Abstract:
A system includes a string that includes a passageway and a plurality of tools. The system further includes an untethered object that is adapted to be deployed in the passageway such that the object travels downhole via the passageway and controllably expand its size as the object travels downhole to selectively cause one of the tools to capture the object.

Description:
This application is a continuation of U.S. patent application Ser. No. 11/834,869, entitled, “SYSTEM FOR COMPLETING MULTIPLE WELL INTERVALS,” which was filed on Aug. 7, 2007 (abandoned), which is a divisional of Ser. No. 10/905,073, filed Dec. 14, 2004, U.S. Pat. No. 7,387,165, entitled, “SYSTEM FOR COMPLETING MULTIPLE WELL INTERVALS,” which issued on Jun. 17, 2008. The Ser. No. 11/834,869 application and the U.S. Pat. No. 7,387,165 are each hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The present invention relates generally to recovery of hydrocarbons in subterranean formations, and more particularly to a system and method for delivering treatment fluids to wells having multiple production zones. 
     In typical wellbore operations, various treatment fluids may be pumped into the well and eventually into the formation to restore or enhance the productivity of the well. For example, a non-reactive “fracturing fluid” or a “frac fluid” may be pumped into the wellbore to initiate and propagate fractures in the formation thus providing flow channels to facilitate movement of the hydrocarbons to the wellbore so that the hydrocarbons may be pumped from the well. In such fracturing operations, the fracturing fluid is hydraulically injected into a wellbore penetrating the subterranean formation and is forced against the formation strata by pressure. The formation strata is forced to crack and fracture, and a proppant is placed in the fracture by movement of a viscous-fluid containing proppant into the crack in the rock. The resulting fracture, with proppant in place, provides improved flow of the recoverable fluid (i.e., oil, gas or water) into the wellbore. In another example, a reactive stimulation fluid or “acid” may be injected into the formation. Acidizing treatment of the formation results in dissolving materials in the pore spaces of the formation to enhance production flow. 
     Currently, in wells with multiple production zones, it may be necessary to treat various formations in a multi-staged operation requiring many trips downhole. Each trip generally consists of isolating a single production zone and then delivering the treatment fluid to the isolated zone. Since several trips downhole are required to isolate and treat each zone, the complete operation may be very time consuming and expensive. 
     Accordingly, there exists a need for systems and methods to deliver treatment fluids to multiple zones of a well in a single trip downhole. 
     SUMMARY 
     In an embodiment of the invention, a technique includes providing a string that includes a passageway and a plurality of tools. The technique includes deploying an untethered object in the passageway such that the object travels downhole via the passageway; and expanding a size of the object as the object travels downhole to selectively cause one of the tools to capture the object. 
     In another embodiment of the invention, a system includes a string that comprising a passageway and a plurality of tools. The system further includes an untethered object that is adapted to be deployed in the passageway such that the object travels downhole via the passageway and controllably expand its size as the object travels downhole to selectively cause one of the tools to capture the object. 
     In yet another embodiment of the invention, a system includes a string; a plurality of valves disposed in the string; and a dart. Each of the valves includes a seat, and each of the seats is sized to catch an object that has substantially the same size traveling through the passageway of the string. Each of the valves is adapted to control fluid communication between the passageway of the string and a region that is exterior to the string. The dart is adapted to be deployed in the passageway such that the dart travels downhole via the passageway and controllably expands its size as the dart travels downhole to selectively cause the dart to lodge in one of the seats. 
     Advantages and other features of the invention will become apparent from the following drawing, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The manner in which these objectives and other desirable characteristics can be obtained is explained in the following description and attached drawings in which: 
         FIG. 1  illustrates a profile view of an embodiment of the multi-zonal well completion system of the present invention having zonal communication valves being installed/deployed in a wellbore. 
         FIGS. 2A-2B  illustrate profile and cross-sectional views of an embodiment of a sliding sleeve zonal communication valve of the present invention. 
         FIG. 3  illustrates a cross-sectional view of an embodiment of an actuating dart for use in actuating the sliding sleeve of the zonal communication valve. 
