Patent Publication Number: US-2023160375-A1

Title: Linear frac pump assembly

Description:
FIELD 
     The present disclosure relates to positive displacement pumps, and in particular, to a linear frac pump assembly with a folded configuration. 
     BACKGROUND 
     Large powerful pumps are commonly used for mining and oilfield applications, such as, for example, hydraulic fracturing. During hydraulic fracturing, fracturing fluid (i.e., cement, mud, frac sand and other material) is pumped at high pressures into a wellbore to cause the producing formation to fracture. One commonly used pump in hydraulic fracturing is a high-pressure reciprocating pump, like the SPM® Destiny™ TWS 2500 frac pump or the SPM® QEM 3000 Continuous Duty Frac Pump, manufactured by S.P.M. Oil &amp; Gas, a Caterpillar Company located in Fort Worth, Tex. In operation, the fracturing fluid is caused to flow into and out of a pump fluid chamber as a consequence of the reciprocation of a piston-like plunger respectively moving away from and toward the fluid chamber. As the plunger moves away from the fluid chamber, the pressure inside the chamber decreases, creating a differential pressure across an inlet valve, drawing the fracturing fluid through the inlet valve into the chamber. When the plunger changes direction and begins to move towards the fluid chamber, the pressure inside the chamber substantially increases closing the inlet valve increasing the differential pressure across an outlet valve and causes the outlet valve to open, enabling the highly pressurized fracturing fluid to discharge through the outlet valve into the wellbore. 
     A typical frac unit is powered with a diesel engine driving a frac pump through a multispeed transmission. The rotational energy transferred to the reciprocating frac pump is channeled to horizontal plunger bores for pumping via crankshafts and connector rods. The operating conditions are often extreme involving high fluid flow and high operating pressures (oftentimes up to 15,000 psi). Pressure fluctuations as seen in diesel powered units or other internal combustion-based units often cause undesirable cyclic stresses on components, shortening their lives. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of an embodiment of a linear pump according to the teachings of the present disclosure; 
         FIG.  2    is a cross-sectional view of an embodiment of a linear pump according to the teachings of the present disclosure; 
         FIG.  3    is a schematic cross-sectional view of an embodiment of the linear pump according to the teachings of the present disclosure; and 
         FIG.  4    is a schematic cross-sectional view of an embodiment of a linear pump having a folded configuration according to the teachings of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The introduction of natural gas as “free fuel” for frac operations has led to investigation of the best way to utilize natural gas to generate pumping power. One option is to use a large gas turbine generator that creates electrical power to run the frac job on electricity. Since electric drive is not limited to the maximum diesel engine power feasible for a mobile frac unit, a larger pump is possible. The ability to deploy larger pumps would lead to fewer units required on a frac site. Fewer units on location translates to a lower total cost of ownership and operating cost. 
     Reciprocating pumps have many moving parts and so do the power systems that drive them. Replacing reciprocating pumps and their associated drive systems with a linear pump that is actuated electrically through a planetary thread drive provides many advantages. The linear pumping action is created by the movement of the screw through the electrically-powered planetary drive. 
     In a first embodiment of a linear pump (described in a co-pending PCT Application No. WO2017/139583), a linearly actuated double-action pump includes a centrally-disposed drive system coupled to two fluid ends at either end along the linear axis, where the drive system drives the plunger rod to move the fluid in both fluid ends. In an example embodiment, an electric linear pump may use a planetary screw drive (e.g., planetary gears surrounding a threaded rod to convert rotational motion of the planetary gears to the linear translation movement of the threaded rod) to linearly move (i.e., translate) plunger rods instead of the traditional diesel engines. The threaded rod coupled to the drive system has plunger sections on both ends such that when the plunger rod moves in either direction, one of the two ends will be pumping out fluids while the other drawing in fluids. In other embodiments, the electric actuator may be in the form of a winding that uses electric current to create a magnetic field to move the rod along its axis (e.g., similar to solenoid actuation). A fluid end is coupled with each of the two plunger ends to control fluid charging on the suction stroke and pressure discharge on the power stroke. The electricity supplied to the planetary thread drive may be provided from the grid or produced by an onsite generator using local natural gas, thus minimizing fuel costs. 
