WO2020198535A1 - Novel integrated plunger and packing assembly - Google Patents

Abstract

A plunger assembly for reciprocating within a fluid bore in a fluid end of a hydraulic frac pump includes an elongated plunger body having first and second ends, a first annular portion having an outer diameter proximate the first end and substantially equal to the overall outer diameter of the plunger assembly, and a second annular portion having an outer diameter less than the overall outer diameter of the plunger assembly. The second annular portion has a circumferential thread defined thereon proximate the second end. The plunger assembly further includes a seal packing disposed about the second portion of the plunger body, and a tubular packing nut disposed circumferentially about the second annular portion of the plunger body and having a threaded interface configured to engage the circumferential thread proximate the second end of the plunger body. The annular packing nut is configured to rotate about the circumferential thread to advance toward and adjust an overall linear dimension of the seal packing.

Description

NOVEL INTEGRATED PLUNGER AND PACKING ASSEMBLY

RELATED APPLICATION

The present application claims the benefit of U.S. Provisional Patent Application No. 62/824,289 filed on March 26, 2019.

FIELD

The present disclosure relates to hydraulic fracturing pumps, and in particular, to a novel integrated plunger and packing assembly.

BACKGROUND

Hydraulic fracturing (a.k.a. fracking) is a process to obtain hydrocarbons such as natural gas and petroleum by injecting a fracking fluid or slurry at high pressure into a wellbore to create cracks in deep rock formations. The hydraulic fracturing process employs a variety of different types of equipment at the site of the well, including one or more positive displacement pumps, slurry blender, fracturing fluid tanks, high-pressure flow iron (pipe or conduit), wellhead, valves, charge pumps, and trailers upon which some equipment are carried.

Positive displacement pumps are commonly used in oil fields for high pressure hydrocarbon recovery applications, such as injecting the fracking fluid down the wellbore. A positive displacement pump typically has two sections, a power end and a fluid end. The power end includes a crankshaft powered by an engine that drives the plungers. The fluid end of the pump includes cylinders into which the plungers operate to draw fluid into the fluid chamber and then forcibly push out at a high pressure to a discharge manifold, which is in fluid communication with a well head. A seal assembly, also called a packing assembly or stuffing box, disposed in the cylinder chamber of the pump housing is used to prevent leakage of frac fluid from around the plunger during pumping operations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example embodiment of an integrated plunger and packing assembly for the fluid end of a positive displacement frac pump according to the teachings of the present disclosure; FIG. 2 is a side view of an example embodiment of a plunger for an integrated plunger and packing assembly according to the teachings of the present disclosure;

FIGS. 3 and 4 are end views of an example embodiment of a plunger for an integrated plunger and packing assembly according to the teachings of the present disclosure;

FIG. 5 is a cross-sectional side view of an example embodiment of an integrated plunger and packing assembly according to the teachings of the present disclosure;

FIG. 6 is a cross-sectional view of an example embodiment of a novel integrated plunger and packing assembly for the fluid end of a positive displacement frac pump according to the teachings of the present disclosure;

FIG. 7 is a cross-sectional view of an example embodiment of a plunger for an integrated plunger and packing assembly according to the teachings of the present disclosure;

FIG. 8 is a cross-sectional view of an example embodiment of a seal packing stack for an integrated plunger and packing assembly according to the teachings of the present disclosure;

FIG. 9 is a cross-sectional view of an example embodiment of a packing nut and packing ring for an integrated plunger and packing assembly according to the teachings of the present disclosure;

FIGS. 10 and 11 are perspective and side views of an example embodiment of a plunger for an integrated plunger and packing assembly according to the teachings of the present disclosure; and

FIG. 12 is a perspective view of an exemplary embodiment of a positive displacement pump according to the teachings of the present disclosure.

