Abstract:
A method of installing multiple strings within a wellbore. The method utilizes a carrier string having carrier string joints, a plurality of side strings each having side string joints, and a carrier tool for transferring the weight of the side strings to the carrier string permitting the side strings to be held, raised, and lowered within the wellbore by holding, raising, and lowering the carrier string. The carrier tool includes a body having a threaded through bore extending through the body and at least one threaded blind bore on the body. The method comprises the steps of engaging the carrier string joint into the carrier tool at the through bore so that the carrier string extends vertically upward and downward from the carrier tool, and engaging side string joints into the carrier tool at the at least one threaded blind bore.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to oil well drilling equipment, and, in particular, to a method for simultaneously installing multiple strings within a wellbore, and related tools. 
     2. Description of Related Art 
     The need to install multiple strings of tubing or casing (strings) into a well is well known in the art. For example, oil and gas wells may produce at two or more different zones within the well. A separate string is often installed into the well for each zone to be produced. Additionally, strings allow an operator to control the well&#39;s production by placing special tools and devices in or on the string. An example is the use of downhole chokes or surface adjustable regulators to control flow. Additionally, multiple strings may be utilized in injection wells to inject various fluids into the adjacent formation at different depths. In such uses, each string carries fluid at a unique pressure corresponding to the depth at which the fluid is being injected into the adjacent formation. 
     However, the installation of multiple strings is extremely time consuming and requires specialized handling equipment. Tubing or casing strings are comprised of individual joints which typically are available in three lengths. Range 1 tubing joints are about 20 to 24 feet whereas range 2 tubing joints are about 28 to 32 feet. Range 3 casing joints are about 38 to 42 feet long. Typically, joints are connected using threaded connections. Thus, installing a string to a modest depth of 3000 feet would require from 75 to 150 individual joints depending upon the range of the tubing/casing joint used. Using conventional installation procedures, the time required to run multiple strings to this depth linearly increases with the number of strings. That is, installing two strings generally takes about one and half to twice as long as installing a single string. 
     Strings are installed within a wellbore by connecting successive tubing/casing joints together and lowering the resulting string into the wellbore one joint at a time. An elevator is used to lift the tubing joint at one open end, direct the tubing joint over the open end of a string protruding from the wellbore, and lower the joint to the string where the joint can be rigidly connected to the string using a threaded connection. The string is suspended within the wellbore using a slip or spider which are well known in the art. This process is repeated until the string can be lowered to the desired depth within the wellbore. If a second string is required to be installed within the wellbore, the process is repeated again with the second string, if single string elevators and slips are being used. Alternatively, dual or triple elevators and slips can be used to install up to three strings simultaneously. However, if more than three strings are required to be installed within the wellbore, then the entire process must be repeated again. Consequently, there is a need for a method and apparatus for simultaneously installing more than three strings within a wellbore. 
     As noted above, existing methods of simultaneously installing multiple strings in a wellbore have been limited to installing a maximum of three strings. However, such methods require a uniquely modified elevator to pick-up up to three joints as well as a specially designed slip to hold multiple strings while additional joints are being attached. Further, annular blowout preventors used for well control during the installation of strings also must be specifically designed for multiple string installations. Thus, there is a need for a method and apparatus for simultaneously installing multiple strings in a wellbore utilizing conventional single string elevators, slips, and annular blowout preventors. 
     Additionally, one drawback of existing methods of simultaneously installing up to three strings is that such methods cannot utilize spacers or clamps to bundle the strings in order to optimize both the spacing and orientation of the strings. Tubular joints typically are not of the same length which results in considerable variation in the length and depth of the side strings after a number of joints have been installed. When clamps or spacers are used to rigidly bundle the strings together as they are installed simultaneously within the wellbore, the side strings will extend above the wellbore to different heights. Moreover, a dual or triple elevator lifting two or three tubing joints to maneuver them over the existing strings prior to connection must necessarily lift all strings to the same height. After the connections have been made, the design of the elevators necessitates that the tops of all strings are at the same height to be lifted off the slips. Consequently, all strings cannot continue to be installed simultaneously using a multi-string elevator unless additional effort is taken to use joints of exactly the same length, or unless the side strings are individually installed within the wellbore. Either way, the installation method loses its economy when clamps and spacers are used. Thus, a need exists for a method or apparatus of simultaneously installing multiple strings within a wellbore which can be used in combination with clamps or spacers intended to optimize string spacing and orientation. 
