None.
This invention relates to down hole rod pumps that are typically used to pump liquids from the bottom of a hydrocarbon wells.
As one travels through Texas and Oklahoma and other oil producing regions, it is common to see oil wells with rocking beam pumps in action. The beam is rocked like a seesaw by a motor while one end the beam lifts and lowers a sucker rod string to drive the down hole pump. The sucker rod string is typically made up of a number of twenty-five foot to thirty foot steel rod sections connected end to end to form a long string of rods that extend down into the production tubing of a well. The production tubing itself was inserted into the wellbore after the wellbore was drilled and cased. The production tubing is fixed in the wellbore with a down hole rod pump positioned near the bottom. As the sucker rod moves up and down in the production tubing, the pump draws liquids from the wellbore into a chamber of the pump through a first check valve during a first stroke and then pushes the liquids in the chamber through a second check valve during the return stroke. The liquids pass through the second check valve and into the production tubing above the pump so that the liquids are eventually pumped to the surface and are either piped or trucked to market.
Natural gas wells and many low rate oil wells are sometimes provided with pumps to periodically withdraw liquids that enter the wellbore from the formation and tend to accumulate and slow and eventually stop the production of hydrocarbons the natural gas. The liquid may be water, but may also include hydrocarbon liquids which are sufficiently valuable to collect and transport to market.
One of the problems associated with pump systems for small volumes of liquids in wells is that any solids, particularly small particles, that are produced tend to collect and cause trouble for the pump. If the liquid volume were substantially higher, the particles would likely be carried to the surface and not collect at the bottom of the production tubing. With low liquid production rates and intermittent pumping, the particles tend to collect in the production tubing on top of the pump and have been known to damage the pumps and pumping systems well short of their expected service life. This can be especially challenging in coal seam gas production wells where the particles tend to be very fine and abrasive and are susceptible of stacking out rod strings by caking up and packing between plungers and barrels and blocking the travel of check valves and other vital pumping equipment. Coal seam gas wells produce water and along with highly abrasive coal fines.
Many other wells produce sand which is a problem on a much larger scale in terms of total numbers of pumps exposed to particles. Some wells have sand delivered into the formation to hold open the fissures, fractures and perforations to enhance production of gas and liquids. This kind of sand is called proppant. Unfortunately such proppant sand causes many rod pump failures every year as some amounts exit the formation and creates hazard for moving equipment such as the pump in the wellbore. Another type of sand that is even more difficult for pumps to handle is formation sand, often referred to as flour sand. Formation sand is quite fine in nature and very difficult to control due to its fine size and mobility. It is highly abrasive and will wear out the polished surfaces of a pump or bury and stack out the pump.
The invention more particularly includes a system for producing liquids and solids from the bottom of a natural gas well including a string of production conduit installed in a wellbore where a lower end thereof is near the bottom of the wellbore. The system further includes a pump comprising a barrel and a plunger wherein the barrel is connected to the production conduit near its lower end and a string of hollow rod string is disposed within said production conduit such that a tubing annulus is formed around the hollow rod string where the hollow rod string is connected to the plunger that is positioned within the barrel of the pump for movement up and down the barrel. The system further includes a column of filtered liquid within the tubing annulus on top of the barrel and plunger.
In a further aspect of the system, check valves are provided within the hollow rod string to prevent particles that might settle in liquid from descending below the check valves and maintaining the particles at a level in the wellbore closer to the surface so that when the pump is operating, the particles are pushed closer and closer to the surface to eventually be fully removed from the well.
The invention may further be viewed as a process for producing liquids and solids from the bottom of a natural gas well where an open ended string of production conduit is installed in a wellbore with a seating nipple near the open lower end of the production conduit and a pump is installed at the end of a string of hollow rod string where the pump includes a barrel and a hollow plunger and where the hollow plunger is connected to and in fluid communication with the hollow rod string and further includes a traveling valve to admit liquids into the hollow interior of the plunger and wherein the barrel includes a standing valve to admit liquids from below the seating nipple into the barrel. A barrel is connected to the seating nipple and seal the interior of the production tubing from the open lower end of the production tubing wherein a tubing annulus is defined within the production tubing above the seating nipple and outside the hollow rod string. Substantially particle free liquid is provided into the tubing annulus to be in contact with the barrel and the outside of the plunger and as the plunger is raised and lowered, it draws liquids through the standing valve and through the traveling valve and eventually into the hollow rod string.
