Patent Description:
In a hydrocarbon well, an electric submersible pump may be used to move wellbore fluid from downhole to the surface, such as by using artificial lift for hydrocarbon extraction. The electric submersible pump may be used to manage the pressure of the fluid or the flow of fluid extracted from the wellbore. Patent document <CIT> discloses an electric submersible pump comprising a seal between the electric motor and the pump.

The electric submersible pump may contain one or more electric motors, one or more seals, and one or more pumps, and can be positioned downhole in a wellbore. The electric motor is susceptible to premature failure due to an electrical fault caused by infiltration of wellbore fluids into the electric motor. The infiltration of wellbore fluid into the motor can be a result of a seal failure during the operation of the electrical submersible pump.

Certain aspects and examples of the present disclosure relate to a seal bag that includes multiple layers and that can be used in a seal for an electric submersible pump. The multiple layers can include an inner layer and an outer layer. In case of a tear in the seal, the inner layer can swell to seal the tear against an outer housing of the seal and effectively self-heal the tear. For example, the inner layer may be exposed to motor oil in a chamber defined by the seal and the motor oil may be for an electric motor of the electric submersible pump. A tear may allow water or other polar substances into the chamber. A polar substance, of which water is an example, can be a covalently bonded substance that contains partially positive and negative charges. In response to contact with the water or other polar substance, the inner layer can expand, such as by swelling, against the outer layer and the outer housing to seal the tear.

The seal bag can provide a barrier to protect the electric motor and motor oil from contamination by the wellbore fluid. A tear may develop in the seal bag downhole that can result in wellbore fluid entering the chamber holding the motor oil. The seal bag may have the ability to self-heal when a tear develops in the seal bag. The ability to self-heal the tear can result in an increased functional life of the electric submersible pump and prevent tears from impeding the electric submersible pump from performing downhole operations.

For example, wellbore fluid that contaminates motor oil within the electric motor and seal of an electric submersible pump can cause the motor oil to degrade and can cause the electric submersible pump to fail due to electrical failure or improper bearing operation. A seal bag that fails, such as by having a tear, can provide a path for wellbore fluid ingress. An elastomer seal bag can be used that has multiple plies or layers as a positive barrier within the seal. In one example, an outer layer is resistant to water, other polar substances, and hydrocarbons in wellbore fluid. And, an inner layer can include a polymer that can swell in response to contact with water and polar substances. The seal bag can provide a self-healing capability to the elastomer seal bag and can increase resistance to wellbore fluid infiltrating the electric submersible pump due to a tear in the elastomer seal.

In an example, an elastomer seal bag can include multiple layers or plies and can be installed in a seal. The layers can include an outer layer that may be resistant to polar fluids and hydrocarbons found in wellbore fluid and can include an inner layer that may be a water-sensitive or polar-substance sensitive polymer that can swell. The seal can provide a positive barrier between wellbore fluid and oil contained within the seal. When the integrity of the outer layer of the elastomer seal bag is compromised, contact between the inner layer of the bag and water or other polar substance in the wellbore fluid can cause the polymer of the inner layer to swell to completely or partially seal the tear and prevent or slow the ingress of wellbore fluid into the seal. The self-healing quality of the elastomer seal bag can reduce the contamination of the oil contained within the seal. Using a multi-ply elastomer seal bag according to some examples can increase the resiliency of the seal section and can increase the electric submersible pump run-life. For example, when the integrity of the bag is compromised and the inner layer contacts wellbore fluid, the polymer material of the inner layer can swell as a result of the reaction to the wellbore fluid and can seal the tear in the seal bag.

In some examples, a seal bag includes layers in addition to the outer layer and the inner layer. For example, the seal bag may include an additional layer between the inner layer and outer layer that may provide stiffness, permeability resistance, or other beneficial effects to the characteristics of the elastomer bag. Or, the middle layer may be considered to be a first inner layer that is made from a material that swells in response to contact with polar substances. In that example, the inner layer may be considered to be a second inner layer that may be made from a material that swells in response to contact with polar substances or from a different material that does not swell. The first inner layer can be a layer to provide self-healing in case of a tear.

In addition, a seal bag has an outer layer with a slick or anti-stick surface that can promote movement of the seal bag along an inner surface of the seal housing and that may prevent friction coupling that can result in sticking and bunching of the bag that can lead to the tearing of the seal bag.