     Another problem with conventional methods of installing multiple strings in a wellbore is the tendency of the strings to twist relative to each other. When strings have been installed within a wellbore and cemented in place, the strings must be perforated so the strings can communicate directly with the adjacent formation. As discussed above, each string may be directed to a specific producing or injection zone within the wellbore, thereby requiring perforation at a depth different from the adjacent strings. However, damage to adjacent strings often occurs during perforation of a string because the string twist causes the perforating charges to be inadvertently mis-directed toward adjacent strings rather than the adjacent formation. 
     In practice, risk of damage to adjacent strings can be mitigated, but not entirely eliminated, by using shorter perforating guns. That is, perforating guns having a shorter length can be better oriented since the strings do not twist relative to each other significantly over a short length. The tradeoff is that instead of using a single perforating gun a 100 feet long to perforate a string over a 100 foot region, ten perforating guns 10 feet long must be used to perforate a string over the same 100 feet region. Thus, there is a need for a method and apparatus of installing multiple strings in a wellbore that maintains the relative orientation of the strings (i.e., no twisting) to avoid damage to adjacent strings during perforation. 
     Another problem with conventional methods of installing multiple strings in a wellbore is the tendency of the strings to come into contact with each other owing to the random deviation of the well from vertical. Sufficient space between the strings is required in order to obtain cement fillage and the resulting hydraulic isolation between strings. Hydraulic isolation between strings is necessary to avoid fluid or pressure communication from one string to another. Further, a minimum distance between the strings is required where the strings are used to inject steam into the formation at different temperatures. This distance is optimized once the thermal conductivity of the cement between strings is known. If the distance is not optimal, one string will transfer heat to other strings resulting in the injection of steam into the formation at non-optimal quality (i.e., vapor content). Consequently, there is a need for a method of simultaneously installing multiple strings in a wellbore to properly space the strings from one another. 
     Another problem with existing methods of simultaneously installing multiple strings within a wellbore is well control during the installation of the strings. Oil well drill operators must have a means of sealing the wellbore in the event that high pressure within the wellbore forces gas or oil up through the well during installation. Typically, such means are known as blowout preventors. Annular blowout preventors are mounted below the rig floor and seal around a single string to close the wellbore and prevent the high pressure gas or oil from blowing out of the wellbore. During the simultaneous installation of multiple strings using existing methods, more than one string extends from the wellbore. Thus, annular blowout preventors must be modified to seal around more than a single string in such installations. The modification is specific to the number of strings being installed. Thus, there is a need for an apparatus and method of installing multiple strings within a wellbore which can be used with less costly and readily available single string annular blowout preventors for well control. 
     Accordingly, there has existed a definite need for a simple and economical method and apparatus for simultaneously installing multiple strings within a wellbore in a manner which addresses the shortcomings present in existing methods as identified above. The present invention satisfies these needs and provides further related advantages. 
     SUMMARY OF THE INVENTION 
     To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method for simultaneously installing multiple strings within a wellbore, and related tools. 
     This invention provides a method for simultaneously installing multiple strings within a wellbore, including installation of more than three strings. Further, the present invention also provides a carrier tool utilized in the method for simultaneously installing multiple strings within a wellbore. The carrier tool attaches to a carrier string and side strings in a manner that permits the carrier string and side strings to be suspended, raised or lowered within the wellbore by simply suspending, raising, or lowering the carrier string. Moreover, the present invention can be used in combination with clamps and spacers to prevent string twisting and to optimize string spacing within the wellbore. Further, the present invention permits the use of existing single string elevators, slips, and blowout preventors without requiring any modification to accommodate the simultaneous installation of multiple strings. 
