The present invention relates to petroleum production and has significant application to gas wells which use plunger lift systems to aid in production from the well. In particular, the invention relates to delivery of treatment chemicals downhole to prevent to scale deposits, paraffin buildup, and corrosion and for other purposes.
This invention relates to production from petroleum wells, and in particular, the delivery of chemicals downhole. The invention will find the greatest use in wells which produce gas. Thus, the background description and the description of the preferred embodiments of the invention will focus on gas wells.
Typically, as gas is produced from a well the production decreases as the pressure in the formation decreases with the quantity of gas produced from the well. Usually, a well produces not only gas but also liquids, such as water and petroleum condensates with some asphaltines. As the pressure in the formation decreases the volume and velocity of the gas flow slows. Initially, the flow rate and velocity may be sufficient to remove the liquids with the gas. At some point in time the flow rate of gas will be insufficient to carry liquids out of the well, e.g., carry water and petroleum condensates, to the surface. As a result, the liquid loading in the well will increase, and liquid will collect in the bottom of the borehole. This liquid will exert back pressure on the formation which will further decrease the production rate from the formation, and in some cases cause production to cease altogether. When production by natural reservoir pressure becomes uneconomical, artificial lift techniques can be utilized to increase well production. A number of artificial lift systems are known in the industry, including sucker rod pumps, gas lift techniques and plunger lift techniques. Also, it has been known to utilize a combination of plunger and gas lifting techniques within a well as discussed in U.S. Pat. No. 3,090,316 entitled “Gas Lifting System.” Depending upon well conditions, economics and many other factors, a suitable lift technique is selected. Each technique has certain advantages and disadvantages.
Conventional plunger lift systems, which are also known as free piston systems, utilize a plunger (piston) that is dropped into the well by closing the valve on the wellhead and stopping the upward flow of gas in the well. The plunger is “free” because it is not attached to a sucker rod, cable or other mechanism to pull the plunger to the surface. The plunger falls to the bottom of the tubing and onto a bumper or stop at the bottom of the tubing. Liquid in the tubing will flow around the plunger as it falls in the tubing. After pressure in the well has built up to a predetermined load, the valve at the wellhead is opened and the gas pushes the piston upward to the surface, thereby pushing the liquid on top of the plunger to the surface. This sequence can be repeated by closing the wellhead off and allowing the plunger to fall again to the bottom of the well. Another technique is the use of a bypass plunger which is designed so as not to require the well to be shut in. U.S. Pat. No. 6,209,637 entitled “Plunger Lift with Multi Piston and Method” relates to this technique.
Frequently, a well that is utilizing plunger lift is an older well. As a result, the bottom of the well is subject to corrosion, scale, paraffin deposits, deposits of petroleum distillates and other undesirable deposits. Frequently, treatment chemicals are deposited downhole. These treatment chemicals can include such things as soap, acid, corrosion inhibitors, solvents for paraffin and petroleum distillates, stabilizers and other known treatment chemicals. A number of techniques have been employed to deliver treatment chemicals downhole. These techniques have many drawbacks, especially when they are employed with plunger lift production methods.
One method of treatment is to continuously pump a small amount of treatment chemical into the well during production. The treatment chemical falls to the bottom of the well, where it mixes with other fluids and is drawn up with the liquid lifted by the plunger. This continuous treatment approach usually requires a conduit to deliver the chemical to the bottom of the well and uses an unnecessarily large amount of chemicals. Another method is to use a batch treatment that involves pumping liquid treatment chemicals down the borehole relying on a dead space below the perforations to retain residual chemical for a period of time. The method is not reliable, and is unsuitable for use in some wells due to lack of perforations to retain the residual chemical, or because well production rates are so high as to quickly remove the chemicals. Thus, there has been a need for a method and apparatus to provide treatment chemicals down a wellbore which is efficient in the delivery of chemicals, minimizes waste of treatment chemicals, and minimizes disruption to production from the well. The current invention has the advantages of repeatedly delivering chemicals to the bottom of the oil or gas well to prevent scale deposits and/or corrosion. The current invention has the advantages of being economical, requiring little in the way of additional equipment and allowing continuous treatment of the wellbore. Thus, the system is much more efficient than existing delivery methods, in that it can concentrate chemical where it is often most needed which is at and below the stop (seating nipple), and is much less expensive to install than the continuous chemical injection method.