DETAILED DESCRIPTION

Current plunger seal packing technology utilizes several different types of metallic and/or elastomer seal components inserted into a stuffing box during installation into the fluid end. This seal stack is energized by a packing nut that is also installed in machined contours and threads in the fluid end. The packing nut preloads the seals to insure positive engagement with the plunger. Currently, the conventional packing around the plunger only lasts around 100 hours during down hole operation. Because the packing seals require mechanical compression exerted by the packing nut to energize or pre-load the seal packing to ensure a constant contact with the plunger and seal bore, the seals can wear prematurely if the packing nut is not installed or maintained properly. As the seals wear, fracking fluids and debris can leak to the environment and require a more frequent maintenance schedule. Further, due to the cyclic nature of the pressure acting on the packing stack, the seals can move back and forth on the seal bore causing wear in the metallic seal bore, known as packing bore wash or washboarding. This type of wear is detrimental and requires significant labor and cost to repair, with the worst scenario requiring a complete replacement of the pump fluid end. As the current packing wears (or loses its energization), the plunger may be subject to jetting or premature wear. The cost and time lost to remove or replace the plunger is a heavy burden to the end user.

The conventional packing (also referred to as the packing gland and stuffing box) is installed in annular grooves machined in the plunger bore of the fluid end, including the threads for the packing nut. Therefore, the fluid end bore geometry is fairly complex. Further, accessing the packing for maintenance purposes requires navigating the confined space where stay rods connect the fluid end and the power end of the pump. It’s challenging and time consuming to disconnect the plunger and disassemble the packing for repairs and maintenance. Further, improper alignment in the bore can block access to grease ports necessary to lubricate the packing and plunger, also leading to premature failure.

FIGS. 1-4 are various views of an example embodiment of a novel integrated plunger and packing assembly 10 for the fluid end of a positive displacement frac pump according to the teachings of the present disclosure. The seal packing 12 and packing nut 14 are integrated with the elongated plunger 16 so these components are pre-assembled together prior to installation into the plunger bore in the fluid end. The integrated plunger and packing assembly 10 includes a packing ring 18 that has an inner annular surface that is threaded and is configured to engage a threaded outer circumferential surface 20 of a back end 16’ of the plunger 16. Coupled to the back end 16’ of the plunger 16 is an annular flanged end 22 configured for joining a pony rod (not shown) typically using a clamp (not shown). At the front end 16” of the plunger 16, a threaded counter bore slot 24 is formed to enable removal of the plunger 10 using a threaded tool (not shown). The packing ring 18 further has a plurality of circular openings 26 circumferentially arranged about the plunger. The plunger 16 further includes a longitudinal bore 28 defined along its center axis from its back end 16’. The central bore 28 does not extend the entire length of the plunger 16 but is short of reaching the threaded counter bore 24 at the front end 16”. The front end 16” of the plunger 16 further includes an annular chamfered edge 30.

As best shown in the cross-sectional view in FIG. 5, the seal packing 12 includes a plurality of metal, elastomer, or combination annular seals and may include, for example, a junk ring, header ring, pressure ring, adapter, spacer, lantern ring, and/or wiper ring (not all shown). Instead of being disposed within grooves machined in the plunger bore, the seal packing 12 is integrated with the plunger 16 into a single assembly 10. It may be seen that the integrated assembly 10 has a straight profile so that the plunger bore in the fluid end no longer requires complex machined grooves and other features to accommodate the packing nut 14 and packing 12. Optionally, a sleeve of hardened material can be used to envelope the integrated plunger and packing assembly to further protect it from washout. An example of this sleeve is described in WO2019195279 entitled“Plunger Bore Sleeve for a Reciprocating Pump” filed on April 2, 2002, incorporated herein in its entirety by reference.

FIG. 6 is a cross-sectional perspective view of the plunger packing assembly 10, and its components: the plunger 16 (FIG. 7), the packing 12 (FIG. 8), and the packing nut 14 and packing ring 18 (FIG. 9). The back end 16’ of the plunger 16 incorporates annular threads 20 for engaging the packing nut 14 and packing ring 18 and an annular flanged end 22 for coupling with a pony rod. The packing 12, shown in FIG. 8, are disposed near the front end 16” of the plunger 16. As best shown in FIGS 10 and 11, the front end 16” of the plunger 16 includes a front portion 36 that has an outer diameter that is the full outer diameter of the plunger 16, and the back portion 38 of the plunger 16 has a smaller outer diameter to accommodate the thickness of the packing 12, packing nut 14 and packing ring 18.