         FIGS. 4A-4E  illustrates a cross-sectional view of an embodiment of the sliding sleeve zonal communication valve being actuated by a dart using RF receivers/emitters. 
         FIG. 5A  illustrates a cross-sectional view of an embodiment of the zonal communication valve having an integral axial piston for actuating the sleeve. 
         FIG. 5B  illustrates a schematic view of an embodiment of the well completion system of the present invention having a control line network for actuating one or more zonal communication valves. 
         FIG. 6  illustrates a profile view of an embodiment of the multi-zonal well completion system of the present invention having zonal communication valves being actuated by one or more drop balls. 
         FIG. 7  illustrates a cross-sectional view of a sliding sleeve zonal communication valve having an additional filtering position. 
         FIGS. 8A-8D  illustrate cross-sectional views of various embodiments of pump-out piston ports of a zonal communication valve. 
         FIGS. 9A-9H  illustrate cross-sectional views of an embodiment of a sliding sleeve zonal communication valve being installed in a wellbore. 
         FIGS. 10A-10C  illustrate profile views of an embodiment of the well completion system of the present invention being deployment in an open or uncased hole. 
         FIGS. 11A-11E  illustrate profile views of an embodiment of a plurality of sliding sleeve zonal communication valves being actuated by a latching mechanism suspended by a working string. 
     
    
    
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     In the specification and appended claims: the terms “connect”, “connection”, “connected”, “in connection with”, and “connecting” are used to mean “in direct connection with” or “in connection with via another element”; and the term “set” is used to mean “one element” or “more than one element”. As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and “downwardly”, “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention. Moreover, the term “sealing mechanism” includes: packers, bridge plugs, downhole valves, sliding sleeves, baffle-plug combinations, polished bore receptacle (PBR) seals, and all other methods and devices for temporarily blocking the flow of fluids through the wellbore. Furthermore, the term “treatment fluid” includes any fluid delivered to a formation to stimulate production including, but not limited to, fracing fluid, acid, gel, foam or other stimulating fluid. 
     Generally, this invention relates to a system and method for completing multi-zone wells by delivering a treatment fluid to achieve productivity. Typically, such wells are completed in stages that result in very long completion times (e.g., on the order of four to six weeks). The present invention may reduce such completion time (e.g., to a few days) by facilitating multiple operations, previously done one trip at a time, in a single trip. 
       FIG. 1  illustrates an embodiment of the well completion system of the present invention for use in a wellbore  10 . The wellbore  10  may include a plurality of well zones (e.g., formation, production, injection, hydrocarbon, oil, gas, or water zones or intervals)  12 A,  12 B. The completion system includes a casing  20  having one or more zonal communication valves  25 A,  25 B arranged to correspond with each formation zone  12 A,  12 B. The zonal communication valves  25 A,  25 B function to regulate hydraulic communication between the axial bore of the casing  20  and the respective formation zone  12 A,  12 B. For example, to deliver a treatment fluid to formation zone  12 B, valve  25 B is opened and valve  25 A is closed. Therefore, any treatment fluid delivered into the casing  20  from the surface will be delivered to zone  12 B and bypass zone  12 A. The valves  25 A,  25 B of the well completion system may include any type of valve or various combinations of valves including, but not limited to, sliding or rotating sleeve valves, ball valves, flapper valves and other valves. Furthermore, while this embodiment describes a completion system including a casing, in other embodiments any tubular string may be used including a casing, a liner, a tube, a pipe, or other tubular member. 
     Regarding use of the well completion system of the present invention, some embodiments may be deployed in a wellbore (e.g., an open or uncased hole) as a temporary completion. In such embodiments, sealing mechanisms may be employed between each valve and within the annulus defined by the tubular string and the wellbore to isolate the formation zones being treated with a treatment fluid. However, in other embodiments the valves and casing of the completion system may be cemented in place as a permanent completion. In such embodiments, the cement serves to isolate each formation zone. 
