Patent Description:
Electrical submersible pumps (ESP) are commonly used in hydrocarbon producing wells. An ESP includes a pump driven by an electrical motor filled with a motor lubricant. A seal section connected between the motor and the pump has a shaft seal to retard the entry of well fluid into contamination with the motor lubricant. The seal section also typically has a pressure equalizer that reduces a pressure differential between the motor lubricant and exterior well fluid. The pressure equalizer may be an elastomeric bag or a metal bellows. Motor lubricant in communication with motor lubricant in the motor fills the pressure equalizer. A well fluid port admits well fluid to a pressure equalizing chamber on the exterior of the pressure equalizer, causing the motor lubricant pressure in the motor to substantially equal the hydrostatic well fluid pressure.

During operation, the temperature of the motor will elevate, which causes the motor lubricant to expand. If the pressure equalizer is full and cannot expand more, a check valve will open to expel some of the motor lubricant into the pressure equalizing chamber. The check valve has one side exposed to the well fluid in the pressure equalizing chamber and an opposite side in communication with the motor lubricant in the pressure equalizer. The check valve needs to reseat when the motor cools down to keep well fluid out of the motor. The check valve is susceptible to damage from contact with well fluids in the pressure equalizing chamber. Contact with well fluid can foul the check valve mechanism with debris or degrade the components of the check valve due to material compatibility issues. <CIT> discloses a motor oil-filled protector device for use with an electric submergible pump motor, including a tubular extension to inhibit contaminated fluid from contacting an internal pressure relief valve. A motor oil pressure relief valve within the protector has an intake in fluidic communication with at least one motor oil-filled expandable chamber and has a discharge in fluidic communication with a fluid-filled section of the housing. Over a period of time, wellbore fluids tend to leak into and displace motor oil within the fluid-filled section. A tubular extension is connected to the discharge of the pressure relief valve and extends into a lower portion of the fluid filled section. When motor oil is discharged from the pressure relief valve, such motor oil will tend to stay within the tubular extension, because the oil is lighter than the wellbore fluids, and thereby inhibit the wellbore fluids from contacting and possibly harming the operation of the pressure relief valve. <CIT> discloses a seal section for a submersible well pump assembly having a housing for connection between a pump and a motor. A central radial bearing support rotatably supports a drive shaft and defines upper and lower chambers in the housing. A well fluid passageway leads from an exterior portion of the housing to the upper chamber. Upper and lower isolation tubes extend around the shaft within the upper and lower chambers, defining an annular passage for fluid communication with lubricant contained in the motor. A bladder surrounds the upper isolation tube for separating lubricant from well fluid in the upper chamber. A labyrinth tube within the bladder has an upper end in fluid communication with a labyrinth port leading through the upper isolation tube and a lower end in fluid communication with the lower chamber.

The claimed invention refers to a submersible well pump assembly as well as to a method of retarding entry of a well fluid into contact with a pressure equalizer motor lubricant check valve in a check valve passage of a pump end of a seal section of a submersible pump assembly as set forth in independent claims <NUM> and <NUM>.

The submersible well pump assembly for pumping well fluid includes a pump and a motor that drives the pump, the motor being filled with a motor lubricant. A housing having a longitudinal housing axis is operatively mounted to the motor. An expandable and contractible pressure equalizer within the housing defines a pressure equalizing chamber in the housing that surrounds an exterior of the pressure equalizer. A motor lubricant communication path communicates motor lubricant from the motor to an interior of the pressure equalizer. A well fluid inlet port in the housing admits well fluid into the pressure equalizing chamber. A check valve passage leads from the motor lubricant communication path to the pressure equalizing chamber. A dip tube has a dip tube inlet at the check valve passage and extends from the check valve passage into the pressure equalizing chamber. The dip tube has a dip tube outlet at a lower elevation relative to the housing axis than the dip tube inlet. A check valve in the check valve passage is at a higher elevation relative to the housing axis than the dip tube inlet and configured to expel motor lubricant from the motor lubricant communication path into the dip tube inlet when the pressure of the motor lubricant in the interior of the pressure equalizer is at a selected level above the pressure of the well fluid in the pressure equalizing chamber.