The invention will be better understood with reference to the drawings taken in connection with the detailed description which follows:
The drawings illustrate certain preferred embodiments of the invention and like elements have been provided with like reference numerals to corresponding items between various drawings.
The present invention relates to a method and apparatus for delivery of treatment chemicals to a wellbore utilizing artificial lift techniques. In the method of the present invention treatment chemical for treating a downhole formation that is delivered to the bottom of the wellbore in association with the placement of a plunger at the bottom of the wellbore. One embodiment, the invention relates to a method of applying the treatment chemical to a known plunger, such as a coiled tube plunger, or a brush plunger in the form of a gel, putty, paste or other suitable consistency such that a significant portion of the treatment chemical will be retained on the plunger as it is dropped from the well head to the bottom of the wellbore. Once at the bottom of the wellbore, the fluid in the wellbore dissolves or mixes with the treatment chemical which dissociates into the wellbore, treating the wellbore and the near wellbore area. At predetermined times when the plunger returns to the surface additional treatment chemical can be applied to the plunger before it is again dropped to the bottom of the wellbore. Alternatively, the method can be conducted by placing the treatment chemical within a chemical dispenser attached to a standard plunger, or in a specifically designed plunger/dispenser device which is a combination of a plunger and dispensing unit.
In another aspect, the present invention relates to a plunger/dispenser apparatus. The apparatus includes an interface area and a dispenser section which includes one or more receptacles for receipt of treatment chemical. The plunger/dispenser may also have a neck for engagement with a plunger catcher, and/or downhole tools.
In yet another aspect, the present invention relates to a chemical dispenser which can be attached to a known plunger. The dispenser includes a head with an attachment mechanism for attaching to a known plunger, and one or more receptacles for receipt of treatment chemicals. In one embodiment of the invention, the receptacle may be an elongate chamber having lower ports and upper ports. In a preferred embodiment, a valve is associated with the lower ports to control flow of liquid through the lower ports.
In one embodiment, the valve may be a flexible polymeric sheet which is pressed against the lower ports as the dispenser falls through the wellbore and liquid. When the dispenser comes to rest at the bottom of the wellbore, the flexible sheet will fall away from the lower ports of the dispenser, opening the lower ports to liquid flow so that the chemical within the dispenser can be dissolved into the liquid.
Also, in a preferred embodiment of the invention, the dispenser may include an extension or standoff section which allows the receptacle holding the treatment chemical to be positioned below the lower end of the tubing when the plunger assembly comes to rest at the bottom of the well. This allows the treatment chemical to be dissolved into or mixes with the liquid located in the near wellbore area, thereby increasing the efficiency of the chemical delivery.
In another aspect, the invention relates to a chemical application apparatus. The apparatus is a modification to manifold systems used in plunger lift operations. In this embodiment an applicator is positioned in the section of the manifold which receives the delivery system, e.g., plunger, or plunger/dispenser apparatus, or plunger with attached chemical dispenser. The applicator is positioned such that it will be operatively adjacent to the receptacle portion of the plunger, plunger/dispenser or chemical dispenser attached to a plunger. The nature of the applicator can vary depending upon the form in which the chemical is utilized.
The invention also includes the recharging of chemical to the chemical delivery system. This method involves catching the chemical delivery system in a manifold, applying chemical to the assembly without removing the assembly from the manifold.
The automated application of chemicals to the delivery system is especially suited to the application of gels and paste. In these applications the applicator can include a nozzle which communicates with an opening in the manifold and is aligned such that it delivers chemical at the desired portion of the chemical delivery system. The nozzle can be connected to a storage tank for the chemical via a conduit. A control valve to control the flow of chemical from the storage container to the nozzle can be provided in the conduit between the storage container and the nozzle, or at other suitable locations.