In a preferred arrangement, a portion of the liquids are produced through the hollow rod string are directed through a filter and then back into the tubing annulus.
In another preferred arrangement, gas is produced through gas production annulus and a quiet zone is defined below the seating nipple above the open end of the production tubing and gas that enters the quiet zone is allowed to exit back into the gas production annulus from an upper portion of the quiet zone.
The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:
Turning now to the preferred arrangement for the present invention, reference is made to the drawings to enable a more clear understanding of the invention. However, it is to be understood that the inventive features and concept may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.
In
In natural gas wells, liquids that are also produced from the formation tend to slow or block the production of the natural gas into the wellbore 10 so it is generally more productive to maintain the level of liquids below the lowest of the perforations 18. The liquid level is drawn down by a production system including a pump, generally indicated by the arrow 20 that is associated with production tubing 50. The pump 20 and production tubing 50 are run into wellbore 10 separately with the production tubing 50 being first inserted into the wellbore 10. The production tubing 50 is sufficiently smaller than the casing 12 so that gas is easily able to flow up to the surface through annulus 19. The production tubing 50 also has an open bottom end 51 preferably below the lowest of the perforations 18 and above the bottom of the wellbore 10. Production tubing further includes a segment 52, generally called a seating nipple, that includes an inside contour and dimension to receive barrel 30 and seal the barrel in place. Seating nipples typically have a shoulder stop or a reduction of the interior dimension also referred to as “ID”, and a highly machined surface or polished bore for packing seals on barrel 30 to engage into. Thus, the barrel 30 is installed after the production tubing 50, but may be sealed in seating nipple 52 and therefore sealed and isolating the interior 55 of the production tubing 50 from the annulus 19 of casing 12. The production tubing 50 is therefore divided into a small segment at the bottom, called a quiet zone 53 and a production path 55 above the seating nipple 52.
The pump 20 includes a plunger 30 arranged to move up and down within the barrel 40. The plunger 30 is attached to the bottom end of a hollow rod string 22 and is able to move up and down within the barrel 40 that is firmly connected or locked into the seating nipple 52, but it should be understood that the periphery of the plunger 30 and the interior of the barrel 40 are each machined and sized so that any liquid flow around the plunger 30 is substantially restricted. The preferred path for liquids to travel through the barrel 40 is also through the interior of the plunger 30. Below the barrel 40 is a strainer nipple 42 having a number of holes to allow liquids or gas that is in the quiet zone 53 to pass into the barrel through stranding valve 44. Standing valve 44 is shown to be a ball and seat, but may be any suitable one-way valve technology. As the plunger 30 is lifted relative to the barrel 40, liquids are drawn up through the strainer nipple 42 and through standing valve 44 to fill the space in the barrel 40 below the plunger 30. The plunger 30 includes a travelling valve 34, that like the standing valve 44, is shown as a ball and seat, but may be any suitable one-way valve technology. As the plunger 30 is lowered in the barrel 40, standing valve 44 closes to keep liquid in the barrel but unseat the travelling valve so that the liquids in the barrel below the plunger 30 enter and flow into the plunger 30. Liquids that were already in the plunger 30 before the plunger began its downward movement in the barrel exit the top of the plunger 30 through one or more vent holes 36. Liquids that pass out of the vent holes 36 fill the production path 55 and are eventually delivered to the surface.
In operation, pump 20 operates intermittently to lift liquids out of the bottom of the wellbore 10 so that hydrocarbon production is optimized. A number of operation schemes can be employed, but typically, the pump 20 is started based on elapsed time from the most recent pump operation cycle and continues until a reduced weight of the plunger 30 is detected, meaning that the liquids at the bottom of the well are reduced and that the pump 20 has had a gas break through. One of the problems with this arrangement that has been identified by the inventor is that particles such as sand and grit are going to pass into the and through the pump 20, but tend to settle back down in the production path 55 during times of inactivity. In some wells, it is common for just a barrel, or two or three barrels to be pumped off the bottom to maintain natural gas production, but these few barrels may not make it to the surface for days or weeks. By the time a certain volume of liquid makes it to the surface, the small entrained solids are quite likely to have settled and even when stirred up, never make it to the surface. These solids collect around the top of the pump 20 and are prone to cause premature failure of the pump by getting into the top of the gap between the outside of the plunger 30 and the inside of barrel 40. Wear on these highly machined surfaces will likely to cause a pump failure.
