Abstract:
A method of installing a conductor or a casing in the sea bed, the conductor or casing being caused to penetrate a sea bed, the conductor or casing being substantially suspended from a length of coiled tubing. The conductor or casing being lowered to the sea bed by means of the coiled tubing, the coiled tubing being deployed from a reel on a floating vessel. Ideally a conductor may be deployed in the sea bed at the desired location, and subsequently a casing is introduced to the conductor. Alternatively the casing is introduced into a conductor, the casing and conductor substantially suspended from a length of coiled tubing, lowered to the sea bed by means of the coiled tubing, and caused to penetrate the sea bed. A length of coiled tubing is then introduced to the conductor or casing.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a conductor system, that is, a system including a well conductor which may be installed in the ground, particularly in off shore environments, for the production of oil and gas and associated tasks.  
         BACKGROUND OF THE INVENTION  
         [0002]    Well conductors are commonly used when drilling in an off shore environment. A well conductor, usually a steel pipe typically 30 inches (0.76 meters) in diameter, is lowered to the sea bed from a derrick on a rig, and is driven into the sea bed, for example by pre-drilling and/or hammering. Sections may be added to the conductor to extend it. A conductor may be lowered several hundred meters into the ground in this way. Adding new sections to the conductor string is obviously cumbersome and time consuming.  
         OBJECTS OF THE INVENTION  
         [0003]    It is an object of the present invention to provide a conductor system that may be installed more easily. Other objects of the invention will become apparent from time to time in the description.  
         SUMMARY OF THE INVENTION  
         [0004]    According to the present invention there is provided a method of installing a conductor or a casing in the sea bed, the conductor or casing being caused to penetrate the sea bed, characterized in that the conductor or casing is substantially suspended from a length of coiled tubing, the conductor or casing being lowered to the sea bed by means of the coiled tubing.  
           [0005]    Preferably the conductor or casing is a conductor deployed in the sea bed at the desired location, and subsequently a casing is introduced into the conductor  
           [0006]    Alternatively, a casing is introduced into a conductor, substantially suspended from a length of coiled tubing, lowered to the sea bed by means of the coiled tubing, and caused to penetrate the sea bed. Preferably the length of coiled tubing is introduced to the conductor or casing, and preferably extends along the length of the conductor or casing.  
           [0007]    The penetration may be effected or assisted by fluid being passed through the length of coiled tubing.  
           [0008]    According to another aspect of the present invention there is provided a method of installing a well conductor or casing in the sea bed, the conductor or casing being caused to penetrate the sea bed, characterized in that there are included sensor means held in proximity to the conductor or casing, such that the sensor means gather data by which means information regarding the position of the conductor or casing may be calculated.  
           [0009]    Preferably a casing is introduced into a conductor, substantially suspended from a length of coiled tubing, lowered to the sea bed by means of the coiled tubing, and caused to penetrate the sea bed.  
           [0010]    The sensor means may comprise one or more sensors including gyroscopes. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The invention will now be described, by way of example and not intended to be limiting, reference being made to the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 shows a side view of the system being deployed,  
         [0013]    [0013]FIG. 2 shows a sectional side view of the system during installation,  
         [0014]    [0014]FIG. 3 shows a cross section of a sensor,  
         [0015]    [0015]FIG. 4 shows a sectional side view of another embodiment of the system during installation,  
         [0016]    [0016]FIG. 5 shows a sectional side view of the system after installation,  
         [0017]    [0017]FIG. 6 shows a sectional side view of the system after installation and a pilot exploration,  
         [0018]    [0018]FIG. 7 shows a sectional side view of the system immediately prior to use, and  
         [0019]    [0019]FIG. 8 shows a section side view of a further embodiment of the system during installation. 
     
    
       [0020]    The some of the elements present in the figures are schematically represented, being drawn at a different scale to the other elements, or drawn in a foreshortened manner.  
       DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    Referring to FIG. 1, a well conductor  10  is suspended from a mast  12  and hang off beam  14  located at one end of a ship  16 . The well conductor  10  is typically between 80-160 feet (18-55 meters). A length of casing  20  is introduced into the conductor  10  from a reel (not here shown). The conductor  10  is moved from its storage area, and the casing  20  moved from its storage area and introduced to the conductor, by a conductor/casing handling machine  22 . The casing  20  is typically 350-500 feet long (106.68-152.4 meters), and 13⅜ inches (0.34 meters). The casing  20  being longer than the well conductor  10 , the majority of its length extends from beneath the lower end of the conductor. The top of the casing  20  is anchored to the top of the conductor  10 . Referring for a moment to FIG. 2, at the top of the casing is included a wellhead housing  35 .  
         [0022]    Referring back to FIG. 1, the length of coiled tubing  30  is introduced by an injector  32  to the casing  20  from a reel  34 . The length of the coiled tubing  30  is greater than the length of the casing. The thickness of the coiled tubing is typically 3½ inches (0.089 meters). When the lower end of the coiled tubing  30  reaches the lower end of the casing  20 , the coiled tubing is anchored to the top of the casing by a centralizer  43 . The centralizer  43  (visible in FIG. 2) also spaces the coiled tube centrally inside the casing.  
         [0023]    Referring to FIG. 2, the ship  16  is anchored by means of mooring lines (not shown) attached to a number of anchor points  36 , 37  embedded on the sea bed. The ship may be positioned by adjusting the length and tautness of the mooring lines using the mooring line reels.  
         [0024]    The conductor  10  is released from the hang off beam  14 , and the conductor  10  and casing  20  are lowered by the coiled tubing  30 . The coiled tubing  30  is paid out by the injector  32  until its lower end reaches the surface of the sea bed  45 . This may be detected by measuring the weight on the coiled tubing, for example. The injector  32  includes heave compensation means so that the coiled tubing system  40  (that is the coiled tubing  30 , conductor  10  and casing  20  collectively) is held steadily at the sea bed  45 .  
         [0025]    Two ‘gyro sensors’  42 , 43  (that is, a sensor containing one or more gyroscopes, and from which orientation may be deduced) are slidably attached to the coiled tubing  30 . Referring to FIG. 3, these sensors  42 , 43 , when considered in section, are approximately annular in form, having a bore  46  through which the coiled tubing  30  may pass. Each sensor is somewhat elongated, with the through bore offset, in order to accommodate the gyroscope and associated circuitry; nevertheless, it is such a size that it may be accommodated within the inner diameter of the coiled tubing. A wireline  48 , 49  is attached to each sensor, so that it may be raised and lowered to alter its position along the length of the coiled tubing. Referring back to FIG. 1, the wirelines  48 , 49  is wound upon a reel  15  for this purpose. Data from the sensors  42 , 43  are also transmitted along the wireline  48 , 49  to be analyzed on the ship  16 . Referring again to FIG. 2, the upper sensor  43  may thus be positioned anywhere above the centralizer  34  along the coiled tubing, and the lower sensor  42  may be positioned anywhere below the centralizer  34 , so that between them they may provide all the necessary readings by being moved along the length of the coiled tubing.  
         [0026]    The position of the gyro sensor  42 , 43  may be determined from its output, in particular giving the inclination of the coiled tubing system  40  from the vertical at a particular point, and the azimuth of the coiled tubing system, the position of the gyro then being calculated by the length of wireline paid out. The lowest point of the coiled tubing system  40  may be vertically below the vessel  16 , but the length of the coiled tubing system bowed. The gyro sensors will also give an indication of this.  
         [0027]    Generally, the coiled tubing system  40  will not remain vertical as it is lowered, but instead become inclined through the action of currents in the sea. It is highly desirable that the coiled tubing system is installed vertically into the sea bed  45 . The ship  16  may be repositioned so that the coiled tubing system is vertical, with continuous readings being taken from the gyro sensors. If bowing is occurring, the coiled tubing  30  may be taken up to reduce slack. It may not be possible to orient the coiled tubing system precisely vertically, and a small inclination may be felt acceptable. The inclination, and the azimuth of the coiled tubing system  40  will be accurately known, whether or not it is decided to reposition the ship. The location of penetration will also be accurately known, as will the path of the bore hole as it is produced, since the gyro sensors may be continuously employed as the coiled tubing system is advanced.  