The chemical in the delivery system can also be recharged by removing the delivery system from the manifold and recharging the chemical. This method can be used for any form the chemical is used, such as, stick, time release capsules, gel, paste, putty, liquid, emulsion, etc.
For purposes of background, an abbreviated discussion of the plunger lift technique will be presented. Those skilled in the art will recognize that there are many variations which have been used to the lift technique and system which is described. The preferred embodiment of the invention specifically described can be modified for variations of the described lift system. Further, those skilled in the art will appreciate that the present invention need not be used to the exclusion of other chemical treatment methods. Costs and other considerations can result in the use of the present invention together with other treatment methods.
The petroleum well will have a wellbore 10 which typically contains a casing 12 either throughout the entire bore or a portion of the wellbore. The wellbore 10 can also contain tubing 14 within the casing 12. In a typical arrangement, the well production will flow through the tubing 14 to the wellhead 16. For purposes of illustrating the invention, the invention is discussed in relation to a gas well. For gas lift operations the tubing 14 can be provided with a stop 18 at the lower end of the tubing 14, a plunger 20 which travels in the tubing 14, at the wellhead 16. In a typical arrangement, a manifold 22 is provided at the wellhead 16 which can have a plunger catch 30 to hold the plunger in place, a lubricator 32 to lubricate the plunger 20, and a control box 34 to control the flow of gas and liquid from the well by operating the valves 24, 26, and 28 and related conduits.
The stop 18 is to prevent the plunger 20 from falling below the position of the stop 18. The stop 18 can include a spring 36 or other shock absorbing device to reduce the impact of the falling plunger 20. The plunger 20 can be of any of the numerous designs which are known in the art or another delivery system as described herein. The plunger 20 provides a mechanical interface between the gas 38 and the liquid 40 present in the well. Shutting the well off at the surface allows the plunger 20 to fall to the bottom of the well and rest on the stop 18. The pressure differential between gas trapped in the wellbore between the casing 12 and tubing 14 and in the tubing 14 above the plunger increases. The fluid will pass around the plunger 20 through a space left between the plunger 20 and the tubing 14 or through passageways in the plunger. Gas pressure builds in the well, and when the well is opened, the gas will push the plunger 20 and the liquid on top of the plunger up the tubing 14 to the surface.
When the plunger 20 reaches the top of the well it enters or is received by the manifold 22. The manifold 22 can include a shock absorbing spring 42 or other mechanism to reduce the impact of the plunger. Appropriate sensors are provided to detect arrival of the plunger 20 at the surface and to activate plunger catch 30 which holds the plunger 20 until a signal is received to release the plunger 20. The control box 34 contains circuitry for opening and closing the appropriate valves 24, 26, and 28 during the different phases of the lift process, applying lubrication, if desired, to the plunger from lubricator and releasing the plunger to return to the bottom of the tubing 14.
Various plunger designs and plunger lift control systems are well known in the art. For example, U.S. Pat. No. 6,209,637 entitled “Plunger Lift with Multi-Part Piston and Method of Using the Same” discloses a multi-part plunger. This multi-part plunger is designed to allow the piston to drop into the well while the well is still flowing. After the plunger drops a ball is dropped on top of the plunger which seals a passageway through the plunger. This allows the two-part plunger then to function as a one-piece plunger. The present invention is suitable for use with any known plunger lift system.
Other types of plungers include a wobble washer plunger which has a series of shifting rings placed along the length of the plunger to maintain contact with the inside of the tubing; and a snake plunger.
