Abstract:
A method for drilling formations below the bottom of a body of water includes disposing a drilling system on the bottom of the body of water. The formations are drilled by rotating a first drill rod having a first core barrel latched therein and advancing the drill rod longitudinally. At a selected longitudinal position, an upper end of the first drill rod is opened and a cable having a latching device at an end thereof is lowered into the first drill rod. The winch is retracted to retrieve the first core barrel. The first core barrel is laterally displaced from the first drill rod. A second core barrel is inserted into the first drill rod and latched therein. A second drill rod is affixed to the upper end of the first drill rod. Drilling the formation is then resumed by longitudinally advancing and rotating the first and second drill rods.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates generally to the field of drilling Earth formations below the bottom of a body of water. More specifically, the invention relates to remotely operated drilling devices that are positioned on the sea floor. 
   2. Background Art 
   Drilling through Earth formations located below the bottom of a body of water generally require the use of drilling equipment deployed from a barge or ship, and in the case of deep water sites, from a drillship or semisubmersible floating drilling platform. Such drilling is a complicated and expensive operation, particularly in deep water where a drilling riser must be extended from the floating drilling structure to the sea floor to provide a return conduit for drilling fluid from the well as it is drilled. In addition to cost, drilling using such riser is not well suited to drilling tasks requiring precise control of bit weight, stability (motion compensation) of the drill string and exact positioning of tools within the borehole. Positioning of the surface vessel over the borehole on the seabed is of critical importance when a drilling riser is used. Multiple anchors or dynamic positioning are required to maintained the required degree of positional stability of the floating drilling platform. The in-water weight of the riser limits the water depth in which risers can be deployed. Floating drilling platforms capable of handling long risers for deep water are by necessity very large vessels. 
   In an attempt to minimize the above noted aspects of drilling in deep water, several seafloor based drilling systems have been developed and are in current operation. “BMS #1” and “BMS #2” are owned by JOGMEC (Japan), “PROD” is owned by Benthic Geotech Pty. Ltd. (Australia), “MeBo” is owned by the University of Bremen (Germany) and “RD2” is owned by the British Geologic Survey. The forgoing remotely operated systems have proven effective in drilling into the seabed, particularly in deep water. Because they all use a flexible umbilical rather than a drilling riser, the in-water weight of such systems is typically less than 20 tons and as a result drilling operations can be conducted from vessels as small as 50 m in length. Station keeping (positional stability) requirements for the vessel are much less stringent than for floating drilling platforms using riser, and an operational watch circle of about 20% of the water depth is adequate in most cases. Because the drilling systems are disposed on the water bottom while drilling and are necessarily heavy enough to provide sufficient reactive mass to advance the drill string, the stability of tools disposed within the borehole is excellent. Complete decoupling of drill string motion from ship motion is accomplished. 
   When used to drill core samples of the subsurface below the bottom of a body of water, all of such remotely operated water bottom drilling systems depend upon rod coring methodology. A core barrel is disposed at the bottom of a drill string. The core barrel is typically about the same length as one segment of drill pipe or string. As the borehole is extended by drilling, the core barrel is filled and then must be retrieved from the borehole to extract the core therein. Such methodology requires the retrieval of the entire drill string each time a core barrel is recovered. While the foregoing method operated from a water bottom disposed drilling unit eliminates the drill pipe riser extending from the floating drilling platform to the water bottom, the extensive tool handling required by such coring techniques results in a significant operational time to complete boreholes deeper than about 30 meters. A single 100 meter deep borehole using rod coring with standard 3 meter core barrels and drill rods requires more than two thousand tool handling operations and over one hundred hours complete. The extensive time on station and the large number of tool manipulations make rod core drilling impractical for all but shallow holes in deep water. 
   There exists a need for a water bottom based drilling unit that can obtain core samples with reduced tool handling an operating time. 
