Field of the Invention

[001] This invention relates generally to the field of submersible pumping systems, and more particularly, but not by way of limitation, to a system in which the thrust chamber is isolated from other chambers in the seal section and also to a system in which different lubricants are used in the motor and seal section portions of the pumping system.

Background

[002] 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.

[003] 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 provides 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.

[004] 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. Although generally effective, prior art designs allow fluid communication between the motor and the seal section through the thrust chamber and rely on the communication of fluid between the motor and the seal section. Because the lubricant is common to both the motor and the seal section, the same fluid must be used. It is to this and other restrictions in the prior art that the preferred embodiments are directed.

Summary of the Invention

[005] 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 a motor lubricant, a pump driven by the motor, a thrust chamber connected between the motor and the pump and a seal section. The thrust chamber is filled with a thrust chamber lubricant and the seal section and motor are in fluid isolation from the thrust chamber.

[006] In another aspect, the preferred embodiments include an electric submersible pumping system that includes a motor that is filled with a first lubricant, a pump driven by the motor, an upper seal section connected to the pump and a thrust chamber connected between the motor and the upper seal section. The thrust chamber is filled with a second lubricant that is different than the first lubricant.

[007] In yet another aspect, the electric submersible pumping system preferably includes a motor that is filled with motor lubricant. The electric submersible pumping system further includes a pump driven by the motor and a lower seal section connected to a lower side of the motor. The lower seal section is in fluid communication with the motor. The electric submersible pumping system also includes a thrust chamber connected between the motor and the pump. The thrust chamber is filled with thrust chamber lubricant and the thrust chamber is in fluid isolation from the motor. The isolation of the thrust chamber from the motor prevents mixing of the thrust chamber lubricant and motor lubricant.

Brief Description of the Drawings

[008] FIG. 1 depicts a submersible pumping system constructed in accordance with a preferred embodiment of the present invention.

[009] FIG. 2 provides a cross-sectional view of the motor, thrust chamber, and upper seal section constructed in accordance with a presently preferred embodiment.

[010] FIG. 3 depicts a submersible pumping system constructed in accordance with an alternate preferred embodiment of the present invention.

[011] FIG. 4 provides a cross-sectional view of the thrust chamber, motor and lower seal section constructed in accordance with a presently preferred embodiment.

[012] FIG. 5 provides a cross-sectional view of a mechanical seal from the seal section of FIGS. 2 and 4.

Detailed Description of the Preferred Embodiments

[013] In accordance with a first preferred embodiment of the present invention, FIG. 1 shows an elevational view of a pumping system 100 attached to production tubing 102. The pumping system 100 and production tubing 102 are disposed in a wellbore 104, which is drilled for the production of a fluid such as water or petroleum. As used herein, the term "petroleum" refers broadly to all mineral hydrocarbons, such as crude oil, gas and combinations of oil and gas. [014] The pumping system 100 preferably includes a pump 108, a motor 110, an upper seal section 112 and a thrust chamber 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.

[015] The motor 110 receives power from a surface-based facility through power cable 116. 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.

[016] In the preferred embodiments, the upper seal section 112 is positioned above the motor 110 and below the pump 108. The thrust chamber 114 is positioned between the motor 110 and the seal section 112. 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.

[017] It will be noted that although the pumping system 100 is depicted in a vertical deployment in FIG. 1, the pumping system 100 can also be used in non- vertical applications, including in horizontal and non-vertical wellbores 104. Accordingly, references to "upper" and "lower" within this disclosure are merely used to describe the relative positions of components within the pumping system 100 and should not be construed as an indication that the pumping system 100 must be deployed in a vertical orientation.

[018] Turning to FIG. 2, shown therein is a cross-sectional view of the upper seal section 112, motor 110 and thrust chamber 114. As depicted in the close-up view of the motor 110 in FIG. 2, the motor 110 preferably includes a motor housing 120, stator assembly 122, rotor assembly 124, rotor bearings 126 and a motor shaft 128a. The stator assembly 122 includes a series of stator coils (not separately designated) that correspond to the various phases of electricity supplied to the motor 110. The rotor assembly 124 is keyed to the motor shaft 128a and configured for rotation in close proximity to the stationary stator assembly 122. The size and configuration of the stator assembly 122 and rotor assembly 124 can be adjusted to accommodate application-specific performance requirements of the motor 110.

[019] Sequentially energizing the various series of coils within the stator assembly 122 causes the rotor assembly 124 and motor shaft 128a 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 1 10 on the motor shaft 128a.