       FIGS. 2A and 2B  illustrate an embodiment of a zonal communication valve  25 . The valve  25  includes an outer housing  30  having an axial bore therethrough and which is connected to or integrally formed with a casing  20  (or other tubular string). The housing  30  has a set of housing ports  32  formed therein for establishing communication between the wellbore and the axial bore of the housing. In some embodiments, the housing  30  also includes a set of “lobes” or protruding elements  34  through which the ports  32  are formed. Each lobe  34  protrudes radially outward to minimize the gap  14  between the valve  25  and wellbore  10  (as shown in  FIG. 1 ), yet cement may still flow through the recesses between the lobes during cementing-in of the casing. By minimizing the gap  14  between the lobes  34  and the formation, the amount of cement interfering with communication via the ports  32  is also minimized. A sleeve  36  is arranged within the axial bore of the housing  30 . The sleeve  36  is moveable between: (1) an “open port position” whereby a flowpath is maintained between the wellbore and the axial bore of the housing  30  via the set of ports  32 , and (2) a “closed port position” whereby the flowpath between the wellbore and the axial bore of the housing  30  via the set of ports  32  is obstructed by the sleeve  36 . In some embodiments, the sleeve  36  includes a set of sleeve ports  38 , which are aligned with the set of ports  32  of the housing  30  in the open port position and are not aligned with the set of ports  32  of the housing  30  in the closed port position. In other embodiments, the sleeve  36  does not include ports and the valve  25  is moved between the open port position and the closed port position by moving the sleeve  36  out of proximity of the set of ports  32  and moving the sleeve  36  to cover the set of ports  32 , respectively. While in this embodiment, the sleeve  36  is moved between the open port position and closed port position by sliding or indexing axially, in other embodiments, the sleeve may be moved between the open port position and the closed port position by rotating the sleeve about the central axis of the housing  30 . Furthermore, while this embodiment of the valve  25  includes a sleeve  36  arranged within the housing  30 , in an alternative embodiment, the sleeve  36  may be located external of the housing  30 . 
     Actuation of the zonal communication valve may be achieved by any number of mechanisms including, but not limited to, darts, tool strings, control lines, and drop balls. Moreover, embodiments of the present invention may include wireless actuation of the zonal communication valve as by pressure pulse, electromagnetic radiation waves, seismic waves, acoustic signals, and other wireless signaling.  FIG. 3  illustrates one embodiment of an actuation mechanism for selectively actuating the valves of the well completion system of the present invention. A dart  100  having a latching mechanism  110  (e.g., a collet) may be released into the casing string  20  and pumped downhole to engage a mating profile  37  formed in the sliding sleeve  36  of a valve  25 . Once engaging the sleeve, hydraulic pressure behind the dart  100  may be increased to a predetermined level to shift the sleeve between the open port position and the closed port position. Certain embodiments of the dart  100  may include a centralizer  115  (e.g., guiding fins). 
     In some embodiments of the dart of the present invention, the latching mechanism  110  is static in that the latching mechanism is biased radially outward to engage the mating profile  37  of the sleeve  36  of the first valve  25  encountered (see  FIG. 3 ). In other embodiments, the latching mechanism  110  is dynamic in that the dart  100  is initially run downhole with the latching mechanism collapsed (as shown in  FIG. 4A ) and is programmed to bias radially outward upon coming into proximity of a predetermined valve (see  FIG. 4B ). In this way, the valve  25  of a particular formation interval may be selected for opening to communicate a treatment fluid to the underlying formation. For example, with respect to  FIG. 4A , each valve  25 A,  25 B,  25 C includes a transmitter device  120 A,  120 B,  120 C for emitting a particular signal (e.g., a radio frequency “RF” signal, an acoustic signal, a radioactive signal, a magnetic signal, or other signal). Each transmitter  120 A,  120 B,  120 C of each valve  25 A,  25 B,  25 C may emit a unique RF signal. A dart  100  is pumped downhole from the surface having a collet  110  (or other latching mechanism) arranged in a collapsed (i.e., non-radially biased) position. The dart  100  includes a receiver  125  for receiving a particular target RF signal. As the dart  100  passes through valves  25 A,  25 B emitting a different RF signal, the collet  110  remains collapsed. With respect to  FIG. 4B , as the dart  100  comes into proximity of the valve  25 C emitting the target RF signal, the collet  110  springs radially outward into a biased position. With respect to  FIG. 4C , the biased collet  110  of the dart  100  latches to the mating profile  37 C valve of the sleeve  36 C. The dart  100  and the sleeve  36 C may then be pumped downward until the valve  36 C is moved into the open port position whereby delivering a treatment fluid to the formation interval  12 C may be achieved. 
