Abstract:
In some embodiments, a method of delivering at least one chemical into an underground well equipped with a reciprocating plunger includes retaining the plunger above the well after the well is unloaded and shut in, dispensing at least one chemical into the well and releasing the plunger so that the plunger may drop in the well after the chemical(s).

Description:
This application claims priority to U.S. Provisional Application Ser. No. 60/833,133 filed Jul. 25, 2006 and entitled “Apparatus and Methods for Delivering Chemicals into an Underground Well”, the entire disclosure of which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to apparatus and methods for providing at least one chemical into an underground well. In some embodiments, the present invention relates to apparatus and methods for providing treatment chemicals into hydrocarbon producing wells equipped with a plunger lift system. 
     BACKGROUND OF THE INVENTION 
     Various artificial lift techniques have been used to improve recovery of oil and/or gas from subterranean reservoirs, such as when production by natural reservoir pressure becomes uneconomical. In particular, plunger lift systems have been effective at improving oil and/or gas recovery in various situations. These systems, for example, often utilize a free-traveling plunger or piston that drops to the bottom of the well. In such systems, also know as free piston systems, as the plunger falls, fluid in the tubing flows around and above the plunger. When desired, one or more wellhead valve is opened, allowing gas in the well to push the plunger up to the surface. As the plunger moves up, liquids above the plunger are pushed to the surface and recovered. This sequence can be repeated by closing the wellhead off and allowing the plunger to fall back into the well. 
     The ability to produce oil and/or gas from subterranean reservoirs may be enhanced by providing treatment chemicals in the well to reduce viscosity of fluids in the well, corrosion, scale and deposits of undesirable materials, such as paraffin and distillates, in the well or for other purposes. Treatment chemicals can include soap, acid, corrosion inhibitors, scale inhibitors, solvents, dispersants, and inhibitors for paraffin and petroleum distillates, stabilizers, surface active agents and other chemical-based liquids and/or solids. 
     Various techniques have been employed to deliver treatment chemicals downhole. Some example chemical delivery techniques for use in wells equipped with plunger lift systems are described in U.S. Pat. No. 7,004,258, entitled “Method and Apparatus for Enhancing Oil and Gas Flow in a Well” and issued on Feb. 28, 2006, and U.S. Pat. No. 7,117,947, entitled “Well Chemical Treatment Utilizing Plunger Lift Delivery System” and issued on Oct. 10, 2006. 
     Existing chemical delivery techniques used in wells equipped with plunger lift systems have limitations. For example, many delivery techniques do not ensure effective delivery of the treatment chemicals to the desired downhole locations. For another example, various existing delivery techniques require the manufacture, installation and effective operation of additional equipment that must be used within the well. For further examples, various existing procedures are uneconomical, unreliable, cumbersome to employ or unsuitable for use in certain wells. 
     It should be understood, however, that the above-described examples, features and/or disadvantages are provided for illustrative purposes only and are not intended to limit the scope or subject matter of the claims of this patent or any patent or patent application claiming priority hereto. Thus, none of the appended claims or claims of any related patent application or patent should be limited by the above discussion or construed to address, include or exclude the cited examples, features and/or disadvantages, except and only to the extent as may be expressly stated in a particular claim. Further, the above exemplary disadvantages should be evaluated for any particular existing downhole applications on a case-by-case basis. 
     Accordingly, there exists a need for apparatus and methods useful for providing chemicals into wells equipped with plunger lift systems having one or more of the following attributes, capabilities or features: effectively uses treatment chemicals; minimizes waste of treatment chemicals; assists in providing ideal chemical treatment; assists in ensuring chemicals do not trickle down well or dry up before reaching the well bottom; ensures chemicals are delivered to the well bottom; efficiently delivers chemicals to the desired location in the well; generally uniformly coats the tubing walls with chemicals; provides chemicals into the well quickly at every plunger stroke; repeatedly delivers chemicals to the bottom of the well to prevent scale deposits and/or corrosion; automatically maintains continuous chemical presence in the well; allows nearly continuous treatment of the wellbore; prevents injected chemicals from flowing out of the well with fluid exiting the well; prevents the plunger from preceding chemicals down the well; allows the plunger to be held above the well to allow insertion of chemicals before the plunger drops; allows the plunger to follow the chemicals down the well, pushing chemicals to the bottom, assisting in evenly dispersing chemicals in the borehole or evenly distributing chemicals along the inner surface of the tubing. 
