Abstract:
A slim hole production system for pumping liquids to the surface of a hydrocarbon well and especially a hydrocarbon well that is producing both natural gas and liquids where the diameter of the hole in the production area is too small to get production tubing and a sucker rod into a productive arrangement. The slim hole pump includes a hollow tube that raises and lowers the plunger and carries the liquids to the surface and uses the annulus to produce the gas.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/247,313 filed Sep. 30, 2009, entitled “Slim Hole Production System,” and to U.S. Provisional Application Ser. No. 61/247,386 filed Sep. 30, 2009, entitled “Producing Gas and Liquid from Below a Permanent Packer in a Hydrocarbon Well,” and also to U.S. Provisional Application Ser. No. 61/247,331 filed Sep. 30, 2009, entitled “Double String Pump for Hydrocarbon Wells,” all of which are incorporated herein in their entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
     FIELD OF THE INVENTION 
     This invention relates to pumping liquids from hydrocarbon wells that are producing natural gas. 
     BACKGROUND OF THE INVENTION 
     The process of drilling hydrocarbon wells results in many wells with small diameter tubing or casing in the hydrocarbon bearing zone due to problems encountered during drilling and more casing strings being installed than were originally anticipated. Each string of casing is inherently smaller in diameter than the previously installed string to allow the successive casing string to be installed through the previous casing strings. For whatever the reason, many wellbores exist with casing in the hydrocarbon bearing zone with a diameter of less than three inches. When these wells are producing some amount of gas, the flow rate is sufficient to entrain and carry the liquids with the gas to the surface. Eventually, these slim holes mature to the point that the gas flow rate is not sufficient to carry the liquids to the surface. At the same time, there is still enough gas in the formation to continue to provide an economic incentive to keep the well open and producing. 
     Typically, some have installed coiled tubing that has a much smaller diameter than the small diameter casing to use the same gas productivity in the well to flow upwardly at a faster rate and keep the liquids entrained with the gas. This may work for a while, but the productivity of gas wells eventually diminishes to a point where it must be shut in. 
     In an ideal world, production tubing would be installed and a rod pump installed to positively pump the liquids from the bottom of the well and allow gas production to continue for the longest potential time and greatest potential recovery. However, many slim holes are not large enough to accommodate production tubing in which a rod pump can operate. 
     SUMMARY OF THE INVENTION 
     The invention more particularly includes a system for producing liquids and solids from the bottom of a slim hole natural gas well where the system comprises a string of casing installed in a wellbore where a lower end of the casing string is near the bottom of the wellbore and a pump including a barrel and a plunger is inserted into the casing string such that the barrel is secured to the casing near the lower end of the casing string. A string of hollow rod is disposed within the casing string such that an annulus is formed around the hollow rod string within the casing and 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 and liquids are produced to the surface from the plunger up through the hollow rod string. 
     In a preferred arrangement, check valves are placed at intervals in the hollow rod string equivalent to expected pumped volume per pump cycle to aid in transporting solids to surface. Solids and liquid will advance from one ball check to at least the next per pump cycle on low liquid volume wells. 
     In another aspect, the invention more particularly comprises a process for producing liquids and solids from the bottom of a cased slim hole natural gas well where the process includes installing a pump 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. The plunger includes a traveling valve to admit liquids into the hollow interior of the plunger and the barrel is secured to the inside of the casing wherein an annulus is formed between the inside of the casing and the outside of the hollow rod string. The process further includes raising and lowering the plunger to draw liquids through the standing valve and through the traveling valve and eventually into the hollow rod string so that natural gas is produced through the annulus to the surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a cross section of a conventional wellbore with rod pump installed to produce liquid from the bottom of the wellbore; 
         FIG. 2  is a cross section of a slim hole wellbore with hollow rod pump of the present invention installed to produce the liquids and allow continuous production of the natural gas; and 
         FIG. 3  is an exploded perspective view of a hollow shear tool for providing preferred breakaway for the production system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
     A hydrocarbon well having an internal diameter in the hydrocarbon bearing zone of less than about 3 inches is generally described as a slim hole well. Many such slim hole wells have accessed rich hydrocarbon deposits and produce natural gas and recoverable liquids. Typically, these slim hole wells produce sufficient gas to entrain and carry most liquids that were produced from the formation to the surface due to the high gas flow rate. Both the liquids and gases are collected and if the liquids comprise hydrocarbons, they are taken to market. Typically the liquid by-product is water which is disposed of. As a slim hole well produces hydrocarbons over time, its flow rate gradually diminishes until liquids start accumulating at the bottom. High production rates may last many months or may last many years. However, gas rates inherently diminish as the reservoir is drained. As the gas rate diminishes, less of the liquid is carried with the gas flow to the surface such that a liquid volume at the bottom of the well is above the perforations that allow the hydrocarbons into the wellbore. Although gas may continue to bubble through the liquid, the diminishing production rate typically gets quite choked down to a substantially lower rate. 
