Patent Application
20150132158
This invention relates generally to the field of submersible pumping systems, and more particularly, but not by way of limitation, to a system for accommodating the expansion of motor lubricants in high-temperature environments.
Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps located above the motor. When energized, the motor provides torque to the pump, which pushes wellbore fluids to the surface through production tubing. Each of the components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment.
Components commonly referred to as “seal sections” protect the electric motors and are typically positioned between the motor and the pump. In this position, the seal section provide several functions, including transmitting torque between the motor and pump, restricting the flow of wellbore fluids into the motor, protecting the motor from axial thrust imparted by the pump, and accommodating the expansion and contraction of motor lubricant as the motor moves through thermal cycles during operation. Prior art seal sections typically include a “clean side” in fluid communication with the electric motor and a “contaminated side” in fluid communication with the wellbore. Bellows or bags have been used to separate the clean side of the seal section from the contaminated side.
Recently, manufacturers have employed polymer expansion bags within the seal section to accommodate the expansion and contraction of motor lubricants while isolating the lubricants from contaminants in the wellbore fluid. Although generally effective at lower temperatures, the currently available polymers become somewhat permeable at extremely elevated temperatures and allow the passage of moisture across the membrane. The moisture reduces the insulating properties of polyimide and other films used to electrically isolate components within the downhole pumping system. Although piston-based systems may provide an alternative to the use of polymer expansion bags, prior art piston-based seal assemblies are susceptible to failure from sand, scale or other particulates. There is, therefore, a need for improved designs that can be used to accommodate expansion of motor fluids in elevated temperature applications. It is to this and other needs that the preferred embodiments are directed.
In preferred embodiments, the present invention includes an electric submersible pumping system that is configured to pump fluids from a wellbore. The electric submersible pumping system includes a motor that is filled with motor lubricant fluid and a pump driven by the motor. The electric submersible pumping system further includes a fluid expansion module connected to the motor that is designed to accommodate the expansion and contraction of the motor lubricant fluid in the motor.
The fluid expansion module preferably includes a piston seal housing in fluid communication with the motor and a bag seal housing in fluid communication with the piston seal housing. The fluid expansion module further includes at least one axially movable barrier in the piston seal housing and at least one expansible barrier in the bag seal housing. The axially movable barrier and the expansible barrier cooperate to permit the expansion of the motor lubricant fluid without contaminating the motor lubricant fluid with fluids or and solids from the wellbore.
In accordance with a preferred embodiment of the present invention,
The pumping system 100 preferably includes a pump 108, a motor 110, a seal section 112 and a fluid expansion module 114. The production tubing 102 connects the pumping system 100 to a wellhead 106 located on the surface. Although the pumping system 100 is primarily designed to pump petroleum products, it will be understood that the present invention can also be used to move other fluids. It will also be understood that, although each of the components of the pumping system are primarily disclosed in a submersible application, some or all of these components can also be used in surface pumping operations.
Generally, the motor 110 is configured to drive the pump 108. In a particularly preferred embodiment, the pump 108 is a turbomachine that uses one or more impellers and diffusers to convert mechanical energy into pressure head. In alternate embodiments, the pump 108 is configured as a positive displacement pump. The pump 108 includes a pump intake 118 that allows fluids from the wellbore 104 to be drawn into the pump 108. The pump 108 forces the wellbore fluids to the surface through the production tubing 102.
In the preferred embodiments, the seal section 112 is positioned above the motor 110 and below the pump 108. The fluid expansion module 114 is positioned below the motor 110. Although only one of each component is shown, it will be understood that more can be connected when appropriate, that other arrangements of the components are desirable and that these additional configurations are encompassed within the scope of preferred embodiments. For example, in many applications, it is desirable to use tandem-motor combinations, gas separators, multiple seal sections, multiple pumps, sensor modules and other downhole components.
It will be noted that although the pumping system 100 is depicted in a vertical deployment in
Referring now also to
Sequentially energizing the various series of coils within the stator assembly 122 causes the rotor assembly 124 and motor shaft 128 to rotate in accordance with well-known electromotive principles. The motor bearings 126 maintain the central position of the rotor assembly 124 within the stator assembly 122 and oppose radial and axial forces generated by the motor 110 on the motor shaft 128.
The motor 110 is filled with non-conductive lubricating oil during manufacture that reduces frictional wear on the rotating components within the motor 110. As the motor 110 cycles during use and as the motor 110 is exposed to the elevated temperatures in the wellbore 104, the lubricating oil expands and contracts. It is desirable to prevent the clean motor oil from becoming contaminated with fluids and solids in the wellbore. To permit the expansion and contraction of the lubricating oil under elevated wellbore temperatures, the seal section 112 and fluid expansion module 114 are connected to the motor 110 and placed in fluid communication with the motor oil.