     BRIEF SUMMARY OF THE INVENTION 
     In some embodiments, the present invention involves a method of delivering at least one treatment chemical into an underground hydrocarbon well equipped with a reciprocating plunger. The method includes retaining the plunger above the well when the plunger is at an upstroke and shutting in the well. The plunger is retained above the well and at least one treatment chemical is dispensed into the well. The plunger is released, allowing the plunger to drop in the well after the dispensed treatment chemical(s). 
     In various embodiments, the present invention involves a method of providing chemicals into an underground well equipped with a plunger lift system. The plunger lift system including at least one plunger capable of moving up and down in a tubing disposed in the well and, on its upstroke, pushing well fluid out of the tubing into at least one flow passage. The method includes providing at least one chemical insertion inlet to the tubing. After an upstroke of the plunger, the plunger is held proximate to the top of the well. When desired, the at least one flow passage is closed to prevent fluid flow out of the well. The plunger is held generally above the location of the at least one chemical insertion inlet. Chemicals are inserted into the well through the at least one chemical insertion inlet(s) and the plunger is released to allow the plunger to drop in the well. 
     There are embodiments of the invention that involve an apparatus for delivering at least one chemical into an underground borehole equipped with a plunger lift system. The plunger lift system includes a plunger capable of moving up and down in the borehole and a plunger catcher capable of holding the plunger generally above the borehole. The apparatus includes at least one chemical supply source, and at least one chemical supply line in fluid communication with the chemical supply source and the borehole. At least one controller is electronically engaged with the plunger catcher and capable of controlling the flow of fluids into the borehole from the chemical supply source. The controller causes chemicals to be provided into the borehole while the plunger is held by the plunger catcher and causes the plunger to be released into the borehole thereafter. 
     Accordingly, the present invention includes features and advantages which are believed to enable it to advance underground chemical delivery technology. Characteristics and advantages of the present invention described above and additional features and benefits will be readily apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments and referring to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following figures are part of the present specification, included to demonstrate certain aspects of preferred embodiments of the invention and referenced in the detailed description herein. 
         FIG. 1  is a longitudinal schematic showing an exemplary prior art well equipped with a plunger lift system; 
         FIG. 2  is a longitudinal schematic showing an embodiment of a chemical delivery system of the present invention installed in an exemplary well equipped with a plunger lift system; and 
         FIGS. 3A ,  3 B,  3 C and  3 D are perspective views of example prior art plungers. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Characteristics and advantages of the present invention and additional features and benefits will be readily apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments of the claimed invention and referring to the accompanying figures. It should be understood that the description herein and appended drawings, being of preferred embodiments, are not intended to limit the appended claims or the claims of any patent or patent application claiming priority to this application. On the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the claims. Many changes may be made to the particular embodiments and details disclosed herein without departing from such spirit and scope. 
     In showing and describing the preferred embodiments, like or identical reference numerals are used to identify common or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
     As used herein and throughout various portions (and headings) of this patent application, the terms “invention”, “present invention” and variations thereof are not intended to mean the invention of every possible embodiment of the invention or any particular claim or claims. Thus, the subject matter of each such reference should not be considered as necessary for, or part of, every embodiment of the invention or any particular claim(s) merely because of such reference. Also, it should be noted that reference herein and in the appended claims to components and aspects in a singular tense does not necessarily limit the present invention to only one such component or aspect, but should be interpreted generally to mean one or more, as may be suitable and desirable in each particular instance. 
     Referring initially to  FIG. 1 , an example hydrocarbon well  12  equipped with a plunger lift system is shown. The exemplary well  12  may be a gas or oil well, or produce a combination of gas and oil. The well  12  has a wellbore  16  within which a casing  20  extends into the earth to a production zone  24 . A tubing  28  is shown installed within the casing  20 . A free-traveling plunger  36  is shown in the tubing  28 . 