     In some embodiments, the dart may include a sealing mechanism to prevent treatment fluid from passing below the dart once it is latched with the sliding sleeve of the valve. With respect to  FIG. 4D , in these embodiments, another dart  200  may be released into the casing string  20  and pumped downhole. As with the previous dart  100 , the collet  210  of dart  200  remains in a collapsed position until the dart  200  comes into proximity of the transmitter  120 B of the valve  25 B emitting the target RF signal corresponding to the receiver  225  of the dart  200 . With respect to  FIG. 4E , once the signal is received, the collet  210  springs radially outward into a biased position to latch and seal with the mating profile  37 B of the valve sleeve  36 B. The dart  200  and the sleeve  36 B may then be pumped downward until the valve  25 B is moved into the open port position and whereby valve  25 B is isolated from valves  25 A and  25 C. In this way, a treatment fluid may be delivered to the formation interval  12 B. In one embodiment of the present invention, the darts may include a fishing profile such that the darts may be retrieved after the treatment fluid is delivered and before the well is produced. 
     In another embodiment of the well completion system of the present invention, with reference to  FIGS. 11A-11E , instead of pumping a latching mechanism downhole on a dart, a latching mechanism  700  (e.g., a collet) may be run downhole on a work string  705  (e.g., coiled tubing, slickline, drill pipe, or wireline). The latching mechanism  700  is used to engage the sleeve  36 A,  36 B,  36 C to facilitate shifting the sleeve between the open port position and the closed port position. In well stimulation operations, the latching mechanism  700  may be used to open the corresponding valve  25 A,  25 B,  25 C of the formation interval  12 A,  12 B,  12 C targeted for receiving a treatment fluid. In this way, the target formation interval is isolated from any other formation intervals during the stimulation process. For example, in one embodiment, a latching tool  700  having a collet  710  may be run downhole on a slickline  705 . The collet  710  includes a plurality of fingers  712  having protruding elements  714  formed on each end for engaging a mating profile  39 A,  39 B,  39 C formed on the inner surface of the sliding sleeve  36 A,  36 B,  36 C of each valve  25 A,  25 B,  25 C. The collet  710  may be actuated between a first position whereby the fingers  712  are retracted (see  FIG. 11A ) and a second position whereby the fingers are moved to extend radially outward (see  FIG. 11B ). The collet  710  may be actuated by pressure pulses emitted from the surface for reception by a controller included in the latching tool  700 . Alternatively, the latching tool  700  may also include a tension converter such that signals may be delivered to the controller of the latching tool by vertical motion in the slick line  705  (e.g., pulling on the slickline form the surface). In operation, the latching tool  700  is run to the bottom-most valve  25 C with the collet  710  in the first retracted position. Once the latching tool  700  reaches the target depth proximate the formation interval  12 C, the collect  710  is activated from the surface to extend the fingers  712  radially outward such that the elements  714  engage the mating profile  39 C of the sliding sleeve  36 C. The latching tool  700  is pulled axially upward on the slickline  705  to shift the sliding sleeve  36 C from the closed port position to the open port position, thereby permitting delivery of a treatment fluid into the underlying formation interval  12 C. After treating the formation interval  12 C, the latching tool  700  is again pulled axially upward on the slickline  705  to shift the sliding sleeve  36 C from the open port position to the closed port position. The collet  710  is then again actuated to retract the plurality of fingers  712  and disengage from the sliding sleeve  36 C. The latching mechanism  100  may then be moved upward to the next valve  25 B such that the valve may be opened, a treatment fluid may be delivered to the formation interval  12 B, and then the valve may be closed again. This process may be repeated for each valve in the well completion system. 
