Patent Grant
8037897
Not Applicable
Not Applicable.
This invention relates generally to fluid delivery systems and more particularly to valve assemblies that handle (i.e., that are in fluid contact with) particulate-containing fluids at high pressure. Aqueous fracturing fluids containing proppant are examples of such particle-containing fluids.
It is common to pump fluids that contain particulates into oil and gas wells. For example, fracturing fluids typically contain proppant particles, such as sand or small ceramic or glass beads, that typically range in size from U.S. Standard Sieve sizes 60 through 16 (0.01 to 0.05 inches, 0.025 to 0.12 cm), and occasionally from U.S. Standard Sieve sizes 100 through 10 (0.006 to 0.079 inches, 0.015 to 0.20 cm). Other fluids containing particles are used for abrasive jetting in oil or gas wells. Slurries (mixtures of liquids and solid particles) are more difficult to pump than particle-free fluids. The presence of solid particles adversely affects pump efficiencies and valve lifetimes, especially at high pressures and/or high flow rates.
Reciprocating plunger pumps are frequently used by oil field service companies to pump proppant-containing fracturing fluids into oil and gas formations. These pumps typically include valve assemblies that are biased toward the closed position. When the motion of the plunger creates fluid flow resulting in a differential pressure across the valve, the differential pressure forces the valve open. However, when the forward motion of the plunger slows and the valve begins to close, solid particles in the fluid can become trapped within the valve assembly. The trapped solids prevent the valve from fully closing and thereby reduce the efficiency of the pump. Trapped solids can also damage the valve assembly components and reduce the useful life of the valve assembly.
The valve assemblies in reciprocating plunger pumps typically contain an area where the metal surface of the valve closure member contacts the metal surface of the valve seat member when the valve is closed. That area is commonly referred to, and is defined herein, as the “strike face area.” There is little or no damage done to the metal surfaces of the valve components when only clear fluids (e.g., clear liquids, such as water or gelled aqueous fluids) are pumped through the valve assembly. The valve lifetime can be quite long and may even outlast the fluid end of the pump in endurance test runs when the pumping medium is a clear fluid. However, when the pumping medium is a slurry, such as a fracturing fluid with proppant, the metal contact surfaces in the strike face area are severely damaged by erosion, abrasion and by pitting caused by solid particles in the fluid. If solid particles are trapped between the metal surfaces as the valve closes, the closing force of the valve is applied to the metal surfaces through the particles rather than being spread uniformly across the strike face area. The localized contact forces, Hertzian contact forces, at the interface of the trapped particles and the metal surface cause pitting in the metal surface. The damage caused by trapped particles is extensive. The valve life can be less than an hour under extreme conditions. Attempts to mitigate the damage to the valve assemblies have been made. One such technique involved an attempt to minimize or replace the metal-to-metal contact in the strike face area by including a resilient elastomeric insert in the closure member or the valve seat. While useful, this technique has not been wholly successful. Solid particles are still trapped at the outer perimeter where the resilient insert forms a hydraulic seal as it closes against the metal surface of the valve seat member. Damage to the metal surfaces near to and along that perimeter increases the extrusion gap size that the resilient insert has to span in order to form an effective hydraulic seal.
The mechanisms by which pitting and other valve damage occurs have been addressed in various patents and publications. For example, U.S. Pat. No. (“USP”) 6,701,955 B2, “Valve Apparatus” by McIntire et al., describes how solid particles in a pumped slurry can become trapped between the two metal contact surfaces in the strike face area. The particles tend to be concentrated in specific locations rather than randomly distributed across those surfaces when concentrated slurries of particles are pumped. This creates concentrated stress forces at these locations and leads to localized pitting. The resulting pits or indentations in the metal surfaces are much wider than single particles. Once such pitting has occurred, the pits act as collection points and solid particles tend to concentrate at these locations on subsequent plunger strokes. This greatly accelerates the damage at these locations.
The above-mentioned technique involving resilient inserts has also been addressed by the present inventor. Valves used for slurry service typically have a resilient sealing insert around the outer perimeter of the valve closure member to provide effective valve sealing. Pressure applied to a closed valve forces the resilient sealing insert to become a hydraulic seal and a portion of the insert is extruded into the gap between the valve closure member and the valve seat member. For the insert to affect a hydraulic seal upon valve closure, the insert must protrude from the valve closure member toward the valve seat member when the valve is open. The amount of protrusion of the insert is called the insert offset. When the valve is nearly closed, the resilient sealing insert contacts the valve seat member before the contact surfaces of the valve closure member and the valve seat member make contact. When the valve is closed, the resilient sealing insert is deformed against the seat member to form the hydraulic seal, and metal-to-metal contact occurs between the valve closure member and the valve seat member in the strike face area. The resilient insert material does not compress but deforms. Repeated deformation of the insert material causes internal heat build-up and material stress within the insert material, and this can damage it. The insert material has low thermal conductivity, and even when bathed in flowing fluid the insert can overheat and be permanently deformed if exposed to large percentage deformations of the insert material.
Damage to the valve insert is also caused by large deformations of the insert material beyond its elastic limit. The elastic limit is an intrinsic property of the material, so the critical deformation is the percentage deformation defined as the deformation per volume unit of the material. If a large insert deformation occurs over a large volume of the insert material, then the percentage deformation can be low, causing minimal damage.