   SUMMARY OF THE INVENTION 
   A water bottom drilling system according to one aspect of the invention includes a frame configured to rest on the bottom of a body of water. A support structure is movably coupled to the frame. The support structure is configured to enable at least vertical movement of a drill head mounted on the support structure. A winch is movably coupled to the support structure and configured to enable lateral movement of the winch mounted on the support structure. The winch includes a cable thereon. An end of the cable includes a latching device thereon configured to latch onto an upper end of a core barrel disposed in the lower end of a drill string. A storage area is associated with the frame for drill rods and for core barrels. The core barrels each include a latch configured to releasably engage with a lowermost drill rod on a drill string. Each core barrel includes a latch configured to engage the latching device at the end of the cable. At least one clamp is associated with the frame and is arranged to fix a vertical position of a drill string over a drill hole. 
   A method for drilling formations below the bottom of a body of water includes disposing a drilling system on the bottom of the body of water. The formations are drilled by rotating a first drill rod having a first core barrel latched therein and advancing the drill rod longitudinally. At a selected longitudinal position, an upper end of the first drill rod is opened and a cable having a latching device at an end thereof is lowered into the first drill rod. The winch is retracted to retrieve the first core barrel. The first core barrel is laterally displaced from the first drill rod. A second core barrel is inserted into the first drill rod and latched therein. A second drill rod is affixed to the upper end of the first drill rod. Drilling the formation is then resumed by longitudinally advancing and rotating the first and second drill rods. The above procedure may be repeated by opening the upper end of the uppermost drill rod, retrieving the core barrel using the winch, displacing the retrieved core barrel, inserting a new core barrel in the drill string until it latches in the first drill rod, affixing a new drill rod to the upper end of the drill string, and resuming drilling. 
   Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a ship deploying a drilling system on the bottom of a body of water. 
       FIG. 2  shows a plan view of an example drilling system according to the invention. 
       FIG. 3  shows a side view of the drilling system shown in  FIG. 2 . 
       FIG. 4  shows an end view of the drilling system shown in  FIG. 2 . 
       FIGS. 5A through 5H  show one example of a drilling method according to the invention. 
       FIG. 6  shows a cut away view of a core barrel latched inside a drill rod. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a ship or vessel  2  having a winch  3  or similar spooling device thereon on the surface of a body of water  4  such as the ocean. The winch  3  can spool and unspool a deployment cable  6  and an umbilical cable  34  used to deploy a drilling system  10  on the bottom  11  of the body of water. The deployment cable  6  may nor may not be part of the same physical cable as the umbilical cable  34 . A water bottom based drilling system  10  is deployed using the cable  6  and is caused to rest on the bottom  11  of the body of water. After drilling operations are completed, the system  10  may be retrieved and returned to the vessel  2 . 
   A plan view of an example drilling system is shown in  FIG. 2 . The system  10  is mounted on a frame  12  that provides support for the various components of the system  10 . The frame  12  may have support legs  14  disposed on two corners to maintain the frame  12  in suitable orientation when the system  10  is disposed on the bottom of a body of water. An adjustable height leveling leg  16  may be disposed on the opposite side of the frame. Alternatively, all the legs  14 ,  16  may be adjustable height. An electrical and hydraulic power unit  30  may accept electrical and/or hydraulic power through the umbilical cable ( 34  in  FIG. 1 ) that extends from the system  10  to the vessel ( 2  in  FIG. 1 ) on the water surface. The frame  12  may include one or more features used to lower the system  10  through the water using the winch ( 3  in  FIG. 1 ) or similar device deployed on the vessel ( 2  in  FIG. 1 ). Deployment of the system can be similar to that using water bottom deployed drilling systems known in the art, and the manner of deployment of the system  10  is not intended to limit the scope of the invention. Electrical and/or hydraulic power supplied by and through the power unit  30  may operate the various devices disposed on the frame  12  as will be further explained below. The power unit  30  may include a fluid pump (not shown separately) to circulate flushing fluid for drilling operations. 