     Well production flows through the tubing  28  to a wellhead  32 . At the exemplary wellhead  32 , a manifold  40  includes a plunger catcher  44 , such as, for example, an electromagnetic or pneumatic device, capable of engaging and holding the plunger  36  to temporarily prevent it from re-entering the tubing  28  below. The illustrated manifold  40  also includes a lubricator  46  and one or more valve  49  through which gas and/or liquids may flow from the well  12  into a flow passage  52 , such as a sales flow line  54 . A controller  56  controls the valve(s)  49  and the plunger catcher  44 . In this example, based upon the pressure or flow rate in the well  12 , the controller  56  can shut-in the well  12  by causing the valve  49 , such as a flow control motor valve, to close. 
     In typical operation of the example of  FIG. 1 , the plunger  36  provides a mechanical interface between produced liquids and gas in the well  12 . Shutting in the well  12  at the surface allows the free traveling plunger  36  to fall to the bottom  14  of the well  12  (or other desired location). Fluids typically pass around the plunger  36  through a space (not shown) between the plunger  36  and the tubing  28 , or passageways (not shown) in the plunger  36 . When the well  12  is open, such as by opening the valve  49 , gas in the well  12  will push the plunger  36  and the liquid above the plunger  36  up the tubing  28  to the surface  26 . Using the energy of the well  12  for lift, liquids are thus delivered to the surface  26  by movement of the plunger  36 . When the plunger  36  reaches the top of the well  12 , it enters or is received by the lubricator  46 , which may include a bumper  47  to reduce the impact of the plunger  36 . The plunger catcher  44  is activated to hold the plunger  36  until a signal is received to release the plunger  36 , which typically occurs as soon as the well is shut-in. 
     The illustrated controller  56  contains circuitry for opening and closing the appropriate valve(s)  49  during the different phases of the lift process. When flow in the well  12  diminishes to a predetermined flow rate or pressure in the well drops to a predetermined set point, the controller  56  shuts the valve  49  to shut-in the well  12  and release the plunger  36  to drop back into the tubing  28 . This cycle is typically repeated numerous times per day. 
     Additional descriptions of various example plunger lift systems are available in publicly available documents, such as U.S. Pat. No. 6,209,637 entitled “Plunger Lift with Multi-Part Piston and Method of Using the Same” and issued on Apr. 3, 2001, U.S. Pat. No. 7,004,258, entitled “Method and Apparatus for Enhancing Oil and Gas Flow in a Well” and issued on Feb. 28, 2006 and U.S. Pat. No. 7,117,947, entitled “Well Chemical Treatment Utilizing Plunger Lift Delivery System” and issued on Oct. 10, 2006, the disclosures of which are all hereby incorporated by reference herein in their entireties. 
     The above-referenced components may have any suitable form, construction, configuration and operation as is or becomes know. Moreover, the above-referenced components are not limiting upon the present invention, the appended claims or the claims of any patent application or patent claiming priority hereto. Accordingly, the present invention may be used in wells that do not include all of the above components or have additional components. For example, the present invention may be used with any suitable plunger and plunger lift system that is or becomes known. Example types of plungers with which the present invention may be used include the coiled tubing plunger  60  of  FIG. 3A , the brush plunger  62  of  FIG. 3B , the solid bar stock plunger  64  of  FIG. 3C  and the pad plunger  66  of  FIG. 3D , the neck(s)  68  of which may provide an area where the plunger  36  may be engaged by the plunger catcher  44 . Yet other types of potentially compatible plungers  36  include wobble washer plungers, snake plungers and multi-part plungers (not shown). 
     Now in accordance with an embodiment of the present invention, referring to  FIG. 2 , chemicals are insertable into the well before the plunger  36  drops back into the well  12 . In this example, one or more chemical injection pump  70  is capable of dispensing chemicals through a chemical supply line  74  from a chemical supply source  78  into the tubing  28 . The chemical insertion interface, or inlet,  80  into the tubing  28  is shown located below the position of the plunger  36  when the plunger  36  is held by the catcher  44  to ensure chemicals are insertable into the well  12  below the plunger  36 . However, the inlet(s)  80  of this embodiment may be positioned anywhere, as long as chemicals are insertable into the well before the plunger  36  drops back into the well  12 . 
     The chemicals may take any suitable form, composition and characteristics and may include one or more liquids, gels, films, oil-based products, solvent-based products, solids and/or gases, as desired. Examples of treatment chemicals that may be used are scale inhibitors, corrosion preventatives, paraffin inhibitors, microorganisms, foaming agents, gas expansion agents and multi-purpose chemicals. Fluid treatment chemicals, for example, may be water soluble and disperse in water in the well. It should be understood, however, the chemicals are in no way limiting upon the present invention. 
