Automatic cementing system with improved density control

A method of controlling the density of a slurry of cement and mix water, comprising the steps of:

• injecting mix water into a mixing chamber;
• injecting dry cement into a mixing chamber;
• mixing the mix water and dry cement to form a slurry;
• opening a discharge valve to discharge the slurry from the mixing chamber;
• measuring the discharge rate of the slurry;
• calculating the fraction of mix water in the discharging slurry from a desired slurry density, the density of the cement, and the density of the mix water according to the relation ##EQU4## using a microprocessor based system controller.

An automatic cementing system, comprising:

• a mixing chamber for receiving liquid and dry cement, said mixing chamber mixing the liquid and dry cement to form a cement slurry;
• an input line for supplying the liquid to the mixing chamber;
• a slide-gate valve actuated by a control valve for regulating the flow rate of dry cement to the mixing chamber;
• a pump for regulating the flow rate of mix water to the mixing chamber;
• a sonic level sensor for measuring the slurry level in the mixing chamber and generating an electrical signal representative of the slurry level;
• a first flow meter for measuring the flow rate of mix water to the mixing chamber and generating an electrical signal representative thereof;
• a second flow meter for measuring the flow rate of slurry discharging from the mixing chamber and generating an electrical signal representative thereof;
• a density meter for measuring the density of the slurry and generating an electrical signal representative thereof;
• a system controller electrically connected to the level sensor, the first and second flow meters, the density meter;
• the control valve, and pump, said controller comprising:
• an input device through which data may be entered;
• one or more read-only memory units;
• and
• an output device for displaying information;
• a mix water servo-loop electrically connected to the system controller and to the pump, for controlling the speed of the pump as a function of the flow rate of slurry discharging from the mixing chamber;
• and
• a dry cement servo-loop electrically connected to the system controller and to the control valve, for controlling the actuation of the slide-gate valve as a function of the slurry level.