Proppant trapped under the resilient sealing insert can become temporarily or permanently embedded in the resilient insert material, so that the insert can contact the valve seat and affect a hydraulic seal in the presence of proppant. In the presence of proppant, the metal surfaces of the valve closure member and valve seat member do not form a good hydraulic seal. Under pressures typical of oilfield operations, the resilient insert deforms to press against the outer perimeter of the metal-to-metal contact area and makes the hydraulic seal there.
If proppant is trapped between the contact surfaces of the valve seat member and valve closure member, the metal-to-metal seal is not made. The resilient insert is extruded into the gap between the contact surfaces by the differential pressure across the valve. That differential pressure across the valve apparatus will build from zero, before the valve closes, to the full pump output pressure as the valve closes and the plunger actions continue. When the pressure forces on the valve closure member become high enough to crush proppant trapped between the metal contact surfaces, the gap between the contact surfaces decreases from the proppant diameter to the height of the crushed proppant particles. Just before the proppant is crushed, the insert is subjected to extrusion into a gap width defined by the proppant particles' diameter, with an extrusion pressure just less than the pressure required to crush the proppant. If proppant particles are piled up in the contact area, the extrusion gap can be larger than the diameter of individual particles. After the proppant is crushed, the gap between the two contact surfaces is reduced to the width of the crushed proppant debris. Then the insert is subjected to extrusion into that smaller gap, with an extrusion pressure equal to the maximum differential pressure across the pump.
The resilient sealing insert contacts the valve seat member before the valve closure member contacts the valve seat member. The gap between the sealing insert and the seat of an open valve is smaller than the gap between the valve closure member and the valve seat. This is required in order to have the resilient sealing insert contact the valve seat before the valve closure member and make a hydraulic seal. As the valve closes, the gap between the sealing insert and the valve seat member becomes too small to pass particles in the fluid, while the gap between the valve closure member and the valve seat member is still large enough to pass particles into the region between them. Thus, a standard valve-sealing insert can act as a forward-screening element that concentrates proppant particles in the strike face area, particularly in the critical area near the outer perimeter of the strike face. Such concentrations of proppant particles enhance damage to the contacting surfaces of the valve closure member and the valve seat member.
If the pump is operated in such a way as to have valve lag, i.e. the discharge valve does not close until after the plunger starts its suction stroke, there will be reverse flow through the valve before it closes. Before the valve closes, the insert will approach the valve seat so that the gap between them is less than the proppant diameter. The sealing insert will screen out proppant particles from the reverse fluid flow, preventing the particles from entering the region between the valve closure member and the valve seat member. However, the volume of fluid without proppant, which flows through current valves during the short time interval between the onset of such reverse particle screening and the closure of the valve, typically is insufficient to displace the proppant-laden fluid from the valve before closure. Particles are still trapped between the valve closure member and the valve seat member. Additional fluid without proppant would be required to flush the gap between the contact surfaces of the valve closure member and the valve seat member before the valve closes enough to trap proppant particles in that gap.
The resilient insert should extend down below the frustoconical contact surface of the valve closure member by a distance greater than the diameter of the solid particles in the slurry being pumped. Otherwise, the valve can be held open by solid particles caught between the metal contact surfaces of the valve seat member and valve closure member, without the resilient insert member reaching the valve seat member to affect a hydraulic seal. The extension of the insert member below a parallel extension of the frustoconical contact surface of the valve closure member is referred to as the valve insert member's offset. Current valve assemblies have insert member offsets typically of 0.06 to 0.08 inches. Larger offsets would result in larger insert material deformations leading to heating and material failure. Current valve assemblies were developed for pumping slurries with proppant particles that typically would pass through a U.S. Standard Sieve of 20 mesh. The maximum proppant particle diameter to pass through that mesh is 0.032 inches, so an insert offset of 0.06 inches will allow the valve insert to contact the valve seat while there is proppant between the contact surfaces of the valve body and the valve seat. The insert will be deformed over particles trapped under the insert. However, larger proppant particles are being used today to increase the efficiency of oil and gas withdrawal following fracturing operations. Proppants pumped today can include some particles with diameters larger than the typical insert offsets of current valve assemblies.
Increasing the offset of the resilient insert member to accommodate larger diameter proppant particles, by allowing the insert member to contact the valve seat member while there are proppant particles between the contact surfaces of the valve closure and valve seat members, increases the deformation of the insert member when the valve is closed. That increases heating and deformation damage to the insert member. Additional deformation damage to the resilient insert member is caused by trapping proppant particles between the resilient insert member and the valve seat member when the valve is closed. Proppant particles trapped between the resilient insert member and the valve seat member deform the resilient insert member and may be embedded in the insert. Larger proppant particles will cause significantly increased deformation damage and embedment damage when trapped between the resilient insert member and the valve seat member when the valve closes.
U.S. Pat. No. 6,701,955 B2, “Valve Apparatus” by McIntire et al., describes the problems of packing proppant particles between the frustoconical contact surfaces of the valve closure member and the valve seat member, particularly near the outer perimeter of the strike face area, and teaches some ways to flush the proppant out of that space, mainly by trapping proppant particles between the resilient insert and the valve seat. The present invention has advantages over the apparatus described in U.S. Pat. No. 6,701,955 in that: a) it provides a volume of trapped slurry from which proppant is screened as that slurry is pumped through the area between the contact surfaces, b) it provides a cavity to accommodate proppant particles trapped under the insert without deforming and damaging the insert, and c) it provides an insert that will seal in the presence of large proppant particles without requiring large percentage deformation of the insert material.