     The method of the present invention is performed atop a rig floor positioned over the wellbore and blowout preventors. After initially attaching a carrier string and side string(s) to a carrier tool, the carrier string and side string(s) are lowered into the wellbore by lowering the carrier string using an elevator until the carrier string extends above the rig floor and the side string(s) are below the rig floor. Next, the carrier string and side string(s) are suspended within the wellbore by landing the carrier string in a slip assembly on the rig floor. With the carrier string and side string(s) suspended within the wellbore, the elevator may be used to pick up a carrier string joint and maneuver it so that it can be attached to the carrier string extending above the wellbore. After the carrier string connection has been made, string weight is transferred from the slip back to the elevator. The slips are retracted sufficiently to allow the side string(s) to pass through the slip assembly. Then, after retracting the slip, the elevator raises the carrier string and side string(s) by lifting the carrier string until the side string(s) also are above the rig floor. With the carrier string and side string(s) suspended by the elevator, a second elevator or winch line (or alternative lifting device) is used to pick up side string joints one at a time and maneuvers them so that they can be attached to the side string(s) extending above the wellbore. Then, the elevator suspending the carrier string lowers the carrier string until the carrier string extends above the rig floor and the side string(s) are below the rig floor and the process of adding additional joints is repeated until the carrier string and side string(s) can be lowered into the wellbore to a desired depth. 
     The carrier tool comprises a body having an upper surface extending radially relative to the axis of the wellbore, an axially extending threaded through bore extending through the body, and at least one axially extending threaded blind bore having its open end on the upper surface of the body. A carrier string having a plurality of carrier string joints engages the axially extending threaded through bore at the upper and lower surfaces of the carrier tool. At least one side string having a plurality of side string joints engages the carrier tool at the at least one axially extending threaded blind bore. This structural arrangement allows the carrier tool to transfer the weight of the side strings to the carrier string enabling the side strings to be suspended, raised, or lowered by suspending, raising, or lowering the carrier string. The carrier tool also defines the spacing and orientation of the strings relative to each other. 
     Thus, the carrier tool of the present invention enables the simultaneous installation of multiple strings in a wellbore, including configurations with more than three strings, in less time than conventional methods. Further, the present invention permits the use of single string elevators, slips, and annular blowout preventors without modification. Existing methods of simultaneously installing up to three strings within a wellbore require modified elevators (triple elevators) and modified slips (triple slips). Further, the present invention allows for the use of single string annular blowout preventors since, at any time during the installation, the side string(s) can be lowered into the wellbore so that only the carrier string extends through the blowout preventor and above the wellbore. If required, the blowout preventor may be closed on the carrier string. Thus, such a configuration mirrors a single string installation for purposes of using a single string annular blowout preventor for well control. 
     To prevent the carrier string and side string(s) from twisting relative to each other within the wellbore and to maintain proper spacing of the carrier string and side strings, the present invention includes clamps which are rigidly attached to the carrier string and side strings. The clamps are attached intermittently along segments of the carrier string and the side string(s) where the carrier string and or side strings will be perforated. The placement of the clamps corresponds to intended perforating zones within the wellbore after the strings have been lowered into the wellbore. Some allowance is made in determining the location of clamps for any inherent depth measurement inaccuracy. Along segments of the carrier string and side string(s) where proper string spacing is required, but a rigid orientation of the carrier string and side string(s) is not required, i.e., segments other than the perforated segments, spacers can be substituted for clamps. 
     One advantage of using clamps is the ability to use the longer perforating guns to create perforations over a greater interval of the strings in a single gun run. Because the carrier string and side strings are rigidly attached and prevented from twisting relative to each other, perforating charges can be directed from within the strings toward the adjacent formation without risk that the charges will be inadvertently directed to adjacent strings. Without the use of clamps to maintain a rigid orientation, shorter perforating guns can be used to mitigate the risk of damaging adjacent strings caused by mis-orienting the perforating charges due to string twist, but the use of such guns requires more time and effort to perforate the same region of the strings. 
     Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate the invention. In such drawings: 
     FIG. 1A is a top view of a carrier tool having an axially extending threaded through bore and three axially extending threaded blind bores; 
     FIG. 1B is a side view of the carrier tool of FIG.  1 A. 
     FIG. 2A is a top view of a carrier tool having an axially extending threaded through bore and two axially extending threaded blind bores; 
     FIG. 2B is a side view of the carrier tool of FIG.  2 A. 
