Patent Description:
Hydraulically fracturing subterranean formations with oilfield pressure pumping systems to enhance flow in oil and gas wells is known. Hydraulic fracturing increases well productivity by increasing the porosity of, and thus flow rate through, production zones that feed boreholes of the wells that remove underground resources like oil and gas.

Oilfield pressure pumping systems include heavy-duty industrial-type components to create the extreme hydraulic pressures, for example, <NUM>,<NUM> kPa (<NUM>,<NUM> psi) or more, which are needed to fracture the subterranean geological formations. Positive displacement, high pressure, plunger pumps are used as fracturing (fracking or frac) pumps to generate the extreme hydraulic pressures that are capable of fracturing subterranean geological formations.

Flow and pressure of frac fluids from frac pumps must be closely regulated at the various fracturing stages in order to adequately control the fracturing process. Accordingly, prime movers that deliver power to the frac pumps are variable speed devices, since driving the frac pumps at variable speeds at least partially provides the flow and pressure control.

Typically, the prime movers are high horsepower stationary diesel engines that deliver power to the frac pumps through multi-speed gearboxes or transmissions. High horsepower stationary diesel engines are expensive and require maintenance and operational attention, such as refueling.

Other attempts have been made to use variable speed electric motors to power frac pumps. Variable speed electric motors are able to vary flow and pressure of the frac pumps through speed-varying motor controls, which facilitates control of the fracturing operation. Variable speed electric motors either directly drive the frac pumps at the motors' variable speeds or with an intervening single-speed gearbox or transmission. Such variable speed electric motors include shunt wound, variable speed, DC (direct current) traction motors and variable speed, for example, variable frequency, AC (alternating current) electric motors. Although variable speed electric motors can require less operational attention than high horsepower stationary diesel engines, they are expensive and require sophisticated motor controls.

Constant speed AC motors are more straightforward than variable speed electric motors but have not been used to deliver power to frac pumps. That is because the fixed speed(s) of constant speed AC motors do not provide the desired amount of flow and pressure control of the frac pumps to allow operators to suitably control the fracturing operation. Typical multi-speed gearboxes are unable to resolve this problem with constant speed AC motors because they are unable to shift under full load and have range ratios that are ill-suited to provide a sufficient variety of output shaft speeds or corresponding frac pump flow and pressure control.

Furthermore, constant speed AC motors of high-enough horsepower ratings to power frac pumps are difficult to start because they require extremely high starting currents as in-rush (locked rotor) currents to begin their rotations.

Document <CIT> discloses an electro-hydraulic high-pressure oilfield pumping system, comprising: a fracturing (frac) pump configured to pressurize a frac fluid for delivery into a well that extends into a subterranean geological formation; a primary electric motor that has a motor shaft and defines a prime mover of the electro-hydraulic high-pressure oilfield pumping system; a transmission arranged between and configured to deliver power from primary electric motor to the frac pump, and a starting motor coupled by means of a gear set to the shaft of the frac pump.

Document <CIT> discloses a plunger adjusting device for a fracturing pump in the technical field of oil equipment, which includes a rotating drive unit connected to the input end of a crank shaft at the power end of the fracturing pump for driving the fracturing pump, and a control unit connected with the rotating drive unit. The control unit is used for control the rotation of the drive unit to adjust the plunger at the liquid end of the fracturing pump. The rotating drive unit includes a hydraulic motor assembly, a hydraulic pump assembly and an engine assembly; the engine assembly is connected to the hydraulic pump assembly, the hydraulic pump assembly is connected to the hydraulic motor assembly, and the power output end of the hydraulic motor assembly is connected to the crankshaft. Further, the input end of the crankshaft has a first gear and a second gear, the crankshaft is coaxially connected with the first gear, the first gear meshes with the second gear, and the second gear is in transmission connection with the power output end of the hydraulic motor assembly.

What is therefore needed is a prime mover for high pressure pumping applications, like powering frac pumps, employing a constant speed AC motor, but without the above-noted drawbacks primarily directed to flow and pressure control.

