Patent Description:
This disclosure relates to downhole pumps designed to avoid a gas locking condition and related methods of operating such downhole pumps.

A sucker rod pump is commonly-used type of artificial lift system for oil and gas wells. However, the performance of a sucker rod pump can be negatively affected by the presence of free gas and limited capabilities for handling such free gas. The target fluid to be lifted from a well by a sucker rod pump is liquid. However, if free gas is present with the produced liquid, then the lifting efficiency of the sucker rod pump can be severely reduced. Some solutions exist for handling free gas in sucker rod pump, but these solutions are expensive and may reduce a volumetric pumping efficiency of the sucker rod pump.

<CIT> describes a pump apparatus for pumping undergound fluids from a well. The pump includes inner and outer chambers, and a float slidable within the outer chamber. A source of compressed air is directed to a valve on the pump. The valve controls the flow of the compressed air into the outer chamber during the pumping cycle, and also controls the opening of a vent during the intake cycle. The float, while sliding up and down within the outer chamber in response to the fluid level within the chamber, activates the valve to begin the pumping of fluid when the chamber is full. When the chamber is empty, the float activates the valve is turn off the compressed air.

<CIT> describes a well pump that has a standing valve seat with a standing valve mounted in a lower end of a barrel. A plunger is carried within the barrel for axial stoking movement. A travelling seat with a travelling valve are mounted in a lower end of the plunger. The travelling valve has a head that lands on the travelling valve seat while the travelling valve is in a closed position. The travelling valve has a stem extending downward from the head through a hole in the travelling seat. The stem is a permanent magnet. Another permanent magnet is carried by the barrel below the travelling magnet.

<CIT> describes a plunger valve for an oil well pump.

<CIT> describes a downhole pump that includes a pump body connected to the lower end of tubing extending inside a well. Pumping is effected below the standing valve by a plunger reciprocating within a slidable barrel.

<CIT> describes a downhole pump that has a barrel with a reciprocating plunger therein. The barrel has a first one-way valve, while the plunger has a second one-way valve. A barrel chamber is formed between the two one-way valves. The barrel chamber expands when the reciprocal movement between the plunger and the barrel is an upstroke movement and then contracts when the reciprocal movement is a downstroke movement. A bypass channel is provided between the barrel and the plunger so as to provide communication around the plunger and its one-way valve. The bypass channel is open when the reciprocal movement is near an end of the upstroke movement. When open, pressure across the plunger can equalize and gas inside the barrel chamber can vent around the plunger and/or pressure can equalize across the plunger one-way valve so as to prevent gas lock and minimize stress on the sucker rods.

This patent relates to downhole pumps that are designed to artificially lift well fluid in a manner that avoids development of a gas locking condition at the downhole pumps without sacrificing volumetric pumping efficiency. An example downhole pump includes a magnet for ensuring that a traveling valve carried on a plunger of the downhole pump is forced to open at the end of an upstroke to vent free gas trapped below the plunger. Escape of the free gas from the downhole pump prevents a gas locking condition during a subsequent downstroke of the downhole pump.

In one aspect, a downhole pump is defined in claim <NUM>.

Embodiments may provide one or more of the following features.

In some embodiments, the housing includes a standing valve disposed at a downhole end of the housing.

In some embodiments, the standing valve includes a platform that defines an opening and a ball that is sized to seat within the opening to close the standing valve to prevent fluid flow into the housing.

In some embodiments, the magnet is perforated to allow fluid flow therethrough.

In some embodiments, the rod passes through the magnet.

In some embodiments, the rod further includes an isolating shaft that magnetically isolates the conducting shaft from the magnet while the conducting shaft is spaced axially apart from the magnet.

In some embodiments, the plunger includes a connector that couples the plunger to the rod, and the connector is perforated to allow fluid flow therethrough.

In some embodiments, the traveling valve includes a platform that defines an opening and a ball that is sized to seat within the opening to close the traveling valve to prevent fluid flow into the plunger.

In some embodiments, the ball is magnetic.

In some embodiments, the traveling valve further includes a stopper that is spaced apart from the platform for limiting an axial movement of the ball.

In another aspect, a method of operating a downhole pump is defined in claim <NUM>.

In some embodiments, the method further includes flowing gas from a fluid reservoir of the housing upward and into the plunger through the traveling valve in the open state.

In some embodiments, the method further includes flowing the gas upward and out of the plunger into the housing through openings in the plunger and flowing the gas upward and out of the housing through openings in the magnet to release the gas from the downhole pump.