   The frame  12  may include a drill head support structure  18 . Such structure may include devices for vertically raising and lowering a drill head ( 32  in  FIG. 3 ) and for moving the drill head laterally along the frame  12  so that the drill head may be coupled to a drill string, and may be moved out of the way of the drill string so that certain operations described below may be performed on and within the drill string. 
   The frame  12  also supports a wireline winch  20 . The winch may include a selected length of armored cable  22  thereon (see also  22 A in  FIG. 5D ). The cable may or may not have one or more insulated electrical conductors therein. The cable  22  may also be slickline, wire rope or synthetic fiber line. The purpose for the winch  20  and cable  22  will be further explained below with reference to  FIGS. 5A through 5H . The winch  20  may be mounted on a support structure  23  that enables the winch  20  to be moved laterally along the frame. Either or both support structures  18 ,  23  may include devices such as hydraulic rams (not shown) to enable lateral movement of the drilling head and the winch, respectively. Other examples of devices to provide lateral movement capability may include a toothed rack and motor driven spur gear. The particular implementation used to laterally move either support structure  18 ,  23  is not intended to limit the scope of the invention. 
   The frame  12  may also include storage area for drill rods  24  and for core barrels  26 , respectively. A tool handling gantry  28  may be coupled to the frame  12  and arranged to remove drill rods (see  60  in  FIG. 5A ) from the storage area  24  or to replace drill rods in the storage area  24 . The tool handling gantry  28  may also be arranged to move core barrels (see  62  in  FIG. 5A ) to and from the storage area. Typically the tool handing gantry  28  will move the drill rods or core barrels so that they can be retained by jaws or grippers on a tool handling arm ( 44  in  FIG. 3 ) that grabs the respective core barrel or drill rod from its outer surface so that the interior of the respective core barrel or drill rod is accessible. 
   A side view of the system  10  is shown in  FIG. 3 . A drill head  32  is shown in its rest position to enable operations within the interior of the drill string. The lower portion of the frame  12  supports an alignment clamp  48 , upper foot clamp  50 , lower foot clamp  52  and casing clamp  54 . The various clamps are used to lock in place elements of the drill string as additional drill rods are added thereto or removed therefrom. The tool handing gantry ( 28  in  FIG. 1 ) may also include a grabber  42  for oversized drilling tools. The tool handing gantry  28  may also include a handling arm and jaw  44  as explained above. Drilling tools may be stored in a respective tool magazine  46 . 
   An end view of the system is shown in  FIG. 4 . 
   Having explained the principal components of a water bottom disposed drilling system, a method of operating such system will now be explained with reference to  FIGS. 5A through 5H . First referring to  FIG. 5A , at the start of drilling operations, an assembly of a drill rod  60  and core barrel  62  latched inside the drill rod  60  is coupled to the drill head  32  and is suspended above the water bottom  11 . In some implementations the drill head  32  may include an hydraulically operated motor or electric motor (neither shown separately) to cause rotation of the drill rod  60 . The drill head  32  may also include an hydraulic swivel (not shown) to enable pumping of flush fluid through the interior of the drill rod  60  during drilling operations and in particular while the drill rod  60  is being rotated. Other implementations may include a means for rotating the drill rod  60  coupled to the frame proximate one or more of the clamps (see  FIG. 3 ). The manner of rotating the drill rod  60  is left to the discretion of the system designer and is not intended to limit the scope of the invention. An annular opening core bit  63  may be disposed at the bottom of the drill rod  60  to drill the subsurface formations while enabling a substantially cylindrical core of such formations to be moved into the interior of the core barrel  62  as the drill string advances downwardly below the water bottom  11 . The beginning of such drilling a borehole  13  using the first assembly of drill rod  60  and core barrel is shown in  FIG. 5B . 