     In yet other embodiments of the present invention, the valves of the well completion system may be actuated by a network of control lines (e.g., hydraulic, electrical, fiber optics, or combination). The network of control lines may connect each of the valves to a controller at the surface for controlling the position of the valve. With respect to  FIGS. 5A-5B , each valve  25 A,  25 B,  25 C includes an integral axial piston  60  for shifting the sleeve  36  between the open port position and the closed port position and a solenoid  62 A,  62 B,  62 C for energizing the piston of each valve  25 A,  25 B,  25 C. An embodiment of this network may include an individual control line for every valve  25  running to the surface, or may only be a single electric control line  64  and a hydraulic supply line  66 . With regard to the embodiment including the single electric control line  64 , a unique electrical signal is sent to an addressable switch  68 A,  68 B,  68 C electrically connected to a solenoid  62 A,  62 B,  62 C. Each addressable switch  68 A,  68 B,  68 C recognizes a unique electric address and passes electric power to the respective solenoid  62 A,  62 B,  62 C only when the unique signal is received. Each solenoid  62 A,  62 B,  62 C ports hydraulic pressure from the supply line or vents hydraulic pressure to the formation, casing or back to surface. When activated each solenoid  62 A,  62 B,  62 C moves the sleeve  36  between the open port position and the closed port position. 
     In still other embodiments of the well completion system of the present invention, the actuation mechanism for actuating the valves may include a set of drop balls. With respect to  FIG. 6 , the valves  25 A,  25 B,  25 C may each include a drop ball seat  300 A,  300 B,  300 C for landing a drop ball in the sleeve  36 A,  36 B,  36 C and sealing the axial bore therethrough. Pressure can then be applied from the surface behind the drop ball to shift each sleeve  36 A,  36 B,  36 C between the open port position and closed port position. In one embodiment, each valve may have a seat sized to catch a ball of a particular size. For example, the seat  300 B of an upper valve  25 B may have an axial bore therethrough having a diameter larger than the seat  300 C of a lower valve  25 C such that the drop ball  310 C for actuating the lower valve  25 C may pass through the axial bore of the seat  300 B of the upper valve  25 B. This permits opening of the lower valve  25 C first, treating the formation  12 C, then opening the upper valve  25 B with drop ball  310 B and treating the formation  12 B. As with the darts, the balls may seal with the seats to isolate the lower valves during the delivery of a treatment fluid. 
       FIG. 7  illustrates another embodiment of a zonal communication valve  25  for use with the well completion system of the present invention. As with the embodiment shown in  FIG. 2 , the valve  25  includes a housing  30  having a set of housing ports  32  formed therein and a sliding sleeve  36  having a set of corresponding sleeve ports  38  formed therein. However, in this embodiment, the sleeve  36  also includes a filter  400  formed therein. When aligned with the set of housing ports  32  of the housing  30 , the filter  400  of the sleeve  36  provides a third position in which the valve  25  may operate. In well operations, an embodiment of the valve  25  includes three positions: (1) closed, (2) fully open to deliver a treatment fluid, and (3) open through a filter  400 . The “filtering position” may be selected to prevent proppant or alternatively for traditional sand control (i.e., to prevent produced sand from flowing into the wellbore). The filter  400  may be fabricated as any conventional sand control screen including, but not limited to, slotted liner, wire wrapped, woven wire cloth, and sintered laminate sand control media. 
