This disclosure relates in general to electrical submersible well pumps and in particular to a cap located within a seal section adjacent a flexible compensator element to limit expansion of the compensator element in one direction.
Electrical submersible well pumps are commonly used for pumping well fluid from wells producing oil, water and possibly gas. A typical submersible pump assembly has a rotary pump driven by an electrical motor. A seal section locates between the motor and the pump. The seal section has a flexible compensator element that reduces a pressure differential between lubricant in the motor and the surrounding hydrostatic well fluid pressure. The compensator element may be a tubular elastomeric bag, with an interior in communication with motor lubricant and an exterior in communication with well fluid. The upper end of the bag is secured by a bag clamp to an adapter on the upper end of the seal section.
The motor lubricant will expand with temperature. At the typical depths, the well fluid in most wells will be at a higher temperature than the temperature of the air surrounding the wellhead. Also, when the motor begins to operate, the lubricant temperature increases. Consequently, the compensator element will normally expand from its initial state.
Seal sections have check valves to expel excess lubricant if the interior pressure becomes too much greater than the hydrostatic well fluid pressure. However, even if the check valves are pre-set to a relatively low differential pressure, there still may be enough pressure in the bags due to thermal lubricant expansion to expand the bags up and over the bag clamp. When the bags are expanded around the bag clamp, it causes excessive stress in the area where the edge of the clamp contacts the bag.
The submersible pump assembly disclosed herein has a cap mounted around a first end of the compensator element. The cap has a skirt extending radially outward relative to an axis of the shaft to limit expansion of the compensator element in a first direction.
In the embodiment shown, the skirt of the cap is conical with a diameter increasing in a direction away from the first end of the compensator element. Also, the cap has a cylindrical neck. The skirt joins the neck and flares radially outward from the neck in a direction away from the first end. The skirt of the cap has an outer edge spaced radially inward from an inner sidewall of the seal section.
The first end of the compensator element comprises a cylindrical compensator neck. A conical compensator shoulder may join the compensator neck and extends in a direction away from the first end at a diverging angle. The cylindrical cap neck circumscribes the compensator neck. The skirt joins the cap neck and extends conically around the compensator shoulder and away from the first end at the same diverging angle. The cylindrical cap neck may be radially spaced from the compensator neck, defining an annulus between the cap neck and the compensator neck.
The seal section includes an adapter secured to a first end of the housing, the adapter having an axial passage through which the shaft extends. A tubular retainer is mounted in the axial passage and extends from the adapter in a direction away from the first end of the housing. The first end of the compensator element may be secured or clamped around the retainer. The cap may have a rim that is secured around the tubular retainer.
The skirt of the cap has a first side surface facing toward a first end of the seal section and a second side surface facing away from the first end of the seal section. A vent port may be in the cap to vent any trapped well fluid from the first side surface to the second side surface.
The present technology will be better understood on reading the following detailed description of nonlimiting embodiments thereof, and on examining the accompanying drawings, in which:
The foregoing aspects, features, and advantages of the present technology will be further appreciated when considered with reference to the following description of preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. In describing the preferred embodiments of the technology illustrated in the appended drawings, specific terminology will be used for the sake of clarity. However, it is to be understood that the specific terminology is not limiting, and that each specific term includes equivalents that operate in a similar manner to accomplish a similar purpose.
Referring to
Referring to
A shaft 34 extends through seal section 18 for transmitting rotary motion from motor 16 to pump 20. Shaft 34 has an upper splined end 36 that optionally may have a latch member 38. Latch member 38 latches to the shaft (not shown) of pump 20 so as to transmit tension. Shaft 34 has lower splined end 40 that engages the shaft of motor 16 (not shown).
A conventional thrust bearing 42 is located in seal section 18, as illustrated in
A lower radial bearing support 52 is supported in housing 32 against downward movement by retainer ring 50. Lower radial bearing support 52 has a bushing 54 that is slidingly engaged by shaft 34. Bushing 54 does not form a seal on shaft 34 and may have passages or channels through it to freely allow the passage of motor lubricant. Lower radial bearing support 52 has seals 56 on its exterior that sealingly engage the inner diameter of housing 32. A lower isolation tube 58 extends sealingly into a counterbore in lower radial bearing support 52 at the upper end of bushing 54. Lower isolation tube 58 has an inner diameter that is larger than the outer diameter of shaft 34, creating an annular passage for the flow of motor lubricant. Motor lubricant is free to flow between the area surrounding thrust bearing 42 and the annular clearance within lower isolation tube 58.
