The present invention generally relates to methods of connecting two expandable tubulars. In one aspect, the method includes flash welding the ends of the expandable tubulars together. Thereafter, the connected tubulars are lowered into the wellbore for expansion. The flash welding process provides a highly reliable joint for expansion.

BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to wellbore completion. More particularly, the invention relates to apparatus and methods of connecting two tubulars. More particularly still, the invention relates to apparatus and methods of connecting two expandable tubulars at the well site. 
   2. Description of the Related Art 
   In the drilling of oil and gas wells, a wellbore is formed using a drill bit that moves downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and bit are removed, and the wellbore is typically lined with a string of steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent hydrocarbon bearing formations. The casing typically extends down the wellbore from the surface of the well to a designated depth. An annular area is thus defined between the outside of the casing and the earth formation. This annular area is filled with cement to permanently set the casing in the wellbore and to facilitate the isolation of production zones and fluids at different depths within the wellbore. 
   It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well to a depth whereby the upper portion of the second liner overlaps the lower portion of the first string of casing. The second liner string is then fixed or hung in the wellbore, usually by some mechanical slip mechanism well-known in the art, and cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth. 
   However, one drawback of this process is that as the wellbore is extended, the inner diameter of the well progressively decreases. This is because subsequent liners must have an outer diameter that is smaller than an inner diameter of earlier casings in order to pass through the earlier casings. As a result, top-hole sizes must be sufficiently large so that the final casing has the desired inner diameter size. 
   Recently, expandable tubular technology has been developed to overcome this problem. Generally, expandable technology enables a smaller diameter tubular to pass through a larger diameter tubular, and thereafter expanded to a larger diameter. In this respect, expandable technology permits the formation of a tubular string having a substantially constant inner diameter, otherwise known as a monobore. Accordingly, monobore wells have a substantially uniform through-bore from the surface casing to the production zones. 
   A monobore well features each progressive borehole section being cased without a reduction of casing size. The monobore well offers the advantage of being able to start with a much smaller surface casing but still end up with a desired size of production casing. Further, the monobore well provides a more economical and efficient way of completing a well. Because top-hole sizes are reduced, less drilling fluid is required and fewer cuttings are created for cleanup and disposal. Also, a smaller surface casing size simplifies the wellhead design as well as the blow out protectors and risers. Additionally, running expandable liners instead of long casing strings will result in valuable time savings. 
   Typically, expandable liners are constructed of multiple tubulars connected end to end. The tubulars are generally connected using a threaded connection. As the threads are made up, a metal-to-metal seal is created between the two tubulars. Thereafter, the entire length of the expandable liner is deployed into the wellbore. The expandable liners are typically expanded by the use of a cone-shaped mandrel or by an expander tool, such as a rotary expander tool having one or more rollers. 
   A problem arises when the threaded connection is expanded. Generally, the male and female threads of a threaded connection are specifically designed to mate with each other to form a fluid tight seal. However, the specifications of the threads do not take into account the expansion of the threaded connection. By plastically deforming or expanding the threaded connection, the requirements of the threads to form a fluid tight seal are necessarily altered. For example, the tight metal-to-metal seal created between the female thread and the male thread becomes slack, thereby jeopardizing the seal at the threaded connection. 
   A need, therefore, exists for an expandable tubular connection. There is a further need for a method of forming a tubular connection that maintains a fluid tight seal upon expansion of the tubular connection. 
   SUMMARY OF THE INVENTION 
   The present invention generally relates to methods of connecting two expandable tubulars. In one aspect, the method includes flash welding the ends of the tubulars together. The flash welding process provides a highly reliable joint for expansion. 
   In another aspect, the present invention provides an apparatus for connecting a first tubular to a second tubular. The apparatus includes a housing disposed around an end of the first tubular and the second tubular. The apparatus may also include one or more sealing elements disposed within each of the tubulars. A conductive member may be connected to each end of the tubulars to conduct a current. The apparatus may also include a translational member for moving the first tubular toward the second tubular to join the heated tubular ends. 
   In another aspect, the present invention generally relates to methods of completing a well. In one embodiment, the method includes flash welding the ends of two expandable tubulars together. Thereafter, the connected tubulars are lowered into the wellbore to a predetermined location. Then, the connected tubulars are expanded in the wellbore. 