         [0028]    At the lower end of the casing  20  is a jetting member  50 , which includes a central jetting aperture  52  with which the lower end of the coiled tubing  30  engages, and inlet apertures  54  which communicate with the annulus  60  between the outer surface of the coiled tubing  30  and the inner surface  20  of the casing.  
         [0029]    To advance the coiled tubing system  40  and produce the bore hole, fluid is pumped down the coiled tubing  30 , this fluid being emitted from the lower end of the coiled tubing as a jet. The jet of fluid erodes the portion of sea bed underneath it into suspended particles, which are carried with the fluid through the inlet apertures  54  of the jetting member, and up through the casing  20 . The coiled tubing  30  is meanwhile paid out, and so advances into the bore hole that it is creating.  
         [0030]    Referring to FIG. 4, a number of sensors  43  may be spaced equidistantly above the centralizer  34  along the coiled tubing  30 . All the sensors  42 , 43  are connected to a single wireline  48 , so that they may be raised or lowered simultaneously. The distance separating the sensors  43  above the centralizer  34  should ideally be a similar distance to the length of the coiled tubing  30  beneath the centralizer  34 , so that the entire length of the coiled tubing may be efficiently covered by the sensors. By using several sensors in this way, the position of the coiled tubing  30  over its entire length may be ascertained more quickly, and its instantaneous position estimated more accurately.  
         [0031]    When the bore hole has been advanced and the conductor  10  and casing  20  installed to a satisfactory depth, the centralizer  34  is removed and the coiled tubing  30  is disconnected from the casing, wound back upon the reel, being withdrawn from the casing  20  to leave the casing  20  and the conductor  10  embedded in the sea bed, and the wellhead housing  55  exposed as shown in FIG. 5.  
         [0032]    Rather than using sensors containing gyroscopes, similar sensors, such as laser gyroscopes or accelerometers, from which the orientation or position of the coiled tubing system may be calculated, may instead by disposed on the coiled tubing system.  
         [0033]    Other sensors could be included in the coiled tubing system, particularly upon the coiled tubing. In this manner, further data about the drilling environment such as coil or rock type, shallow gas, and shallow water flow, so that details of the well design, such as the casing design and the drill type, may be tailored to the site.  
         [0034]    Once the casing  20  and conductor  10  have been installed to the correct depth, the centralizer  43  and jetting member  50  could be released from the casing to free the coiled tube  30 , and then the coiled tubing could be advanced further into the ground to bore a pilot hole  56  shown in FIG. 6, and collect further data on the on the environment beneath the sea bed.  
         [0035]    Referring to FIG. 7, since the exact position of the wellhead housing  55  is known, a rig  70  may moored to the previously installed anchor points  36 , 37 , and accurately position vertically above the conductor  10 , casing  20  and wellhead housing  55  by adjusting the length and tautness of the mooring lines  72 , 73 . A riser and/or drill string  80  may now be lowered to meet and enter the casing.  
         [0036]    The principles of the invention disclosed herein could be adapted for different components. Referring to FIG. 8, the a casing pipe  20  (without a conductor) is suspended from an introduced length of coiled tubing  30  and lowered and installed in the sea bed  45 , the casing pipe  20  here terminating in a wellhead housing  55  assembly that is sufficiently robust to not require a conductor. If desired, additional support and guide base means may be added later.  
         [0037]    In a similar manner, a length of coiled tubing could be introduced and attached to a conductor pipe (with no casing being included), the conductor being lowered on the coiled tubing and embedded in the ground in a similar manner to that described above. A separate casing means and wellhead housing may then be installed in a later step. Additional components and casings could of course be included.  
         [0038]    Position transducers, guide lines, or other locating means for allowing a vessel returning after having installed the conductor and casing, or having installed only a conductor, or only a casing, may be included with the installed components to help the returning vessel locate and access the installation. These locating means may be used additionally or alternatively to the gyro sensors disclosed above.  
         [0039]    Other soil penetration means, such as electrically powered of fluid powered drill bits, could be used with the coiled tubing, or used in addition to the fluid jetting described above.  
         [0040]    Alternative embodiments using the principles disclosed will suggest themselves to those skilled in the art, and it is intended that such alternatives are included within the scope of the invention, the scope of the invention being limited only by the claims.