In some embodiments, the method further includes flowing liquid from a fluid receptacle of the plunger downward and into the fluid reservoir of the housing through the traveling valve in the open state.

In some embodiments, the method further includes moving the plunger downward through the housing with the traveling valve in the open state.

In some embodiments, the method further includes magnetically isolating the conducting shaft of the rod with an isolating shaft of the rod.

In some embodiments, the method further includes preventing fluid from flowing into the housing at a standing valve disposed at a downhole end of the housing.

In some embodiments, the method further includes lifting a column of fluid disposed above the plunger through the housing to the uphole end of the housing and flowing the fluid out of the housing.

In some embodiments, the method further includes flowing fluid into the housing through a standing valve in an open state at a downhole end of the housing.

In some embodiments, the traveling valve includes a platform that defines an opening and a magnetic ball that is sized to seat within the opening to close the traveling valve to prevent fluid flow into the plunger.

The details of one or more embodiments are set forth in the accompanying drawings and description. Other features, aspects, and advantages of the embodiments will become apparent from the description, drawings, and claims.

<FIG> illustrates an example downhole pump <NUM> that is designed to artificially lift well fluid <NUM> in a manner that avoids development of a gas locking condition at the downhole pump <NUM> without sacrificing volumetric pumping efficiency. In some embodiments, the downhole pump <NUM> may be provided as a modified sucker rod pump that may be disposed within a tubing <NUM> located within a casing at a well of a rock formation. The downhole pump <NUM> includes a housing <NUM> for receiving the well fluid <NUM>, which can include incompressible liquid <NUM> (for example, a mixture of oil and water) and compressible gas <NUM>. The downhole pump <NUM> further includes a plunger <NUM> for lifting well fluid <NUM> out of the housing <NUM> and a rod <NUM> that carries the plunger <NUM>.

The housing <NUM> includes a cylindrical wall <NUM> (for example, a barrel) that defines a fluid reservoir <NUM> for receiving well fluid <NUM> from the tubing <NUM>. The housing <NUM> also includes a magnetic guide <NUM> that is located at an uphole end <NUM> of the housing <NUM>. The magnetic guide <NUM> is formed as a shoulder with a tapered portion <NUM> (for example, having a generally frustoconical shape) that is perforated with openings <NUM> to allow well fluid <NUM> to exit the housing <NUM> at the surface, as will be discussed in more detail below. The magnetic guide <NUM> and the housing <NUM> are separated by an isolator <NUM> (for example, made of ceramic or plastic) that does not transmit magnetic force.

The housing <NUM> further includes a standing valve <NUM> (for example, a ball valve) located at a fixed axial position <NUM> that coincides with a downhole end <NUM> of the housing <NUM>. The standing valve <NUM> is openable to allow well fluid <NUM> to enter the downhole pump <NUM> from the tubing <NUM> and closeable to seal the downhole pump <NUM> to prevent well fluid <NUM> from falling back to the tubing <NUM>. The standing valve <NUM> includes a platform <NUM>, a ball <NUM> that is sized to seat within an opening <NUM> of the platform <NUM> to close the standing valve <NUM>, and a stopper <NUM> (for example, a plate or another component) that is located at a fixed axial position with respect to the wall <NUM> of the housing <NUM> to limit an upward movement of the ball <NUM> within the fluid reservoir <NUM>. The platform <NUM> and the stopper <NUM> may be provided by a cage (not shown) that is secured to the housing <NUM>. The wall <NUM> and the components of the standing valve <NUM> are typically made of one or more non-conducting materials. In some embodiments, the magnetic guide <NUM> may be made of or one or more ferromagnetic materials, such as iron, steel, nickel, and cobalt.

Still referring to <FIG>, the plunger <NUM> includes a cylindrical wall <NUM> (for example, a piston cylinder) that defines a fluid receptacle <NUM> for receiving well fluid <NUM> from the fluid reservoir <NUM> of the housing <NUM>. The plunger <NUM> also includes a connector <NUM> that is located at an uphole end <NUM> of the plunger <NUM>. The connector <NUM> is formed as a tapered structure (for example, having a generally frustoconical shape) that is perforated with openings <NUM> to allow well fluid <NUM> disposed within the fluid receptacle <NUM> to exit the plunger <NUM>, as will be discussed in more detail below.