     FIG. 3A is a top view of a carrier tool having an axially extending threaded through bore and one axially extending threaded blind bore; 
     FIG. 3B is a side view of the carrier tool of FIG. 3A; 
     FIG. 4A is a top view of a carrier tool having an axially extending threaded through bore and five axially extending threaded blind bores; 
     FIG. 4B is a side view of the carrier tool of FIG. 4A; 
     FIG. 5A is a perspective view of a carrier tool being attached to a carrier string joint suspended within a wellbore by a single string slip; 
     FIG. 5B is a perspective view of a carrier string joint being attached to the carrier tool and carrier string of FIG. 5A; 
     FIG. 5C is a perspective view of a side string joint being attached to the carrier tool and carrier string of FIG. 5B; 
     FIG. 5D is a perspective view showing the carrier tool, carrier string and side string of FIG. 5C supported by an elevator lowered within the wellbore so that the carrier string extends above the rig floor and the side string is below the rig floor and slip; 
     FIG. 5E is a perspective view of a carrier string joint being attached to the carrier tool, carrier string and side string of FIG. 5D suspended within the wellbore by a single string slip; 
     FIG. 5F is a perspective view of a side string joint being attached to the side string of FIG. 5E using a second elevator after raising the side string above the rig floor and suspending the side string by suspending the carrier string with the first elevator; 
     FIG. 5G is a perspective view of a clamp or spacer attached to the carrier tool, carrier string and side string of FIG. 5F; 
     FIG. 6 is a perspective view of a single string blowout preventor closing on a carrier string joint within a wellbore with a single string slip retracted or open; 
     FIG. 7 is a perspective view of a four string installation including a four string carrier tool, a carrier string, and three side strings within a wellbore; 
     FIG. 8 is a perspective view of a four string installation including three two string carrier tools, a carrier string, and three side strings within a wellbore; 
     FIG. 9A is a top view of a four string clamp; 
     FIG. 9B is a side view of the clamp in FIG. 9A; 
     FIG. 10A is a top view of a three string clamp; 
     FIG. 10B is a side view of the clamp in FIG. 10A; 
     FIG. 11A is a top view of a dual string clamp; 
     FIG. 11B is a side view of the clamp in FIG.  11 A. 
     FIG. 12A is a top view of a four string spacer; 
     FIG. 12B is a side view of the four string spacer of FIG. 12A; 
     FIG. 12C is a front view of the four string spacer of FIG. 12A; 
     FIG. 12D is a top view of the four string spacer of FIG. 12A with a band around the carrier and side strings; 
     FIG. 13A is a top view of a three string spacer; 
     FIG. 13B is a side/front view of the three string spacer of FIG. 13A; 
     FIG. 13C is a top view of the three string spacer of FIG. 13A with a band around the carrier and side strings; 
     FIG. 14A is a top view of a dual string spacer; 
     FIG. 14B is a side view of the dual string spacer of FIG. 14A; 
     FIG. 14C is a front view of the dual string spacer of FIG. 14A; 
     FIG. 14D is a top view of the dual string spacer of FIG. 14A with a band around the carrier and side string; 
     FIG. 15A is a top view of a four string centralizer; and 
     FIG. 15B is a side view of the four string centralizer of FIG.  15 A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in the exemplary drawings, the present invention includes a carrier tool, indicated generally by the reference numeral  10 , for transferring the weight of side strings to a carrier string enabling the side strings to be suspended, raised or lowered by suspending, raising, or lowering the carrier string. As shown in a four string configuration in FIGS. 1A and 1B, the carrier tool  10  comprises a body  11  having an upper surface  12  extending radially relative to the axis of a wellbore (not shown), an axially extending threaded through bore  14  extending through said body  11  for attaching the carrier string (not shown), and three axially extending threaded blind bores  16  in said body  11  for attaching the side strings (not shown). Additionally, the threaded through bore  14  includes openings  18  and  22  and the threaded blind bores  16  include openings  20  which are slightly larger than the diameter of the bores. The slightly larger openings  18 ,  20  and  22  are tapered to permit the carrier string and side strings to be self-centering when inserted into the threaded through bore and threaded blind bores, respectively. In the preferred embodiment, the body  11  includes a lower surface  24  having a flat region  26  at the through bore opening  18  and tapered in a region  28  to facilitate insertion of the carrier tool  10  into the wellbore. A center hole  32  located at the center of the body  11  provides a pathway for fluid flow during circulating and cementing operations. This promotes good cement fillage between strings. 
     The carrier tool  10  is preferably made of steel or another material that is rigid enough to support the weight of the side strings at their maximum length. Further, the diameter of the bores  14  and  16  must be constructed to correspond to the outer threaded diameter of the carrier string joint and side string joints so that the carrier string joint and side string joints can engage the through bore and blind bores by threading the strings into the bores, respectively. In this regard, the carrier string joint and side string joints can engage the through bore  14  and side bores  16  by means other than integral threads  30 . For example, the carrier string joint and side string joints can be welded to the through bore and blind bores. 