   In another aspect, the present invention provides a method of completing a well. The method involves flash welding a first tubular to a second tubular. The method includes disposing a housing around an end of the first tubular and an end of the second tubular. Thereafter, a non-flammable gas may be provided within the housing to facilitate the welding process and/or prevent ingress of flammable mixtures of hydrocarbons. After the tubulars have been joined, the tubulars may be expanded downhole. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. 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. 
       FIG. 1  is a cross-sectional view of a tubular positioned above another tubular held in a wellhead. 
       FIG. 2  is schematic view of an apparatus for flash welding two tubulars. 
   


   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Aspects of the present invention provide apparatus and methods of connecting expandable tubulars using flash welding.  FIG. 1  is a schematic view of a first tubular  10  ready to be joined with a second tubular  20 . As shown, the first tubular  10  at least partially extends above the wellhead  5  and is held in place by a spider (not shown). The second tubular  20  is suspended above the first tubular  10  by an elevator  25  operatively connected to the rig  30 . A tubular handling device  40  attached to the rig  30  may be used to help position the second tubular  20 . 
   In one embodiment, the first and second tubulars  10 ,  20  are expandable tubulars to be joined and expanded downhole. Examples of expandable tubulars include expandable solid tubulars, expandable slotted tubulars, expandable screens, and combinations thereof. Further, the first and second tubulars  10 ,  20 , as used herein, may include a single tubular or a tubular string formed by more than one tubular. 
     FIG. 2  shows an apparatus  100  for flash welding the second tubular  20  to the first tubular  10  according to aspects of the present invention. The apparatus  100  includes a tubular housing  110  at least partially disposed around the first and second tubulars  10 ,  20 . One end of the housing  110  overlaps the first tubular  10  while the other end of the housing  110  overlaps the second tubular  20 . Preferably, an inner diameter of the housing  110  is larger than an outer diameter of the tubulars  10 ,  20  such that an annular space  115  is formed therebetween. The housing  110  should be made from a material capable of tolerating high temperatures, such as metal. In one embodiment, the housing  110  defines a single sleeve tubular. In another embodiment, the housing  110  defines two arcuate portions hinged together. Spacers  120  may be placed at each end of the housing  110  to seal off the annular space  115 . The spacers  120  may be made from an elastomeric material, metal, or combinations thereof. 
   One or more sealing elements  131 ,  132  may be placed within the first and second tubulars  10 ,  20  to seal off the bores of the tubulars  10 ,  20 . In one embodiment, inflatable packers  131 ,  132  are used to seal off the tubulars  10 ,  20 . The inflatable packers  131 ,  132  may be connected to a tubular conveying member  140  for positioning the inflatable packers  131 ,  132 . The conveying member  140  may be in fluid communication with the packers  131 ,  132  so that it may provide pressure to actuate the packers  131 ,  132 . In another embodiment, the sealing elements  131 ,  132  may be formed of a water soluble material. The water soluble sealing elements  131 ,  132  may be caused to dissolve immediately after flash welding the tubulars together. Alternatively, the water soluble sealing elements  131 ,  132  may remain in the tubulars  10 ,  20  after the connection is made and dissolved at a later time. 
   In another aspect, the conveying member  140  may optionally include a second conveying member  142  for providing gas into the area enclosed by the packers  131 ,  132  and the housing  110 . Preferably, the supplied gas is an inert gas, a non-flammable gas, or combinations thereof. The inert gas may supplant or dilute the air in the enclosed area, thereby decreasing the possibility of oxide forming on the heated tubulars  10 ,  20 . Impurities such as oxide formed during the welding process are undesirable because they weaken the bond between the joined tubulars  10 ,  20 . In another embodiment, the inert gas may be delivered through one or more ports  150  formed in the housing  110 . As shown in  FIG. 1 , the ports  150  are formed on a wall of the housing  110 . However, the ports  150  may also be formed in the spacers  120  or other suitable surface of the housing  110  as is known to a person of ordinary skill in the art. It must be noted that the ports  150  may be used in combination with the second conveying member  142  to inject inert gas into the enclosed area. 
