NO20181402A1 - A method of controlling a prime mover - Google Patents

Description

A method of controlling a prime mover

Field of the invention

The invention concerns a method of controlling a prime mover which is configured to drive one or more fluid delivery systems for delivering a fluid in a conduit, and an associated plant, as set out by the preambles in claims 1 and 6, respectively. The invention is particularly useful in the extraction of shale oil and/or gas by means of pressure pumping equipment for well stimulation, commonly known as “hydraulic fracturing” or “fracking”, but is not limted to such operations.

Background of the invention

The majority of the equipment used for pressure pumping has been following the same principle for several decades: Trailer or truck mounted power pack (diesel-powered reciprocating engine, or a gas turbine engine), driving a pressure pump through a multispeed transmission gear box. All parts are mechanically connected.

A typical pressure pump comprises two major parts: a “fluid end” and a “power end”. The fluid end is the actual pressure pump, pressurizing the fracturing fluid. It is normally a plunger/piston pump, typically operating at 150-300 strokes per minute, and is an exchangeable unit. The power end is part of the drivetrain, and it is connected to a multi-speed transmission. The power end has a reduction gear box on the inlet, and is connected to the plunger on the fluid end via a crankshaft and a crosshead. The power is normally provided by a reciprocating engine, although gas turbine engines are also used.

Some of the problems associated with the prior art are shortened expected lifecycles of the equipment, as well as high maintenance costs during the lifecycle of the drivetrain. In addition, the prior art plants have a large surface footprint.

The prior art includes CN 104806220 A, which describes “fully-hydraulic driven” fracturing equipment with a power unit and a fracturing pump. The power unit comprises an engine unit, a transfer case unit and a hydraulic pump unit. Three hydraulic pumps are installed on each transfer case, and the hydraulic pump unit is connected through hydraulic pipelines. The fracturing pump comprises a left and a right pump head; three two-way hydraulic oil cylinders which are arranged in parallel are installed on the fracturing pump. The fracturing pump is driven by the two-way hydraulic oil cylinders, so that the equipment power is increased, the equipment discharge flow is increased; the equipment weight and size are reduced.

The prior art also includes CN 104727797 A and CN 204552723 U, which describe a system where an engine, a transfer case, a plurality of variable displacement plunger pumps and a double-acting fracturing pump are arranged on a chassis. The output end of the engine is connected with the input end of the transfer case, and the output end of the transfer case comprises a plurality of power take-off ports. Each power take-off port is connected with one variable displacement plunger pump. The plunger pumps drive the double-acting fracturing pump through a hydraulic system.

The prior art also includes CN 104728208 A, which describes a high-power hydraulic driving fracturing-pump pump station system, in which the hydraulic cylinders are connected with the fracturing cylinders. Electric motor driven hydraulic pump provides high-pressure oil and fluid outlet manifold outputs a high-pressure fracturing fluid.

The prior art also includes CN 104453825 A, which describes a modularized fracturing pump set which comprises a power unit and a fracturing pump unit. An auxiliary engine is arranged on the power unit and is connected to a hydraulic pump. A torque converter is arranged in the fracturing pump, and the input end of the torque converter is connected to the main engine. The output end of the torque converter is connected to a gearbox, and the output end of the gearbox is connected to the fracturing pump.

The prior art also includes WO 2014/078236 A1, which describes a turbo-shaft engine having a drive shaft and a high pressure, and a high-RPM centrifugal pump coupled to the drive shaft.

Summary of the invention

The invention is set forth and characterized in the main claims, while the dependent claims describe other characteristics of the invention.

It is thus provided a method of controlling a prime mover which is configured to drive one or more positive displacement fluid delivery systems for delivering a fluid in a conduit, characterized by sensing the pressure variations in the fluid in the conduit; and - based on the sensed pressure variations, controlling at least one of said positive displacement fluid delivery system and controlling the power output of the prime mover.

The method may further comprise determining an estimated power consumption. In one embodiment, the method comprises controlling the prime mover fuel supply by variations in the sensed pressure. The at least one positive displacement fluid delivery system may be controlled based on a set-point (rate/pressure) identified and set by an operator or an overall control system.