     In alternative embodiments, the carrier tool  10  can be constructed with a through bore  14  and blind bores  16  of different sized diameters provided that the diameters correspond to the outer threaded diameters of the carrier string joint and side string joints, respectively. Additionally, the carrier too  10  can be constructed with any number of blind bores  16  depending upon the specific application. For example, while exemplary configurations showing a carrier too  10  with one, two, three and five blind bores  16  have been described below, the present invention is not limited only to these configurations. Other configurations of the carrier tool  10  having four blind bores  16  or more than five blind bores  16  can be constructed using the principles disclosed in the present invention. In particular, the number of blind bores  16  is only limited by the diameter of the wellbore, the diameter of the tubing/casing joints, and the spacing requirements to ensure the side strings are thermally and hydraulically isolated. 
     In FIGS. 2A and 2B is shown a carrier tool  10  for simultaneously installing three strings. In this illustration, the carrier tool  10  comprises a body  11  having an upper surface  12  extending radially relative to the axis of a wellbore (not shown), an axially extending threaded through bore  14  extending through said body  11  for threadingly engaging the carrier string (not shown), and two axially extending threaded blind bores  16  in said body. Additionally, the threaded through bore  14  includes openings  18  and  22  and the threaded blind bores  16  include openings  20  which are slightly larger than the diameter of the bore. The slightly larger openings  18 ,  20  and  22  are tapered to permit the carrier string and side strings to be self-centering when inserted into the threaded through bore and threaded blind bores, respectively. In the preferred embodiment, the body  11  includes a lower surface  24  having a flat region  26  at the through bore opening  18  and tapered in a region  28  to facilitate insertion of the carrier tool  10  into the wellbore. A center hole  32  located at the center of the carrier tool  10  provides a pathway for fluid flow during circulating and cementing operations. 
     In FIGS. 3A and 3B is shown a carrier tool  10  for simultaneously installing two strings. In this illustration, the carrier tool  10  comprises a body  11  having an upper surface  12  extending radially relative to the axis of a wellbore (not shown), an axially extending threaded through bore  14  extending through said body  11  for threadingly engaging the carrier string (not shown), and a single axially extending threaded blind bore  16  in said body. Additionally, the threaded through bore  14  includes openings  18  and  22  and the threaded blind bore  16  includes opening  20  which are slightly larger than the diameter of the bore. The slightly larger openings  18 ,  20  and  22  are tapered to permit the carrier string and side string to be self-centering when inserted into the threaded through bore and threaded blind bore, respectively. In the preferred embodiment, the body  11  includes a lower surface  24  having a flat region  26  at the through bore opening  18  and tapered in a region  28  to facilitate insertion of the carrier tool  10  into the wellbore. 
     In FIGS. 4A and 4B is shown a carrier tool  10  for simultaneously installing six strings. In this illustration, the carrier tool  10  comprises a body  11  having an upper surface  12  extending radially relative to the axis of a wellbore (not shown), an axially extending threaded through bore  14  extending through said body  11  for threadingly engaging the carrier string (not shown), and five axially extending threaded blind bores  16  in said body. Additionally, the threaded through bore  14  includes openings  18  and  22  and the threaded blind bore  16  includes opening  20  which are slightly larger than the diameter of the bore. The slightly larger openings  18 ,  20  and  22  are tapered to permit the carrier string and side string to be self-centering when inserted into the threaded through bore and threaded blind bore, respectively. In the preferred embodiment, the body  11  includes a lower surface  24  having a flat region  26  at the through bore opening  18  and tapered in a region  28  to facilitate insertion of the carrier tool  10  into the wellbore. The threaded through bore  14  is located in the center of the carrier tool  10  with the threaded blind bores  16  located around the threaded through bore. Center holes  32  are located around the through bore  14  and inside of the blind bores  16 . The center holes  32  provide a pathway for fluid flow during circulating and cementing operations. In a preferred embodiment as best shown in FIGS. 5A-5G, the carrier tool  10  of the present invention is utilized for the simultaneous installation of two strings within a wellbore  50 . The installation is performed atop a rig floor  52  positioned over the wellbore  50  with a single string annular blowout