The preferred embodiments overcome the above-noted drawbacks by providing an electro-hydraulic high-pressure pumping system that incorporates a constant speed AC motor. This can be incorporated as an electro-hydraulic frac pump system for use in an oilfield pressure pumping system. The invention is defined by the features of independent claim <NUM> and the features of independent claim <NUM>, respectively. The dependent claim is directed to a preferred embodiment of the invention.

The above, and other aspects and objects of the present invention, will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description is given by way of illustration and not of limitation.

A clear conception of the advantages and features constituting the present invention, and of the construction and operation of typical embodiments of the present invention, will become more readily apparent by referring to the exemplary and, therefore, non-limiting, embodiments illustrated in the drawings accompanying and forming a part of this specification, wherein like reference numerals designate the same elements in the several views, and in which:.

In describing preferred embodiments, which are illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is to be understood that each specific term includes all technical equivalents, which operate in a similar manner to accomplish a similar purpose. For example, the words "connected", "attached", "coupled", or terms similar thereto are often used.

Referring to <FIG>, one embodiment including a part of the invention is shown as an electro-hydraulic high-pressure pumping system <NUM>. The electro-hydraulic high-pressure pumping system <NUM> is shown here implemented as an electro-hydraulic frac pumping system <NUM>, which includes an electro-hydraulic drive system <NUM> that delivers power to a fracturing pump or frac pump <NUM>. Frac pump <NUM> can be a positive displacement, high-pressure, plunger pump or other suitable pump that can deliver high flow rates and produce high pressures, for example, <NUM>,<NUM> kPa (<NUM>,<NUM> psi) or more. This oilfield site is shown with multiple electro-hydraulic frac pumping systems <NUM> that operate together for a subterranean geological formation fracturing or fracking operation to stimulate well production. The electro-hydraulic frac pumping systems <NUM> can be activated or brought online and implemented separately or together, depending on the particular pumping needs for a given fracking operation or operational stage. Each of the electro-hydraulic frac pumping systems <NUM> may define a singularly-packaged unit, for example, mounted on a trailer that can be towed by a semi-tractor or other tow vehicle. Each frac pump <NUM> receives fracturing fluid or frac fluid <NUM> that is stored in a frac fluid storage system <NUM> and delivers the frac fluid <NUM> to the frac pumps <NUM> through frac fluid delivery lines <NUM>. Pressurized frac fluid <NUM> is delivered from the frac pumps <NUM>, through manifold delivery lines <NUM>, to manifold <NUM> that delivers the pressurized frac fluid <NUM> through manifold outlet line <NUM> to wellhead <NUM>. At the wellhead <NUM>, the frac fluid <NUM> is directed to flow through a borehole that extends through a well casing <NUM> for fracturing the subterranean formation.

Still referring to <FIG>, electro-hydraulic frac pumping system <NUM> selectively receives electrical power through conductors <NUM> from electrical power system <NUM>. Electrical power system <NUM> includes a generator and prime mover such as a combustion engine which may be a gas turbine engine. Control system <NUM> includes a computer that executes various stored programs while receiving inputs from and sending commands to the electro-hydraulic frac pumping system <NUM> for controlling, for example, energizing and de-energizing various system components as well as bringing the electro-hydraulic frac pumping system <NUM> online for fracking the subterranean formations by controlling the various electronic, electromechanical, and hydraulic systems and/or other components of each electro-hydraulic frac pumping system <NUM>. Frac site control system <NUM> may include the TDEC-<NUM> electronic control system available from Twin Disc®, Inc. for controlling the electro-hydraulic frac pumping system(s) <NUM>.

