Spacer fluids for cementing well bores
Spacer fluids are provided for use in cementing liners in oil and gas wells. The fluids comprise pumice and a suspending agent. Pumice is the first-in weighting agent and is added in amounts sufficient to stabilize the rheology of the fluid over time and temperature.
1. A non-settable weighted aqueous well fluid, said fluid comprising:
(a) pumice; and
(b) a suspending agent;
(c) wherein said fluid has a time-temperature stability factor of about 10% or less; and
(d) wherein said time-temperature stability factor is defined as the average deviation coefficient of the viscosity of said fluid over time and temperature expressed in percentage.
2. The fluid of claim 1 , wherein pumice comprises at least about 60 wt % of weighting agents in said fluid.
3. The fluid of claim 1 , wherein said fluid has a density of from about 8.5 to about 13 ppg.
4. The fluid of claim 1 , wherein said fluid has a time-temperature stability factor of about 5% or less.
5. The fluid of claim 1 , wherein said fluid has a time-temperature stability factor of about 3% or less.
6. The fluid of claim 1 , wherein pumice comprises at least about 40 wt % of weighting agents in said fluid.
7. The fluid of claim 1 , wherein said fluid is weighted with from about 1 to about 8 ppg of pumice.
8. The fluid of claim 1 , wherein said fluid is weighted with from about 2 to about 7 ppg of pumice.
9. The fluid of claim 1 , wherein said fluid comprises:
(a) primary weighting agents selected from the group consisting of pumice and fly ash, wherein pumice comprises at least about 40 wt % of said primary weighting agents; and
(b) wherein when said fluid has a density of less than about 13 ppg, said fluid comprises, as a percentage of all weighting agents in said fluid, less than about 5 wt % of secondary weighting agents.
10. The fluid of claim 9 , wherein said fluid comprises, as a percentage of all weighting agents in said fluid, less than about 5 wt % of secondary weighting agents when said fluid has a density of less than about 12 ppg.
11. The fluid of claim 1 , wherein said fluid comprises weighting agents consisting essentially of weighting agents selected from the group consisting of pumice and fly ash, wherein pumice comprises at least about 40 wt % of said weighting agents.
12. The fluid of 11 , wherein pumice comprises at least about 60 wt % of said weighting agents.
13. The fluid of claim 11 , wherein said weighting agents consists essentially of pumice.
14. A method of cleaning a well in preparation for injecting a cement composition into said well, the method comprising:
(a) injecting a non-settable weighted aqueous treatment fluid into said well in advance of said cement composition, wherein said treatment fluid is a fluid of claim 1 ; and
(b) energizing said treatment fluid to displace fluids present in said well.
15. A method of cleaning a well in preparation for injecting a cement composition into said well, the method comprising:
(a) injecting a non-settable weighted aqueous treatment fluid into said well in advance of said cement composition, wherein said treatment fluid is a fluid of claim 4 ; and
(b) energizing said treatment fluid to displace fluids present in said well.
16. A method of cleaning a well in preparation for injecting a cement composition into said well, the method comprising:
(a) injecting a non-settable weighted aqueous treatment fluid into said well in advance of said cement composition, wherein said treatment fluid is a fluid of claim 5 ; and
(b) energizing said treatment fluid to displace fluids present in said well.
17. A method of cleaning a well in preparation for injecting a cement composition into said well, the method comprising:
(a) injecting a non-settable weighted aqueous treatment fluid into said well in advance of said cement composition, wherein said treatment fluid is a fluid of claim 9 ; and
(b) energizing said treatment fluid to displace fluids present in said well.
18. A method of cleaning a well in preparation for injecting a cement composition into said well, the method comprising:
(a) injecting a non-settable weighted aqueous treatment fluid into said well in advance of said cement composition, wherein said treatment fluid is a fluid of claim 11 ; and
(b) energizing said treatment fluid to displace fluids present in said well.
19. A method of stabilizing a rheology of a non-settable weighted aqueous well treatment fluid over time and temperature, said method comprising:
(a) weighting said fluid with pumice in an amount effective to provide said fluid with a time-temperature stability factor of less than about 10%;
(b) wherein said time-temperature stability factor is defined as the average deviation coefficient of the viscosity of said fluid over time and temperature expressed in percentage.
20. A method of cementing a well, said method comprising;
(a) providing a cleaning fluid stabilized according to claim 19 ;
(b) injecting said cleaning fluid into said well and energizing said cleaning fluid to displace fluids in said well; and
(c) injecting a cementitious slurry into said well after said cleaning fluid.