POLISHED ROD STUFFING BOX WITH SAFETY VALVE FOR A BEAM PUMPED PRODUCTION WELL

Abstract: A wellhead assembly for a beam pumped production well com­ prises a stuffing box for providing a seal around a polished rod (1) of the beam pump assembly and a flapper type safety valve (7) for sealing off the wellhead in case of polished rod failure. The safety valve comprises a wear plate (11) which is pressed against the polished rod and means are provided for monitoring the amount of wear of the wear plate on the basis of the angular orientation of the safety valve relative to the stuffing box.

Description: The invention relates to a wellhead assembly for a beam pumped production well and in particular to a wellhead assembly comprising a stuffing box provided with a safety valve for sealing off the wellhead in case of a failure of the polished rod. At its lower end such a wellhead assembly is provided with connecting means to join the wellhead assembly to a well. U.S.A. patent specification No. 4 377 206 discloses a normally vertical wellhead assembly for a beam pumped production well having an axial passage for a polished rod of the beam pump assembly, the wellhead assembly comprising a stuffing box in which packing is arranged which provides a seal around the polished rod, a safety valve including a valve seat and a valve body rotatably arranged in the wellhead assembly about a horizontal hinge pin between an open position and a closed position resting against the valve seat to stop upward flow of fluid through the passage, and an indicator indicating changes in the position of the valve body to allow monitoring the wear of the valve body. During operation the polished rod moves up and down through the stuffing box. The polished rod is subjected to several mechanical loads and these loads in combination with poor lubrication lead to occasional failure of the polished rod. The broken polished rod drops into the well and the packing of the stuffing box does not anymore provide a seal. To prevent escape of fluid out of the well, the wellhead assembly is provided with a safety valve. The safety valve is a flapper valve which is kept open by the polished rod and which closes in the absence of the polished rod. During normal operation the polished rod keeps the safety valve in an open position as the polished rod moves up and down in contact with the valve body. Consequently the valve body will wear. The flapper valve has to be replaced when the wear exceeds a predetermined amount. To monitor the wear, the wellhead assembly is provided with an indicator. In the known wellhead assembly the indicator is mounted on the horizontal rotatable hinge pin of the valve body which extends out of the housing. This extended hinge pin requires a seal which has to have a long service life. In an increasing number of oil fields which are produced with the aid of beam pumps steam injection is being applied to heat the oil so as to improve its mobility. Thus the pressures in the oil bearing formation are increased and thus the pressure in the well. It is an object of the present invention to provide a simple indicator which seals when not in use. To this end the wellhead assembly according to the present invention is characterized in that the indicator consists of a pin slidably arranged in a radial hole through the wall of the stuffing box, which pin can, against the action of a spring, be pressed against the valve body over a distance corresponding the amount of wear of the valve body. Monitoring the wear of the valve body can be done without interrupting pumping. In a suitable embodiment, the stuffing box comprises a lower tubular element, a middle tubular element and an upper tubular element, the middle tubular element at least partly surrounding and being screwed on top of the lower tubular element and the upper tubular element at least partly surrounding and being screwed on top of the middle tubular element, wherein the upper tubular element is provided with the safety valve, wherein between the middle tubular element and the upper tubular element an upper soft packing is arranged which can be forced to swell inwardly by tightening the screw connection between the middle tubular element and the upper tubular element, and wherein between the lower tubular element and the middle tubular element a lower soft packing is arranged which can be forced to swell inwardly by tightening the screw connection between the lower tubular element and the middle tubular element. During normal operation, the lower soft packing is not used This packing does not seal. The upper soft packing is set, so that it is only the upper soft packing that wears. When it is required to replace the upper soft packing, the screw connection between the lower tubular element and the middle tubular element is tightened so that the lower soft packing is compressed and swells inwardly so as to provide a seal around the polished rod. The upper soft packing can be released and removed. When the safety valve is replaced both soft packings can be compressed so that the two packings provide a seal around the polished rod to improve the safety. To further improve safety, back-up seals can be present at the ends of the threaded sections of the tubular elements to prevent fluid leakage via the screw connections between the tubular elements. The invention will now be explained in more detail with reference to the accompanying drawings, in which Fig. 1 is a vertical sectional view of a wellhead assembly according to the invention. Reference is now made to Fig. 1 showing a wellhead assembly of a beam pumped oil production well. The polished rod 1 of the beam pump passes through a stuffing box consisting of a lower tubular element 2, a middle tubular element 3 and an upper tubular element 4. The lower tubular element 2 is clamped on a ball coupling 5 by means of a clamping nut 6. The middle tubular element 3 is screwed on the lower tubular element 2 and the upper tubular element 4 is screwed on the middle tubular element 3. The upper tubular element 4 contains a housing 10 which carries a safety valve having a flapper type valve body 7. The valve body 7 is secured to a horizontally oriented hinge pin 8 which allows the valve body to rotate between a first substantially horizontal position or closed position (as illustrated in phantom lines) and a second substantially vertical position or open position. During operation of the beam pump the valve body 7 is oriented in the second position thereof and a torsion spring 9 exerts a torque to the valve body 7 which induces the valve body to rotate in the direction of the first position thereof. In this manner a bronze or teflon wear plate 11 carried by the valve body 7 is pressed against the polished rod 1. A wear monitoring pin 12 is arranged behind the valve body 7. The pin 12 can, against the action of a spring 13, be pressed against the valve body 7. Since wear of the wear plate 11 will result in a rotation of the valve body 7 towards the first position thereof the depth over which the pin 12 can be pressed into the stuffing box corresponds to the amount of wear of the wear plate 12. Thus the amount of wear of the wear plate can be regularly controlled by operating personel without interruption of the pumping operations. In case of failure of the polished rod 1 the rod 1 will fall into the well and the spring 9 will push the safety valve 7 to the first, horizontal, position thereof in which it lies against a valve seat 15 and closes the wellhead. Since in case of polished rod failure the resulting decompression of packings 16 and 17 between the three tubular elements 2, 3 and 4 may cause leakage of fluid from the well via the screw thread connections 18, 19 between said elements back-up seal rings 20, 21 are provided in the annular spaces between the tubular elements 2, 3 and 4. The upper packing 17 is composed of reinforced polytetrafluoroethylene and solids containing seal rings, which are held under axial compression by bronze bushings 22 and 23. The upper packing 17 provides a seal around the polished rod 1 during operation of the beam pump. If inspection or replacement of the upper packing 17 is required pumping operations are interrupted and after loosening a counter nut 25 below the middle tubular element 3, the middle element 3 is screwed downwardly towards the lower tubular element 2 so as to axially compress the lower packing 16 via adjacent bronze bushings 26, 27. Then the lower packing 16 provides a seal around the polished rod 1 until the upper packing 17 has been replaced or inspected. Before unscrewing the middle tubular element 3 again to raise it to its normal operative position a high pressure test liquid is injected via a test port 28 into the annular space 29 between the packings 16, 17 so as to test the fluid tightness of the packings. To avoid early wearing of the packings 16, 17 and of the wear plate 11 and bushings 22, 23, 26 and 27 a flexible scraper ring 30 is arranged at the upper end of the wellhead assembly so as to remove solid particles such as dust or sand from the polished rod 1 as it moves down through the wellhead assembly. The scraper ring 30 is mounted in a bushing 31 which is fixed to a second bushing 32. Said second bushing 32 is locked to the wellhead assembly by a wing nut 33. The wellhead assembly according to the invention is designed such that it can be safely operated without requiring frequent maintenance or repair operations. Thus it is of importance that the state of wear of the potentially wear-prone wear plate 11 of the safety valve can be monitored regularly, without requiring disassembling of the wellhead assembly. Since even during maintenance or repair operations or after failure of the polished rod the wellhead is sealed off in a reliable manner the wellhead is particularly suitable for use in wells in reservoirs where steam injection takes place and where toxic or flammable gases such as hydrogen sulphide or methane could escape to the atmosphere via the wellhead. It will be understood that the flapper valve in the wellhead assembly according to the invention provides a more reliable wellhead seal than the known ball valve since the sealing capacity of the flapper valve remains unchanged as long as the wear plate has not completely worn away, whereas the sealing provided by a ball valve immediately reduces if the ball valve becomes unround because of wear. Because moreover in the wellhead assembly according to the invention the amount of wear of the wear plate can be monitored accurately and without interruption of pumping operations the safe operation of the valve is maintained over a long interval of time whilst avoiding regular disassembling of the wellhead assembly for maintenance or inspection. Thus it can be seen that the wellhead assembly according to the invention meets because of its high reliability the highest safety standards and is therefore particularly suitable for use in wells producing from oil reservoirs where steam injection takes place and hot or dangerous gases, such as methane or hydrogen sulphide, could escape via the wellhead to the atmosphere.