Another problem that comes up with the arrangement shown in
To alleviate these and other problems identified in the embodiment of
Focusing on the differences between the invention and the embodiment in
In one aspect of the invention, hollow rod string 125 is connected to plunger 130 by a hollow shear tool 126. The hollow shear tool 126, which will be more fully explained in relation to
A second aspect of the embodiment in
While abrasion and wear are the primary concern of the inventor, another aspect of the present invention that may help avoid gas locks is to provide a vent 158 to allow any gas that has entered the quiet zone 53 such as gases dissolved from the hydrocarbon liquid to pass back into the annulus 119 and exit the well 10. The vent 158 is above the highest opening in the strainer nipple 42 so that the liquid level inside the quiet zone 153 is not lower than the liquid level outside the quiet zone in the annulus 119. Another strategy to alleviate gas lock is to increase the fluid slippage past the plunger/barrel interface from annulus 160 into barrel 140 to displace traveling valve 134 and push gas into flow path 155.
Turning now to
In another aspect of the invention, the tubing annulus 160 provides other options for dealing with challenges in wellbores. For example, in the event the a well produces a lot of sand, a perforated pipe section may be installed just above the seating nipple to allow clean liquids to descend into the wellbore 112 without interfering with the gas production. Once the clean liquids are past or below the perforations 118, the perforated section allows the liquids to entrain the sand or solids and provide sufficient liquids to operate the pump 120 continuously. While a full column of clean liquid would no longer be practical once the production tubing 150 is pierced, the primary concern of sand collection would have been addressed. However solids free liquid would either be maintained on top of the pump or would continuously pass by the pump depending on the location of the liquid exit port(s).
The production tubing 150, may also be provided with an opening to the annulus 119 to provide a path to direct a chemical treatment such as a scale, corrosion or paraffin inhibitor to a location that is prone to such problems anywhere up or down the length of the wellbore. It should be noted that even hot liquid such as water or oil to enhance production. The tubing annulus 160 provides many new options for addressing a near endless list of challenges in the oil field.
In one further preferred aspect related to
While it should be understood that the invention introduces two tubing strings which enables operators of wells to control the operating environment of the pump 120. The invention provides a way to flush water or other liquid to the pump from above (through the inside of the production tubing 150) or from below the pump through the annulus 119. In one particular advantage, the seating nipple or short section of pipe may be slotted or ported to provide a path for injection of liquids or chemicals or both into the wellbore anywhere up or down the production tubing 150. In cold weather circumstances, the string may be warmed with heated liquids injected into production tubing 150 that would thaw any ice that may have formed during a cold night or extended cold period. Some formations produce paraffins that may precipitate into waxy solids when exposed to temperatures below the formation temperature. Solvents may be added to the liquids in the production tubing 150 in the tubing annulus 160 that dissolves the waxy solids. Paraffin control may be accomplished by a combination of heated liquids and solvents.
It should further be understood that while the adjacent surfaces of the outside of the plunger 130 and inside of barrel 140 are preferably machined with close tolerances to prevent liquids from passing through the gap, some amount of liquids will pass through the gap. In fact, with the arrangement of the tubing annulus 160 providing clean liquids and liquids with additives for paraffin control, lubrication of the pump 120, control of scale, and other preventive measures, it may be preferable to open the tolerances of the barrel and plunger. This small amount of flow can be described as liquid slippage and opening up the tolerances slightly would increase the pump slippage. Such added pump slippage reduces the potential for gas lock and provides a direct route to lubricate the pump and any places along the production tubing where the hollow rod string comes into contact with the production tubing.
Turning now to a second embodiment of the present invention shown in
Turning now to
One interesting aspect of this arrangement is that with the liquids coming to the surface within a hollow rod string, the liquids exit the well pumping system on the “downstroke” of the rod pump. In conventional rod pumps, the liquid production occurs on the “upstroke.” This point may not seem significant, but it does reveal that the present invention is quite different than prior systems.
Finally, the scope of protection for this invention is not limited by the description set out above, but is only limited by the claims which follow. That scope of the invention is intended to include all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are part of the description and are a further description and are in addition to the preferred embodiments of the present invention. The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application.
This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/247,331 filed Sep. 30, 2009, entitled “Double String Pump for Hydrocarbon Wells,” which is incorporated herein in its entirety.
Number | Date | Country | |
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61247331 | Sep 2009 | US |