The seal packing 12, packing nut 14 and packing ring 18 can be assembled onto the plunger 16 and the packing nut 14 and packing ring 18 are rotated to engage the threaded interface between the packing ring and the plunger surface. After the flanged end 22 of the plunger 16 is connected to the pony rod and fixed from rotation, the integrated packing nut 14 and packing ring 18 are rotated to tighten the unit against the annular sealing elements in the packing 12. The tightening of the packing nut 14 decreases the axial height of the integrated stuffing box (packing) 12 and energizes the seal components. The compressed packing 12 provides the proper seal in between the reciprocating plunger and the fluid end. All sealing rings in the packing 12 and the packing nut 14 are incorporated with the plunger 16 as a single unit. Combined into a single plunger and packing cartridge, the integrated plunger packing assembly greatly minimizes the potential for improper installation. As a result, this significantly decreases the amount of time needed to perform maintenance and repairs on the plunger and packing in the fluid end.

FIG. 12 is a pictorial representation of an exemplary positive displacement pump 40. The positive displacement pump 40 has two sections, a power end 42 and a fluid end 44. The fluid end 44 of the pump 40 includes a fluid end block or fluid cylinder, which is connected to the power end housing via a plurality of stay rods 46. In operation, the crankshaft (not explicitly shown) reciprocates a plunger rod assembly between the power end 42 and the fluid end 44. The crankshaft is powered by an engine or motor (not explicitly shown) that drives a series of plungers (not explicitly shown) to create alternating high and low pressures inside a fluid chamber. In this instance, the plungers are integrated plunger and packing assemblies 10 as described above. The cylinders operate to draw fluid into the fluid chamber from an intake manifold 48 and then discharge the fluid at a high pressure to a discharge manifold 50. The discharged liquid is then injected at high pressure into an encased wellbore. The injected fracturing fluid is also commonly called a slurry, which is a mixture of water, proppants (silica sand or ceramic), and chemical additives. The pump 40 can also be used to inject a cement mixture down the wellbore for cementing operations. The pump 40 may be freestanding on the ground, mounted to a skid, or mounted to a trailer.

The crankshaft (not shown) is typically mechanically connected to a motor. In one embodiment, a gear is mechanically connected to the crankshaft and is rotated by the motor through additional gears. A connecting rod connects to a crosshead through a crosshead pin, which holds the connecting rod longitudinally relative to the crosshead. The connecting rod is pivotally secured by a bushing within the crosshead, which holds the connecting rod longitudinally relative to the crosshead. The connecting rod pivots within the crosshead bushing as the crankshaft rotates with the other end of the connecting rod. The pony rod extends from the crosshead in a longitudinally opposite direction from the crankshaft. The connecting rod and the crosshead convert the rotational movement of the crankshaft into the longitudinal movement of the pony rod, which is connected to a plunger that draws and pushes the pump fluid passing through the cylinder housing. The plunger extends through a plunger bore and into a pressure chamber formed inside the fluid cylinder. It should be noted that the plunger packing assembly may be utilized in pumps of other configurations, such as a linearly actuated pump having a centrally-disposed drive system coupled to two fluid ends at either end along the linear axis, where the drive system drives the plunger assembly to move the fluid in both fluid ends. In an example embodiment, an electric linear pumps 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 plunger packing assembly may be utilized in a second embodiment of the linear actuated pump that includes a centrally-disposed fluid end coupled to two hydraulic actuators on its two sides along a linear axis. The hydraulic actuators are in fluid communication with a hydraulic drive system that incorporates a planetary screw drive or a solenoid drive system. In this configuration, the stroke length of each plunger rod can be halved and a smaller screw drive system may be employed and still achieve the same horsepower and fluid rate output as in the first embodiment pump described above. In this more compact configuration, the overall length of the pump assembly 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.

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 exemplary embodiments described above will be apparent to those skilled in the art, and the novel integrated plunger and packing assembly for the fluid end described herein thus encompasses such modifications, variations, and changes and are not limited to the specific embodiments described herein.

Claims

WHAT IS CLAIMED IS:

1. A plunger assembly for reciprocating within a fluid bore in a fluid end of a hydraulic frac pump, the plunger assembly having an overall outer diameter and comprising: an elongated plunger body having first and second ends, a first annular portion having an outer diameter proximate the first end and substantially equal to the overall outer diameter of the plunger assembly, and a second annular portion having an outer diameter less than the overall outer diameter of the plunger assembly, wherein the second annular portion having a circumferential thread defined thereon proximate the second end;

a seal packing disposed about the second portion of the plunger body; and

a tubular packing nut disposed circumferentially about the second annular portion of the plunger body and having a threaded interface configured to engage the circumferential thread proximate the second end of the plunger body, the annular packing nut configured to rotate about the circumferential thread to advance toward and adjust an overall linear dimension of the seal packing.

