A method for making stable cement slurry for downhole injection, which comprises the step of entraining air into a cement slurry further comprising the steps of:
- circulating process water in a process water supply circuit for a predetermined period, the supply including:
- a process water supply tank having a temperature monitoring device and a level detecting device, the temperature monitoring device and level detecting device providing signals to a controller indicating the level of process water in the water supply tank and the temperature of the process water in the process water supply circuit;
- a closed loop circulating system for controlling the temperature of the water in the process water supply tank including a circulating pump and a water heater, the circulating pump pumping water from the process water supply tank through the water heater and back to the process water supply tank to control the temperature of the process water, wherein the controller receives a signal from the temperature monitoring device and energizes or de-energizes the circulating pump and water heater based upon a preprogrammed temperature set point;
- a process water circulating loop including a process water supply pump that pumps water from the process water supply tank through the process water circulating loop and back to the process water supply tank, a first variable speed drive for driving the pump and a flow meter for determining the flow rate of process water in the process water circulating loop whereby the controller receives a signal from the flow meter and controls the speed of the first variable speed drive based upon a preprogrammed set point;
- circulating aqueous-based air-entrainment solution in an aqueous-based air entrainment solution supply circuit during the predetermined period, the aqueous-based air entrainment solution supply circuit including:
- an aqueous-based air entrainment solution batch tank having an aqueous-based air entrainment solution level detecting device for monitoring the level of aqueous- based air entrainment solution in the batch tank, the level detecting device transmitting signals to a controller indicating the level of aqueous-based air entrainment solution in the aqueous-based air entrainment solution batch tank;
- an aqueous-based air entrainment solution circulating loop including an aqueous-based air entrainment solution supply pump that pumps aqueous-based air entrainment solution from the aqueous-based air entrainment solution batch tank through the aqueous-based air entrainment solution circulating loop and back to the aqueous-based air entrainment solution batch tank, a second variable speed drive for driving the aqueous-based air entrainment solution supply pump and an aqueous-based air entrainment solution flow meter for determining the flow rate of aqueous-based air entrainment solution in the aqueous-based air entrainment solution circulating loop whereby the controller receives a signal from the aqueous-based air entrainment solution flow meter to control the speed of the second variable speed drive to control the flow rate of aqueous-based air entrainment solution in the aqueous-based air entrainment solution circulating loop;
- after the predetermined period, actuating first and second valves in the process water circulating loop and the aqueous-based air-entrainment solution circulating loop, respectively, to divert process water and aqueous-based air-entrainment solution to a mixing chamber for mixing;
- adding compressed air to the mixed process water and aqueous-based air-entrainment solution;
- directing the process water, aqueous-based air-entrainment solution and compressed air to a stationary mixer to produce an air-entrained foam;
- directing the air-entrained foam to a discharge line;
- discharging the air-entrained foam into a cement composition to produce a concrete composition including entrained air;
- using the air-entrained foam to make cement of varying density before it is pumped downhole;
- and,
- deploying the cement slurry of varying density into a wellbore to set as a cement column having a constant density;
- and continuously repeating said making of the cement slurry until a desired amount of cement slurry for a wellbore casing has been satisfied.