U.S. Pat. No. 2,495,880 by Volpin shows a cylindrical plug, as part of the valve closure member, that protrudes down into the throat of the valve seat member when the valve is closed. U.S. Pat. No. 6,701,955 B2, “Valve Apparatus” by McIntire et al., teaches the use of such cylindrical plugs to increase the speed at which the valve closure member rises when the plunger starts to move forward and pump fluid through the valve apparatus, and to retard the descent of the valve closure member at the end of the plunger forward stroke. Retarding the descent of the valve closure member promotes valve lag that reduces the amount of proppant particles trapped under the valve and makes the reverse pumping aspect of the current invention more effective.
U.S. Pat. No. 7,000,632 B2, “Valve Apparatus” by McIntire et al., teaches the use of protrusions around the outer perimeter of the contacting surface of the resilient insert to provide a screening gap between that surface and the valve seat. This allows clear fluid (i.e., fluid without proppant particles) to flow in a reverse direction, from downstream of the valve, through the valve and to flush proppant particles from the gap between contact surfaces of the valve closure member and the valve seat member before the valve closes.
Another problem with conventional valves for high-pressure slurry pumps, such as the reciprocating plunger pumps mentioned above, is the impact of the valve closure member on the valve seat member when the valve exhibits valve lag, closing after the pump plunger has reversed direction. Valve lag can be useful for slurry pumps, because it can reduce the number of particles concentrated in the valve before closure. However, large amounts of valve lag lead to damage of conventional valves, as the valve closure member slams into the valve seat member with high velocity and considerable force in closing.
There is a need for improved valve assemblies that reduce the incidence of damage to the valve closure member and valve seat member caused by particulates in slurries. There is also a need to reduce valve insert damage due to compressive deformation, particularly for inserts with offsets large enough to accommodate large particles. There is also a need for valve assemblies that can operate efficiently while pumping slurries with large proppant particles. These needs are addressed by the present invention.
A valve apparatus that closes without particles trapped between the two metal contact surfaces in the strike face area would permit one to pump slurries without valve damage. Valve damage could also be significantly diminished by reducing or eliminating particles trapped near the outer perimeter of the metal contact surfaces. These are some of the objects of the present invention.
A novel valve apparatus has now been discovered having a longitudinal axis therethrough, comprising:
The present invention relates to valve assemblies that can reduce the problem of solid particle damage within the valve thereby increasing valve life, can help reduce or avoid the insert deformation problems associated with pumping proppant particles and can increase pump efficiencies when pumping slurries containing particles. The present invention is well suited for use with pumps that inject particle-laden fluid during the treatment of oil and gas wells, but can be used for other purposes as well. Although reciprocating plunger pumps are specifically mentioned, the valves of the present invention can be used with piston pumps and other pumps.
The present invention addresses the need for reducing particulate damage to valve closure members and valve seat members, the need for accommodating large proppant particles without damage to valve insert members and the need for improving pump efficiencies when pumping slurries of solid particles. It does this by providing a cavity between the valve insert member and valve seat member. The cavity traps a volume of the pumped slurry as the valve closes. The cavity separates an inner insert sealing surface near the inner diameter of the insert from an outer insert sealing surface near the outer diameter of the insert. The outer sealing surface has a greater offset than the inner sealing surface. When the valve is closing, the outer sealing surface contacts the valve seat before the inner sealing surface does. Further closure of the valve deforms the insert and decreases both the volume of slurry between the insert and the valve seat and the volume of slurry in the cavity. The insert deformation and resulting decrease in those two volumes pump slurry in reverse flow from under the valve closure member toward the hollow bore (throat) of the valve seat. As the valve closes further, the gap between the inner sealing surface and the valve seat gets smaller. As the valve continues to close, that gap becomes too small for the particles in the slurry to pass through the gap. Then further valve closure and deformation of the insert pump particle-free fluid through the gap to flush particles from the space between the metal-to-metal contact areas of the valve closure member and valve seat member. The solid particles screened from the slurry by the gap are concentrated in a volume of slurry that remains in the cavity when the valve is completely closed. During the next plunger stroke, the valve opens and the concentrated slurry is displaced from the cavity and replaced by unconcentrated slurry, and the insert cavity returns to approximately it's original dimensions and volume.
The description above is for the common practice of the valve insert member attached to the valve closure member. If the valve insert member is attached to the valve seat member, then the cavity will be between the valve insert member and the valve closure member, and the cavity could be manufactured into the insert alone, into the valve closure member alone or as two cavity portions, one in the insert and the other in the valve closure member. In another embodiment, two inserts can be used, one attached to the valve closure member and the other attached to the valve seat member. In that case, the cavity would be formed between the two inserts.