preventor  54  installed between the rig floor and the top of the wellbore. Initially, as shown in FIG. 5A, a carrier string joint  56   a  is suspended within the wellbore  50  by a single string slip  58  mounted to the rig floor  52 . The carrier tool  10  is attached to the carrier string joint  56   a  by positioning the open end  18  of the threaded through bore  14  on the lower surface  24  of the carrier tool onto the carrier string joint  56   a  and rotating the threaded through bore of the carrier tool down onto the carrier string joint. As shown in FIG. 5B, with the carrier tool  10  attached to the carrier string joint  56   a  suspended in the slip  58  over the wellbore  50 , a second carrier string joint  56   b  is attached to the carrier tool  10  at the open end  22  of the threaded through bore  14  on the upper surface of the carrier tool  12 . Using a first elevator  57  to lift the carrier string joint  56   b  over the carrier string  56 , the carrier string joint is attached to the carrier tool  10  by threading the carrier string joint into the through bore  14  of the carrier tool. In a preferred embodiment, the carrier string joint  56   b  is approximately six (6) feet in length to create an offset between the carrier string  56  and the side string  62  (not shown) for reasons discussed below. After connecting the carrier string joint  56   b  to the carrier tool  10 , a third carrier string joint  56   c , shown in FIG. 5C, is coupled to carrier string joint  56   b  by again using the first elevator  57  to raise carrier string joint  56   c  and connect it to the carrier string  56 . The carrier string joints  56   b  and  56   c  are connected using threaded connections of the kind known in the art. Carrier string joint  56   a ,  56   b , and  56 C are of normal size for the type of tubular joint being used. 
     With the carrier string  56  suspended over the wellbore  50  by the slip  58 , a side string joint  62   a  is connected to the carrier tool  10  by inserting one end of side string joint  62   a  into the threaded blind bore  16  of the carrier tool as shown in FIG.  5 C. After side string joint  62   a  has been attached to the carrier tool  10 , the top of the carrier string  56  should extend approximately the length of carrier string joint  56   b  above the top of the side string  62 . Next, the first elevator  57  lowers the carrier string  56  and the side string  62  into the wellbore  50  through the open slip  58  by lowering the carrier string until the carrier string extends above the rig floor  52  and the side string is below the rig floor and slip. This configuration, shown in FIG. 5D, is possible because the six (6) foot carrier string joint  56   b  created an offset between the top of the carrier string  56  and the side string  62 . 
     Next, as shown in FIG. 5E, the carrier string  56  and side string  62  are suspended within the wellbore  50  by landing the carrier string in a single string slip  58 . When the carrier string  56  and side string  62  are suspended within the wellbore  50  by the sip  58 , the first elevator  57  picks up a carrier string joint  56   d  and maneuvers it so that it can be attached to the carrier string extending above the wellbore. Then, as shown in FIG. 5F, the first elevator  57  raises the carrier string  56  and side string  62  by lifting the carrier string until the side string also is above the rig floor  52 . The carrier string  56  and side string  62  are suspended within the wellbore  50  by the first elevator attached to the carrier string. A winch line or second elevator  59  then picks up side string joint  62   b  and maneuvers it so that it can be attached to the side string  62  extending above the wellbore  50 . This process, as shown and described in reference to FIGS. 5D and 5F, is repeated until the carrier string  56  and side string  62  can be lowered into the wellbore  50  to the desired depth. 
     In another embodiment of the present invention, the simultaneous installation of multiple strings within a wellbore further comprises securing the carrier string  56  and side string  62  together with a clamp  66   a . In particular, FIG. 5G shows the two string installation of FIG. 5F in combination with a clamp  66   a . The clamp  66   a  prevents the carrier string  56  and side string  62  from twisting relative to each other within the wellbore  50  and maintains proper spacing between the carrier string and side string. A rigid orientation is necessary in order to orient the perforating charges which will create holes in the carrier string  56  and or side string  62  in order for the carrier string and or side string to directly communicate with the adjacent formation. The clamp  66   a  is rigidly attached to the carrier string  56  and side string  62  intermittently along segments of the carrier string and the side strings where the carrier string and side string will be perforated. The perforated segments correspond to perforating zones (not shown) within the wellbore after the strings are lowered into the wellbore. 