The plunger <NUM> further includes a traveling valve <NUM> (for example, a ball valve) located at a downhole end <NUM> of the plunger <NUM>. Thus, the traveling valve <NUM> rides on the plunger <NUM>. The traveling valve <NUM> is openable to allow well fluid <NUM> to enter the fluid receptacle <NUM> of the plunger <NUM> and closeable to seal the plunger <NUM> to prevent well fluid <NUM> from entering the plunger <NUM> at the downhole end <NUM>. The traveling valve <NUM> includes a platform <NUM> and a magnetic ball <NUM> that is sized to seat within an opening <NUM> of the platform <NUM> to close the traveling valve <NUM>, and a stopper <NUM> (for example, a plate or another component) that is located at a fixed axial position with respect to the wall <NUM> of the plunger <NUM> to limit an upward movement of the magnetic ball <NUM> within the fluid receptacle <NUM>. The platform <NUM> and the stopper <NUM> may be provided by a cage (not shown) that is secured to the wall <NUM>.

In some embodiments, the magnetic ball <NUM> is made of a diamagnetic material that produces magnetization opposing a magnetic field generated by the magnetic guide <NUM>. In other embodiments, the magnetic ball <NUM> is made of a magnetic material that has a polarization that is different from that of the magnetic guide <NUM>. The stopper <NUM> is coated with a non-conducting material that can extend a magnetic field generated by the magnetic guide <NUM> when the plunger <NUM> is sufficiently close to the magnetic guide <NUM> to attract the magnetic ball <NUM> and accordingly pull the magnetic ball <NUM> upward from the opening <NUM> of the platform <NUM>. For example, upon contact between the conducting shaft <NUM> and the magnetic guide <NUM>, the conducting shaft <NUM> becomes magnetized, and due to different polarizations between the magnetic ball <NUM> and the magnetic guide <NUM>, the magnetic ball <NUM> will be pulled from the opening <NUM>.

The wall <NUM>, connector <NUM>, and platform <NUM> of the plunger <NUM> are typically made of one or more conducting materials, such as steel. The magnetic ball <NUM> is typically made of a permanent magnet or a magnetized metal that has different polarity from that of the magnetic guide <NUM> so that when the entire cage is magnetized, the magnetic ball <NUM> will be forced from the platform <NUM>.

The rod <NUM> is attached to a deployment arm <NUM> and supports the plunger <NUM>. The rod <NUM> includes a lower conducting shaft <NUM> that is attached to the connector <NUM> of the plunger <NUM> and an upper insulating shaft <NUM> that magnetically isolates the conducting shaft <NUM> from the magnetic guide <NUM> until the rod <NUM> is pulled upward to an axial position that locates the conducting shaft <NUM> within or sufficiently close to the magnetic guide <NUM>, as shown in <FIG>. At this position, the conducting shaft <NUM> and the stopper <NUM> of the traveling valve <NUM> extend the magnetic field generated by the magnetic guide <NUM>, and the extended magnetic field acts on the magnetic ball <NUM> to pull (for example, reject) the magnetic ball <NUM> upward from the opening <NUM> of the platform <NUM>. The conducting shaft <NUM> is typically made of a ferromagnetic material, while the isolating shaft <NUM> is typically made of or coated with a ceramic material.

As mentioned above, the downhole pump <NUM> is designed to artificially lift well fluid <NUM> in a manner that avoids development of a gas locking condition within the downhole pump <NUM>. Referring to <FIG>, at an initial step of a fluid lifting operation, the downhole pump <NUM> is deployed to a target location near a bottom hole end of a tubing <NUM> before the tubing <NUM> contains any well fluid <NUM> and with the plunger <NUM> located at a reference position <NUM> within the housing <NUM>. The housing <NUM> of the downhole pump <NUM> is maintained at the desired vertical location within the tubing <NUM> at a seating nipple <NUM> on the tubing <NUM>. The seating nipple <NUM> provides fluid isolation and a holding mechanism that prevents the downhole pump <NUM> from unseating during operation.

Once the well begins to produce well fluid <NUM> such that the well fluid <NUM> collects within the tubing <NUM>, the well fluid <NUM> exerts enough pressure on the standing valve <NUM> and subsequently, on the traveling valve <NUM>, to flow into the housing <NUM> and then into the plunger <NUM> of the downhole pump <NUM>. The well fluid <NUM> continues to accumulate within the housing <NUM> to fill the entire fluid reservoir <NUM>, thereby forming a column <NUM> of well fluid <NUM> above the plunger <NUM>. At this stage, with the fluid reservoir <NUM> of the housing <NUM>, with the fluid receptacle <NUM> the plunger <NUM> filled with well fluid <NUM>, and with the plunger <NUM> located at the reference position <NUM>, the standing valve <NUM> is closed, and the traveling valve <NUM> is open.