     The chemical injection pump  70 , supply line  74  and supply source  78  may have any desired form, construction and configuration, and may be located as desired. Moreover, these components are not required for the present invention. For example, the chemicals may be manually poured, dumped or otherwise provided into the well  12  at the chemical insertion inlet(s)  80 . For another example, chemicals may be provided into the well  12  through the flow control valve  49 , such as with the use of a three-way valve. 
     In the illustrated embodiment, the chemical supply line  74  fluidly communicates with the tubing  28  through a check valve  48 , which prevents produced fluids from flowing back to the supply source  78  from the well  12 . In other embodiments, an electronically activated control valve (not shown) may be used in conjunction with the check valve  48  and/or multiple check valves (not shown) may be included. The illustrated chemical injection pump  70  may be a gas-operated, solar-powered or electric, high pressure chemical pump capable of pumping a high fluid volume in a short time and against a potentially significant backpressure from the well. Suitable pumps are presently commercially available from Texsteam, Wilden, Western, Solar Injection Systems, Inc., or Williams Milton Roy. The exemplary chemical supply source  78  is a chemical storage tank  82  located proximate to the well  12 . 
     Still with reference to the embodiment of  FIG. 2 , the exemplary controller  56  controls the catcher  44 , chemical injection pump  70 , flow of well fluid out of the well  12  and insertion of chemicals into the well  12 . Thus, the timing and duration of engagement and release of the plunger  36  and insertion of chemicals may be selectively established to optimize the desired chemical treatment scheme. If desired, the controller  56  may be capable of providing automatic insertion of a desired batch volume of chemicals at each plunger cycle or other intervals. 
     The controller(s)  56  may include one or multiple components and take any suitable form, arrangement and operation as is or becomes known. In the illustrated embodiment, the controller  56  is an electronic control system programmable to control the timing of engagement and disengagement of the catcher  44  with the plunger  36 , operation of the chemical injection pump  70  and flow control valve  49 . 
     A method of providing chemicals into a well in accordance with an embodiment of the present invention will now be described with reference to the example of  FIG. 2 . When the plunger  36  is pushed up the tubing  28  to the manifold  40  during normal operations, the plunger  36  is held above the well  12 . Well production is allowed to exit the tubing  28 . For example, the controller  56  may actuate the valve  49  to open the sales flow line  54  and the catcher  44  to hold the plunger  36 . 
     When well production has sufficiently exited the tubing  28 , or the well flow/pressure decreases to a desired level, the well  12  is shut-in. In the example shown, at a pre-set well pressure, the controller  56  closes the valve  49  to cut off the sales flow line  54 . The plunger  36  remains held above the well  12  and chemicals may be inserted into the well  12 . The chemicals may be provided in any desired manner. For example, fluid chemicals may be pumped, injected or poured into the tubing  28 . For another example, solid chemicals may be effectively dumped into the tubing  28  to generally run down the inside wall  30  of the tubing  28  to the bottom  14  of the well  12  or other desired location. In the embodiment of  FIG. 2 , for example, after the controller  56  closes the motor valve  49 , it actuates the chemical injection pump  70  to pump a batch volume of treatment chemicals through the chemical supply line  74  into the tubing  28  from the chemical supply source  78  for a pre-set duration. 
     In certain exemplary applications, water soluble scale and/or corrosion prevention chemicals may be inserted to treat water at or near the bottom  14  of the well  12 , and as the treated water rises in the well  12 , it is non-corrosive and/or non-scaling. For another example, in certain instances, such as in some gas producing wells, a filming corrosion inhibitor is coated along the entire inside wall  30  of the tubing  28  to prevent corrosion throughout operations. 
     If desired, the quantity of chemicals provided into the well  12  may be controlled, such as by controlling the speed of the pump  70 , diameter of the piston of the pump  70 , length of stroke of the pump  70 , size of flow orifices in the chemical supply line  74 , supply source  78  or insertion interface  80 , a combination thereof or any other desired technique. In the exemplary embodiment, the chemical input quantity is controlled by duration of actuation and size of the chemical pump  70 . 