     Along segments of the carrier string  56  and side string  62  where proper string spacing is still required, but a rigid orientation of the carrier string and side strings is not required, i.e., segments other than the perforated segments, spacers can be substituted for clamps. Spacers maintain a rigid distance between the carrier string  56  and each side string  62 , but do not prevent the carrier string and side strings from twisting relative to one another. Clamps, on the other hand, are rigidly attached to both the carrier string  56  and each side string  62  in order to both prevent the carrier string or any side string from twisting relative to another string and maintain a rigid distance between the carrier string and each side string. 
     As shown in FIG. 6, the foregoing method enables the use of single string annular blowout preventors. In particular, in the event that an oil well operator must control the well to prevent high pressure oil or gas from erupting from the wellbore  50 , the operator can lower the side string below the annular blowout preventor  54  in order to close the annular blowout preventor around the carrier string  56 . In this configuration (with the side string below the closed annular blowout preventor), the slip  58  can be open or closed. 
     FIG. 7 illustrates a preferred embodiment of a four string installation resulting from the method of the present invention. Specifically, carrier string  56  and side strings  62  are installed within a wellbore  50 . The carrier string  56  is connected to a carrier tool  10  by means of a threaded through bore. Side strings  62  are connected to the carrier tool  10  by means of threaded blind bores. Additionally, the carrier string  56  and side strings  62  are perforated along segments  68  corresponding to producing or injection zones within the wellbore  50  when the strings are lowered into the wellbore. The carrier string  56  and side strings  62  are each hydraulically and thermally isolated to optimize production or injection at a specific perforating or injection zone within the wellbore. 
     FIG. 8 illustrates an alternative embodiment of a four string installation using the method and tools of the present invention. In particular, a carrier string  80  is connected to three side strings  82 ,  84  and  86  by three two string carrier tools  81 ,  83  and  85 , respectively. The carrier tools  81 ,  83  and  85  are oriented to enable each side string sufficient space free from interference from the other side strings. In a single four string carrier tool the orientation of the strings is defined by the position of the thread blind bores on the carrier tool which likewise must also be located to allow each side string to be free from interference from the other side strings. Thus, the method and tools of the present invention provides that numerous combinations of multi-string carrier tools can be used together for the simultaneous installation of multiple strings within a wellbore in addition to using a single multi-string carrier tool. 
     The method and tools of the present invention further disclose the use of clamps to prevent the carrier string and side string(s) from twisting relative to each other within the wellbore, and to maintain proper spacing between the carrier string and side string(s). As shown in FIGS. 9A and 9B, a four string clamp  90  comprises a center segment  92 , a first outboard segment  94 , and a second outboard segment  96 . The first outboard segment  94  is rigidly fitted around two strings (not shown) and rigidly attached to the center segment  92  by a bolt  97 . The second outboard segment  96  is rigidly fitted to the remaining two strings (not shown) and rigidly attached to the center segment  92  by a bolt  98 . All segments are sized to provide a semi-circumferential concave shape equal to the semi-circumferential portion of the string&#39;s outer diameter to which the segment will mate in order to provide a secure and rigid fit. The four string clamp  90  also includes an axially extending hole  99  located at the center of the clamp to provide a pathway for fluid flow during circulating and cementing operations. In a preferred embodiment, clamps are installed every 30 feet along the string segments corresponding to perforating or injection zones within the wellbore. 
     Similarly, FIGS. 10A and 10B disclose a three string clamp  100  comprising a center segment  102 , a first outboard segment  104 , and a second outboard segment  106 . The first outboard segment  104  is rigidly fitted around two strings (not shown) and rigidly attached to the center segment  102  by a bolt  107 . The second outboard segment  106  is rigidly fitted around the remaining string (not shown) and rigidly attached to the center segment  102  by bolts  108  and  109 . All segments are sized to provide a semi-circumferential concave shape equal to the semi-circumferential portion of the string&#39;s outer diameter to which the segment will mate in order to provide a secure and rigid fit. 
     FIGS. 11A and 11B disclose a two string dual string clamp  110  comprising a first segment  112  and a second segment  114 . The first segment  112  is rigidly fitted around two strings (not shown) and rigidly attached to the second segment  114  by a bolt  113 . All segments are sized to provide a semi-circumferential concave shape equal to the semi-circumferential portion of the string&#39;s outer diameter to which the segment will mate in order to provide a secure and rigid fit. 
