Patent Application
20150300336
Hydraulic fracturing is a common technique for extracting hydrocarbons from reservoirs in earth formations. In hydraulic fracturing, certain types of liquids are injected into boreholes that penetrate the earth formations at pressures that are high enough to fracture the formation rock. The fractured rock creates spaces that are interconnected and allow the hydrocarbons of interest to flow for extraction purposes.
In order to create a large number of fractures needed to extract the hydrocarbons, high pressure and high flow pumps are required to inject the fracturing liquids. For example, the pumps may be required to pump over 70 gallons per second of the liquid at pressures over 15,000 psi and require over 2000 hp to run at these specifications. In many instances, electric motors may be called upon to operate these types of pumps.
Hydraulic fracturing operations can be very expensive and any down time can only increase the operating costs. Hence, reliable electric motors to operate fracturing pumps would be well received in the hydraulic fracturing industry.
Disclosed is an apparatus configured to hydraulically fracture an earth formation. The apparatus includes: a pump configured to hydraulically fracture the earth formation by pumping a fracturing liquid into a borehole penetrating the earth formation; an electric motor having a rotor coupled to the pump and a stator; and a motor control center configured to apply an alternating electrical voltage having a fixed-frequency to the stator in order to power the electric motor, wherein the apparatus and motor control center do not have a variable frequency drive.
Also disclosed is a method for performing hydraulic fracturing of an earth formation. The method includes applying a fixed-frequency voltage to a stator of an electric motor having a rotor coupled to a pump configured to pump a liquid into a borehole penetrating the earth formation. The fixed frequency voltage is applied without using a variable frequency drive. The method further includes pumping the liquid into the earth formation using the pump to hydraulically fracture the earth formation.
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
A detailed description of one or more embodiments of the disclosed apparatus and method presented herein by way of exemplification and not limitation with reference to the figures.
Disclosed are embodiments of apparatus configured to hydraulically fracture an earth formation.
Refer now to
For controlling operation of the electric motor 5, the MCC 7 includes components such as contactors for applying fixed-frequency voltage to the motor 5. These components may be operated locally such as from a local control panel or remotely. The fixed-frequency is the frequency of the voltage supplied by the on-site power source 8 and/or the off-site power source 9. Hence, neither the hydraulic fracturing system 10 nor the MCC 7 includes a variable frequency drive (VFD) for varying the frequency of the voltage applied to the stator 20. In one or more embodiments, the voltage supplied by the on-site power source 8 and/or the off-site power source 9 is applied directly to the stator 20 by the MCC 7 without any intermediate transformer in order to improve reliability.
The MCC 7 may also include pole-changing circuitry 24 configured to change a configuration of the rotor windings 23 in order to change an operating speed of the motor 5. The pole-changing circuitry 24 allows for operating the motor 5 at multiple rotational speeds. In one or more embodiments, the pole-changing circuitry 24 is configured to operate the motor 5 at a first rotational speed upon start-up from zero rotational speed and then to increase the rotational speed to a second rotational speed for continuous pumping operation in order to limit the associated start-up current. In one or more embodiments, the motor 5 may include slip rings for making connections to the rotor windings 23 and the pole-changing circuitry 24 may include switches for changing the configuration of the rotor windings 23. U.S. Pat. No. 4,644,242 discloses one example of pole-changing circuitry for an electric motor.
The MCC 7 may also include dynamic braking circuitry 25 configured to dynamically brake the motor 5 and thus the pump 3. The dynamic braking circuitry 25 may be configured to change the rotor pole configuration and/or apply voltage to the rotor windings to provide the braking capability.
The MCC 7 may also include power-factor correction circuitry 26 configured to reduce the reactive current and power flowing between the electric motor 5 and the power source in order to reduce power losses due to this current flow (i.e., reduce I2R losses due to the reactive current flow). In that the stator windings generally impose an inductive load, the power-factor correction circuitry 26 may include capacitors and switches (not shown) for switching in capacitors of an appropriate value to counterbalance the inductive load. It can be appreciated that for an electric motor having known specifications the appropriate values of capacitors may be determined by analysis and/or testing.
A controller 27 may be coupled to the pole-changing circuitry 24 and/or the dynamic braking circuitry 25 in order to control operation of the electric motor 5 according to a prescribed algorithm.
It can be appreciated that use of the fixed-frequency electric motor provides many advantages. A first advantage is that by not using a variable frequency drive (VFD) equipment reliability is increased due to less equipment requirements. A second advantage is that not using a VFD eliminates electrical current harmonics due to semiconductor switching and their potentially damaging effects in the electric motor. A third advantage is that by not having the VFD there is no maintenance requirement for the VFD and no associated costs of a technician trained to maintain the VFD. A fourth advantage is that by not having a VFD and associated cooling components the weight loading on a trailer carrying the pump-motor combination is reduced enabling the trailer to carry more pump and motor weight thus providing increased pumping capacity while at the same time being light enough to be below the legal weight limit for transport over public roads. A fifth advantage is that the fixed-frequency electric motor may be powered directly from a power source thus eliminating the need for an intermediate transformer and the associated costs and inherent additional reliability issues.
In support of the teachings herein, various analysis components may be used, including a digital and/or an analog system. For example, the pole-changing circuitry 24, the dynamic-braking circuitry 25, the power-factor correction circuitry 26, and/or the controller 27 may include digital and/or analog systems. The system may have components such as a processor, storage media, memory, input, output, communications link (wired, wireless, optical or other), user interfaces, software programs, signal processors (digital or analog) and other such components (such as resistors, capacitors, inductors and others) to provide for operation and analyses of the apparatus and methods disclosed herein in any of several manners well-appreciated in the art. It is considered that these teachings may be, but need not be, implemented in conjunction with a set of computer executable instructions stored on a non-transitory computer readable medium, including memory (ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives), or any other type that when executed causes a computer to implement the method of the present invention. These instructions may provide for equipment operation, control, data collection and analysis and other functions deemed relevant by a system designer, owner, user or other such personnel, in addition to the functions described in this disclosure.
Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a list of at least two terms is intended to mean any term or combination of terms. The terms “first,” “second” and the like do not denote a particular order, but are used to distinguish different elements. The term “configured” relates to a structural limitation of an apparatus that allows the apparatus to perform the task or function for which the apparatus is configured.
The flow diagram depicted herein is just an example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention.
While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.
It will be recognized that the various components or technologies may provide certain necessary or beneficial functionality or features. Accordingly, these functions and features as may be needed in support of the appended claims and variations thereof, are recognized as being inherently included as a part of the teachings herein and a part of the invention disclosed.
While the invention has been described with reference to exemplary embodiments, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