Illustrative examples are given to introduce the reader to the general subject matter discussed herein and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional features and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative aspects, but, like the illustrative aspects, should not be used to limit the present disclosure.

<FIG> is a schematic of a wellbore <NUM> in which an electric submersible pump <NUM>, with a seal <NUM> that includes a bag, is positioned to communicate with surface equipment according to one example of the present disclosure. The wellbore <NUM> can be in a subterranean environment <NUM> and the electric submersible pump <NUM> may provide artificial lift to wellbore fluid by moving wellbore fluid from a position downhole to a surface <NUM> through a wellhead <NUM>. Artificial lift can be employed during the production phase of a hydrocarbon well after subterranean pressures have abated and a free-flow stage of the well has ended. The electric submersible pump <NUM> in the wellbore <NUM> can provide artificial lift to maintain the production rate from the wellbore <NUM>.

The electric submersible pump <NUM> can have an electric motor <NUM> coupled to a pump <NUM> by a shaft to provide mechanical power to the pump <NUM> from the electric motor <NUM>. The pump <NUM> may have an intake <NUM> and a discharge <NUM>. The intake <NUM> can allow the pump <NUM> to draw in wellbore fluid and direct the wellbore fluid toward the surface <NUM> through the discharge <NUM>. The electric motor <NUM> may be electrically coupled to a variable speed controller <NUM> by a cable <NUM>. The variable speed controller <NUM> can provide both power and control signals to the electric motor <NUM> through the cable <NUM>. The variable speed controller <NUM> and the wellhead <NUM> may be positioned above the surface <NUM>.

Between the pump <NUM> and the electric motor <NUM> is at least one seal <NUM> that can contain at least one seal bag positioned inside the seal <NUM>. The seal <NUM> can transfer torque to the pump <NUM> from the electric motor <NUM>. The seal <NUM> can prevent wellbore fluid from contaminating motor oil for the electric motor <NUM> through isolation, equalization, and expansion. The seal <NUM> may also prevent pump-shaft thrust from impacting motor performance through force absorption. The seal <NUM> and the seal bag can isolate the electric motor <NUM> from wellbore fluid that can otherwise cause electrical and mechanical faults of the electric motor <NUM>.

Seal bags can be positioned in the seal <NUM> in one or more orientations. An example of an orientation is a series installation in which two or more seal bags can be positioned independently and can provide redundant isolation of the electric motor <NUM>. Another example of an orientation is a parallel installation in which two or more bags may be coupled together. The parallel installation can allow greater expansion of the motor oil given certain conditions in the wellbore <NUM>. And, a parallel installation can reduce the redundant isolation of the electric motor <NUM>. In either orientation, the seal bag can include multiple layers that can self-heal a tear in the seal <NUM> in the downhole environment.

<FIG> is a partial cross-sectional schematic of a seal <NUM> that can be installed in an electric submersible pump and that includes seal bags <NUM>-<NUM>, each with multiple layers according to one example of the present disclosure. The seal <NUM> is depicted as having three sections defined between mechanical seals <NUM>-<NUM> and including seal bags <NUM>-<NUM>. Each of the seal bags <NUM>-<NUM> is positioned within an outer housing <NUM>. Although three seal bags <NUM>-<NUM> are shown in <FIG>, a seal according to other examples can have any number of seal bags, including one bag, two bags, or more than three bags.

The seal sections can each include an interdigitated path, such as interdigitated path <NUM>. An interdigitated path may also be referred to as a labyrinth chamber. The interdigitated path <NUM> may be located in the seal bag <NUM>. In operation, the interdigitated path <NUM> may be filled with motor oil for an electric motor of an electric submersible pump. In the case of a tear, wellbore fluid may enter the seal <NUM> and displace the motor oil until the pressure between the two equalizes. The interdigitated path <NUM> can control the flow of wellbore fluid within the seal <NUM> for the purpose of limiting contamination of the motor oil with the wellbore fluid.

The seal <NUM> also includes a guide tube <NUM> in which is positioned a shaft <NUM>. The shaft <NUM> can couple an electric motor to a pump of the electric submersible pump. The mechanical seals <NUM>-<NUM> can prevent fluid from entering the seal <NUM> around the shaft <NUM> through the guide tube <NUM>. The seal bags <NUM>-<NUM> can further isolate the electric motor and prevent ingress of wellbore fluid due to the failure of one of the mechanical seals <NUM>-<NUM>.