Continuing with
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Turning back to
The discharge valves 156 are preferably one-way relief valves that are configured to open at a predetermined threshold pressure that exceeds the exterior wellbore pressure. In this way, if the fluid pressure inside the bladder 152 exceeds the set-point pressure, the discharge valves 156 open and relieve the pressure inside the bladder 152 by discharging a small volume of fluid into the wellbore 104. In a particularly preferred embodiment, the bladder 152 is manufactured from a high-temperature polymer or elastomer. Suitable polymers and elastomers include polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) and polyethether ketone (PEEK).
The bag seal housing 132 also includes the fluid exchange assembly 138. The fluid exchange assembly 138 includes a solids screen 160 and a plurality of exchange ports 162. The exchange ports 162 allow fluids to pass from the wellbore 104 through the solids screen 160 into the bag seal housing 132 around the exterior of the bladder 152. The solids screen 160 reduces the presence of particulates in the bag seal housing 132. The solids screen 160 is preferably manufactured from a metal or polymer fabric mesh.
During manufacture, the fluid expansion module 114 is filled with clean motor lubricant. The piston assemblies 134a, 134b are then placed into the piston seal housing 130. As the fluid in the motor 110 expands during operation, the increased volume exerts pressure on the upper side of the piston assembly 134a. In response, piston assembly 134a moves downward toward piston assembly 134b. When the volume between the piston assemblies 134a, 134b decreases, the increased pressure on piston assembly 134b forces it downward toward the bag seal housing 132. As piston assembly 134b moves downward it pushes clean motor lubricant through the inlet ports 154, through the bag support 152 and into the bladder 152. The bladder 152 expands to accommodate introduction of fluid from the piston seal housing 130. As the bladder 152 expands, fluid external to the bladder 152 is expelled through the exchange ports 162 and solids screen 160. If the pressure inside the bladder 152 exceeds the threshold pressure limit of the discharge valves 156, the discharge valves 156 open and vent a portion of fluid into the wellbore 104.
Conversely, during a cooling cycle, the fluid in the motor 110 contracts and the movement of the components within the fluid expansion module 114 reverses. As the pistons 134a, 134b are drawn upward, fluid is pulled out of the bladder 152. As the volume and pressure inside the bladder 152 decreases, fluid from the wellbore is pulled into the bag seal housing 132 through the solids screen 160 and exchange ports 162. The fluid expansion module 114 provides a robust mechanism for allowing expansion and contraction of lubricants from the motor 110 while maintaining an isolation barrier between the clean motor lubricants and the contaminated fluids from the wellbore 104. Notably, the use of piston assemblies 134a, 134b provide redundant barriers to the bladder 152 that are not susceptible to the increased permeability found in even high-temperature bladders. Accordingly, even if the bladder 152 is exposed to extremely high temperatures and permits the passage of some moisture from the wellbore 104 into the piston seal housing 130, the moisture is isolated from the motor 110 by the redundant piston assemblies 134a, 134b.
In certain applications, it may be desirable to place the pump 108 below the motor 110. In those applications, the fluid expansion module 114 will be positioned above the motor 110 and the seal section 112 will be placed between the motor 110 and the pump 108. In these alternative embodiments, the bag seal housing 132 will actually be positioned above the piston seal housing 130.
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The seal section shaft 164 is coupled to the motor shaft 128, or formed as a unitary shaft with the motor shaft 128, and transfers torque from the motor 110 to the pump 108. The thrust bearing assembly 166 includes a pair of stationary bearings 172 and a thrust runner 174 attached to the seal section shaft 164. The thrust runner 174 is captured between the stationary bearings 172, which limit the axial displacement of the runner 174 and the motor shaft 128 and seal section shaft 164.
In a particularly preferred embodiment, the seal section 112 includes a plurality of mechanical seals. Two mechanical seals 168a, 168b are depicted in
Continuing with
Thus, during thermal cycling of the motor 110, the motor lubricant may expand from the motor 110 into the seal section 112 and the fluid expansion module 114. The fluid expansion module 114 provides the primary system for accommodating the expansion of fluid from the motor 110 and the seal section 112 provides a secondary system for accommodating the expansion of motor oil from the motor 110. In the event that the fluid inside the seal section 112 exceeds a threshold pressure, the relief valves 170 temporarily open to prevent damage to the motor 110 or mechanical seals 168. The primary function of the seal section 112 is to prevent migration of fluids along the shafts between the motor 110 and pump 108.
It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functions of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems without departing from the scope and spirit of the present invention.