One aspect of the invention is a valve apparatus that provides a large valve insert member offset without incurring a large percentage deformation of the insert material when the valve is closed. This valve apparatus has a longitudinal axis therethrough and comprises a valve seat member, a valve closure member, a fluid flow path, and a resilient valve insert member. The valve seat member is usually stationary, and comprises a hollow bore and a first frustoconical contact surface. The valve closure member comprises a body and a second frustoconical contact surface that is adapted to contact against the first frustoconical contact surface. The valve closure member is movable along the longitudinal axis of the valve apparatus (i.e., toward and away from the valve seat member). The fluid flow path extends through the bore of the valve seat member and between the valve seat member and the valve closure member. This fluid flow path is closed when the second frustoconical contact surface contacts the first frustoconical contact surface. The resilient valve insert member is usually attached to the valve closure member, but could be attached to the valve seat member. The resilient valve insert member extends downward from the valve closure member (or upwards from the valve seat member) when the valve is open. The valve insert member contacts the valve seat member, or valve closure member, before the frustoconical contact surfaces of the valve seat member and the valve closure member make contact as the valve closes.
The discussions below describe a valve assembly in which the valve insert member is attached to the valve closure member.
In the present invention, when the valve closes, the resilient valve insert member contacts the valve seat member and pressure forces on the valve deform the resilient valve insert member. Deformation of the valve insert member increases until the frustoconical contact surfaces of the valve closure member and the valve seat member make contact. After the frustoconical contact surfaces make contact, the metal-to-metal contact area between the valve seat member and the valve closure member absorbs the pressure forces closing the valve. The current invention provides for the deformation of the valve insert member to be spread over a larger volume of material than in current valve apparatus designs and thereby reduces the percentage deformation of the resilient valve insert member material. This is accomplished by allowing the outer portion of the insert to deform upwards rather than being confined by the top of the valve closure member. The deformation can also be spread over a larger portion of the insert material by removing some of the insert material to allow deformation within the volume formerly occupied by the insert material.
In current valve apparatus designs, the top of the valve closure member extends outward to the outer diameter of the valve insert member. In one embodiment of the present invention, the diameter of the top of the valve closure member is reduced to allow the valve insert to deform upwards rather than being constrained by the top of the valve closure member. In this embodiment, the top of the valve closure member is terminated at a diameter less than the outer diameter of the valve insert member. This allows the outer portion of the resilient insert member to deform upwards, and spreads the total deformation of the resilient valve insert member over a larger volume of the insert material, thereby decreasing the percentage deformation of the insert material. When the valve closes, the insert material is not forced to bulge out between the valve closure member and the valve seat, but the outer portion of the insert can flex upward in response to its contact with the valve seat member. This modification of the valve closure member does not decrease the effectiveness of the valve closure member to withstand the pressure applied to the closed valve. The reduction of the valve closure member diameter is not new; similar principles are seen in U.S. Pat. No. 2,495,880 by Volpin. However, in the present invention, the diameter reduction provides insert flexibility used in conjunction with an insert cavity described below to accommodate solid particles trapped under the insert and to provide a flow of particle-free fluid to clean the valve strike face prior to closure. Upward movement of the outer portion of the insert is not restricted by the valve closure member. This is beneficial.
Another aspect of this invention is modification of the resilient insert member to accommodate proppant particles trapped under the insert member when the valve closes. A portion of the usual insert material is removed to create a cavity in the insert with cylindrical symmetry about the central axis of the valve assembly. The opening of this cavity is at the bottom of the insert member. The cavity may extend above a geometric extension of the valve closure member's frustoconical contact surface, so that the central portion of the cavity has a negative insert offset. The cavity is bordered by an inner sealing surface and an outer sealing surface of the valve insert member. These sealing surfaces have different amounts of offset from the extension of the valve closure member's frustoconical surface. The resilient insert member in this embodiment has two concentric sealing rings, the sealing surfaces described above. Between the two sealing surfaces is a cavity with cylindrical symmetry in the insert that may extend above the extension of the strike face. There are particular advantages for the outer sealing surface having a larger offset than the inner sealing surface. After the valve has closed enough for the outer sealing surface of the insert to contact the valve seat member, further closure of the valve will force slurry below the insert to flow in reverse direction through the gap between the contact surfaces of the valve seat member and the valve closure member, through the strike face area gap between the valve closure member and the valve seat member. The closing gap between the inner sealing surface of the insert and the valve seat member will screen proppant particles from that slurry before the valve is completely closed, providing a flow of particle-free fluid to flush the gap between the contact surfaces of the valve seat member and the valve closure member. A reduction in the number of particles trapped and crushed between the valve's frustoconical contact surfaces will increase the life of the valve.
It is particularly advantageous to have the bottom of the outer sealing surface narrow enough to move through flowing slurry without trapping proppant particles between the outer sealing surface and the valve seat member. The outer sealing surface does not provide the hydraulic seal at the outer perimeter of the metal-to-metal contact area of the valve closure member and valve seat member. That hydraulic seal is provided by the inner sealing surface. Therefore, the outer sealing surface can be narrow without compromising the effectiveness and durability of the final hydraulic seal. Another advantage to this embodiment is hydraulic cushioning of the impact of the valve closure member on the valve seat member when the valve is operated under conditions with valve lag. The present invention converts at least some of the kinetic energy of the closing valve into kinetic energy for fluid forced out of the cavity and into the fluid flow path between the valve seat member and the valve closure member; this high velocity clear fluid flushes proppant particles from the valve before closure. In addition, the valve closure member is slowed down as the process of pumping fluid from the cavity provides a hydraulic cushioning of the valve closure. This is beneficial.