     In a second embodiment of the linear actuated pump  10  shown in  FIGS.  1 - 3   , a centrally-disposed fluid end  12  is coupled to two actuators  14  and  15  on its two sides along a linear axis. The actuators  14  and  15  may be hydraulic or electro-mechanic actuators that are in fluid communication with a hydraulic/electrical-controlled drive system (not shown) that may incorporate a planetary screw drive or a solenoid drive system. The actuators  14  and  15  each drives or causes linear displacement of respective plungers  16  and  17  that reciprocate within their respective fluid bores defined within respective plunger housings  18  and  19 . In this configuration, the stroke length of each plunger rod  16  and  17  can be halved and a smaller screw drive system may be employed and still achieve the same horsepower and fluid rate output when compared to the above-referenced double-action pump configuration. In this more compact second configuration, the overall length of the pump assembly  10  is reduced by the size of one fluid end. Further, because of the shorter stroke length, it is easier to achieve and maintain accurate alignment of the fluid end and hydraulic drive components. Within the fluid end  12  are an inlet and discharge valves  22  and  23  that regulate the intake and discharge of fluids from the pump through inlet and discharge ports (not explicitly shown). The inlet port is connected to a manifold (not shown) that supplies the frac fluid and the discharge port is connected to a discharge line (not shown) that leads to a wellbore. According to an embodiment, multiple linear pumps can be fluidly coupled at the discharge lines to deliver a constant high-pressure flow to the wellhead. 
     In a third embodiment as shown in  FIG.  4   , the “legs” of a linear pump assembly  40 , including the respective actuators  44  and  45 , plunger pistons  46  and  47 , and piston housings  48  and  49 , are “folded” at the centrally-disposed fluid end  42  so that the “legs” become disposed proximate to and alongside each other. Same as before, the actuators  44  and  45  may be hydraulic or electro-mechanic actuators that are in fluid communication with a hydraulic/electrical-controlled drive system that incorporates a planetary screw drive or a solenoid drive system. In this “folded” configuration, the overall length of the linear pump assembly  40  is greatly reduced to about half of the embodiment shown in  FIG.  3   . The great reduction in overall length enables more flexibility with respect to the arrangement of multiple pump assemblies within a limited footprint, such as on a trailer bed that is typically 48 feet in length and up to 8 feet in width. 
     The linear pump assemblies described herein may operate under or with a control module (not explicitly shown) that include a computer with associated software installed therein, to cooperatively operate the drive system and hydraulic/electrical-mechanical actuators so that the fluid output from the fluid end is smooth with minimized fluid pulsation. A number of sensors may be used to measure and monitor a variety of pump operating characteristics that are provided as input to the control module. The monitored pump characteristics may include, for example, fluid pressures, fluid flow rate, motor speed, etc. 
     In some embodiments, multiple pump assemblies, such as from two to six units, may be used for redundancy and configured to maintain a constant or steady output flow (i.e., smooth output). In different implementations, different plunger sizes and fluid end sizes (e.g., different product families) may be provided for a range of pressures needed for different applications. 
     In some examples, the motor used in the linear electric pump may be a permanent magnet synchronous motor. The bearing may be a spherical axial thrust bearing. The planetary gears may be directly driving a threaded plunger rod without additional transmission assemblies. In some cases, the electric linear pump may have one or more sensors to measure the rotary position of the plunger rod or the planetary gears to determine position, speed, or other information of the plunger rod. The motor, gears or planetary gears, bearings, and the threaded rods may be enclosed within a housing for lubrication and cooling purposes. Cooling system is provided for both the electric motor and the driven gears thereof. A logic control unit (LCU) may be used to accurately control the rotation of the motors and provide control according to control signals per control algorithm or programs. Detailed examples are provided below. One benefit of the electric motor-driven linear pumps described herein is much reduced noise generation than traditional operations using diesel engines and power ends. 
     The features of the present invention which are believed to be novel are set forth below with particularity in the appended claims. However, modifications, variations, and changes to the linear pump configurations described above will be apparent to those skilled in the art, and the linear actuated pump configuration described herein thus encompasses such modifications, variations, and changes and are not limited to the specific embodiments described herein.