[020] The motor 110 is filled with motor lubricant 200 during manufacture that reduces frictional wear on the rotating components within the motor 110. In particularly preferred embodiments, the motor lubricant 200 is a dielectric fluid. As the motor 110 cycles during use and as the motor 110 is exposed to the elevated temperatures in the wellbore 104, the dielectric motor lubricant 200 expands and contracts. It is desirable to prevent the dielectric motor lubricant 200 from becoming contaminated with wellbore fluids 204 and solids in the wellbore 104.

[021] The motor shaft 128a is preferably connected to a seal section shaft 128b that extends through the thrust chamber 114 and upper seal section 112. The seal section shaft 128b transfers torque from the motor 110 to the pump 108. The seal section shaft 128b preferably includes an internal passage 130 that extends at least along the portion of the seal section shaft 128b that extends through the thrust chamber 114.

[022] The thrust chamber 114 includes a thrust chamber housing 132, a thrust bearing assembly 134, a plurality of mechanical seals 136 and a piston expansion assembly 138. The thrust bearing assembly 134 includes a pair of stationary bearings 140 and a thrust runner 142 attached to the seal section shaft 128b. The thrust runner 142 is captured between the stationary bearings 140, which limit the axial displacement of the thrust runner 142 and the seal section shaft 128b.

[023] As best illustrated in the close-up view of the mechanical seal 136 FIG. 5, the mechanical seals 136 each include bellows 144, a coiled spring 146, a runner 148 and a stationary ring 150. These components cooperate to prevent the migration of fluid along the shaft 128 and isolate the motor lubricant 200 from the thrust chamber 114. The stationary ring 150 has an internal diameter sized to permit the free rotation of the shaft 128. In contrast, the bellows 144, coiled spring 146 and runner 148 rotate with the shaft 128. The rotating runner 148 is held in place against the stationary ring 150 by the spring-loaded bellows 144. The bellows 144 preferably includes a series of folds that allow its length to adjust to keep the runner 148 in contact with the stationary ring 150 if the shaft 128 should experience axial displacement. The bellows 144 may be manufactured from thin corrugated metal or from elastomers and polymers, including AFLAS, perfluoroelastomer, polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) and polyethether ketone (PEEK).

[024] Turning back to FIG. 2, the piston expansion assembly 138 preferably includes one or more cylinders 152, a piston 154 in each of the cylinders 152 and spring stops 156. The upstream section of each cylinder 152 includes an opening that places the cylinder 152 in fluid communication with the interior of the thrust chamber 114. Each piston 154 rides in a corresponding cylinder 152 and acts as an expansion system to permit the movement of fluid within the thrust chamber 114. The spring stops 156 are positioned at opposite ends of each cylinder 152 and prevent the pistons 154 from crashing into the ends of the cylinders 152.

[025] During manufacture, the thrust chamber 114 is filled with clean thrust chamber lubricant 202. In preferred embodiments, the thrust chamber lubricant 202 is different than the dielectric motor lubricant 200. The thrust chamber lubricant 202 preferably has a higher viscosity than the motor lubricant 200 that is beneficial in creating hydrodynamic bearing surfaces within the upper seal section 112. As heat builds in the thrust chamber 114, the expansion of the thrust chamber lubricant 202 is accommodated with movement of the pistons 154 within the piston expansion assembly 138. In this way, the thrust chamber lubricant 202 is contained within the thrust chamber 114 and is not mixed or exchanged with other fluids within the pumping system 100. The isolation of the thrust chamber 114 reduces the movement of shavings, particles or other material from the thrust bearing assembly 134 into the motor 110.

[026] The upper seal section 112 is attached to the upper end of the thrust chamber 114. To permit the expansion and contraction of the dielectric motor lubricant 200 under elevated wellbore temperatures, the upper seal section 112 is connected to the motor 110 and placed in fluid communication with the dielectric motor lubricant lubricating oil 200 through the passage 130 in the seal section shaft 128b. Ports 164 extending through the seal section shaft 128b allow motor lubricant to enter and exit the passage 130 on opposite sides of the thrust chamber 114.

[027] The upper seal section 112 preferably includes a bag seal assembly 158. The bag seal assembly 158 in the upper seal section 112 includes a bag support 160, a bladder 162, inlet ports 164 and discharge valves 166. The bag support 160 is rigidly attached to the inside surface of the upper seal section 112. The bladder 162 is secured to the bag support 160. The inlet ports 164 extend through the bag support tube 160 and shaft 128 to place the passage 130 in fluid communication with the interior of the bladder 162. The discharge valves 166 are configured to vent fluid from the interior of the bladder 162 in the event the fluid exceeds a predetermined threshold pressure. The outside of the bladder 162 is in fluid communication with the pump 108 and wellbore 104. Thus, the bag seal assembly 158 in the upper seal section 112 isolates wellbore fluids 204 in the pump 108 from the motor lubricant 200 in the upper seal section 112 and motor 110.