The inner and outer sealing surfaces of the insert member have different materials requirements. The outer seal can be made from material that is more flexible and less resistant to extrusion, while the inner seal material primarily needs extrusion resistance. Separating these two functions in separate regions of the insert means that two or more different resilient materials can be used to provide a more effective insert design.
In another embodiment, the resilient insert member has a plurality of concentric sealing surfaces separated by cavities with cylindrical symmetry in the insert. The cavities may extend above the extension of the strike face of the valve closure member.
In another embodiment, the resilient insert member has a plurality of individual cavities which are not connected and which can accommodate proppant particles trapped under the resilient insert when the valve closes.
In another embodiment, the cavity between the valve insert member and the valve seat member is comprised of two cavity portions, one in the valve insert member and one in the valve seat member. Building the cavity as two portions reduces effects of the cavity shape upon slurry flow through the open valve. It also provides advantages in screening out particles from the slurry to provide particle-free fluid to clean the strike face area gap before the valve closes. It also enhances flushing of concentrated slurry from the cavity when the valve opens and slurry is pumped through the space between the cavity portions.
The present invention can be practiced with various manufacturing techniques for the resilient insert member. The resilient insert member can be manufactured in place on the valve closure member, or can be manufactured independently and installed on the valve seat member by known procedures.
The present invention is illustrated by reference to certain valve assemblies used as discharge valve assemblies in a plunger-type pump. However, the valve assembly of the present invention can also be used in other applications. It will be understood that the valve assemblies of the present invention can be used as a discharge valve or as a suction valve in such reciprocating plunger pumps and other high pressure pumps. In this patent application, terms such as “above”, “below”, “upward” and “downward” will be used relative to the frame of reference shown in the drawings, and the terms “valve assembly” and “valve assemblies” may be used interchangeably with “valve apparatus.”
Referring to
Forward flow and reverse flow through the valve apparatus 10 have separate working mechanisms and are not equivalent. Forward flow results when the pressure in the intake chamber 14 is sufficiently greater than the pressure in the discharge chamber 16 that it overcomes the resistance force applied by the compression spring 34. Forward flow involves hydrostatic pressure and then flowing fluid forces overcoming a resisting force. Reverse flow also needs a pressure differential across the valve assembly 10. However, rather than the pressure differential overcoming an opposing force, reverse flow involves the time lag inherent in the valve closure member 30 closing. Once the pressure has equalized between the intake chamber 14 and the discharge chamber 16, the forward flow of fluid will stop. At that time, the valve closure member 30 will still be in the process of approaching the valve seat member 20, moving in response to the force from the compression spring 34. The time period between the cessation of the forward fluid flow and the closing of the valve closure member 30 upon the valve seat member 20 is commonly referred to (and is defined for use herein) as “valve lag.” As the plunger begins its suction stroke, the pressure within the intake chamber 14 is reduced to less than the pressure within the discharge chamber 16. This results in a reverse fluid flow through the discharge vale until there is an adequate fluid seal between the valve closure member 30 and the valve seat member 20. If an adequate fluid seal (hydraulic seal) between the valve closure member 30 and the valve seat member 20 is not achieved, there will be reverse fluid flow throughout the entire suction stroke, and pump efficiency will be decreased.
Although the resilient insert is attached to a modified valve closure member 30 in
On many valves, the resilient insert 50 has a cylindrical inner bulge 59 that fits into a corresponding cylindrical cavity (groove) 39 in the valve closure member 30. This feature is used to help retain the insert on the valve closure member, particularly when the insert is manufactured separately from the valve closure member and not bonded to it. In such instances, the valve is typically assembled by sliding the circular insert over the cylindrical outer perimeter of the closure member until it snaps into place, much like placing a rubber “O-ring” onto a grooved piece of metal bar. Alternatively, the resilient insert member may be bonded to the valve closure member. In such instances, the resilient insert may be formed in situ by pouring a chemically reactive substance (e.g., a polyurethane reaction mixture) into an appropriate mold around the valve closure member. Either method may be used to prepare the valve apparatus illustrated by
Dashed lines 72 and 74 in
The area where the frustoconical surfaces 32 and 24 meet is called the strike face area of the valve and valve seat. That is the area of metal-to-metal contact when the valve is closed.
The inserts illustrated in
The resilient insert material is typically not very compressible. Under pressure, the insert deforms rather than compresses. Forces required to deform the insert material are small compared to the pressure forces exerted on the valve members during typical operations. When the valve is closed, the insert material transmits pressure and deforms to plug any irregularities or gaps between the frustoconical surfaces 32 and 24 of the valve closure member 30 and the valve seat member 20 at the perimeter 36. When the valve is closed, the insert helps create a hydraulic seal at the outer perimeter 36 of surface 32 of the valve closure member 30.
If the offset of the insert 50 on the left side of
The right side of
Before the proppant particle 41 is embedded in the resilient valve insert material, sufficient downward force must be exerted on the valve to deform the insert material. That force is created by differential pressure across the valve. Before the proppant particle is embedded in the insert, the insert does not affect a hydraulic seal, and an open flow path exists through the valve. Differential pressure across a valve with an open flow path 38 is caused by fluid flow through the flow path. Before sufficient force is generated to deform the insert to embed the proppant particle, fluid flows at high velocities through the gap between the valve insert and the valve seat. This reverse flow through a valve decreases the efficiency of the pump. Abrasive particles in the slurry smaller than the embedding proppant particle flow with the fluid through the gap and erode valve components.