Referring now to
The chemical dispenser 65 should securely attach to plunger 20. In some applications it may be desirable for the chemical dispenser 65 to have some play in the connection between the plunger 20 and the chemical dispenser 65 to permit a slight wobble. Some operators may prefer a more rigid fit, in which case, a portion of the upper surface 90 of head 66 can be a shaped surface which mates with a corresponding surface 92 on the plunger 20 so as to limit the movement of the plunger with respect to the dispenser. In a preferred embodiment, one or more upper ports 94 are provided, and one or more lower ports 96 are provided. Upper ports 94 allow gas and liquid to enter or leave the receptacle 70. While the plunger is falling in the tubing the primary function of ports 94 is to exhaust any gas and liquid which may enter the receptacle to aid the fall of the plunger. Once the plunger has reached the stop at the bottom of the tubing the upper ports 94, if below the liquid level, will function to allow chemical contained in the receptacle to diffuse into or mix with the liquid. Lower ports 96 allow liquid to enter and leave the receptacle 76. In the illustrated embodiment, the lower ports 96 are on the bottom surface of the body 74; however, they can also be positioned on the side walls. Preferably, a valve 98 is provided. In the illustrated embodiment, valve 98 is a flexible rubber sheet 100 having a dimension sufficient to cover lower ports 96. Valve 98 is held in place by a retaining plug 102 which can extend through an opening 104 in the bottom of the member 68. The purpose of valve 98 is to either restrict or close off the flow of liquid through lower ports 96 as the plunger drops. As the plunger drops in the tubing, the flexible sheet 100 will be pushed against the bottom of the member 68. This will either completely seal or partially seal off ports 96. The purpose of valve 98 is to minimize or prevent the flow of fluid through receptacle 70 while the system drops in the tubing. This will prevent or minimize the washing of chemicals out of the receptacle as the chemical dispenser 65 passes through the fluid above the stop of the tubing. Once the delivery system 64 comes to rest on the stop, flexible sheet 100 will fall away from the bottom of member 68 and to a second position 102 (shown in phantom), because there is no force pushing the flexible sheet 100 against the bottom of member 68. This will allow liquid to enter receptacle 70 and leach the treatment chemical 72 out of receptacle 70.
In addition to previously described embodiments of receptacles, an additional embodiment is illustrated in
Referring to
Designs and construction of plunger catchers are well known in the art. Chemical application assembly 240 includes a chemical storage reservoir 246 which is connected by conduit 248 to a valve 250 which is connected to applicator 252. Applicator 252 can be a nozzle, an open end of conduit, or other device. The selection of the specific applicator will be made taking into account the physical characteristics of the form of the treatment chemical. In a preferred embodiment, the treatment chemical for use with the chemical application assembly will be a viscous liquid or gel. Once the receptacle section of dispenser is aligned with the applicator, the valve 252 can be opened and chemical forced onto the plunger or into the chemical dispenser to recharge the treatment chemical. Any suitable mode of force can be utilized to force the chemical from storage container 246 including pressurizing the storage container 246 or by pumping. The use of the chemical application apparatus 240 is not required. Alternatively, the plunger and/or the plunger and chemical carrier can be removed from manifold 16, inspected and the chemical agent recharged if needed.
The chemical carrier can be made out of any material which is suitable for use in the construction of plungers. While necks have been illustrated, any other design known in the art which allows engagement with a recovery tool or with the plunger catcher.
The treatment chemical can be any known treatment chemical. Further, the treatment chemical can be encapsulated in time-release capsules or in water-soluble gels. Treatment chemicals which can be used include paraffin solvents, clay stabilizers, paraffin inhibitors, kelating agents, scale inhibitors, solvents, corrosion inhibitors, acid, and soap. Suitable encapsulated treatment chemicals are described in U.S. Pat. No. 6,279,656 B1 entitled “Downhole Chemical Delivery System for Oil and Gas Wells.”
Although the invention has been disclosed and described in relation to its preferred embodiments with a certain degree of particularity, it is understood that the present disclosure of some preferred forms is only by way of example and that numerous changes in the details of construction and operation and in the combination and arrangements of parts may be resorted to without departing from the spirit of the scope of the invention as claimed here.