The dip tube may be filled initially with motor lubricant prior to installing the assembly in a well.

According to the claimed invention, the dip tube has at least one crest and at least one valley between the dip tube inlet and the dip tube outlet, the crest being at a higher elevation relative to the housing axis than the valley. The dip tube may have a plurality of crests, the crests being separated from each other by valleys of a lower elevation relative to the housing axis than the crests.

In one embodiment, the dip tube extends at least partially around the housing axis and has a labyrinth passage between the dip tube inlet and the dip tube outlet. The labyrinth passage has upper portions that are at higher elevations relative to the housing axis than lower portions. In the embodiment shown, the dip tube extends more than half way around the longitudinal axis of the housing and has an undulating configuration between the dip tube inlet and the dip tube outlet.

In the embodiments shown, a guide tube extends through the housing along the housing axis. A drive shaft extends through the guide tube. The pressure equalizer comprises an elastomeric bag having a neck sealed to the guide tube, the neck defining a bag shoulder. The dip tube outlet is located at a higher elevation relative to the housing axis than the bag shoulder.

While the disclosure will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the disclosure to that embodiment. On the contrary, it is intended to cover all embodiments falling within the scope of the invention as defined by the appended claims.

The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, the scope of the invention being solely defined by the appended claims.

In an embodiment, usage of the term "about" includes +/- <NUM>% of the cited magnitude. In an embodiment, usage of the term "substantially" includes +/- <NUM>% of the cited magnitude.

It is to be further understood that the scope of the present invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, but only by the appended claims. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.

<FIG> illustrates an electrical submersible well pump (ESP) <NUM> of a type commonly used to lift hydrocarbon production fluids from wells. ESP <NUM> has a centrifugal pump <NUM> with intake ports <NUM> for drawing in well fluid. Pump <NUM> could be made up of several similar pumps secured together in tandem by threaded fasteners or bolts, with intake ports <NUM> being in the lowermost pump. Intake ports <NUM> could also be in a separate module connected to pump <NUM>. Further, if a rotary gas separator is employed below pump <NUM>, intake ports <NUM> would be in the gas separator.

An electrical motor <NUM> is operatively mounted to and drives pump <NUM>. Motor <NUM> contains a dielectric motor lubricant for lubricating the bearings within. A seal section <NUM> has a pressure equalizer that communicates with the lubricant in motor <NUM> and with the well fluid for reducing a pressure differential between the lubricant in motor <NUM> and the exterior well fluid. In this example, the pressure equalizing portion of seal section <NUM> locates between motor <NUM> and pump intake ports <NUM>. Alternately, the pressure equalizing portion of seal section <NUM> could be located below motor <NUM>, and other portions of seal section <NUM> could be above motor <NUM>. The terms "upward," "downward," "above," "below" and the like are used only for convenience as ESP <NUM> may be operated in other orientations than vertical.

A string of production tubing <NUM> suspended within casing <NUM> supports ESP <NUM>. In this example, pump <NUM> discharges into production tubing <NUM>. Alternately, coiled tubing could support ESP <NUM>, in which case pump <NUM> would discharge into the annulus around the coiled tubing. Motor <NUM> in that case would be located above pump <NUM>. The power cable for motor <NUM> would be within the coiled tubing instead of alongside production tubing <NUM>.

Referring to <FIG>, seal section <NUM> has a tubular housing <NUM> that includes a head or pump end <NUM> and a base or motor end <NUM>, each secured by threads to the tubular portion of housing <NUM>. When connected into ESP <NUM> (<FIG>), housing pump end <NUM> will be closer to pump <NUM> than it is to motor <NUM> and may be directly connected to the end of pump <NUM> having intake ports <NUM>. Similarly, housing motor end <NUM> will be closer to motor <NUM> than it is to pump <NUM> and may be connected directly to motor <NUM>. Alternately, housing motor end <NUM> could be connected to another seal section in tandem or to other pressure equalizing portions of seal section <NUM>.

