Volumetric control for proppant concentration in hydraulic fracturing

A method of controlling proppant concentration in a hydraulic fracturing slurry, comprising:

• a) transmitting to a non-transient computer readable memory of a blender control unit, a target slurry volumetric flow rate ({dot over (V)}sl-target), a target input value of a slurry volume fraction (Cs-target), and inputs of a known density of a fracturing fluid (ρfl) and known density of a proppant (ρpr);
• b) sending from a transmitter of the blender control unit, a command signal to actuate a first valve to deliver the fracturing fluid to a blender;
• c) sending from the transmitter of the blender control unit, a second command signal to actuate a second valve to deliver the proppant to the blender at a non-zero proppant mass flow rate ({dot over (m)}pr);
• d) measuring, using a first volume flow rate sensor, a volumetric flow rate ({dot over (V)}fl) of the fracturing fluid input to the blender and transmitting a signal corresponding to the measured {dot over (V)}fl to a signal receiver of the blender control unit;
• e) measuring, using a second volume flow rate sensor, a volumetric flow rate ({dot over (V)}sl) of the hydraulic fracturing slurry output from the blender and transmitting a signal corresponding to the measured {dot over (V)}sl to the signal receiver of the blender control unit;
• f) executing computer readable instructions, stored in the memory of the blender control unit to calculate, in a central processing unit of the blender control unit a volumetric flow rate of proppant input ({dot over (V)}pr) to the blender according to the formula:
• {dot over (V)}pr=({dot over (V)}sl−{dot over (V)}fl), and, a slurry volume fraction according to the formula:
• Cs=({dot over (V)}sl−{dot over (V)}fl)/{dot over (V)}sl;
• g) determining, in the central processing unit, a difference (Δ{dot over (V)}sl) between the {dot over (V)}sl-target and the {dot over (V)}sl, and, a difference (ΔCs) between the Cs-target and the Cs;
• and then
• h) if the Δ{dot over (V)}sl is not less than an acceptable slurry volumetric flow rate margin of error (ER-{dot over (V)}sl) or the ΔCs is not less than an acceptable slurry volume fraction margin of error (ER-Cs), then the central processing unit sends instructions to cause the command signal to further actuate the first valve to incrementally change the {dot over (V)}fl or to cause the second command signal to further actuate the second valve to incrementally change the {dot over (m)}pr, and then the central processing unit repeats steps (d)-(h), and
• i) if the Δ{dot over (V)}sl is less than ER-{dot over (V)}sl and the ΔCs is less than the ER-Cs, then the central processing unit sends an output signal to a display unit of the blender control unit to indicate that the target input values have been achieved.

A blending system for controlling proppant concentration of a hydraulic fracturing slurry, comprising:

• blender control unit, the blender control unit including:
• an input device configured accept target input values of a slurry density (ρsl-target) a slurry volumetric flow rate ({dot over (V)}sl-target), or, a slurry volume fraction (Cs-target), and inputs of a known density of a fracturing fluid (ρfl) and known density of a proppant (ρpr);
• a command signal transmitter configured to send a command signal to actuate a first valve to deliver the fracturing fluid to a blender and send a second command signal to actuate a second valve to deliver the proppant to the blender at a non-zero proppant mass flow rate ({dot over (m)}pr);
• a signal receiver configured to a receive a signal corresponding to a measured volumetric flow rate ({dot over (V)}fl) of the fracturing fluid input to the blender and receive a signal corresponding to a measured volumetric flow rate ({dot over (V)}sl) of the hydraulic fracturing slurry output from the blender;
• a non-transient computer readable memory configured to store the target values of ρsl-target, {dot over (V)}sl-target, or Cs-target and the inputs of the ρfl and the ρpr and to store computer readable instructions to calculate a volumetric flow rate of proppant input (V pr) to the blender according to the formula:
• {dot over (V)}pr=({dot over (V)}sl−{dot over (V)}fl), to calculate a slurry density (ρsl) according to the formula:
• ρsl=(({dot over (V)}fl·ρfl)+({dot over (V)}pr·ρpr))/{dot over (V)}sl, and to calculate a slurry volume fraction according to the formula:
• Cs=({dot over (V)}sl−{dot over (V)}fl)/{dot over (V)}sl;
• and
• a central processing unit configured to:
• read the computer readable instructions and to calculate:
• the {dot over (V)}pr and the ρsl, and to determine a difference (Δ{dot over (V)}sl) between the {dot over (V)}sl-target and the {dot over (V)}sl and a difference (Δρsl) between the ρsl-target and the ρsl, or, to calculate:
• the {dot over (V)}pr and the Cs and to determine a difference (Δ{dot over (V)}sl) between the {dot over (V)}sl-target and the {dot over (V)}sl and a difference (ΔCs) between the Cs-target and the Cs, and then:
• if the Δρsl is not less than an acceptable slurry density margin of error (ER-{dot over (V)}sl) or the Δ{dot over (V)}sl is not less than an acceptable slurry volumetric flow rate margin of error (ER-{dot over (V)}sl), then send instructions to cause the command signal to further actuate the first valve to incrementally change the {dot over (V)}fl or to cause the second command signal to further actuate the second valve to incrementally change the {dot over (m)}pr and if the Δρsl is less than ER-ρsl and the Δ{dot over (V)}sl is less than ER-{dot over (V)}sl, then send an output signal to a display unit of the blender control unit to indicate that the target input values have been achieved, or,
• if the Δ{dot over (V)}sl is not less than an acceptable slurry volumetric flow rate margin of error (ER-{dot over (V)}sl) or the ΔCs is not less than an acceptable slurry density margin of error (ER-Cs), then send instructions to cause the command signal to further actuate the first valve to incrementally change the {dot over (V)}fl or to cause the second command signal to further actuate the second valve to incrementally change the {dot over (m)}pr and if the Δ{dot over (V)}sl is less than ER-{dot over (V)}sl and the ΔCs is less than the ER-Cs, then the central processing unit sends an output signal to a display unit of the blender control unit to indicate that the target input values have been achieved.