For example, the seal bags <NUM>-<NUM> may be elastomeric and can provide a barrier to isolate the wellbore fluid from the electric motor. In this example, the three sections in the seal <NUM> and the seal bags <NUM>-<NUM> may provide redundant protection for the electric motor <NUM>. If one of the three sections fails, the electric motor can still function without contamination from wellbore fluid. The seal bags <NUM>-<NUM> in the sections may have the ability to self-heal according to some examples of the present disclosure. Each of seal bags <NUM>-<NUM> can include an inner layer and an outer layer. The outer layer may be resistant to polar fluids and hydrocarbons found in wellbore fluid. The inner layer may be material that is water-sensitive or otherwise sensitive to other polar substances and that can swell in response to contact with water or other polar substances. In an example, if one of the mechanical seals <NUM>-<NUM> fails, the seal section below the failed mechanical seal can fill with wellbore fluid. The seal bag in the failed section may develop a tear in the outer layer and the inner layer of the seal bag may be exposed to wellbore fluid. The inner layer may swell in response to the wellbore fluid to fill the tear. The inner layer can seal the tear in the outer layer preventing or limiting the ingress of wellbore fluid into the seal and can maintain isolation of the motor oil and motor from the wellbore fluid.

<FIG> is a cross-sectional schematic of a seal <NUM> that includes a seal bag <NUM> that has multiple layers according to one example of the present disclosure. The seal <NUM> can have an outer housing <NUM> that can be a pipe that may be bounded at each end by a head and a base. Check valves within the head and base can allow motor oil to move within the seal <NUM> for maintaining a constant and slightly positive pressure through the seal <NUM> relative to ambient wellbore pressure at the pump intake.

The seal bag <NUM> can be positioned inside the outer housing <NUM> in the seal section between mechanical seals <NUM>, <NUM>. A guide tube <NUM> can be positioned axially within the seal <NUM> and can define a cavity in which a shaft <NUM> can rotate to transfer power from the electric motor to the pump of an electric submersible pump. The seal bag <NUM> can be positioned around the guide tube <NUM>. The guide tube <NUM> can provide a path for motor oil to fill the seal bag <NUM> and can maintain adequate clearance between the shaft <NUM> and the seal bag <NUM>.

Motor oil can fill both an interior area <NUM> of the seal bag <NUM> and the external area <NUM> that is inside the outer housing <NUM> and external to the seal bag <NUM>. If the mechanical seal <NUM> fails, the seal section between the mechanical seals <NUM> and <NUM> can be contaminated with wellbore fluid. In this example, the seal bag <NUM> can protect the next section of the seal <NUM> from being contaminated and can maintain the isolation of the motor oil and the electric motor from wellbore fluid.

The seal bag <NUM> has multiple layers. The outer layer may be resistant to polar fluids and hydrocarbons in wellbore fluid. The inner layer may be a water-sensitive or polar-substance sensitive polymer that can swell. If the seal bag <NUM> develops a tear in the outer layer, the inner layer of the seal bag <NUM> may be exposed to wellbore fluid. The inner layer may swell in response to contact with water or other polar substances and press the outer layer against the inside surface of the outer housing <NUM> to seal the tear. The response of the inner layer can seal the tear in the outer layer to prevent or limit the ingress of wellbore fluid into the seal bag <NUM>.

<FIG> is cross-sectional schematic of part of a seal that includes two layers of a seal bag <NUM> and an outer housing <NUM> according to one example of the present disclosure. The two layers include an inner layer <NUM> and an outer layer <NUM>. Both the inner layer <NUM> and the outer layer <NUM> of the seal bag <NUM> can be positioned in an inner area defined by the outer housing <NUM> for an electric submersible pump. The outer layer <NUM> can be positioned adjacent to the outer housing <NUM> and between the outer housing <NUM> and the inner layer <NUM>. In some examples, the inner layer <NUM> may be coupled to the outer layer <NUM>. For example, the inner layer <NUM> and the outer layer <NUM> can be formed together in a mold or die. In other examples, the inner layer <NUM> and outer layer <NUM> may be separate layers that are uncoupled and can be assembled, with the inner layer <NUM> inside the outer layer <NUM>, and mounted within the seal. In still other examples, the inner layer <NUM> and the outer layer <NUM> are formed by different single-layer bags with one bag being the inner layer <NUM> and the other bag being the outer layer <NUM>.