Housing <NUM> has a longitudinal axis <NUM> extending concentrically through housing pump end <NUM> and housing motor end <NUM>. A drive shaft <NUM> with splined ends is rotated by motor <NUM> (<FIG>) and extends along axis <NUM> through shaft passages <NUM> in housing pump end <NUM> and housing motor end <NUM>. Bearings <NUM> in housing pump end <NUM> and in motor end <NUM> radially support shaft <NUM>. Bearings <NUM> are located in shaft passages <NUM> and allow motor lubricant <NUM> to flow through them.

A primary shaft seal <NUM> seals around shaft <NUM> within housing pump end <NUM>. In this embodiment, primary shaft seal <NUM> is a mechanical face seal that may be conventional. One side of primary shaft seal <NUM> will be immersed in well fluid and the other side in contact with motor lubricant <NUM>.

Housing <NUM> has a pressure equalizer <NUM> between housing pump end <NUM> and housing motor end <NUM>. In this example, pressure equalizer <NUM> comprises a flexible elastomeric bag or container. Alternately, metal bellows or labyrinth tubes and other labyrinth arrangements may serve as pressure equalizers. The lower end of bag <NUM> seals to housing motor end <NUM>, and the upper end of bag <NUM> is in a sealing arrangement with housing pump end <NUM>. The space between the exterior of bag <NUM> and housing <NUM> comprises a pressure equalizing chamber <NUM>. A well fluid port <NUM> admits well fluid <NUM> into motor lubricant equalizing chamber <NUM>. Well fluid port <NUM> is located at the bottom of pressure equalizing chamber <NUM> in this embodiment. This placement introduces well fluid <NUM> below the more buoyant motor lubricant <NUM> in pressure equalizing chamber <NUM>.

A guide tube <NUM> extends coaxially through bag <NUM> around shaft <NUM>. Guide tube <NUM> has a lower end sealed to housing motor end <NUM> in shaft passage <NUM>. Guide tube <NUM> has an upper end sealed to housing pump end <NUM> in shaft passage <NUM> in housing pump end <NUM>. In this example, the upper end of bag <NUM> has a neck <NUM> that seals around guide tube <NUM> at a place below housing pump end <NUM>. A shoulder <NUM> connects neck <NUM> to the remaining portion of pressure equalizer <NUM>.

Guide tube <NUM> has a larger inner diameter than an outer diameter of shaft <NUM>, creating a shaft annulus <NUM> between shaft <NUM> and guide tube <NUM>. One or more guide tube ports <NUM> extend through the side wall of guide tube <NUM> within the interior of bag <NUM>. Guide tube ports <NUM> are closer to the upper end of bag <NUM> than to the lower end of bag <NUM> in this example.

Motor lubricant <NUM> in motor <NUM> (<FIG>) is free to flow along a motor lubricant communication path into the interior of bag <NUM>. The motor lubricant communication path passes through or around bearing <NUM> in the portion of shaft passage <NUM> within motor end <NUM>. The communication path includes shaft annulus <NUM> and guide tube ports <NUM>, which lead into the interior of bag <NUM>. The communication path also allows motor lubricant <NUM> to pass through or around bearing <NUM> in pump end <NUM> up to a lower side of primary shaft seal <NUM>.

Threaded bolt holes <NUM> may be formed in the upper side of housing pump end <NUM> for connecting seal section <NUM> to another module, such as pump <NUM> (<FIG>). Alternately, the connection could be made by a rotatable threaded collar.