In prior art valves, illustrated in
The cavity 52, illustrated in cross section in
The straight dashed line 54 extending across below the cavity, from the lowest point on the inner sealing surface 51 to the lowest point on the outer sealing surface 53 of the undeformed insert 50, defines the bottom of the cavity 52. The depth of the cavity is defined as the maximum distance from the bottom of the cavity to the top of the cavity perpendicular to the extension 37 of the frustoconical contact surface 32, when the insert material is not deformed. The depth of the cavity in
It is preferred, but not necessary, for the cavity to have a generally rounded shape in cross section, such as semi-circular or parabolic, to avoid high stress regions in the resilient insert material. Other cavity shapes can be used, as illustrated in
The total width of the cavity is defined as the radial distance from the innermost radius of the cavity to the outermost radius of the cavity. In
Cavity 52 in
The offset of the inner sealing surface 51 in
In order to prevent trapped particles from holding the valve open, the outer sealing surface offset must be larger than the maximum proppant diameter, to allow the outer sealing surface 53 to reach the contact surface 24 when there is proppant in the gap between contact surfaces 32 and 24. Accordingly, for 20 mesh particle diameters, the outer sealing surface offset should be at least about 0.033 inches (0.084 cm), and for 10 mesh particle diameters, the outer sealing surface offset should be at least about 0.079 inches (0.20 cm).
It is desirable for the outer sealing surface offset to be greater than the sum of the inner sealing surface offset plus the proppant diameter. That allows the outer sealing surface to contact the valve seat surface 24 before particles can be trapped under the inner sealing surface. For 20 mesh particle diameters it is desirable for the outer sealing surface offset to be at least 0.033 inches (0.084 cm) greater than the inner sealing surface offset.
It is preferable for the outer sealing surface offset to be about equal to or greater than the sum of the inner sealing surface offset plus twice the proppant diameter. Particles in concentrated slurries can be separated from fluid in the slurry when the slurry flows into a gap with width of twice the proppant diameter or less. This separation mechanism can be advantageously used in the present invention to provide a flow of particle-free fluid to flush solid particles out of the gap between the contact surfaces 24 and 32 as the valve closes. For pumping concentrated slurries of 20 mesh particle diameters, the preferred outer sealing surface offset is greater than the inner sealing surface offset by at least about 0.066 inches (0.17 cm). For larger 10 mesh diameters, the preferred outer sealing surface offset is greater than the inner sealing surface offset by at least about 0.16 inches (0.40 cm).
When the valve is closing, after the outer sealing surface 53 contacts surface 24 but before the inner sealing surface 51 contacts surface 24, pressure above the valve is higher than pressures in the cavity 52 and in the hollow bore 22 of the valve seat 20. Differential pressure across the valve produces a downward force on the valve closure member 30. That force deforms the insert 50 and forces the valve closure member 30 toward the valve seat member 20. Resilient material in the outer portion of the insert is deformed as the valve closure member is pressed down. The insert material above the inner sealing surface 51 is not deformed until the valve is closed enough for the inner sealing surface 51 to reach the contact surface 24
There are three distinct volumes above the valve seat contact surface 24. These are a) below the cavity 52, b) below the inner sealing surface 51 and c) below contact surface 32. All three volumes decrease as valve closure member 30 approaches valve seat member 20. Slurry from those decreasing volumes flows inwards toward the hollow bore 22 of the valve seat member 20. If sealing surface 53 fails to make a good hydraulic seal, differential pressure across the valve will still force flow inwards through the sealing surface 53 rather than outwards. The flow from those three decreasing volumes will be inwards toward the hollow bore 22 of the valve seat member 20, even if sealing surface 53 fails to seal completely. This can be exploited to provide a larger volume of clear fluid without proppant particles to flush the valve.
The size of insert gap 58 between inner sealing surface 51 and contact surface 24 decreases as the valve continues to close. Proppant particles too large to enter the insert gap 58 are trapped in cavity 52. Due to the offset of the inner sealing surface 51, the insert gap 58 is narrower than the gap between the contact surfaces 24 and 32. Any particle small enough to enter the insert gap 58 can also pass through the gap between the contact surfaces 32 and 24. After the valve closes enough to make the insert gap 58 narrower than the proppant particles' diameter, the insert gap 58 separates proppant particles from the flowing slurry and traps the proppant particles in the cavity 52. Fluid without proppant particles is forced from the cavity and flows through the insert gap 58 towards the hollow bore 22 of the valve seat 20. This fluid, without proppant particles, flushes proppant particles from the gap between contact surfaces 24 and 32.
Proppant particles are prohibited from entering the insert gap 58 when the gap width is equal to or less than the proppant diameter. Proppant particles are screened from slurry entering the narrow gap. Some screening of particles from a slurry occurs before the gap width is reduced to the proppant particle diameter. The particles have to enter the gap, and particles in a slurry interfere with each other rather than flow smoothly into the gap. For concentrated slurries, separation of particles from fluid occurs when entering a gap of width approximately equal to twice the particle diameter. Therefore, the volume of fluid without proppant that flows through the gap 58 is greater than the volume calculated using a gap width equal to the proppant diameter.