Referring now to <FIG>, electro-hydraulic frac pumping system <NUM> includes a constant speed AC motor, shown as primary electric motor <NUM>. Primary electric motor <NUM> is a high-powered constant speed motor, for example, about <NUM>,<NUM> HP (horsepower) or having an equivalent torque rating of about a <NUM>,<NUM> HP diesel engine. Primary electric motor <NUM> operates at a relatively fast fixed rotational speed, such as a fixed rated speed of about <NUM>,<NUM> RPM (rotations per minute). Primary electric motor <NUM> is connected and delivers power to a heavy-duty industrial gearbox or transmission, shown as transmission <NUM>. Transmission <NUM> is a multi-speed transmission with multiple ranges that provide multiple substantially evenly spaced drive ratios to facilitate close regulation of rotational speed of the transmission output shaft and, correspondingly, the frac pump's <NUM> operational speed and output flow and pressure. Transmission <NUM> may be, for example, a model TA90-<NUM>, available from Twin Disc®, Inc. , which is capable of changing ranges while the frac pump <NUM> is fully loaded. Driveshaft <NUM> transmits torque from transmission <NUM> to frac pump <NUM>.

Still referring to <FIG>, transmission <NUM> includes a PTO tower or section with a pair of pump pads <NUM>, <NUM> for mounting and mechanically delivering power to or receiving power from various components, for example, hydraulic components. The lower illustrated pump pad <NUM> is shown supporting a pair of transmission pumps <NUM>, <NUM> which may be configured to, for example, supply pressurized oil for transmission lubrication and controlling hydraulically actuated components within the transmission.

Still referring to <FIG>, a hydraulic starting motor <NUM> may be a high speed, low torque, hydraulic motor and is shown mounted to the transmission pumps <NUM>, <NUM>, and therefore transmission <NUM> by way of pump pad <NUM>. Electric motor <NUM> selectively delivers torque to hydraulic starting motor <NUM>. Electric motor <NUM> may be a variable speed AC motor that is substantially smaller than primary electric motor <NUM>, with electric motor <NUM> rated at, for example, about <NUM> HP. Energizing electric motor <NUM> activates hydraulic starting motor <NUM>, which rotates various gear train or other components of transmission <NUM> and correspondingly rotates the shaft of primary electric motor <NUM> when the primary electric motor <NUM> is de-energized. In this way, hydraulic starting motor <NUM> can be activated to rotate primary electric motor <NUM> shaft to bring it sufficiently close to its rated fixed speed or synchronous speed before the primary electric motor <NUM> is energized. Hydraulic starting motor <NUM> can correspondingly rotate at about <NUM>,<NUM> RPM or at an appropriate speed that can rotate the primary electric motor <NUM> shaft at <NUM>,<NUM> RPM or other speed, depending on the particular rated or synchronous speed of primary electric motor <NUM>. Rotating the primary electric motor <NUM> with hydraulic starting motor <NUM> to achieve the synchronous speed of primary electric motor <NUM> allows connection to the electrical power source DoL (Direct on Line) while avoiding the motor's high in-rush (locked rotor) current that would otherwise be required to start the primary electric motor <NUM>. The primary electric motor <NUM> is therefore able to be started at essentially its normal running current, when pre-driven to its synchronous speed by hydraulic starting motor <NUM>.

Still referring to <FIG>, a slow frac hydraulic motor <NUM> may be configured to, for example, supply slow speed or low flow operation of frac pump <NUM>. Slow frac hydraulic motor <NUM> may be a low speed, high torque, hydraulic motor that is mounted to pump pad <NUM>. The rotational speed of slow frac hydraulic motor <NUM> may be a fraction of the rotational speed of hydraulic starting motor <NUM>. Clutch <NUM> is shown arranged between the slow frac hydraulic motor <NUM> and pump pad <NUM> and is configured to disconnect power transfer between the slow frac hydraulic motor <NUM> and transmission <NUM>. Clutch <NUM> may be an overrunning clutch or an actuatable or other clutch to passively or actively connect or disconnect power flow between the slow frac hydraulic motor <NUM> and transmission to correspond to different operational states of the fracking system. It is understood that instead of or in addition to implementing clutch <NUM>, when the slow frac hydraulic motor <NUM> is not being implemented, it can be locked against activation, which may include binding or holding the pistons in the motor fixed, depending on its configuration.