       FIGS. 8A-8C  illustrate yet another embodiment of the zonal communication valve  25  of for use with the cemented-in well completion system of the present invention. In this embodiment, each port  32  of the housing  30  includes an extendable piston  500  having an axial bore therethrough for defining a flowpath between the formation and the axial bore of the valve  25 . Each piston  500  may be extended to engage the formation and seal against cement intrusion during the cementing-in of the casing, thereby permitting cement to flow past the extended pistons. Generally, each valve  25  is run downhole with the casing having the pistons  500  in a retracted position. Once the target depth of the casing is reached, the pistons  500  may be pressurized to extend radially outward and engage and/or seal against the formation. In some embodiments, each piston includes a frangible seal  505  (e.g., a rupture disc) arranged therein for preventing cement from flowing into the piston  500 . Once the cement is cured, the valve  25  may be pressurized to break the seal  505  and establish hydraulic communication with the formation. Treatment fluid may then be delivered to the formation via the extended pistons  500 . Alternatively, a thin metal flap may be attached the housing to cover the ports and block any flow of cement into valve. In this embodiment, the flap may be torn free from the housing by the pressure of the treatment fluid during stimulation of the underlying interval. In an alternative embodiment of the pistons  500 , as shown in  FIG. 5D , each piston  500  may be provided a sharp end  510  to provide an initiation point for delivering a treatment fluid once extended to engage the formation. These alternative pistons  500  may be open ended with a frangible seal  505  or have a closed end with no frangible seal (not shown). In the case of a closed end, the sharp, pointed end  510  of the piston  500  would break under pressure to allow hydraulic communication with the formation. 
     With respect to  FIGS. 9A-9H , an embodiment of a procedure for installing the well completions system of the present invention is provided. In this embodiment, the well completion system is integral with a casing string and is cemented in the wellbore as a permanent completion. The cement provides zonal isolation making any mechanical zonal isolation device (external casing packers, swelling elastomer packers, and so forth) unnecessary. First, a casing string having one or more zonal communication valves  25  is run in a wellbore to a target depth where each valve is adjacent to a respective target formation zone  12  ( FIG. 9A ). A tubing string  600  is run through the axial bore of the casing to the bottom of the casing ( FIG. 9B ) and creates a seal between the casing and the tubing work string  600  (e.g., by stabbing into a seal bore). Hydraulic pressure is applied from the surface around the tubing string  600  to each valve  25  to actuate the set of pistons  500  in each port  32  and extend the pistons  500  radially outward to engage the target formation  12  ( FIGS. 9C and 9D ). In some embodiments, the hydraulic housing ports  32  may be packed with grease, wax, or some other immiscible fluid/substance to improve the chance of the tunnel staying open during the cementing operation. In alternative embodiments, the well completion system of the present invention is run downhole without a set of pistons  500  in the ports  32 . Moreover, in some embodiments, an expandable element  610  is arranged around the set of ports may be formed of a swellable material (e.g., swellable elastomer blend, swellable rubber, or a swellable hydrogel). This swellable material may react with water, oil, and/or another liquid in the wellbore causing the material to expand outward to form a seal with the formation  12  ( FIG. 9E ). In some embodiments, the swellable material may be dissolvable after the cementing operation is complete. In alternative embodiments, a frangible material, permeable cement, or other device may be used to prevent cement from entering the valve  25  from the wellbore annulus side. These devices maybe used with the swellable material, which also helps keep cement from entering the valve or the devices may be used in combination with other devices, or alone. After the set of pistons  500  of each valve  25  are extended, cement  620  is pumped downward from the surface to the bottom of the casing via the tubing string  600  and upward into the annulus between the casing and the wellbore ( FIGS. 9F and 9G ). In one embodiment of the present invention, once cementing of the casing is complete, a liquid may be pumped into the casing to wash the cement away from the set of ports  500  ( FIG. 9H ). Alternatively, a retardant may be injected into the cement via the set of ports  500  such that the treatment fluid can flush the set of ports and engage the formation interval  12 . Moreover, in some embodiments, the external surface of the valve housing  30  may be coated with a slippery or non-bonding material such as Teflon®, Xylan®, Kynar®, PTFE, FEP, PVDF, PFA, ECTFE, or other fluorpolymer coating materials. 
     With respect to  FIGS. 10A-10C , an embodiment of a procedure for deploying the well completions system of the present invention is provided. In this embodiment, the well completion system is part of a tubular string, which includes one or more sealing mechanisms for providing zonal isolation. In operation, the completion system is run in hole to a target depth where the sealing mechanisms are energized. The sealing mechanisms may be set by either pressurizing the entire casing string or by running a separate setting tool through each zonal isolation device. With each production zone isolated from the next, a service tool may be run in hole to treat each zone. 
     Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. .sctn. 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words means for together with an associated function.