Particles within a flow channel of uniform width that decreases with time, such as the channel between contact surfaces 32 and 24, do not interfere with each other in the same manner as particles entering a gap. Particles already within a closing gap will flow freely through the gap, until the gap width equals the particle diameter.
Fluid without proppant particles flushes proppant particles from the gap between contact surfaces 32 and 24 from the time that gap 58 closes enough to exclude proppant from the fluid until the time when the larger gap between contact surfaces 24 and 32 becomes as small as the proppant particle diameter. During that time interval, the volume of fluid without proppant particles that flushes proppant particles out of the gap between contact surfaces 32 and 24 is at least equal to the projected area under the insert, inward from the outer sealing surface 53, multiplied by the maximum offset of the inner sealing surface 51 from the projection 37 of the contact surface 32. To ensure that all or substantially all of the proppant particles are flushed out of the gap between contact surfaces 32 and 24, the volume of fluid pumped without proppant particles should exceed the volume of the gap between contact surfaces 32 and 24 when proppant particles are first excluded from the fluid entering the insert gap 58.
The critical area for particle-induced damage to the valve closure member and insert is near the strike face outer perimeter 36, the interface between contact surface 32 and the insert. This is the first area from which particles are flushed by particle free fluid pumped from under the cavity. Even if the volume of particle free fluid is insufficient to clear particles from the entire volume between contact surfaces 32 and 24, the volume between those surfaces and near the perimeter 36 is flushed free of particles.
The design of the valve apparatus of the present invention addresses problems previously associated with pumping slurries containing large proppant particles. This is a surprising benefit. The design of the present valve apparatus provides a mechanism for flushing proppant particles out of the valve strike face area essentially without regard for the particle size. The service life of the valve closure member 30 and the valve seat member 20 are thereby significantly increased.
Deformation of the insert decreases the cavity volume, and fluid trapped in the cavity is pumped in reverse direction through the gap (flow channel) between contact surfaces 32 and 24 before the inner sealing surface 51 contacts the contact surface 24.
The illustration in
It is common practice to pump slurries of proppant particles with proppant volume fractions up to approximately one-third. If the proppant particles are spherical and of uniform size, they can theoretically be concentrated up to a volume fraction of about two-thirds, based on the maximum packing factor for spheres. If the insert gap 58 screens proppant particles from an initial slurry with solids volume fraction one-third, and the particles are concentrated in the cavity as a concentrated slurry with solids volume fraction two-thirds, then the volume of concentrated slurry in the cavity with the valve in the closed position of
The percentage deformation of insert material near the inner sealing surface 51 can be low because the offset of the inner sealing surface does not have to be as large as proppant particle diameters for the valve to seal initially. The initial sealing is accomplished at the outer sealing surface 53. This is particularly important for pumping fracturing fluids containing large diameter proppants.
The two intermediate sealing surfaces of the insert in
When an insert having a plurality of concentric cavities is used in the present invention, as illustrated in
The cavities in
The discussion of cavity depths in the description of
Insert material 57 near the outer seal area 53, and in the region between the outer seal area and the outer perimeter of the top 35 of the valve closure member 30, is subjected to larger deformations, but is not subjected to extrusion. This material is beneficially selected for properties of elasticity and capability for surviving large repeated deformations. Typically, such materials are softer and more pliable elastomers.
The different operating conditions and materials requirements for the two separate regions indicate that two or more different elastomeric materials can be used to advantage in a composite resilient insert. There are numerous known ways that the two sections, inner and outer sections of a dual elastomer valve insert can be manufactured.
Variations in cavity shape can be selected based on performance or ease of manufacturing. Generally, a cavity with rounded shape, such as the cavity in insert 60, will be preferable in operations compared to shapes with sharp corners, because rounded shapes are less susceptible to stress concentrations in the corners causing damage upon repeated deformation.
Insert 62 illustrates a cavity generally rectangular in cross section, which would perform as the insert 60 and could be easier and/or less expensive to manufacture. The outer sealing surface 53 of insert 62 is parallel to the contact surface 24 of the valve seat member 20. This outer sealing surface is like the constant offset insert surfaces in
Insert 64 is generally like insert 62, but with the outer sealing surface 53 changed to a point in cross section, designed to ensure that no proppant particles are trapped between the outer sealing surface and the valve seat member 20. The outer sealing surface does not contribute to the hydraulic seal at the outer perimeter of the metal-to-metal contact area of the valve closure member and valve seat member. Therefore, narrowing the outer sealing surface to allow it to move easily downward through slurries does not compromise the hydraulic seal formed by the inner contact surface. Narrowing the outer sealing surface to a point is not necessary. As the surface moves down through the slurry, the slurry is flowing through the gap between the outer sealing surface and the valve seat. The flow direction of the slurry is nearly perpendicular to the direction of the insert's motion. The average velocity of the slurry flow is higher than the downward velocity of the insert through the slurry. An outer sealing surface width comparable to the diameter of the proppant particles is narrow enough to prevent trapping particles under the outer sealing surface.