   The apparatus  110  may also include a welding tool  160 , which is schematically shown in FIG.  1 . The welding tool  160  may be used to supply the current necessary to perform the flash welding process. The welding tool  160  may be selected from any suitable flash welding machine as is known to a person of ordinary skill in the art. An exemplary flash welding tool may comprise a bank of 12 volt lead-acid batteries or a direct current generator with appropriate tubular gripping members to handle the relative positioning of the tubular members throughout the joining process. As schematically shown in  FIG. 2 , the welding tool  160  has at least one conductive member  161 ,  162  for contacting each tubular  10 ,  20 . In one embodiment, clamps  161 ,  162  are used to contact the tubulars  10 ,  20  to provide current to the tubulars  10 ,  20  for the flash welding process. The welding tool  160  may further include a translational member  167  for moving the tubulars  10 ,  20  toward each other. In one embodiment, the translational member  167  may comprise a piston and cylinder assembly to bring the clamps  161 ,  162  closer to each other. Upon actuation, the piston and cylinder assembly  167  may cause the first tubular  20  to move closer to the second tubular  20 . 
   In operation and as one example of the process, the second tubular  20  is positioned above the first tubular  10  in the wellbore as shown in FIG.  1 . Once in position, a clamp  161 ,  162  is attached to each tubular  10 ,  20  proximate the ends of the tubular  10 ,  20  to be joined. Thereafter, the housing  110  is disposed around the tubulars  10 ,  20 . An inflatable packer  131 ,  132  is then placed in the bore of each tubular  10 ,  20 . Fluid is supplied to the inflatable packers  131 ,  132  to actuate the packers  131 ,  132 , thereby sealing off the bores of the tubulars  10 ,  20 . After the packers  131 ,  132  are actuated, inert gas is injected into the enclosed area to displace most of the air. Preferably, the inert gas is injected through the ports  150  of the housing  110 . 
   The welding process begins by bringing the tubulars  10 ,  20  into contact with each other. During the flash welding process, current is applied to each tubular  10 ,  20  through the clamps  161 ,  162 . The current applied initially results in heating of each tubular  10 ,  20  due to the electrical circuit formed by contacting the tubular ends. The resistance that naturally occurs at the interface between the tubulars  10 ,  20  causes the “flashing” for which the joining process is known. The flashing action continues until the ends of the tubulars  10 ,  20  reach a plastic state and a predetermined temperature. The plastic portion and the adjacent heated portion of the tubulars  10 ,  20  are commonly referred to as the heat-affected zone, or HAZ. 
   The flash welding process concludes with the upset or forging action. When the tubulars  10 ,  20  have reached the plastic state and the proper temperature, the ends of the tubulars  10 ,  20  are brought together with enough force to cause the tubular ends to upset. Particularly, the piston and cylinder assembly  167  of the welding tool  160  is actuated to cause the contacting end of the second tubular  20  to move into the contacting end of the first tubular  10 . The speed of the movement between tubulars  10 ,  20  for the upset action may be controlled by adjusting the piston size or rate of pressure increase. The upset action forces the plastic portions and most of the impurities out of the formed joint. 
   EXAMPLE 
   In one example, two expandable tubulars having about 2″ outer diameters and about 0.156″ wall thickness are joined in accordance with the aspects of the present invention. The initial spacing gap between the tubulars was 0.25″. The starting flash was set when the relative position between the two clamps was about 3.5″. The upset was initiated at a relative clamp position of about 2″ with an upset pressure of 600 psi. During the welding process, the voltage was set at about 12 VAC and the total cycle time including positioning was about 30 seconds. The final relative clamp position was between about 0.8″ to about 1.2″. 
   The flash welding process may optionally include an additional preheating action. In one embodiment, the ends of the tubulars  10 ,  20  may be caused to oscillate against each other. Initially, the ends are brought together to allow heat to be generated from the resistance of the tubulars  10 ,  20 . 
   When the ends begin to cool and solidify, the preheating action is repeated and continued in a rapid motion until heat is generated at both ends of the tubulars  10 ,  20 . The preheat stage is performed until the proper HAZ is obtained. Thereafter, the flash weld stage is performed and the two tubular ends are forged together. 
   Advantages of the preheating the tubulars include the ability to weld a large cross-sectional area with lower current demand. Additionally, the temperature gradient may remain more uniform during the process. Finally, heat may be generated in high strength alloys without a large loss of material by the flashing action. 
   After the proper length of tubular has been formed, the tubular may be lowered into the wellbore along with an expander tool. When the tubular reaches the proper depth in the wellbore, the expander tool is actuated to expand the tubular. Examples of the expander tool include rotary expander tools and coneshaped mandrels. In this respect, the flash welded joint is plastically deformed, but retains its fluid tight seal. In this manner, expandable tubulars may be joined and expanded downhole. 
   While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.