A check valve passage <NUM> within housing pump end <NUM> leads from shaft passage <NUM> laterally outward, then downward through a lower end of housing pump end <NUM> into pressure equalizing chamber <NUM>. A check valve <NUM>, which may be conventional, is mounted in check valve passage <NUM> near its lower end. In an alternative example outside the scope of the claimed invention, check valve <NUM> could be secured to and extend downward from the lower end of check valve passage <NUM> into pressure equalizing chamber <NUM>. In that instance, check valve <NUM> would be below the downward facing lower end of pump end <NUM>. Check valve <NUM> is schematically illustrated to comprise a ball urged upward against a seat by a spring. The upper side of check valve <NUM> is exposed to motor lubricant <NUM> in check valve passage <NUM>.

A labyrinth or dip tube <NUM> has a dip tube inlet <NUM> secured to a lower portion of check valve passage <NUM> below check valve <NUM>. Dip tube <NUM> extends downward into pressure equalizing chamber <NUM> and has a dip tube outlet <NUM> that is at an elevation below dip tube inlet <NUM>. Dip tube outlet <NUM> is closer to bag <NUM> than dip tube inlet <NUM>. In this embodiment, dip tube <NUM> extends at least partially around guide tube <NUM> and has an undulating or serpentine configuration defining a tortuous or labyrinth flow passage <NUM> through it. In this example, as shown in <FIG>, dip tube <NUM> extends circumferentially more than <NUM> degrees from dip tube inlet <NUM> to dip tube outlet <NUM>. Dip tube <NUM> is located in a space between pressure equalizer shoulder <NUM> and housing pump end <NUM>. Dip tube outlet <NUM> is illustrated as being above pressure equalizer shoulder <NUM>.

In this example, dip tube <NUM> has several upright portions <NUM> that may be vertical or parallel to axis <NUM> (<FIG>) as shown. Alternately, upright portions <NUM> may slope upward and downward. Upright portions <NUM> join valleys <NUM> to crests <NUM>, which are at higher elevations than crests <NUM>. Valleys <NUM> and crests <NUM> extend circumferentially and may be curved or straight as illustrated. In this embodiment, dip tube <NUM> is located entirely above bag <NUM>.

Prior to installing ESP <NUM>, motor <NUM> and seal section <NUM> will be filled with motor lubricant <NUM>. The filling procedure results in motor lubricant <NUM> being initially within shaft passage <NUM> in motor end <NUM>, shaft annulus <NUM>, the interior of bag <NUM>, shaft passage <NUM> in pump end <NUM>, check valve passage <NUM>, dip tube <NUM>, and in pressure equalizing chamber <NUM>. As ESP <NUM> is lowered into casing <NUM>, well fluid <NUM> in casing <NUM> will enter well fluid inlet port <NUM> into contact with motor lubricant <NUM> in pressure equalizing chamber <NUM>. Well fluid <NUM> is often primarily water and does not mix easily with motor lubricant <NUM>, which is lighter in density. Consequently, well fluid <NUM> tends to gravitate to a lower portion of pressure equalizing chamber <NUM>.

The hydrostatic pressure of well fluid <NUM> and motor lubricant <NUM> within pressure equalizing chamber <NUM> exerts a contracting force on bag <NUM>, causing motor lubricant <NUM> within the interior of bag <NUM>, shaft annulus <NUM>, shaft passages <NUM>, check valve passage <NUM> and in dip tube <NUM> to pressure equalize. Even though the pressures on the upper and lower sides of check valve <NUM> are substantially the same, check valve <NUM> will remain closed because of the bias force of its spring.

When ESP <NUM> begins to operate, motor <NUM> will get hotter, which causes motor lubricant <NUM> to expand in volume. When bag <NUM> is fully expanded, the pressure of motor lubricant <NUM> in bag <NUM> will rise above the hydrostatic pressure of well fluid <NUM> in pressure equalizing chamber <NUM>. When the differential pressure on check valve <NUM> reaches a selected level, check valve <NUM> will open, allowing motor lubricant <NUM> in check valve passage <NUM> to flow downward into dip tube <NUM>, as indicated by the arrows. The differential that causes check valve <NUM> to open may be small, only several kPa (a few pounds per square inch). The flow of motor lubricant <NUM> into dip tube <NUM> results in some motor lubricant <NUM> flowing out dip tube outlet <NUM> into pressure equalizing chamber <NUM>.