2. The plunger assembly of claim 1, wherein the elongated plunger body further includes a central bore along its center axis extending from its second end.

3. The plunger assembly of claim 1, wherein the elongated plunger body further comprises an annular flanged end at the second end configured to couple to a pony rod.

4. The plunger assembly of claim 1, wherein the packing nut further comprises an annular packing ring having defined thereon a circumferential thread configured to engage the circumferential thread proximate the second end of the plunger body.

5. The plunger assembly of claim 4, wherein the annular packing ring comprises a plurality of circular openings distributed about its circumference.

6. The plunger assembly of claim 1, wherein the first portion of the plunger body has a counter-threaded bore defined along a center axis of the elongated plunger body extending from the first end, the counter-threaded bore being configured to releasably engage a threaded surface of a removal tool.

7. The plunger assembly of claim 1, wherein the seal packing comprises a plurality of annular seals.

8. The plunger assembly of claim 1, further comprising an elongated sleeve configured for enveloping the plunger.

9. A pump having a fluid end comprising:

at least one plunger assembly disposed in a fluid bore in the fluid end of the pump and having a straight geometry and configured to reciprocate therein, the at least one plunger assembly comprising:

an elongated plunger body having first and second ends, a first annular portion having an outer diameter proximate the first end and equal to the overall outer diameter of the plunger assembly, and a second annular portion having an outer diameter less than the overall outer diameter of the plunger assembly, wherein the second annular portion having a circumferential thread defined thereon proximate the second end; a seal packing disposed about the second portion of the plunger body; and a tubular packing nut disposed circumferentially about the second annular portion of the plunger body and having a threaded interface configured to engage the circumferential thread proximate the second end of the plunger body, the annular packing nut configured to rotate about the circumferential thread to advance toward and adjust an overall linear dimension of the seal packing.

10. The pump of claim 9, wherein the elongated plunger body further includes a central bore along its center axis extending from its second end.

11. The pump of claim 9, wherein the elongated plunger body further comprises an annular flanged end at the second end configured to couple to a pony rod.

12. The plunger of claim 9, wherein the packing nut further comprises an annular packing ring having defined thereon a circumferential thread configured to engage the circumferential thread proximate the second end of the plunger body.

13. The plunger of claim 12, wherein the annular packing ring comprises a plurality of circular openings distributed about its circumference.

14. The plunger of claim 9, wherein the first portion of the plunger body has a counter-threaded bore defined along a center axis of the elongated plunger body extending from the first end, the counter-threaded bore being configured to releasably engage a threaded surface of a removal tool.

15. The plunger of claim 9, wherein the seal packing comprises a plurality of annular seals.

16. A fluid end of a pump comprising:

at least one plunger assembly disposed in a fluid bore in the fluid end of the pump and having a straight geometry and configured to reciprocate therein, the at least one plunger assembly comprising:

an elongated plunger body having first and second ends, a first annular portion having an outer diameter proximate the first end and equal to the overall outer diameter of the plunger assembly, and a second annular portion having an outer diameter less than the overall outer diameter of the plunger assembly, wherein the second annular portion having a circumferential thread defined thereon proximate the second end; a seal packing disposed about the second portion of the plunger body; and a tubular packing nut disposed circumferentially about the second annular portion of the plunger body and having a threaded interface configured to engage the circumferential thread proximate the second end of the plunger body, the annular packing nut configured to rotate about the circumferential thread to advance toward and adjust an overall linear dimension of the seal packing.

17. The pump of claim 16, wherein the elongated plunger body further comprises an annular flanged end at the second end configured to couple to a driving rod.

18. The plunger of claim 16, wherein the first portion of the plunger body has a counter-threaded bore defined along a center axis of the elongated plunger body extending from the first end, the counter-threaded bore being configured to releasably engage a threaded surface of a removal tool.

19. The plunger of claim 9, wherein the seal packing comprises a plurality of annular seals.