Abstract:
Floating systems for well operations are disclosed with a height-adjustable crown assembly movably connected to a derrick; in one aspect, movable within the derrick by movement apparatus; and, in one aspect, movable with a motion compensator. This abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims, 37 C.F.R. 1.72(b).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention is directed to floating systems, rigs and vessels used in wellbore operations; to floating systems, rigs, drill ships and vessels with a height-adjustable derrick; to methods for selectively adjusting a floating system&#39;s center of gravity; and to methods for adjusting derrick height by changing the position of part of a derrick, e.g. a crown block assembly and associated structure. 
         [0003]    2. Description of Related Art 
         [0004]    Well drilling has been conducted in areas where a substantial body of water overlies an oil field. In many cases a variety of fixed drill platforms mounted on legs resting on or driven into a sea floor or lake floor are used. These, however, are typically used only in relatively shallow depths of water, often not greater than about 300 feet, which is a realistic depth limit for many practical commercial operations. 
         [0005]    Often deep water drilling is accomplished using specifically designed and constructed rigs, vessels and drill ships. Deep water and exploratory drilling has been accomplished using surface floating rigs, drilling ships or vessels which are either towed or self-propelled to a drilling site and are self-contained in that the drilling rig, auxiliary equipment, and crew&#39;s quarters form an integral part of the vessel or ship. These floating drilling systems (rigs, vessels, drill ships) are positioned over a drilling site. Certain typical rigs, vessels and drill ships have, in addition to all of the equipment normally found on a large ocean ship, a drilling platform and derrick located on the deck. In addition, such rigs, vessels and drill ships contain a hole (or “moonpool”), extending through the ship down through the hull, which allows for a drill string to extend through the ship, down into the water. 
         [0006]    Drill ships are often used for deepwater drilling in remote locations with moderate weather environments because of their mobility and large load carrying capability. Drill ships can move from one location to the next rapidly and under their own power. On the open seas, size and height are generally not a consideration for drill ship movement; but, in certain specific circumstances, size and height limit a drill ship&#39;s mobility and can significantly increase the expense of movement from one site to another. For example, moving a drill ship through the Panama Canal can require the partial disassembly of a ship&#39;s derrick (and then its reassembly after passing through the canal) at a cost of several million dollars. 
         [0007]    Various prior art drill ships are relatively large. For example Transocean&#39;s Discoverer Enterprise, an ultra-deepwater drill ship, is 835 feet in length and 125 feet wide and can drill a well more than 6.5 miles beneath its drill floor. Drill ships can be, in total, 20 to 30 stories high with an upright derrick over 400 feet high. The JOIDES Resolution drill ship is 470 feet long with a 202 foot high derrick. 
         [0008]    In the past a variety of drill ship tragedies have involved the capsizing of a drill ship, particularly in stormy seas. One factor contributing to the instability of a drill ship is the height of the ship&#39;s center of gravity which is related to the height and the weight of a derrick projecting up from a ship&#39;s deck. The weight of pipe and equipment in and on the derrick can also affect the location of the ship&#39;s center of gravity. In typical drill ships, although pipe can be moved from a vertical to a horizontal position, the derrick itself is a permanent upright structure whose height is not adjustable in adverse conditions. 
         [0009]    There are a variety of known rigs, vessels, and drill ships used in drilling and various wellbore operations; for example, and not by way of limitation, those disclosed in U.S. Pat. Nos. 2,929,610; 3,011,318; 4,064,822; 4,269,543; 4,657,438; 4,885,698; 5,139,366; 5,450,695; 5,622,452; 5,833,396; 5,906,457; 5,975,805; 5,975,806; 6,056,071; 6,047,781; 6,076,996; 6,085,851; 6,068,069; 6,443,240; 6,539,888; 6,682,265; 7,011,471; 7,163,355; 7,186,061; and U.S. Application Pub. No. 2008/0000685, and in the references cited in these patents—all these patents incorporated fully herein for all purposes. 
         [0010]    There are a variety of known systems with a portable and/or erectable derrick or mast; for example U.S. Pat. Nos. 7,308,953; 6,860,337; 6,523,319; 5,450,695; 5,423,158; 5,342,020; 5,216,867; 4,932,175; 4,837,992; 4,757,592; 4,590,720; 4,269,395; 4,134,237; 3,996,754; 3,403,485; 3,340,938; and 2,804,949, 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    The present invention, in certain aspects, provides a floating system, e.g. a vessel, a drill ship, a rig, (e.g., but not limited to, jack-up rigs and semi-submersible rigs) with a height-adjustable derrick; and, in one particular aspect, a rig, vessel or a drill ship with a derrick having a crown assembly (and, in some aspects, associated structure, e.g. but not limited to support structure and/or motion compensator apparatus) whose position is selectively adjustable. In certain aspects, adjusting the position of the crown assembly provides adjustment of the ships&#39;s center of gravity which can be beneficial during various operations and during adverse sea and weather conditions. In one aspect, the crown assembly includes a motion compensation system. 
         [0012]    The present invention, in certain aspects, provides systems and methods for effectively reducing the overall height of a derrick on a floating well operations system by lowering a crown assembly (and, in some aspects, associated items). This is advantageous when moving the system through certain waterways (e.g., under bridges or through a strait or a canal, e.g. the Panama Canal) which present various height-restricted passages. In one aspect, such a system has a hull; a deck on the hull; a derrick on the deck, the derrick having a top and a top portion; a crown assembly (optionally with a motion compensator) on the derrick; and the crown assembly movably mounted to the derrick for movement with respect to the top portion of the derrick to reduce overall height of the derrick. 