Electric motor <NUM> selectively delivers torque to slow frac hydraulic motor <NUM>. Like electric motor <NUM>, electric motor <NUM> may be a variable speed AC motor that is substantially smaller than primary electric motor <NUM>, with electric motor <NUM> rated at, for example, about <NUM> HP. Energizing electric motor <NUM> activates slow frac hydraulic motor <NUM>, which rotates various gear train or other components of transmission <NUM> and correspondingly rotates the shaft of primary electric motor <NUM> when the primary electric motor <NUM> is de-energized. In this way, the slow frac hydraulic motor <NUM> can be activated to rotate primary electric motor <NUM> shaft at slow and precisely controlled speeds to deliver torque through the transmission <NUM> and correspondingly precisely control the frac pump <NUM> to provide high-pressure low speed fracking. The rotational speed of slow frac hydraulic motor <NUM> be between about <NUM> RPM to <NUM>,<NUM> RPM or at an appropriate speed that can rotate the primary electric motor <NUM> shaft at between about <NUM> RPM to <NUM>,<NUM> RPM or other speed, depending on the particular speed required to produce the desired flow rate of frac pump <NUM> for high pressure low speed fracking. Regardless, the precise slow speed control of slow frac hydraulic motor <NUM> may be achieved using a closed-loop controller (e.g., proportional integral derivative (PID) controller) within the control system <NUM> (<FIG>) that controls rotational speed of electric motor <NUM> that powers the slow frac hydraulic motor <NUM>.

Referring now to <FIG>, an exemplary simplified hydraulic schematic layout is shown. The hydraulic components of the system <NUM> share a common tank or sump, shown here as reservoir <NUM> within transmission <NUM>. Hydraulic power pack <NUM> controls flow of hydraulic fluid through various components within the system <NUM>. Mode selector valve <NUM> of hydraulic power pack <NUM> provides three discrete flow paths of hydraulic fluid out of the hydraulic power pack <NUM>. Mode selector valve <NUM> may be, for example, a solenoid actuated spool valve that provides three discrete positions, represented as positions <NUM>, <NUM>, and <NUM>, to selectively allow flow out of three corresponding outlets and provide three corresponding flow paths out of the hydraulic power pack <NUM>. Actuating the mode selector valve <NUM> allows for selectively activating and permitting hydraulic fluid flow through hydraulic starting motor <NUM>, slow frac hydraulic motor <NUM>, or neither.

Still referring to <FIG>, when mode selector valve <NUM> is at a first position shown as position <NUM>, hydraulic fluid directed to hydraulic starting motor <NUM>. This defines a primary electric motor starting mode of system <NUM> in which hydraulic starting motor <NUM> delivers torque to rotate the shaft of the de-energized primary electric motor <NUM> to achieve its synchronous speed in preparation for its energization by connecting to the electrical power source DoL.

Next, when mode selector valve <NUM> is at a second position shown as position <NUM>, hydraulic fluid directed to slow frac hydraulic motor <NUM>. This defines a slow frac mode of system <NUM> in which slow frac hydraulic motor <NUM> delivers torque to rotate shaft of the de-energized primary electric motor <NUM>. The corresponding motor shaft is used as a passively driven torque-transmitting component to deliver power from the slow frac hydraulic motor <NUM> through transmission <NUM> and to the frac pump <NUM> to achieve high-pressure, slow speed, fracking in the slow frac mode of system <NUM>.