     In a conventionally sized well, operators typically install a rod pump. For example, as shown in  FIG. 1 , a conventional wellbore, generally indicated by the arrow  10 , is shown formed or drilled into the ground G. According to conventional procedures, casing  12  has been inserted into the wellbore and sealed against the wall of the wellbore with cement  15  whereafter perforations  18  have been punched through the casing  12  and through the cement  15  and into a hydrocarbon-bearing formation in the ground G by explosive charges. Hydrocarbons in the hydrocarbon-bearing formation are then enabled to flow into the wellbore  10  through perforations  18  where natural gas and other gases would ascend up the wellbore through annulus  19  while liquids accumulate at the bottom of the wellbore  10 . The liquid level is drawn down by a production system including a pump, generally indicated by the arrow  20 , which is associated with a production tubing  50 . The pump  20  and production conduit  50  are run into wellbore  10  separately with the production conduit  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  40  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  40  is installed after the production conduit  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 sucker 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 a slim hole well, there simply is not room for a string of production tubing  50  to be installed that maintains annulus  19  for gas flow while accommodating a barrel and plunger inside the production tubing. 
     A solution for producing liquids at the bottom of slim hole wellbores is shown in  FIG. 2  where like elements are presented with the same reference numbers used in  FIG. 1 , but are identified with reference numbers that are three digit reference numbers with the first digit being “1” where the corresponding element in  FIG. 1  has a two digit reference number. What should be seen as different about the invention as compared to the conventional arrangement is that the pump  120  is connected to hollow rod string  125  and arranged to pump the liquid up the axis of the hollow rod string. Secondly, there is no production tubing equivalent to production tubing  50  in  FIG. 1 . The barrel includes a perforated nipple  142  with a pipe lock  160  attached to the bottom or distal end of the perforated nipple  142 . Pipe lock  160  includes dogs  162  that are deployed radially outwardly to lock into the casing  112  and hold the pipe lock  160 , perforated nipple  142  and barrel  140  in position near the bottom of the wellbore  110 . The perforated nipple  142  is attached to the barrel  140  by a hollow shear tool  126  that will be more fully described in reference to  FIG. 3 , below. As natural gas continues to be produced from the formation through perforations  118 , the gas is allowed to rise up through annulus  119  outside of the hollow rod string  125 . Liquids that are produced descend from the perforations  118  and are drawn through holes in the perforated nipple  142  as the plunger  130  is lifted upwardly in the fixed barrel  140 . The liquid is drawn through standing valve  144  which is a one-way check valve of any suitable form to allow flow up into barrel  140 , but not down into the perforated nipple  142 . When plunger  130  descends in barrel  140 , standing valve  144  seats or closes and travelling valve  134  opens to allow the liquids in the working space  146  of the barrel  140  to enter into the plunger cavity  136 . Liquids in the plunger cavity  136  are pressed up through check valve  145  and into production path  155  inside the hollow rod string  125 . 
     Space in a slim hole is limited and liquid flow into the perforated nipple  142  may enter radially and may enter axially through core  163  of pipe lock  160 . The dogs  162  are spaced around the pipe lock  160  to generally center the barrel  140  and perforated nipple  142  and allow flow from below the pipe lock  160  to the perforated nipple  142  between the dogs. Typically three or four dogs  162  are used to hold the pipe lock  160  in position with respect to the casing  112 . 