Referring to <FIG>, a surface crank (not shown) that is attached to the deployment arm <NUM> is then operated to lift the plunger <NUM> towards the surface in an upward movement (for example, an upstroke). Lifting of the plunger <NUM> transports the column <NUM> of well fluid <NUM> located above the plunger <NUM> to the surface, where the well fluid <NUM> is pushed through the openings <NUM> in the magnetic guide <NUM> to exit the downhole pump <NUM>. Lifting of the plunger <NUM> progressively lowers the fluid pressure within a region <NUM> of the fluid reservoir <NUM> between the plunger <NUM> and the standing valve <NUM> (for example, due to a suction force generated by the upward moving plunger <NUM>). Once the fluid pressure within the region <NUM> falls below the fluid pressure below the standing valve <NUM>, the standing valve <NUM> opens to allow well fluid <NUM> below the standing valve <NUM> to enter the housing <NUM>. For example, the well fluid <NUM> below the standing valve <NUM> pushes the ball <NUM> upward and out of the opening <NUM> of the platform <NUM> to flow into the housing <NUM>. The ball <NUM> moves vertically until it abuts the stopper <NUM> and is maintained in position adjacent the stopper <NUM> by the upward flow of well fluid <NUM> as the plunger <NUM> continues to be lifted through the housing <NUM>.

Referring to <FIG>, as the plunger <NUM> continues to be lifted during the upstroke and the well fluid <NUM> continues to flow into the housing <NUM>, the fluid pressure within the region <NUM> is lower than a fluid pressure within the fluid receptacle <NUM> of the plunger <NUM> such that the traveling valve <NUM> remains closed. Referring to <FIG>, once the conducting shaft <NUM> of the rod <NUM> reaches the axial position of the magnetic guide <NUM>, the magnetic field generated by the magnetic guide <NUM> is extended by the conducting shaft <NUM> and the stopper <NUM> to reach the magnetic ball <NUM>. Under the attractive force of the extended magnetic field, the magnetic ball <NUM> is pulled upward from the opening <NUM> of the platform <NUM> to open the traveling valve <NUM>. The magnetic ball <NUM> abuts the stopper <NUM> and is maintained in position to maintain the traveling valve <NUM> in an open state as long as the conducting shaft <NUM> is sufficiently close to the magnetic guide <NUM>.

With the traveling valve <NUM> open at the end of the upstroke, the incompressible liquid <NUM> (for example, a mixture of oil and water) within fluid receptacle <NUM> flows downward out of the plunger <NUM> and into the region <NUM> of the fluid reservoir <NUM>, while the compressible gas <NUM> within the region <NUM> of the fluid reservoir <NUM> flows upward and into the plunger <NUM>. The gas <NUM> continues to flow upward through the openings <NUM> of the plunger <NUM> and subsequently through the openings <NUM> of the magnetic guide <NUM> to exit the downhole pump <NUM> at the surface. Accordingly, gas <NUM> that would have otherwise been trapped within the region <NUM> of the fluid reservoir <NUM> is permitted to escape the housing <NUM> of the downhole pump <NUM> at the surface. Referring still to <FIG>, while the gas <NUM> is vented from the downhole pump <NUM> at the end of the upstroke, flow of liquid <NUM> from the plunger <NUM> into the region <NUM> of the fluid reservoir <NUM> increases the fluid pressure within the fluid reservoir <NUM> to a level that exceeds the fluid pressure of the well fluid <NUM> below the standing valve <NUM> to force the standing valve <NUM> closed again.

At the end of the upstroke, with the traveling valve <NUM> remaining open and with the standing valve <NUM> remaining closed, the plunger <NUM> is moved downward through the housing <NUM> in a downward movement (for example, a downstroke). Referring to <FIG>, during the downstroke, gas <NUM> within the region <NUM> continues to flow upward into the plunger <NUM>, out of the plunger <NUM> through the openings <NUM> in the connector <NUM>, further upward into the column <NUM>, and out of the housing <NUM> through the openings <NUM> in the magnetic guide <NUM>. During the downstroke, the plunger <NUM> also displaces liquid <NUM> within the region <NUM> of the fluid reservoir <NUM> to the column <NUM> of well fluid <NUM> above the plunger <NUM> for later transport of the column <NUM> to the surface during a subsequent upstroke. The standing valve <NUM> remains closed during the downstroke because the fluid pressure of the well fluid <NUM> within the fluid reservoir <NUM> of the housing <NUM> remains higher than the fluid pressure of the well fluid <NUM> below the standing valve <NUM>.

