Patent Application
20060088423
Not Applicable.
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
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-discreet 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.
For a more detailed description of the present invention, reference will now be made to the accompanying drawings, wherein:
Referring now to an embodiment shown in
Pump 220 is linked to motor 210 without a transmission, such that their speeds are related by a fixed ratio. Thus, the speed of pump 220 may be directly regulated by controlling the speed of motor 210. Displacement control 250 regulates the displacement (or volume of fluid) that pump 220 will move with each revolution or reciprocation. For example, displacement control 250 may act to vary the displacement of pump 220 by changing the volume of fluid pumped per stroke of a pump cylinder.
One embodiment of control system 240 is shown in
Referring now to
As pump 220 operates, I/O device 330 receives flow data 360 from outlet 270 and adjusts motor 210 and displacement control 250 to maintain the desired flow characteristics. The motor speed and displacement can be optimized for horsepower, torque, fuel efficiency, or a combination of those factors. For example, if maximum horsepower is selected, the engine speed (and thus pump speed) and pump displacement would be chosen to give the best rate for maximum engine horsepower to be developed. Thus, maximum horsepower would be transferred to the pump and to the fluid being pumped. Similar choices could be made for optimal efficiency, or for optimal torque. In each case, the engine speed and displacement would be chosen to allow for the optimum parameter value to be developed by the engine and transferred to the pump with much lower loss than with a transmission. So, for example, if optimum efficiency is chosen, the engine speed and the pump stroke (displacement) would be chosen to allow the engine to operate at optimum efficiency, saving fuel and reducing emissions. The efficiency would be greater not only because of operation the engine at its optimal speed for the load but would also be greater than with a transmission because losses from the transmission, which lower efficiency, would be avoided.
A continuous feedback control loop also allows for adjusting to changing fluid conditions, including compressibility and inlet flow rate, and provides a quick-to-neutral capability. The quick-to-neutral capability offers a significant advantage should a pumping shutdown be needed. When activated, a relief valve would quickly release the hydraulic pressure that was holding the current pump displacement and fluid back pressure would rapidly stroke the positioner back to the zero rate pumping position. This could be done much more quickly than stopping the engine or pump from rotating, because to stop them their inertia must be overcome. This ability could be further enhanced by incorporating a spring in the displacement actuator so that when pumping against low pressure the spring would assist in more rapidly returning the pump to the zero pumping rate position.
By controlling the speed of motor 210 and the displacement of pump 220 any desired pressure and flow rate combination within a given operating envelope can be provided at outlet 270. Referring now to
Eliminating the multispeed transmission also eliminates a complex piece of machinery, reducing capital and maintenance costs as well as reducing the weight of the overall system. Many pumping systems are portable systems that are mounted on skids, trailers, or chassis, so weight and size of components is an important issue. For example, to be easily transported by road, the size of a portable component of a system is limited to a width of approximately eight feet and a height of approximately thirteen feet. With the weight of the multispeed transmission eliminated, a higher horsepower or capacity system could be used in applications that were previously limited by the weight and/or size of the components.
Embodiments of pumping system 200 may utilize any combination of motors, variable displacement pumps, and fluid end assemblies as may be desired. For example, an electric or diesel motor may be used to provide power to the pump. The pump may be any variable displacement pump providing easily adjusted variable displacement and capable of the horsepower and pressure requirements needed for the desired application. For example, pumps may be used having mechanisms as described in U.S. Pat. No. 6,742,441, entitled “Continuously Variable Displacement Pump with Predefined Unswept Volume,” or U.S. patent application Ser. No. 10/603,482 filed Jun. 25, 2003, entitled “Transmissionless Variable Output Pumping Unit,” or U.S. patent application filed concurrently herewith, Docket Number HES 2002-IP-008137U1, entitled “Variable Stroke Assembly,” all of which are incorporated herein by reference in their entirety for all purposes.
Referring now to
Variable displacement pump 530 includes a rotating shaft, the position of which can be linearly adjusted to control the displacement of the pump. The shaft is rotated by the motor turning drive line connection 550, which is coupled to the shaft through speed reducer 520. Speed reducer 520 transfers rotation from drive line connection 550 to the shaft at a fixed ratio as established by one or more gears disposed within the speed reducer. Thus, the rotational rate of pump 530 is directly proportional to the rotational rate at which the motor is operated.
The displacement of pump 530 is controlled by axially displacing the rotating shaft that is coupled to the motor. The displacement of the rotating shaft can be controlled by a variety of devices including hydraulic cylinders, jack-screws, ball-screws, pneumatic cylinders, and electric actuators. These devices preferably provide adjustment of the rotating shaft in both directions along its axis. Referring back to
As shown in
Referring now to
Referring back to
Fluid end 540 is coupled to the pistons of pump 530 such that fluid is drawn in through suction inlet 560 and expelled through fluid outlet 570. Fluid end 540 may comprise check valve assemblies 580 that interface with the pistons of pump 530, where each check valve 580 is in fluid communication with both inlet 560 and outlet 570. The check valve assemblies 580 allow fluid to be drawn only from the low pressure inlet 560 and high pressure fluid output only through outlet 570.
By eliminating the need for a heavy-duty, multi-speed transmission, the variable displacement pumping system provides a smaller package for a given pump rating. The table below lists various examples of pumping systems operating at 275 revolutions per minute.
The smaller package allows higher capacity pumping systems to be mounted on chassis, trailers, or skids comparably sized to smaller pumping systems. The variable displacement pumping system also provides a more complete operating envelope as compared to conventional transmission systems.
While exemplary embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.