In one embodiment, a first controller may provide control signals to hydraulic pumps, configured to operate said fluid delivery systems and being driven by the prime mover, whereby the interaction between the hydraulic pumps and the prime mover is controlled based on sensed pressure variations in the conduit.

It is also provided a plant for controlling the delivery of a pressurized fluid in a conduit, said plant comprising a prime mover which is configured to drive one or more positive displacement fluid delivery systems for delivering said fluid in the conduit, characterized by first sensing means configured for sensing pressure variations in the pipe and connected to a first controller; the first controller being configured to provide control signals to control valves for at least one fluid delivery system and to a control system for the prime mover.

The plant may comprise one or more hydraulic pumps configured to communicate with control means and to operate said fluid delivery systems and being driven by the prime mover, whereby the interaction between the hydraulic pumps and the prime mover is controlled based on sensed pressure variations in the pipe. In one embodiment, the prime mover may be a gas turbine engine. The at least one positive displacement fluid delivery system may comprise a positive displacement pump.

Although the invention is particularly useful in hydraulic fracturing (“fracking”) operations, it is also applicable for all positive displacement pumping processes in which control is based on a flow and pressure-setting an feedback pressures. The invention shall therefore not be limited to fracking operations.

Brief description of the drawings

These and other characteristics of the invention will become clear from the following description of an embodiment, given as a non-restrictive example, with reference to the attached schematic drawings, wherein:

Figure 1 is a flowchart showing a typical configuration of the invented plant and illustrating principles of the invention;

Figure 2 is a perspective view of an embodiment of a mobile unit for the invented plant, in a transportation configuration;

Figure 3 is a perspective view of the mobile unit illustrated in figure 2, and illustrates the plant in a pumping (operational) configuration; and

Figure 4 is a perspective view of the mobile unit illustrated in figure 3, but where the housing has been removed in order to illustrate the plant.

Detailed description of an embodiment

The following description may use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”, ”upper”, “lower”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting.

Referring initially to figures 2, 3, and 4, the invented plant is in this illustrated embodiment arranged as a mobile unit 18 on a trailer 19 and enclosed by a housing 20. Doors in the housing provide access to the plant, and rear doors allow the movable unit comprising the fluid end 21 with its double-acting cylinders 22 to be moved out and down (see figure 3) when the plant is in operation. Pipes 21a are configured for connection to well piping (not shown).

Referring to figure 4, the mobile plant comprises in the illustrated embodiment a gas turbine 26, connected via a duct 27a to an air inlet 27, and an exhaust opening 26a. The gas turbine receives fuel from the fuel tank 32. Supply lines and hoses, power lines and control lines, etc., are not shown, as these components are commonly known in the art.

The gas turbine 26 is connected to a set of single or tandem-mounted hydraulic pumps 30 via a gearbox 28. Reference numbers 31 and 29 denote a hydraulics tank and accumulator tanks, respectively. Louvers and air filtration container 23 is arranged towards the read of the mobile unit, behind oil cooler gearbox 25 and hydraulics 24.

The hydraulic pumps 30 operate double-acting cylinders 22 in the plant’s fluid ends 21. Each hydraulic cylinder operates one plunger, in each of the plant’s two fluid ends.

A typical configuration of the invented plant, illustrating the principle of the invention, will now be described with reference to the flowchart in figure 1.

In figure 1 three systems are shown; denoted A, B, C, respectively. It should be understood that only system C is illustrated in detail in figure 1, for clarity of illustration. The skilled person will understand that the components and functions illustrated and described with reference to system C, also can be applied to systems A and B. It should also be understood that the invention shall not be limited to the number of systems shown in figure 1.

Reference number 1 denotes a power source, which comprises a prime mover 2. The prime mover may be a gas turbine engine or a reciprocating engine, controlled via a throttle 3 (controlling fuel supply F and receiving information regarding rotation speed R). The prime mover 2 is connected, and configured to transfer torque T, to a gear unit 8. The gear unit 8 transfers torque T’ to individual hydraulic pumps 9a-c; each pump having respective pump pressure sensors 13a-c.