By the end of the downstroke, the fluid pressure of the well fluid <NUM> above the traveling valve <NUM> (for example, within the column <NUM> above the plunger <NUM> and within the fluid receptacle <NUM> of the plunger <NUM>) has exceeded the fluid pressure of the well fluid <NUM> below the traveling valve <NUM> (for example, in the region <NUM> of the fluid reservoir <NUM>) to force the traveling valve <NUM> closed again, as shown in <FIG>. With the fluid reservoir <NUM> filled with the column <NUM> of well fluid <NUM> above the plunger <NUM>, the plunger <NUM> can be lifted in a next upstroke to transport the column <NUM> of well fluid <NUM> to the surface, as already discussed with respect to <FIG>. The downhole pump <NUM> can be continually and cyclically operated in as described with respect to <FIG> to lift well fluid <NUM> out of the tubing <NUM> (for example, and therefore out of the surrounding well) in an efficient manner (for example, to harvest well fluid <NUM> containing a relatively high fraction of liquid <NUM> and a relatively low fraction of gas <NUM> since much gas <NUM> has already escaped the housing <NUM> of the downhole pump <NUM> during a previous downstroke).

Opening of the traveling valve <NUM> (for example, as a result of the magnetic field generated by the magnetic guide <NUM>) to allow escape of free compressible gas <NUM> at the end of an upstroke and during an immediately following downstroke prevents a gas-lock condition in which compressible gas <NUM> trapped beneath the plunger <NUM> would otherwise be compressed by the plunger <NUM> (for example, with the traveling valve <NUM> closed) during the downstroke. With the gas <NUM> trapped beneath the plunger <NUM> and compressed at a relatively high fluid pressure at the end of the downstroke, a subsequent upstroke would merely cause the trapped gas <NUM> to expand upward within the region <NUM> without reducing the fluid pressure within the region <NUM> enough to allow the standing valve <NUM> to open to permit inflow of additional well fluid <NUM> into the housing <NUM> of the downhole pump <NUM> for ongoing lifting of the well fluid <NUM> out of the well <NUM>.

Under these conditions, the downhole pump <NUM> (for example, the standing valve <NUM> of the downhole pump <NUM>) is in a "locked" state that prevents fluid intake. Forced opening of the traveling valve <NUM> at the end of the upstroke thus prevents a gas locking condition and accordingly provides the downhole pump <NUM> with an extended operating window for operation at wells with relatively high gas to liquid ratios using a simple magnetic mechanism that is more cost-effective than alternative complicated mechanisms of conventional downhole gas handling pumps. This functionality thus provides relatively high production capacity of the downhole pump <NUM>, relatively high volumetric efficiency of the downhole pump <NUM>, maximization of overall system efficiency, and avoidance of broader system-level problems associated with unwanted gas production. In some examples, a conventional sucker rod pump or other pump may be modified or retrofitted with the necessary components at a relatively low cost to be converted into a form of the downhole pump <NUM>.

<FIG> is a flow chart illustrating an example method <NUM> of operating a downhole pump (for example, the downhole pump <NUM>). In some embodiments, the method <NUM> includes a step <NUM> for lifting a plunger (for example, the plunger <NUM>) of the downhole pump through a housing (for example, the housing <NUM>) of the downhole pump with a rod (for example, the rod <NUM>) of the downhole pump that supports the plunger. In some embodiments, the method <NUM> further includes a step <NUM> for locating a conducting shaft (for example, the conducting shaft <NUM>) of the rod adjacent a magnet (for example, the magnetic guide <NUM>) of the housing disposed at an uphole end (for example, the uphole end <NUM>) of the housing. In some embodiments, the method <NUM> further includes a step <NUM> for extending a magnetic field generated by the magnet with the conducting shaft to reach a traveling valve (for example, the traveling valve <NUM>) of the plunger disposed at a downhole end (for example, the downhole end <NUM> of the plunger. In some embodiments, the method <NUM> further includes a step <NUM> for magnetically forcing the traveling valve into an open state with the magnetic field.

Claim 1:
A downhole pump (<NUM>) comprising:
a housing (<NUM>) comprising a magnet (<NUM>) disposed at an uphole end of the housing;
a plunger (<NUM>) disposed within the housing and comprising a traveling valve (<NUM>) disposed at a downhole end of the plunger; and characterized in that the downhole pump comprises
a rod (<NUM>) comprising a conducting shaft (<NUM>) attached to an uphole end of the plunger and configured to extend a magnetic field generated by the magnet when the conducting shaft is positioned adjacent the magnet to magnetically force the traveling valve from a closed state in which the traveling valve seals the plunger into an open state in which the traveling valve allows fluid to enter the plunger.