     One aspect of the present invention is that it is preferred that any solids such as sand or other particles are produced with the liquid. The small diameter of the hollow rod string  125  along with check valves spaced apart up the length of the rod string  125  to the surface entrain the solids with the liquid by high flow rate and when the pump  120  ends a pump cycle, each of the check valves  145  keep such solids from descending all the way to the plunger  136 . In other words, each stroke of the plunger  130  may move the same volume of liquid, but the liquid moves far closer to the surface at a higher velocity so that the entrained solids are more likely to be carried farther up the production path  155  within the hollow rod string  125  during each pump operation cycle. Moreover, check valves such as shown at  145  are provided within the production path  155  so that when a pumping cycle is ended and the pump  20  is idled, the particles only settle down to the last check valve each particle may have passed. Ideally, by calculating the wellbore volume that liquid will be allowed to occupy and by spacing the check valves or ball checks within the string so that the volume between them does not exceed a pumping cycle volume then each operating cycle would cause the particles to pass through at least one check valve. Again, with the smaller diameter in the production path  155 , a pump rate can set at or above the lift velocity required for the well and re-entrainment of the solids into the liquid flow should be quicker and more certain. 
     In one further preferred aspect, a rod rotator may be installed at the top of the well near the location where the lifting mechanism attaches to the rod string  125 . The rod rotator  135  rotates the hollow rod string  125  and spreads any wear from the up and down motion evenly around the outside of the rod string  125  to extend the life of the rod string  125 . Also, with the rod string  125  being hollow, it will likely and preferably have a larger diameter than equivalent non-hollow sucker rod of the same strength and will therefore have a larger radius distributing any load on the inside of the casing  112  in a manner that will reduce the cutting or damaging wear on the casing  112 . 
     It should further be understood that while the plunger  130  is shown with outside walls spaced from the inside surfaces of the barrel  140 , the adjacent surfaces of the outside of the plunger  130  and inside of barrel  140  are machined with close tolerances to prevent liquids from passing through the gap. As noted above, a series of check valves, such as check valve  145  are placed at intervals up the hollow rod string equivalent to expected pumped volume per pump cycle to aid in transporting solids to surface. Solids and liquids are arranged to advance from one check valve  145  to at least the next check valve  145  per pump cycle on low liquid volume wells. 
     Turning now to  FIG. 3 , one particular aspect of the invention it to provide a well operator a way to most easily get back into the wellbore  110  in the event that the pump  120  needs to be withdrawn and the pipe lock  160  is corroded into the casing  112 . A hollow shear tool  126  provides a “weakest link” in the production system so that most of the string is recovered and that other tools may be used to recover only a small portion of the string nearest the most likely to be stuck element and that being the pipe lock  160 . The arrangement and operation of the hollow shear tool  126  will now be explained. The hollow shear tool  126  comprises three segments. Base segment  180  includes screw threads  180   a  to attach to the perforated nipple  142  with ring segment  181  overlying the upper, smaller diameter portion  180   c  of base segment  180 . The ring segment slides down smaller diameter portion  180   c  until it contacts shoulder  180   b . Breakaway segment  182  also slides over smaller the diameter portion  180   c  until holes  184  generally align with groove  188  in smaller diameter portion  180   c . Breakaway segment  182 , like base segment  180  includes screw threads that are arranged to attach to the hollow rod string plunger  140 . O-rings  186   a  and  186   b  are provided to seal the hollow interior passageway from the outside of hollow shear tool  126 . With a preselected number of screws screwed into holes  184  and into groove  188 , a predetermined breakaway strength can be provided so that when a tension between the barrel  140  and perforated nipple  142  exceeds the predetermined breakaway strength, the breakaway portion  182  will separate from the base portion. The predetermined breakaway strength may be easily tested using conventional machine shop stools such as a press and pressure gauge by removing ring segment  181  and inserting a number of screws  185  and applying compression force until the screws break. The screws  185 , in the arrangement of the hollow shear tool, should provide the same breakaway strength in compression and tension. The inventor expects that breakaway strengths of roughly 10,000 pounds or 15,000 pounds may be achieved and using stronger or weaker materials would expand the capacity range of such an arrangement. Clearly, the ease at which the breakaway strength may be successively measured should provide confidence in the actual breakaway strength. Screw holes that are not used are preferably blinded off to reduce the possibility of leaking. 
     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.