Having a narrow outer sealing surface to push down through the slurry to contact the valve seat is preferred for situations in which there is enough valve lag for the plunger to start its suction stroke before the outer sealing surface of the insert comes near enough to the valve seat to start screening particles from the slurry. In such situations, the screened particles would be outside and downstream of the valve apparatus.
Insert 66 shows two more separate modifications of insert 62. The point of the outer sealing surface 53 is moved radially inward to contact the valve seat member 20 inward from its outer perimeter. This prevents the outer sealing surface from deforming over the outer perimeter of the valve seat member 20. In this case the outer perimeter of the insert is defined by the outer point of contact surface 53 and is less than the maximum diameter of the insert material. The geometry of the insert material near the inner sealing surface 51 is also changed. The maximum offset of the inner sealing surface 51 is increased, and the insert shape above the outer perimeter of the inner sealing surface 51 is altered.
U.S. Pat. No. 7,000,632 B2, “Valve Apparatus” by McIntire et al. teaches the use of protrusions located specifically around the outer perimeter of the insert sealing surface to provide a flow of proppant-free fluid specifically from downstream of the valve into and through the valve to flush particles from the gap between the contact surfaces 32 and 24. In the embodiment of the present invention illustrated in
In
It is particularly advantageous to have the same inner radius for each of the two cavity portions as illustrated in
It is well known in the oilfield service industry that proppant particles in a slurry bridge across cylindrical perforations through a wellbore wall when the diameter of the perforation is less than about three particle diameters and the concentration of particles in the slurry approaches or exceeds approximately 20 percent by volume. Cylindrical perforation's diameters must be larger than three proppant diameters for such slurries to be pumped through them successfully.
The abrupt step 81a in surface 24 and the abrupt step 81b in surface 51, at the inner diameters of the cavity portions in
The advantages of a cavity between the insert and valve seat can be obtained using a cavity in the valve insert alone, or using a cavity in the valve seat alone, or using cavity portions in both the valve insert and valve seat. When the cavity is manufactured in the valve seat alone, the resilient insert material is deformed downwards into the cavity to reduce the cavity volume and pump proppant-free fluid back toward the valve seat throat. Having an abrupt step at the inner radius of the cavity and tapering the cavity near its outer diameter is advantageous for a valve apparatus with a cavity in either the valve insert alone or the valve seat alone.
The configuration illustrated in
Another advantage of combining cavity portions in both the insert and the valve seat is that the design provides for a large cavity without having a large disturbance of the flow profile through the valve when the valve is open. Such a disturbance might lead to erosion damage of valve components, especially at high flow rates through the valve and/or when pumping concentrated slurries. The two cavity portions in the insert and seat will also be easier to sweep clear of concentrated proppant during the next plunger stroke.
The cylindrical plug 90 in
The valves are used at a variety of pump rates and with proppant particles of varying diameters. It is not possible to use a different valve spring for each pump rate and proppant diameter in order to tune the valve action and provide the desired amount of valve lag. However, the cylindrical plug 90 in
After the plunger starts its suction stroke, the valve closes on slurry in reverse flow. The outer sealing surface 53 approaches the valve seat surface 24, and screens proppant particles from the slurry in reverse flow, providing a reverse flow of particle-free fluid into the cavity 52. Typical fracturing fluids are shear thinning, and particle free fluids are less viscous than slurries, so the particle-free fluid, entering the cavity in reverse flow before sealing surface 53 reaches the valve seat surface 24, can flow across the surface 24, bypassing the slurry in the cavity above. Particle-free fluid can flow through the cavity and into the strike face area before the valve closes and starts to pump fluid into the strike face area. This enhances the removal of proppant particles from the strike face area between the frustoconical surfaces 32 and 24 of the valve body 30 and the valve seat 20 respectively.
The elements of the valve assembly can be made from a variety of materials depending on design factors such as the type of fluid to be pumped and the pressure rating that is needed. The pump body portion 12 and the valve seat member 20 are usually made of metal. The valve closure member 30 is usually made of metal, but could also be made from composites or other durable materials in an effort to control the weight and balance of the valve closure member 30. The frustoconical contact surfaces 24 and 32 are typically made from a durable metal, while the resilient insert 50 is usually made from an elastomeric material such as a polyurethane. As discussed above, the performance of the present invention can be enhanced with the use of two or more different elastomeric materials (e.g., two different polyurethanes with appropriate properties) to make up the resilient insert 50.
The present invention can be practiced with various manufacturing techniques for the resilient insert member. The resilient insert member can be manufactured in place on the valve closure member, or can be manufactured independently and installed on the valve seat member.
The preceding description of specific embodiments of the present invention is not intended to be a complete list of every possible embodiment of the invention. Persons skilled in this field will recognize that modifications can be made to the specific embodiments described herein that would be within the scope of the present invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2495880 | Volpin | Jan 1950 | A |
| 3039488 | Bowerman | Jun 1962 | A |
| 3057372 | Sutton et al. | Oct 1962 | A |
| 4860995 | Rogers | Aug 1989 | A |
| 4922957 | Johnson | May 1990 | A |
| 4951707 | Johnson | Aug 1990 | A |
| 6701955 | McIntire et al. | Mar 2004 | B2 |
| 7000632 | McIntire et al. | Feb 2006 | B2 |
| 7070166 | Blume | Jul 2006 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20090314979 A1 | Dec 2009 | US |