If the prime mover 2 is a gas turbine, the gear unit 8 may be configured to reduce highrpm output from the turbine. If the prime mover is of another type of engine (e.g. a reciprocating engine), the hydraulic pumps may be driven directly by the engine, and the gear unit 8 may be omitted.

Each hydraulic pump 9a-c supplies hydraulic pressure to respective positive displacement fluid delivery systems, in the illustrated embodiment double-acting hydraulic cylinders 34a-c, via respective control valves 36a-c, 37a-c. A reservoir tank 11 and a cooler 17 are fluidly connected between the hydraulic pump 9c and the control valves 36c, 37c. The circuit also comprises an accumulator 33, for mitigating pressure pulses.

Each hydraulic cylinder 34a-c is drivingly connected to respective sets of fluid plungers 35a1-c1, 35a2-c2. The fluid plungers 35a1-c1, 35a2-c2 supply fluid to the well via the fluid supply line 10. The invention shall, however, not be limited to such fluid plungers. Reference number 12 denotes a suction line from a fluid blending system (not shown).

Well feedback pressure sensor 16 is connected to, and configured to sense the pressure in (and hence pressure variations), the supply line 10. Valve outlet feedback pressure sensors 15 are connected to respective control valves 36c, 37c. Valve inlet pressure sensor 14 is connected to control valve 36c. A valve controller 7 (typically a programmable logic controller – PLC) receives signals from the pressure sensors 14, 15, 16, position feedback Cp from the hydraulic cylinders, and provides control signals Vf to the control valves 36c, 37c.

A main control system 4 controls the throttle 3 based on power request Pr and provides power feedback Pf. The main control system 4 also receives transport security interlock feedback Ts from the gear unit 8, and estimated power consumption data EPC from the PLC 7, based on the sensed pressure variatons by well feedback pressure sensor 16. A louver controller 5 is also in communication with the main control system 4, to open and close louvers (for e.g. ventilation and fire control). The main control system 4 receives data from a hydraulic pump controller 6 (e.g. a PLC) and provides a power command Ac to the hydraulic pump controller 6. The hydraulic pump controller 6 in turn provides the required displacement command Dc to the hydraulic pump 9c based on pump pressure feedback Pp (from the pressure sensor 13c). The main control system 4 also provides data regarding requested cylinder speed RCS to the valve controller 7, which in turn determines and provides the valve flow control signal Vf to the control valves 36c, 37c, as described above.

The invention thus comprises a hydraulic-pressure/flow-controlled power transmission, in which all power from the primer mover is transformed into hydraulic power by the hydraulic pumps. The hydraulic pumps enable the prime mover to start against little or no load.

When the plant is in use in a fracking operation, the prime mover 2 and the hydraulic pumps 9a-c operate the hydraulic cylinders 34a-c and fluid plungers 35a1-c1, 35a2-c2 to supply pressurized fracturing fluid to the line 10 (and thus the subterranean well). The hydraulic fracturing pressure generated in the well is a result of the well pressure and the hydraulic pressure generated by the plungers. The well pressure (which is sensed by the sensor 16) is communicated to the valve controller PLC 7, which controls the control valves 36a-c, 37a-c and also determines the estimated power consumption EPC, which is transmitted to the main control system 4. The prime mover fuel supply (e.g. turbine fuel injection) may thus be governed by the well pressure, or rather the variations in pressure, as sensed continuously by the sensor 16. The blazing turbine fuel control receives pressure reading from the hydraulic control system, based on the pressure and rate reading from the hydraulic fracturing pressure. The hydraulic control system then performs a control action based on a set-point (rate/pressure) identified and set by the operator.

The “delay” which is inherent in the hydraulic components, or as controlled by the main control system 4, provides sufficient time for the turbine fuel control to “predict” what is going to happen, and take action before it happens.