The outer layer <NUM> can be made from an elastomeric material that may swell in response to wellbore fluids, gases, pressure changes, or temperature changes. The elastomeric material can be capable of swelling and deswelling multiple times while maintaining its integrity, such as by maintaining fluid isolation properties in both the swell and deswell states. Examples of the elastomeric material from which the outer layer <NUM> can be made include AFLAS®, Viton®, Highly Saturated Nitrile (HSN), styrene butadiene, acrylonitrile butadiene rubber, hydrogenated acrylonitrile butadiene rubber, carboxlyated acrylonitrile butadiene rubber, ethylene vinyl acetate, ethylene acrylate, vinyl methyl silicone, Hypalon®, ethylene copolymer, tetrafluoroethylene propylene, ethylene propylene diene monomer, and combinations of these or other suitable materials. The inner layer <NUM> can be made from a polymer that may be resistant to motor oil and that may swell in response contact with water and other polar substances. Examples of polymers from which the inner layer <NUM> may be made include a hydrophobic polymer, a polymer blend with crosslinked hydrogel such as polyacrylate, polyvinyl alcohol, polyethylene oxide, starch-acrylate copolymer, carboxymethyl cellulose, or combinations of these or other suitable material.

A tear in the seal bag <NUM>, such as a tear in the outer layer <NUM>, may allow wellbore fluid to enter into an inner area defined by the inner layer <NUM>. The inner layer <NUM> can respond to contact with water or other polar substances in the wellbore fluid by swelling toward the outer layer <NUM> and the outer housing <NUM>. The swelling inner layer <NUM> may force the outer layer <NUM> against the outer housing <NUM> and seal the tear in the seal bag <NUM> by preventing wellbore fluid from entering the inner area defined by the inner layer <NUM>. The ability of the inner layer <NUM> of the seal bag to swell in response to polar substances and fill a tear in the seal bag <NUM> can provide the seal bag <NUM> the ability to self-heal a tear in the seal bag <NUM> in the downhole environment.

The outer layer <NUM> includes a surface facing the outer housing <NUM> and the surface includes a slick or anti-stick substance that can promote movement of the seal bag <NUM> along an inner surface of the outer housing <NUM> and that may prevent friction coupling. Friction coupling can include a coupling between the outer layer <NUM> and the outer housing <NUM> due to resistance between the two components. Friction coupling between the outer layer <NUM> and the outer housing <NUM> can result in the seal bag <NUM> sticking and bunching, that can lead to the seal bag <NUM> tearing. The slick or anti-slick substance, such as Teflon®, can be used to prevent or reduce friction coupling. In addition or alternatively, the outer housing <NUM> can include a substance, such as Teflon®, on an inner surface of the outer housing <NUM> to prevent or reduce friction coupling with the outer layer <NUM>.

<FIG> is cross-sectional schematic of a seal that includes more than two layers of a seal bag <NUM> and an outer housing <NUM> according to one example of the present disclosure. The layers of the seal bag <NUM> can be positioned within an inner area defined by the outer housing <NUM> of the seal for an electric submersible pump. The seal bag <NUM> layers include: an outer layer <NUM>, an inner layer <NUM>, and at least one middle layer <NUM>. The outer layer <NUM> and the inner layer <NUM> may be the same or similar to the inner layer <NUM> and the outer layer <NUM> of <FIG>. The outer layer <NUM> can be positioned adjacent to the inside surface of the outer housing <NUM> and between the outer housing <NUM> and the middle layer <NUM>. The middle layer <NUM> is positioned between the inner layer <NUM> and the outer layer <NUM> of seal bag <NUM>. The middle layer <NUM> may be made from a material that can add stiffness, other structural support, permeability resistance, or other beneficial effects to the seal bag <NUM>. An inner layer <NUM> may be made from a polymer that may be resistant to motor oil and that may respond to water and other polar substances by swelling.

