 1.9 SG.

23. A cement composition as claimed in claim 12 containing at least 100% bwoc of pulverulent aplite on a dry solids basis and containing aplite having a particle size of less than 200 μm.

24. A cement composition as claimed in claim 12 containing at least 100% bwoc of pulverulent aplite on a dry solids basis and containing aplite having a particle size of less than 100 μm.

25. A cement composition as claimed in claim 12 , wherein said composition further comprises carbon fibres.

26. A cement composition as claimed in claim 25 , wherein said carbon fibres are between 0.1 cm and 10 cm in length.

27. A composition as claimed in claim 25 , wherein the amount of carbon fibres added per m 3 of cement mix is 0.1 kg to 10 kg.

28. A fluid extraction or introduction well comprising a bore-hole having at at least one depth therein an annular, borehole well-lining comprising a set-cement produced using a pulverulent aplite containing cement composition.

29. A well as claimed in claim 28 wherein said cement composition is a cement composition comprising at least 30% by weight of cement (bwoc) pulverulent aplite on a dry solids basis.

30. The fluid extraction or introduction well of claim 28 , wherein the well is sealed.

31. A cement composition comprising pulverulent aplite and carbon fibres.

32. A cement composition as claimed in claim 31 , wherein said carbon fibres are between 0.1 cm and 10 cm in length.

33. A cement composition as claimed in claim 31 , wherein the amount of carbon fibres added per m 3 of cement mix is 0.1 kg to 10 kg.

34. A cement composition as claimed in claim 31 , further comprising blast furnace slag and pulverulent aplite.

35. A cement composition as claimed in claim 31 , wherein the silicon content of said aplite is at least 68 wt. %, expressed as oxide content.

36. A cement composition as claimed in claim 31 , further comprising a non-aplite silicate wherein the weight ratio of non-aplite silicate to aplite is in the range of 2:98 to 70:30.

37. A cement composition as claimed in claim 31 , wherein said cement composition has a shrinkage on setting of less than 3% by volume.

38. A set cement formed from a cement composition as claimed in claim 31 , wherein said set cement has a permeability of no more than 0.0005 mD at a density of 1.9 SG.

39. A set cement formed from a cement composition as claimed in claim 31 , wherein said set cement has a permeability of no more than 0.0003 mD at a density of 1.9 SG.

40. A fluid extraction or introduction well comprising a borehole having at least one depth therein an annular, borehole well comprising a set-cement using a pulverulent aplite and carbon fibre containing cement composition.

41. The fluid extraction or introduction well of claim 40 , wherein said well is sealed.