     The quantity of chemicals may be based upon any desired variable(s), such as the type of chemical, desired action of the chemicals, frequency of insertion of the chemicals and nature and condition of the well  12 . For example, the quantity of chemicals may be based, at least in part, upon the objective(s) of ensuring the chemicals reach the bottom  14  of the well  12  and/or uniformly coating the inner surface of the wall  30  of the tubing  28 . Chemical input quantities may range, for example, from one cup to multiple gallons per insertion. In applications involving low pressure producing wells, for example, it may be desirable to use a minimal quantity (e.g. 2 gallons per day) of scale inhibitor chemicals sufficient to reach the bottom  12  of the well  14  and effectively treat the water therein. However, the present invention is not limited to the above examples or ranges of chemical volume. 
     The timing of chemical insertion may be based upon any desired variables. Depending upon the application, a steady state chemical treatment equilibrium of injected chemical volume and frequency may be desirable. For example, chemicals may be automatically inserted into the tubing  28  on every cycle or stroke of the plunger  36 , such as to maintain chemicals in the tubing  28  continuously, or nearly-continuously, to provide uninterrupted treatment of well fluids. Alternatively, chemicals may not be inserted into the well  12  on every cycle or stroke of the plunger  36 , but at other desired times or intervals. For example, chemicals may be inserted into the tubing  28  for a total of one, two or “x” times per day, at every 2 nd , 3 rd  or n th  plunger cycle or otherwise as desired. 
     Still with reference to the example of  FIG. 2 , after the chemicals are inserted into the tubing  28 , or otherwise when desired, the plunger  36  is released. In this embodiment, if the plunger cycle includes the insertion of chemicals, the plunger  36  follows the chemicals down the tubing  28 , forcing the chemicals to the bottom of the tubing  28  where fluids are accumulating or other desired location(s), assisting in evenly dispersing the chemicals in the tubing  28 , evenly distributing the chemicals across the inside wall  30  of the tubing  28  or for another suitable purpose. The type of plunger  36  may be selected to assist achieving the desired objective. For example, a brush plunger (e.g. item  62 ,  FIG. 3B ) may be used to assist in evenly distributing chemicals on the inside surface of the wall  30  of the tubing  28 . 
     The timing of the release of the plunger  36  may be established depending upon any pertinent parameter(s), such as well pressure, chemical type or quantity and treatment objective. In the embodiment shown, for example, the controller  56  may be programmed to cause the catcher  44  to disengage with the plunger  36  immediately after a desired quantity of chemicals is inserted into the tubing  28 . In some instances, it may be desirable to delay the release of the plunger  36  for a certain period of time to allow inserted chemical to begin its descent in the tubing  28 . In other instances, it may be desirable to release the plunger  36  at some time during insertion of the chemicals into the tubing  28 . For another example, when chemicals are inserted intermittently (not at every plunger cycle), the plunger  36  may be released as soon as the well  12  is shut-in for cycles not including the insertion of chemicals. 
     Preferred embodiments of the present invention thus offer advantages over the prior art and are well adapted to carry out one or more of the objects of the invention. However, the present invention does not require each of the components and acts described above and is in no way limited to the above-described embodiments, methods of operation, variables, values or value ranges. Any one or more of the above components, features and processes may be employed in any suitable configuration without inclusion of other such components, features and processes. Moreover, the present invention includes additional features, capabilities, functions, methods, uses and applications that have not been specifically addressed herein but are, or will become, apparent from the description herein, the appended drawings and claims. 
     The methods described above and claimed herein and any other methods which may fall within the scope of the appended claims can be performed in any desired suitable order and are not necessarily limited to the sequence described herein or as may be listed in the appended claims. Further, the methods of the present invention do not necessarily require use of the particular embodiments shown and described in the present application, but are equally applicable with any other suitable structure, form and configuration of components. 
     While preferred embodiments of the invention have been shown and described, many variations, modifications and/or changes of the system, apparatus and methods of the present invention, such as in the components, details of construction and operation, arrangement of parts and/or methods of use, are possible, contemplated by the patent applicant(s), within the scope of the appended claims, and may be made and used by one of ordinary skill in the art without departing from the spirit or teachings of the invention and scope of appended claims. Thus, all matter herein set forth or shown in the accompanying drawings should be interpreted as illustrative, and the scope of the invention and the appended claims should not be limited to the embodiments described and shown herein.