Still referring to <FIG>, when mode selector valve <NUM> is at a third position shown as neutral position <NUM>, hydraulic fluid that would otherwise be directed to hydraulic starting motor <NUM> or slow frac hydraulic motor <NUM> is instead directed to tank or reservoir <NUM> of transmission <NUM>. Selector valve <NUM> is actuated to or held in this neutral or third position <NUM> when, for example, primary electric motor <NUM> is energized and driving frac pump <NUM> through transmission <NUM> and shaft <NUM>, which provides normal or default fracking operation as a normal frac mode or frac mode of system <NUM>. During frac mode, selector valve <NUM> is in its neutral or third position <NUM> and correspondingly avoids any non-desired pumping through hydraulic starting motor <NUM> or slow frac hydraulic motor <NUM> by preventing flow to or through the hydraulic starting motor <NUM> or slow frac hydraulic motor <NUM>. Such inadvertent passive pumping can be yet further prevented with respect to slow frac hydraulic motor <NUM> by, for example, clutch <NUM> (<FIG>) that either allows the rotating mechanism(s) of pump pad <NUM> to overrun the slow frac hydraulic motor <NUM> or disengage a selective driving engagement between the pump pad <NUM> and the slow frac hydraulic motor <NUM>.

A method <NUM> of fracking using the above-described systems is set forth in <FIG>. Method <NUM> includes providing one or more prime movers in Block <NUM>. The prime movers are primary electric motors such as those described previously. In Block <NUM>, the system determines if the primary electric motor is energized and, if so, maintains Frac Mode in Block <NUM>. In Frac Mode, mode selector valve is held in a neutral position for default fracking while power is delivered from primary electric motor to drive one or more frac pumps in Block <NUM>, typically through a transmission (<NUM> in <FIG>).

If, on the other hand, the primary electric motor is not energized, method <NUM> determines whether the user wants to engage Slow Frac Mode, in Block <NUM>. If not, Method <NUM> directs hydraulic fluid to hydraulic starting motor in Block <NUM>, Starting Mode. In Block <NUM>, a second electric motor is employed to energize the hydraulic starting motor. Hydraulic starting motor delivers power to the transmission that selectively delivers power to the primary electric motor to bring it to its rated fixed or synchronous speed, allowing connection to the electrical power source DoL (Direct on Line) in Block <NUM>. Once connected to the DoL, primary electric motor can drive the frac pump(s) of the system in Block <NUM>.

Claim 1:
An electro-hydraulic high-pressure oilfield pumping system (<NUM>), comprising:
a fracturing (frac) pump (<NUM>) configured to pressurize a frac fluid for delivery into a well that extends into a subterranean geological formation;
a primary electric motor (<NUM>) that has a motor shaft and defines a prime mover of the electro-hydraulic high-pressure oilfield pumping system (<NUM>);
a transmission (<NUM>) with multiple ranges that provide multiple drive ratios, the transmission (<NUM>) arranged between and configured to deliver power from primary electric motor (<NUM>) to the frac pump (<NUM>);
a hydraulic starting motor (<NUM>) selectively delivering power through the transmission (<NUM>) to rotate the motor shaft of the primary electric motor (<NUM>);
a slow frac hydraulic motor (<NUM>) selectively delivering power through the transmission (<NUM>) to rotate the motor shaft of the primary electric motor (<NUM>);
a hydraulic power pack (<NUM>) configured to selectively permit or prevent flow of hydraulic fluid to each of the hydraulic starting motor (<NUM>) and the slow frac hydraulic motor (<NUM>) for activating or deactivating the hydraulic starting motor (<NUM>) and the slow frac hydraulic motor (<NUM>),
wherein the system defines:
a primary electric motor starting mode in which the hydraulic starting motor (<NUM>) delivers power through the transmission (<NUM>) to rotate the motor shaft of the primary electric motor (<NUM>) to a first speed that corresponds to a fixed rated speed of the primary electric motor (<NUM>);
a slow frac mode in which the slow frac hydraulic motor (<NUM>) delivers power through the transmission (<NUM>) to rotate the motor shaft of the primary electric motor (<NUM>) to a second speed that is less than the fixed rated speed of the primary electric motor (<NUM>); and
a frac mode in which the primary electric motor (<NUM>) is energized and delivers power through the transmission (<NUM>) and to the frac pump (<NUM>).