Automatic density control system for blending operation

Apparatus for remotely manually or automatically controlling, from a frac van, the delivery, via a screw conveyor, of a solid particulate additive into a mixing tank into which a pregelled liquid is concurrently flowed so that a fracturing slurry having a desired density is provided at the output of the mixing tank, which screw conveyor and mixing tank are parts of a blender trailer also having:

• a flow meter for detecting the flow rate of the pregelled liquid flowing into the mixing tank, and a transducer for detecting the rotational speed of the screw conveyor, said apparatus comprising:
• a control valve, mounted on the blender trailer, for controlling the rotational speed of the screw conveyor;
• connector terminal means, mounted on the blender trailer and having a first connector mount, for communicating each of a flow rate indicating signal derived from the flow meter and a rotational speed indicating signal derived from the transducer to respective terminals of said first connector mount and for communicating a valve control signal from a terminal of said first connector mount to said control valve;
• a display unit mounted in the frac van, said display unit including:
• a first housing disposed in the frac van;
• a second connector mount having respective terminals, said second connector mount attached to said first housing;
• valve drive means, retained in said first housing, for providing said valve control signal to a terminal of said second connector mount;
• visual display means, mounted on said first housing, for indicating the rotational speed of the screw conveyor, said visual display means connected to a terminal of said second connector mount;
• and
• a third connector mount, attached to said first housing, said third connector mount having a plurality of terminals connected to said valve drive means, said visual display means and said second connector mount;
• a computer unit mounted in the frac van, said computer unit including:
• a second housing disposed in the frac van;
• a fourth connector mount having a pluraity of terminals, said fourth connector mount attached to said second housing;
• and
• computer means, disposed in said second housing and connected to terminals of said fourth connector mount, for providing a valve drive means control signal to a terminal of said fourth connector mount in response to the flow rate indicating signal and the rotational speed indicating signal;
• first conductor means, adapted for connection to said first connector mount and said second connector mount, for connecting terminals of said first connector mount to terminals of said second connector mount so that the flow rate indicating signal and the rotational speed indicating signal are communicated through said first conductor means to said display unit and so that the valve control signal is communicated through said first conductor means to said connector terminal means;
• and
• second conductor means, adapted for connection to said third connector mount and said fourth connector mount, for connecting terminals of said third connector mount to terminals of said fourth connector mount so that the flow rate indicating signal and the rotational speed indicating signal transferred from said second connector mount to said third connector mount through said display unit are communicated through said second conductor means to said computer unit and so that the valve drive means control signal is communicated through said second conductor means to said display unit.

Method of remotely controlling the quantity of a solid substance added to a liquid substance by each of two screw conveyors, which control occurs at a remote control station having computer means for automatically operating the screw conveyors, and having first potentiometer means for manually operating one of the screw conveyors, and having second potentiometer means for manually operating the other of the screw conveyors, and having first switch means for connecting either the computer means or the first potentiometer means to control the one screw conveyor, and having second switch means for connecting either the computer means or the second potentiometer means to control the other screw conveyor, said method comprising:

• selecting whether the one screw conveyor is to be operated automatically or manually and setting the first switch means in an automatic position or a manual position accordingly;
• selecting whether the other screw conveyor is to be operated automatically or manually and setting the second switch means in an automatic position or a manual position accordingly;
• transmitting to the computer means a signal indicating whether the first switch means is in the automatic position or the manual position;
• transmitting to the computer means a signal indicating whether the second switch means is in the automatic position or the manual position;
• determining in the computer means the actual rotational speed of the one screw conveyor;
• computing in the computer means, in response to the actual rotational speed of the one screw conveyor, the actual quantity delivery rate of the solid substance by the one screw conveyor;
• determining in the computer means the actual rotational speed of the other screw conveyor;
• computing in the computer means, in response to the actual rotational speed of the other screw conveyor, the actual quantity delivery rate of the solid substance by the other screw conveyor;
• determining in the computer means the desired total quantity delivery rate of the solid substance needed to be delivered by both of the screw conveyors;
• subtracting, in the computer means, from the desired total quantity delivery rate the actual quantity deliver rate of the one screw conveyor if the first switch means is in the manual position and the actual quantity delivery rate of the other screw conveyor if the second switch means is in the manual position, thereby defining a difference;
• dividing, in the computer means, the difference by the total number of the first and second switch means in the automatic position, thereby defining a quotient;
• providing from the computer means, in response to the actual rotational speed of the one screw conveyor and the quotient, a control signal for automatically controlling the one screw conveyor when the first switch means is in the automatic position;
• providing from the computer means, in response to the actual rotational speed of the other screw conveyor and the quotient, a control signal for automatically controlling the other screw conveyor when the second switch means is in the automatic position;
• providing from the first potentiometer means a control signal for manually controlling the one screw conveyor when the first switch means is in the manual position;
• and
• providing from the second potentiometer means a control signal for manually controlling the other screw conveyor when the second switch means is in the manual position.

Retrofit apparatus for controlling the blending of a solid substance with a liquid substance, said apparatus comprising:

• a multiple-conductor electrical cable;
• local terminal means, mountable on a conventional blender previously manufactured for use at a well site, for connecting respective ones of the conductors at one end of said cable to respective components mounted on said blender;
• and
• control means, mountable at a location within the vicinity of the well site but spaced from said blender and connectable to said respective ones of the conductors at the othe end of said cable, for providing control signals through conductors of said cable in response to signals received by said control means through other conductors for said cable from said components of said blender connected by said terminal means to said cable, said control signals controlling the amount of the solid substance added to the liquid substance, wherein said components of said blender include:
• a mixing container wherein the solid substance and the liquid substance are mixed;
• screw conveyor means for conveying the solid substance into said mixing container, said screw conveyor means having a screw element;
• hydraulic means for rotating said screw element, said hydraulic means including an electrohydraulic valve controlling the flow of a driving fluid used to rotate said screw element, said valve having first transducer means connected thereto for providing an electrical signal representative of the state of opeation of said valve;
• second transducer means for providing an electrical signal representative of the rotational speed of said screw element;
• and
• flow meter means for providing an electrical signal representative of the flow rate of the liquid substance flowing into said mixing container;
• and
• said local terminal means includes:
• a housing;
• a first connector attached to said housing and adapted to connect to said first transducer means so that the electrical signal of said first transducer means is provided to said terminal means;
• a second connector attached to said housing and adapted to connect to said second transducer so that the electrical signal of said second transducer means is provided to said terminal means;
• a third connector attached to said housing and adapted to connect to said flow meter means so that the electrical signal of said flow meter means is provided to said terminal means;
• a fourth connector attached to said housing and adapted to connect to said valve;
• a fifth connector attached to said housing and adapted to connect to said one end of said cable;
• and
• interconnect means, attached to said housing, for communicating the electrical signals of said first transducer means, said second transducer means, and said flow meter means received through said first, second and third connectors to respective conductors of said fifth connector and for communicating said control signals from said control means, received over said cable, to said valve connected to said fourth connector.