   In  FIG. 5C , the borehole  13  is drilled such that the first drill rod is moved to the lowermost possible position within the drilling system, and to continue extending the borehole  13  would require lengthening the drill string by coupling to an upper end thereof an additional drill rod  60 . In  FIG. 5C , the drill string is raised so that the drill rod  60  may be securely locked in the foot clamp  50 . The drill head  32  may then be removed from the upper end of the drill rod  60 . Such removal may be performed by rotationally locking the drill rod and counter rotating the drill head  32 , or by rotationally locking the drill head  32  and rotating the drill rod  60  using a breakout device (not shown) in the foot clamp  50 . Alternatively, the drill head  32  may include a top drive having an hydraulic chuck. The manner of making and breaking connections between the drill head  32  and the drill rods  60  and between adjacent interconnected drill rods  60  is not intended to limit the scope of the invention. After the drill head  32  is uncoupled from the drill rod  60 , the drill head  32  may be laterally repositioned using, for example, the device shown at  18  in  FIG. 1 . Laterally repositioning the drill head  32  enables moving devices inside the drill rod  60  and/or coupling additional drill rods to the drill rod  60  partially disposed in the borehole  13 . When one or more additional drill rods are coupled to the drill rod  60  disposed in the borehole  13 , the assembly is referred to as a “drill string.” As an alternative to lateral repositioning, the drill head  32  may be moved longitudinally to a height above the upper end of the drill rod  60  sufficient to enable moving the winch over the drill rod to provide access by cable  20  to the interior of the drill rod  60 . 
   In  FIG. 5D , the winch  22  is laterally repositioned such that an end of the cable  22 A is disposed directly above the drill rod  60  locked in the foot clamp  50 . The winch  22  is then operated such that an overshot  56  of any type known in the art is lowered into the interior of the drill rod  60  and is then latched to a mating feature ( FIG. 6 ) in the upper end of the core barrel  62 . The core barrel  62  may then be removed from the interior of the drill rod  60  by unlatching by the action of the overshot  56 . The winch  22  may then be laterally repositioned such that the core barrel  62  previously retrieved from the inside of the drill rod  60  may be grabbed by the tool arm ( 44  in  FIG. 3 ) and moved to be stored in the storage area ( 26  in  FIG. 1 ). 
   In  FIG. 5E , another core barrel  62  may be retrieved from the storage area ( 26  in  FIG. 2 ) and coupled to the drill head  32 . Such coupling may be performed by using the tool handling device ( 28  in  FIG. 2 ) to hold the core barrel in a lateral position above the drill rod  60  still in the borehole  13  and latching the drill head  32  to the upper end thereof. The drill head  32  may then be lowered such that the new core barrel  62  is inside the drill rod  60 . The new core barrel  62  may then be pumped to the bottom of the drill rod  60  and latched into position in the drill rod  60 . 
   In  FIG. 5F , an additional drill rod  60  may be coupled to the drill head  32 , and the drill head  32  lowered so that the additional drill rod  60  is affixed to the drill rod  60  still locked in the foot clamp  50 . The foot clamp  50  may then be released, and as shown in  FIG. 5G , drilling may resume by rotating and longitudinally advancing the drill string. Drilling continues typically until the uppermost drill rod reaches the lowest possible position in the system, as shown in  FIG. 5H . At such time, the procedure explained with reference to  FIGS. 5C through 5F  can be repeated, and drilling may continue for each successive additional drill rod coupled to the drill string until the borehole  13  is extended to the intended depth. 
   By retrieving core barrels  62  from the lowermost drill rod  60  using the wireline overshot  56  as explained above, successive core samples may be withdrawn from the borehole  13  without the need to retrieve the entire drill string each time a core barrel is retrieved. Such capability substantially reduces the number of tool operations and amount of time needed to drill a borehole below the bottom of a body of water. 
   A cut away view of a drill rod  60  having a core barrel  62  therein is shown in  FIG. 6 . The core barrel  62  may include a fishing neck  64  configured to engage the overshot ( 56  in  FIG. 2 ). The core barrel  62  may include a latch  68  that can be released by the upward force exerted by the cable ( 22  in  FIG. 1 ) when the core barrel  62  is to be retrieved from the drill rod  60 . A shoulder  66  inside the drill rod  60  may provide a seat to retain the core barrel  62  when it is pumped into the drill rod  60 . 
   While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.