This means that the prime mover can – before the requirement arises – either increase the fuel injection (open throttle) to be ready for the higher demand from the hydraulic pumps, or lower the fuel injection (restrict throttle) to adapt to the estimated future requirement of torque, and therby accommodate the change in rate/pressure. This function is particularly useful in embodiments where the prime mover is a gas turbine engine, as such turbines normally operate at high rotational speeds, and have low torque. The control system may in this fashion prevent the gas turbine engine from over-speeding, and further give the gas turbine engine a head-start on a predicted increased torque demand.

When the requirement for fracturing fluid in the well changes, or actual consumption of fracturing fluid is changing and not complying with the set point as set by the operator or as determined by an overall control system, the valve controller 7 and pressure sensor 16 are sensing this, based on sensed pressure variations. The set point may also be defined based on a prioritized list, defined by an overall control system, of how deviating conditions are to be handled. Based on rate/pressure difference between the set point and the actual pressure reading (as sensed by 16), there will occur a situation that the actual power command Ac (fed to main controller 4 by the pump controller 6) differs from (less or more) the estimated power consumption EPC (fed to the main controller 4 by the valve controller 7). This will lead to a situation that the main controller 4 will be able to give control signal, and being able to control the instant in which the control signal is given, to both the pump controller 6 and to the prime mover throttle control 3, simultaneously, or a controlled difference to achive the prime mover to act in a predictive manner.

Although the invention has been described with reference to three hydraulic pumps, it should be understood that the invention is equally applicable to fewer or more hydraulic pumps.

Although the invention has been described with reference to a mobile unit, it should be understood that the invention is equally applicable as a stationary plant.

Although the invention has been described with reference to driving fluid ends (doubleacting hydraulic cylinders), it should be understood that the invention is equally applicable to other pumping principles driven by hydraulic flow and pressure, i.e positive displacement pumps. The invention shall thus not be limited to the doubleacting hydraulic cylinders.

Claims (9)

Claims

1. A method of controlling a prime mover (2) which is configured to drive one or more positive displacement fluid delivery systems (34a-c, 35a1-c1, 35a2-c2) for delivering a fluid in a conduit (10), characterized by

- sensing (16) the pressure variations in the fluid in the conduit (10); and

- based on the sensed pressure variations,

-- controlling (36a-c, 37a-c) at least one of said positive displacement fluid delivery system and

-- controlling (4) the power output of the prime mover (2).

2. The method of claim 1, further comprising determining an estimated power consumption (EPC).

3. The method of claim 1 or claim 2, further comprising controlling the prime mover (2) fuel supply by variations in the sensed pressure.

4. The method of any one of claims 1-3, wherein the at least one positive displacement fluid delivery system is controlled based on a set-point (rate/pressure) identified and set by an operator or an overall control system.

5. The method of any one of claims 1-4, wherein a first controller (7) provides control signals to hydraulic pumps (9a-c), configured to operate said fluid delivery systems (34a-c, 35a1-c1, 35a2-c2) and being driven by the prime mover, whereby the interaction between the hydraulic pumps and the prime mover is controlled based on sensed pressure variations in the conduit (10).

6. A plant for controlling the delivery of a pressurized fluid in a conduit (10), said plant comprising a prime mover (2) which is configured to drive one or more positive displacement fluid delivery systems (34a-c, 35a1-c1, 35a2-c2) for delivering said fluid in the conduit (10), characterized by

- first sensing means (16) configured for sensing pressure variations in the pipe (10) and connected to a first controller (7);

- the first controller (7) being configured to provide control signals to control valves (36a-c, 37a-c) for at least one fluid delivery system and to a control system (4, 3) for the prime mover (2).

7. The plant of claim 6, further comprising one or more hydraulic pumps (9a-c) configured to communicate with control means (6; 7) and to operate said fluid delivery systems (34a-c, 35a1-c1, 35a2-c2) and being driven by the prime mover, whereby the interaction between the hydraulic pumps and the prime mover is controlled based on sensed pressure variations in the pipe (10).

8. The plant of any one of claims 6-7, wherein the prime mover is a gas turbine engine.

9. The plant of any one of claims 6-8, wherein at least one positive displacement fluid delivery system comprises a positive displacement pump.