When ESP <NUM> is shut down, motor <NUM> cools and motor lubricant <NUM> contracts. The pressure differential on check valve <NUM> drops to a level below its set amount, causing check valve <NUM> to close. Some of the motor lubricant <NUM> and well fluid <NUM> within pressure equalizing chamber <NUM> may migrate upward into dip tube outlet <NUM>. The fluid entering well fluid outlet <NUM> may include droplets of well fluid <NUM>. It will be difficult for any well fluid <NUM> entering well fluid outlet <NUM> to migrate through the upright portions <NUM>, valleys <NUM> and crests <NUM> because the well fluid <NUM> is heavier than the motor lubricant <NUM> within dip tube <NUM>. The well fluid <NUM> would have to migrate upward and downward in dip tube passage <NUM> as it passes through upright portions <NUM>, valleys <NUM> and crests <NUM> toward dip tube inlet <NUM>. The upward and downward portions of flow passage <NUM> in dip tube <NUM> reduces the chance for well fluid <NUM>, along with debris, from coming into contact with the lower side of check valve <NUM>.

In the alternate embodiment of <FIG> which is not according to the claimed invention, dip tube <NUM> is a straight tube with its outlet <NUM> directly below its inlet <NUM>. A central longitudinal axis <NUM> of dip tube <NUM> is parallel to and offset from housing longitudinal axis <NUM>. Dip tube <NUM> may have different lengths, but in this embodiment, its outlet <NUM> is above pressure equalizer shoulder <NUM> (<FIG>). Dip tube <NUM> will be directly below check valve <NUM>. Check valve <NUM> may be the same as check valve <NUM> (<FIG>), having a spring <NUM> that urges a movable element, such as a ball <NUM>, upward against a seat. Dip tube <NUM> operates in the same manner as dip tube <NUM> (<FIG>), requiring any well fluid <NUM> that may enter dip tube outlet <NUM> to migrate upward through the less dense motor lubricant <NUM> in dip tube <NUM>. Dip tube <NUM> retards well fluid <NUM> from contacting the seat of check valve <NUM>.

The present disclosure described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While two embodiments of the disclosure have been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results.

Claim 1:
A submersible well pump assembly (<NUM>) for pumping well fluid, comprising:
a pump (<NUM>);
a motor (<NUM>) that drives the pump, the motor being filled with a motor lubricant (<NUM>);
a housing (<NUM>) having a longitudinal housing axis (<NUM>) and operatively mounted to the motor;
an expandable and contractible pressure equalizer (<NUM>) within the housing, defining a pressure equalizing chamber (<NUM>) in the housing that surrounds an exterior of the pressure equalizer;
a motor lubricant communication path (<NUM>, <NUM>) for communicating motor lubricant from the motor to an interior of the pressure equalizer;
a well fluid inlet port (<NUM>) in the housing for admitting well fluid into the pressure equalizing chamber;
a check valve passage (<NUM>) leading from the motor lubricant communication path to the pressure equalizing chamber;
a check valve (<NUM>) in the check valve passage configured to expel motor lubricant from the motor lubricant communication path into the pressure equalizing chamber when the pressure of the motor lubricant in the interior of the pressure equalizer is at a selected level above the pressure of the well fluid in the pressure equalizing chamber;
a dip tube (<NUM>) having a dip tube inlet (<NUM>) at the check valve passage and extending from the check valve passage into the pressure equalizing chamber, the dip tube having a dip tube outlet (<NUM>) that, when the dip tube is in a mounted state, lies at a lower elevation relative to the housing axis than the dip tube inlet; and wherein:
the check valve is at a higher elevation relative to the housing axis than the dip tube inlet; and characterized in that:
the dip tube has at least one crest (<NUM>) and at least one valley (<NUM>) between the dip tube inlet and the dip tube outlet, the crest being at a higher elevation relative to the housing axis than the valley when the dip tube is in the mounted state.