Variable rate pumping system

The present application is a divisional of U.S. patent application Ser. No. 10/974,437, filed Oct. 27, 2004, and entitled “Variable Rate Pumping System,” which is incorporated herein by reference as if reproduced in its entirety.

Not Applicable.

The present invention relates generally to methods and apparatus for supplying pressurized fluids. More particularly, the present invention relates to methods and apparatus for pumping fluids into a wellbore at a wide range of pressures and flow rates.

The construction and servicing of subterranean wells often involves pumping fluids into the well for a variety of reasons. For example, fluids may be pumped into a well in conjunction with activities including fracturing, completion, stimulation, remediation, cementing, workover, and testing operations. A variety of fluids used in these operations include fracturing fluids, gels, drilling mud, barite, cement, slurries, acids, and liquid CO₂. In each of these different applications, the fluid may be required to be pumped into the well at any point within a wide range of pressures and flow rates.

Pumping units often utilize a power source, such as a diesel or electric motor, to drive one or more pumps. Many pumping units utilize a multispeed transmission connected between the power source and the pumps. The transmission operates to expand the speed and torque range produced by the power source by providing a set number of gears that transfer the motion produced by the power source to the pump.

Most multispeed transmissions provide a broad operating envelope of speed and torque within which a pump can operate. This operating envelope 10 can be illustrated as a relationship between pressure and flow rate as is shown in FIG. 1. Line 15 defines the peak hydraulic horsepower at which the pump can operate and line 16 defines the peak torque output. Because the transmission comprises a limited set of gear ratios 17, the operating envelope 10 of the pump has discrete points 20 at which the pump can operate at peak hydraulic horsepower. These discrete points 20, in effect, create gaps 25 where the pump cannot operate with a given gearing.

Although gaps 25 can be reduced by increasing the numbers of gear ratios within a transmission, as the number of gear ratios increases so does the complexity and weight of the transmission. Therefore, there are often practical limits on the number of gear ratios at which a transmission can operate. Thus, there remains a need to develop methods and apparatus for pumping fluids into a wellbore at wide range of pressures and flow rates, which overcome some of the foregoing difficulties while providing more advantageous overall results.

Disclosed herein is a wellbore pumping system comprising a motor, wherein the motor has an operating speed, a pump coupled to the motor, wherein the pump has a volumetric displacement, a fluid end coupled to the pump, wherein the fluid end is operable to draw fluid from an input and provide fluid to an output that is in fluid communication with a wellbore, and a control system operable to regulate the motor and the pump in order to provide fluid to the output at a selected pressure and flow rate within a continuous range of pressures and flow rates between the peak horsepower output and peak torque output of the motor.

Further disclosed herein is a method for operating a wellbore pumping system, the method comprising operating a pumping system to provide fluid to a wellbore at a selected pressure and flow rate operating conditions within a continuous range of pressures and flow rates between the peak horsepower and peak torque of the pumping system, monitoring the pressure and flow rate of the fluid provided by the pumping system, and controlling the pumping system to provide non-discrete variations in the pressure and flow rate of the fluid provided to the wellbore. Further disclosed herein is a pumping system comprising a motor having an operating speed, a variable displacement pump coupled to the motor, wherein the positive displacement pump has an operating speed that is related to the operating speed of the motor by a fixed ratio, a fluid end coupled to the pump, wherein the fluid end is operable to draw fluid from an inlet and provide fluid to an outlet that is in fluid communication with a wellbore, and a control system operable to regulate the operating speed of the motor and the displacement of the pump so as to control the pressure and flow rate of the fluid provided to the outlet.

Further disclosed herein is a method of operating a wellbore servicing pump comprising controlling the operating parameters of the pump to provide a fluid output at any combination of pressure and flow rate within a range defined by the peak hydraulic horsepower, the peak torque, the maximum pressure, and the maximum flow rate of the pump, monitoring pressure and flow rate of the fluid output, adjusting at least one of the operating parameters of the pump to provide a desired pressure and flow rate of the fluid output.

Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the invention, and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the present invention, reference will now be made to the accompanying drawings, wherein:

FIG. 1 is a graphical representation of the output characteristics of a prior art pumping system employing a multispeed transmission.

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