     The present invention further discloses the use of spacers to space the strings in order to hydraulically and thermally isolate the strings from one another. While the spacers maintain a fixed position of the strings relative to one another, the spacers do not prevent the strings from twisting relative to one another. Therefore, preferably spacers are not used along sections of the strings which will be perforated because of the potential risk of damage to the adjacent strings caused by mis-directing the perforating gun and creating holes in the adjacent strings due to the string twist. In a preferred embodiment, spacers are installed about every 30 feet along the string segments within the wellbore from the carrier tool to the surface. 
     FIGS. 12A-12D illustrates a preferred embodiment of a four string spacer tool disclosed in the present invention. With reference to FIG. 12A, the four string spacer tool  120  comprises four semi-circumferential shaped saddles  122  rigidly connected by a first, second, third and fourth saddle supports  124 ,  125 ,  126  and  127 , respectively. As shown in FIG. 12D, the saddles  122  are positioned in a generally rectangular shape to receive four strings  121  so that the strings are received by the saddle at the interior circumferential sections of the strings. The saddles  122  are further secured to the strings by a steel band  128  as shown in FIG.  12 D. The steel band  128  is wrapped around the exterior circumferential portion of the strings  121  forcing the strings against the saddles and thereby rigidly securing the strings within the saddles. As shown in FIG. 12B, the saddles  122  have notches  129  to receive the steel band  128 . 
     FIGS. 13A-13C illustrates a preferred embodiment of a three string spacer tool disclosed in the present invention. The three string spacer tool  130  comprises three semi-circumferential shaped saddles  132  rigidly connected by a first, second, and third saddle supports  134 ,  135 , and  136 , respectively. As shown in FIG. 13C, the saddles  132  are positioned in a generally triangular shape to receive three strings  131  so that the strings are received by the saddle at the interior circumferential sections of the strings. The saddles  132  are further secured to the strings by a steel band  138  as shown in FIG.  13 C. The steel band  138  is wrapped around the exterior circumferential portion of the strings  131  forcing the strings against the saddles and thereby rigidly securing the strings within the saddles. As shown in FIG. 13B, the saddles  132  and saddle supports  134 ,  135 , and  136  have notches  139  to receive the steel band  138 . 
     FIGS. 14A-14D illustrates a preferred embodiment of a two string spacer tool disclosed in the present invention. The two string spacer tool  140  comprises two semi-circumferential shaped saddles  142  rigidly connected by a first and second saddle supports  144  and  145 , respectively. As shown in FIG. 14D, the saddles  142  are positioned in a generally square shape with the open end of the saddles facing opposite directions to receive two strings  141  so that the strings are received by the saddle at the interior circumferential sections of the strings. The saddles  142  are further secured to the strings by a steel band  148  as shown in FIG.  14 D. The steel band  148  is wrapped around the exterior circumferential portion of the strings  141  forcing the strings against the saddles  142  and thereby rigidly securing the strings within the saddles. As shown in FIG. 14B, the saddles  142  have notches  149  to receive the steel band  148 . 
     FIGS. 15A and 15B illustrate a preferred embodiment of a four string centralizer tool disclosed in the present invention. The four string centralizer tool  150  comprises four semi-circumferential shaped saddles  152  rigidly attached to an upper collar  154  and four semi-circumferential shaped saddles  156  rigidly attached to a lower collar  158 . The upper and lower collars  154  and  158  are connected by four steel bands  160  running parallel to the strings when the centralizer  150  is installed around the strings. The steel bands  160  act as bow springs positioned round the circumference of the collars  154  and  158  at about 0 , 90 , 180, and 270 degrees to oppose the side walls of the wellbore and force the strings to the center of the wellbore. The collars  154  and  158  of the centralizer  150  are positioned around the strings at a clamp or spacer. In a preferred embodiment, centralizers are attached about every 30 feet along segments corresponding to injection or producing zones within the wellbore, and about every 60 feet along the remaining sections. 
     From the foregoing, it will be appreciated that this invention allows a simple and effective method of installing multiple strings within a wellbore and discloses related tools. While a particular form of the invention has been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims. 
     With continued reference to FIGS. 15A and 15B, the centralizer of the present invention also includes a hinge  162  and a hinge latch  164  on both the upper and lower collars  154  and  158 . The hinge allows the centralizer to be opened in a clamshell manner and to be fitted around a carrier and side string bundle by simply closing the centralizer and setting the latch.