The upper end of lower isolation tube 58 extends into sealing engagement with a counterbore in a central radial bearing support 60. Central radial bearing support 60 has seals 62 on its exterior that seal against the inner diameter of housing 32. Central radial bearing support also has a bushing 64 that slidingly engages shaft 34 but does not seal against the flow of lubricant. A lower chamber 66 is defined by the annular space between radial bearing supports 52 and 60 and surrounding lower isolation tube 58. A passage 68 extends through central radial bearing support 60 from its lower end to its upper end.
Still referring to
A tubular elastomeric compensator element, bag or bladder 74 is located within upper chamber 72. Bladder 74 has a lower end 76 that fits sealingly around an upper neck portion of central radial bearing support 60. Bladder 74 has a neck 78 on its upper end that is sealingly secured or clamped to a bladder retainer 80, as shown in
Referring to
A bladder stress reducer cap 86 is positioned adjacent bladder retainer 80. Bladder stress reducer cap 86 is configured to prevent an upper end of the bladder 74 from extending upward toward upper adapter 28.
Referring to
A mechanical seal assembly 106 is located at the upper end of shaft 34 for sealing against the encroachment of well fluid from cavity 104 into motor 16 (
As mentioned above, bladder stress reducer cap 86 is positioned adjacent the bladder retainer 80, and configured to prevent an upper end of the bladder 74 from extending upward toward the upper adapter 28. An enlarged view of the bladder stress reducer cap 86 is shown in
Skirt 120 flares outward in a downward direction and has an outer diameter less than an inner diameter of seal section housing 32 (
Cap neck 118 of the bladder stress reducer cap 86 connects cap rim 116 to the lower skirt 120, and spans the length of neck 78 at the upper end of bladder 74. In the embodiment shown, the inner diameter of cap neck 118 is greater than the outer diameter of bladder neck 78, creating an annulus 121 between them. Annulus 121 is in fluid communication with the well fluid in seal section housing 32. Annulus 121 may be advantageous because it allows for the use of the bladder stress reducer cap 86 with ESPs 10 having shafts 34 of different diameters, thereby making the bladder stress reducer cap 86 more universal and adaptable to ESPs 10 other than that specifically described herein.
In practice, rim 116 is configured to engage an outer surface of bladder retainer 80. This may be accomplished by any appropriate means. For example, in the embodiment of
Skirt 120 of bladder stress reducer cap 86 tapers radially outward from cap neck 118 toward the lower end of seal section 18. The junction between skirt 120 and cap neck 118 may be positioned adjacent the bottom of bladder neck 78 at the upper end of bladder 74. Skirt 120 is designed so that as bladder 74 expands, the top of bladder 74 is restrained by skirt 120 from extending upwardly around bladder retainer 80. One advantage to this is that bladder 74 will not expand around bladder retainer 80 and experience excessive stress in the area where the edge of bladder retainer 80 contacts bladder 74.
At least one vent 126 may extend through bladder stress reducer cap 86 to allow fluids to pass from above to below bladder stress reducer cap 86, and vice versa. One reason for such vents 126 is that as bladder 74 expands, it may seal against lower skirt 120 of bladder stress reducer cap 86 and trap well fluid. However, in most instances, a space will remain above such a seal, between neck 78 of the bladder 74 and cap neck 118 of bladder stress reducer cap 86. Provision of the vents 126 allows the pressure within this space to equalize with the pressure in the upper chamber 72, thereby preventing damage to bladder 74 or any other components.
During filling, lubricant flows upward through the spaces around thrust bearing 42 (
After filling, a plug is installed in receptacle 88 and ESP 10 is lowered into the well. As ESP 10 is lowered into the well, well fluid enters upper chamber 72 via cavity 104 and passage 102. The hydrostatic pressure of the well fluid is exerted via bladder 74 to the lubricant within bladder 74 and motor 16. When at the desired depth, the operator supplies power to motor 16, causing pump 20 to draw well fluid in through intake 22 and discharge the well fluid through tubing 14 to the surface.
During operation, bladder 74 will tend to expand or contract depending on the relative pressures of the lubricant within bladder 74, and the fluids outside bladder 74. For example, in some instances the hydrostatic pressure of the fluids outside bladder 74 will be higher than the pressure of the lubricant within bladder 74, thereby causing the bladder to contract. However, during operation of motor 16, the lubricant within motor 16 and bladder 74 will heat. As the lubricant heats, it will expand, thereby expanding bladder 74. Because the bladder is elastomeric, it can expand or contract, thereby allowing the pressure of the lubricant to equalize with the pressure outside the bladder. Furthermore, as the bladder expands, it is restrained by bladder stress reducer cap 86 from expanding upwardly around bladder retainer 80, as described above.
Although the technology herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present technology. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present technology.
This application claims priority to provisional application 61/756,298, filed Jan. 24, 2013.
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Number | Date | Country | |
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20140202681 A1 | Jul 2014 | US |
Number | Date | Country | |
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61756298 | Jan 2013 | US |