[028] Although the upper seal section 112 is depicted as including a bag seal assembly 158, it will be appreciated that other seal mechanisms may be incorporated into the upper seal section as additional or alternative seal mechanism to the bag seal assembly 158. Such additional seal mechanisms include bellows, pistons, labyrinths and combinations of these mechanisms.

[029] Thus, the preferred embodiment in FIG. 2 provides a mechanism for transferring motor lubricant 200 from the motor 110 to the upper seal section 112, while maintaining fluid isolation with the thrust chamber 114. Thrust chamber lubricant 202 is contained within the thrust chamber 114 and prevented by mechanical seals 136 from entering the motor 110 and upper seal section 112.

[030] Turning to FIG. 3, shown therein is an elevational view of the pumping system 100 constructed in accordance with a second preferred embodiment. Unless otherwise specified, the elements identified above in connection with the first preferred embodiment are also present in the second preferred embodiment.

[031] Unlike the first preferred embodiment, the pumping system 100 of the second preferred embodiment includes a lower seal section 168. The lower seal section 168 is used in place of the upper seal section 112 and is positioned below the motor 110. Alternatively, the lower seal section 168 is used in combination with the upper seal section 112. The thrust chamber 114 is constructed in accordance with the first preferred embodiment and prevents the mixing of motor lubricant 200 with thrust chamber lubricant 202. [032] Turning to FIG. 4, shown therein is a cross-sectional view of the lower seal section 168, motor 110, and thrust chamber 114. The pump 108 (not shown in FIG. 4) is connected to the upper end of the thrust chamber 114. Like the upper seal section 112, the lower seal section 168 includes a bag seal assembly 158 that in turn includes a bag support 160, a bladder 162 and discharge valves 166. Although the lower seal section 168 is depicted as including a bag seal assembly 158, it will be appreciated that other seal mechanisms may be incorporated into the upper seal section as additional or alternative seal mechanism to the bag seal assembly 158. Such additional seal mechanisms include bellows, pistons, labyrinths and combinations of these mechanisms.

[033] Because the motor shaft 128 does not extend into the lower seal section 168, motor lubricant 200 is not carried into the lower seal section 168 through the shaft 128. Instead, the lower seal section includes clean fluid ports 170 that place the interior of the bladder 162 directly in fluid communication with the motor lubricant 200 in the motor 110. The discharge valves 166 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 162 exceeds the set-point pressure, the discharge valves 166 open and relieve the pressure inside the bladder 162 by discharging a small volume of motor lubricant 200 into the wellbore 104. In a particularly preferred embodiment, the bladder 162 is manufactured from a high-temperature polymer or elastomer. Suitable polymers and elastomers include AFLAS, polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), and polyetherether ketone (PEEK). Alternatively, the bladder 162 can be manufactured from a metal expansible bellows. [034] The lower seal section 168 also includes a fluid exchange assembly 172. The fluid exchange assembly 172 includes a solids screen 174 and a plurality of exchange ports 176. The exchange ports 176 allow fluids to pass from the wellbore 104 through the solids screen 174 into the lower seal section 168 around the exterior of the bladder 162. The solids screen 174 reduces the presence of particulates in the lower seal section 168. The solids screen 174 is preferably manufactured from a metal or polymer fabric mesh.

[035] During manufacture, the lower seal section 168 is filled with the dielectric motor lubricant 200. As the fluid in the motor 110 expands during operation, it moves downward into the lower seal section 168, through the clean fluid ports 170 and into the bladder 162. The bladder 162 expands to accommodate introduction of fluid from the motor 110. As the bladder 162 expands, fluid external to the bladder 162 is expelled through the exchange ports 176 and solids screen 174. If the pressure inside the bladder 162 exceeds the threshold pressure limit of the discharge valves 166, the discharge valves 166 open and vent a portion of the motor lubricant 200 into the wellbore 104.

[036] Conversely, during a cooling cycle, the fluid in the motor 110 contracts and fluid is drawn upward out of the bladder 162. As the volume and pressure inside the bladder 162 decreases, fluid from the wellbore 104 is pulled into the lower seal section 168 through the solids screen 174 and exchange ports 176. The lower seal section 168 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 200 and the contaminated wellbore fluids 204 from the wellbore 104. [037] 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.