Claims: A normally vertical wellhead assembly for a beam pumped production well having an axial passage for a polished rod (1) of the beam pump assembly, the wellhead assembly comprising a stuffing box in which packing (16, 17) is arranged which provides a seal around the polished rod (1), a safety valve including a valve seat (15) and a valve body (7) rotatably arranged in the wellhead assembly about a horizontal hinge pin (8) between an open position and a closed position resting against the valve seat (15) to stop upward flow of fluid through the passage, and an indicator (12, 46) indicating changes in the position of the valve body (7) to allow monitoring the wear of the valve body (7), characterized in that the indicator consists of a pin (12) slidably arranged in a radial hole through the wall of the stuffing box, which pin (12) can, against the action of a spring (13), be pressed against the valve body (7) over a distance corresponding the amount of wear of the valve body (7). The wellhead assembly of claim 1, wherein the stuffing box comprises a lower tubular element (2), a middle tubular element (3) and an upper tubular element (4), the middle tubular element (3) at least partly surrounding and being screwed on top of the lower tubular element (2) and the upper tubular element (4) at least partly surrounding and being screwed on top of the middle tubular element (3), wherein the upper tubular element (4) is provided with the safety valve, wherein between the middle tubular element (3) and the upper tubular element (4) an upper soft packing (17) is arranged which can be forced to swell inwardly by tightening the screw connection between the middle tubular element (3) and the upper tubular element (4), and wherein between the lower tubular element (2) and the middle tubular element (3) a lower soft packing is arranged which can be forced to swell inwardly by tightening the screw connection between the lower tubular element (2) and the middle tubular element (3). The wellhead assembly of claim 2, wherein back-up seals (20, 21) are present at the ends of the threaded sections of the tubular elements (2, 3 and 4) to prevent fluid leakage via the screw connections between the tubular elements (2, 3 and 4).

Inventors: KLAMER, ALBERTUS, LUGTMEIER, LUBERTUS
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1988
Main classification: E21B34
IPC codes: E21B33, E21B34