In one example, if the seal integrity is compromised, wellbore fluid may infiltrate seal bag <NUM>. A tear in the outer layer <NUM> and the middle layer <NUM> of the seal bag <NUM> can allow wellbore fluid to penetrate to the inner layer <NUM> that can swell in response to a polar substance, such as water, in the wellbore fluid. The inner layer <NUM> can swell into the tear in the outer layer <NUM> and the middle layer <NUM> to force the outer layer <NUM> against the inner surface of the outer housing <NUM> and seal the tear. Sealing the tear can reduce or prevent the motor oil from being contaminated and can reduce or prevent the electric motor from failing from contaminated motor oil. The middle layer <NUM> of seal bag <NUM> may be one layer or more than one layer. The middle layer <NUM> may be coupled to at least one of the inner layer <NUM> or the outer layer <NUM>. Alternatively, the middle layer <NUM> may be assembled with the inner layer <NUM> and the outer layer <NUM> as separate bags to form the seal bag <NUM>.

In some examples, the middle layer <NUM> is a tape or a mesh material that can support the structure of the seal bag <NUM> during swell and deswell. An example of the tape material can be Teflon® or other suitable tape. An example of the mesh material may be a nylon mesh or other mesh material that can provide structural support.

In other examples, the middle layer <NUM> can be a material that can support permeability resistance of the seal bag <NUM>. For example, the middle layer <NUM> can be a material similar to that of the outer layer <NUM> that is resistant to wellbore fluid and that provides additional protection to the inner layer <NUM>.

In still other examples, the middle layer <NUM> can be a liquid contained between the inner layer <NUM> and the outer layer <NUM> that responds to water and other polar substances by swelling. The liquid that forms the middle layer <NUM> may aid the inner layer <NUM> in sealing a tear in the outer layer <NUM>. In another example, the middle layer <NUM> can be a liquid that may swell when exposed to water and other polar substances in the wellbore fluid. The inner layer <NUM> in this example may be similar to the outer layer <NUM> in material and function. If a tear forms in the outer layer <NUM> of the seal bag <NUM>, the middle layer <NUM> can swell in response to the polar substances in the wellbore fluid and fill the tear in the outer layer <NUM>.

<FIG> is a flowchart of a process <NUM> for sealing a tear in an outer layer of a seal bag with an inner layer according to one example of the present disclosure. In block <NUM>, an electric submersible pump is run downhole into a wellbore. The electric submersible pump can be run downhole using a conveyance mechanism such as coiled tube or wireline. The electric submersible pump can include an electric motor and a pump coupled by a shaft that transmits power from the electric motor to the pump. The electric motor can power the pump so that the pump provides artificial lift for the wellbore. A seal can be positioned between the electric motor and the pump. The seal can include a seal bag that has an inner layer and an outer layer in an outer housing. The seal bag may contain the inner layer and the outer layer, or may include one or more layers in addition to the inner layer and the outer layer. The seal including the seal bags can isolate the electric motor from wellbore fluids.

In block <NUM>, the outer layer of a seal bag swells to contact the inner surface of the outer housing of the seal. The outer layer of the seal bag may be an elastomeric material and can swell and deswell in response to pressure changes, temperature changes, or exposure to wellbore fluid or gases. During pump operation, the outer layer of the seal bag can swell to contact an inner surface of the outer housing of the seal that is a section of a pipe. The outer housing provides structural support for the bag to limit the swell of the bag.

In block <NUM>, the inner layer of a seal bag swells to repair a tear in the outer layer. During operation of the electric submersible pump, the outer layer of the seal bag can experience a cycle of swell and deswell that can cause the elastomeric material of the outer layer to tear. The tear can expose the inner layer of the bag to wellbore fluid. The inner layer of the seal bag may be a material that responds to polar substances in the wellbore fluid by swelling. The inner layer of the seal bag can swell into the tear to seal the tear in the outer layer and press the outer layer against the inner surface of the outer housing of the seal. This self-heal action can prevent or restrict the contamination by wellbore fluid of the motor oil and electric motor of the electric submersible pump.

Claim 1:
A seal (<NUM>) comprising:
an outer housing (<NUM>; <NUM>) positionable between a pump (<NUM>) and an electric motor (<NUM>) of an electric submersible pump (<NUM>); and
a seal bag i (<NUM>-<NUM>) internal to the outer housing, the seal bag including an outer layer (<NUM>; <NUM>) and an inner layer (<NUM>; <NUM>), the outer layer being made from a first material to retain a structure of the outer layer in a swellable state in a wellbore;
characterized in that
the inner layer is made from a second material that is swellable in the wellbore in response to contact with a polar substance to seal a tear in the outer layer, wherein the outler layer has a surface that comprises a third material to prevent friction coupling of the outer layer in the swellable state to an inside surface of the outer housing.