Mixing apparatus and method

An apparatus for producing a cement slurry at a well site, comprising:

• a vehicle transportable to a well site;
• first and second displacement tanks mounted on said vehicle;
• a mixing tub mounted on said vehicle;
• a flow mixer connected to said mixing tub, said flow mixer including a cement inlet for receiving dry cement, a water inlet for receiving water, and a mixture output for outputting a mixture of received cement and water into said mixing tub;
• and
• means for communicating mixture from said mixing tub to either of said first and second displacement tanks so that said first and second displacement tanks are used as, in addition to displacement tubs, averaging tubs wherein cement slurry is obtained from mixture received from said mixing tub.

An apparatus for producing a mixture having a desired density, comprising:

• flow mixing means for receiving and mixing a first substance and a second substance and for outputting a mixture including the first and second substances;
• first containment means for containing a body of a first averaged mixture including the mixture received from said flow mixing means;
• second containment means for containing a body of a second averaged mixture including a portion of the first averaged mixture received from said first containment means;
• first recirculation means for recirculating at least a portion of said first averaged mixture from said first containment means to said flow mixing means;
• second recirculation means for recirculating at least a portion of said second averaged mixture from said second containment means to said flow mixing means;
• and
• control means for controlling, in response to a desired density and to measured densities of both the recirculated first averaged mixture and the recirculated second averaged mixture, both the first substance and the second substance received and mixed by said flow mixing means so that said second averaged mixture has the desired density.

An apparatus for producing a mixture including a first substance and a second substance, comprising:

• a first tub;
• an axial flow mixer connected to said first tub, said axial flow mixer including a valve through which a first substance flows in response to said valve being opened;
• means, connected to said axial flow mixer, for selectably admitting a second substance into said axial flow mixer;
• a second tub;
• a third tub;
• means for communicating from said first tub to said second tub and said third tub a mixture including the first and second substances communicated through said axial flow mixer;
• a first densimeter;
• a first pump, said first pump having an inlet connected to said first tub and having an outlet connected through said first densimeter to said axial flow mixer;
• a second densimeter;
• a second pump, said second pump having an inlet connected to said second and third tubs and having an outlet connected through said second densimeter to said axial flow mixer;
• a data entry terminal;
• and
• a computer connected to said first and second densimeters and to said data entry terminal, said computer including means for generating, in response to inputs from said first and second densimeters and said data entry terminal, a control signal for controlling said valve of said axial flow mixer and a control signal for controlling said means for selectably admitting a second substance into said axial flow mixer.

A method of controlling the production of a mixture so that the mixture has a desired density, which mixture includes a first substance and a second substance passed through a flow mixer into a first tub and from the first tub into a second tub where the mixture is defined, said method comprising the steps of:

• (a) recirculating contents of the first tub to the flow mixer;
• (b) recirculating contents of the second tub to the flow mixer;
• (c) measuring density of recirculated contents of the first tub;
• (d) measuring density of recirculated contents of the second tub;
• (e) controlling the introduction of the first substance into the flow mixer in response to a desired density and both of the measured densities;
• and
• (f) controlling the introduction of the second substance into the flow mixer in response to the desired density and both of the measured densities.