         [0013]    The present invention discloses, in certain aspects, a floating well operations system with a derrick having one or more apparatuses for pivotably connecting derrick equipment to the derrick so that the equipment is selectively movable away from the path of a crown assembly being lowered in the derrick. In one particular aspect, a top drive system is included with a guide rail structure on which a top drive moves up and down in the derrick. According to the present invention, part of the guide rail of the derrick is pivotably connected to the derrick so that it can be moved aside to permit the crown assembly to be moved down into the derrick. 
         [0014]    Accordingly, the present invention includes features and advantages which are believed to enable it to advance floating well operations systems technology. Characteristics and advantages of the present invention described above and additional features and benefits will be readily apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments and referring to the accompanying drawings. 
         [0015]    Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of them distinguished from the prior art in their structures, functions, and/or results achieved. Features of the invention have been broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described below and which may be included in the subject matter of the claims to this invention. Those skilled in the art who have the benefit of this invention, its teachings, and suggestions will appreciate that the conceptions of this disclosure may be used as a creative basis for designing other structures, methods and systems for carrying out and practicing the present invention. The claims of this invention are to be read to include any legally equivalent devices or methods which do not depart from the spirit and scope of the present invention. 
         [0016]    What follows are some of, but not all, the objects of this invention. In addition to the specific objects stated below for at least certain preferred embodiments of the invention, other objects and purposes will be readily apparent to one of skill in this art who has the benefit of this invention&#39;s teachings and disclosures. It is, therefore, an object of at least certain preferred embodiments of the present invention to provide the embodiments and aspects listed above and: 
         [0017]    New, useful, unique, efficient, nonobvious floating systems for well operations, including drilling operations, including rigs, vessels and drill ships and new, useful, unique, efficient, nonobvious floating systems with a height-adjustable derrick; 
         [0018]    Such systems with a derrick and with a crown assembly movably mounted on the derrick for selective height adjustment; and 
         [0019]    Such systems with an adjustable center of gravity. 
         [0020]    The present invention recognizes and addresses the problems and needs in this area and provides a solution to those problems and a satisfactory meeting of those needs in its various possible embodiments and equivalents thereof. To one of skill in this art who has the benefits of this invention&#39;s realizations, teachings, disclosures, and suggestions, various purposes and advantages will be appreciated from the following description of certain preferred embodiments, given for the purpose of disclosure, when taken in conjunction with the accompanying drawings. The detail in these descriptions is not intended to thwart this patent&#39;s object to claim this invention no matter how others may later attempt to disguise it by variations in form, changes, or additions of further improvements. 
         [0021]    The Abstract that is part hereof is to enable the U.S. Patent and Trademark Office and the public generally, and scientists, engineers, researchers, and practitioners in the art who are not familiar with patent terms or legal terms of phraseology to determine quickly from a cursory inspection or review the nature and general area of the disclosure of this invention. The Abstract is neither intended to define the invention, which is done by the claims, nor is it intended to be limiting of the scope of the invention or of the claims in any way. 
         [0022]    It will be understood that the various embodiments of the present invention may include one, some, or all of the disclosed, described, and/or enumerated improvements and/or technical advantages and/or elements in claims to this invention. 
         [0023]    Certain aspects, certain embodiments, and certain preferable features of the invention are set out herein. Any combination of aspects or features shown in any aspect or embodiment can be used except where such aspects or features are mutually exclusive. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0024]    A more particular description of embodiments of the invention briefly summarized above may be had by references to the embodiments which are shown in the drawings which form a part of this specification. These drawings illustrate certain preferred embodiments and are not to be used to improperly limit the scope of the invention which may have other equally effective or equivalent embodiments. 
           [0025]      FIG. 1  is a side view of a prior art drill ship. 
           [0026]      FIG. 2  is a schematic side view of a drill ship according to the present invention. 
           [0027]      FIG. 3A  is a front view of part of the ship of  FIG. 2 , including, among other things, a crown block assembly. 
           [0028]      FIG. 3B  is a front view of the part of the ship of  FIG. 3A  showing the crown block assembly lowered. 
           [0029]      FIG. 4A  is a front view of a derrick (shown partially) with a crown assembly according to the present invention. 
           [0030]      FIG. 4B  is a front view of the crown assembly of the derrick of  FIG. 4A . 
           [0031]      FIG. 5A  is a front view of a derrick according to the present invention and a crown assembly according to the present invention. 
           [0032]      FIG. 5B  shows a line of the derrick of  FIG. 5A . 
           [0033]      FIG. 5C  is a front view of the derrick and crown assembly of  FIG. 5A  with the crown assembly lowered. 
           [0034]      FIG. 5D  shows the line of  FIG. 5B  in the position shown in  FIG. 5C . 
           [0035]      FIG. 6A  is a front view of a derrick according to the present invention. 
           [0036]      FIG. 6B  is a front view of the derrick of  FIG. 6A  with a top part tilted. 
           [0037]      FIG. 6C  is a front view of the derrick of  FIG. 6A  with a top part tilted. 
           [0038]      FIG. 7  is a front view of a derrick according to the present invention. 
           [0039]      FIG. 7A  is a front view of the crown assembly of the derrick of  FIG. 7 . 
           [0040]      FIG. 7B  is an illustration of a lowered position of the crown assembly of the derrick of  FIG. 7 . 
           [0041]      FIG. 8A  is a rear view of a derrick according to the present invention on a drill ship according to the present invention approaching a bridge. 
           [0042]      FIG. 8B  is a side view showing the beginning of lowering of a crown assembly of the derrick of the drill ship of  FIG. 8A . 
           [0043]      FIG. 8C  is a side view further showing the beginning of lowering of a crown assembly of the derrick of the drill ship of  FIG. 8A . 
           [0044]      FIG. 8D  shows the drill ship of  FIG. 8A  passing under the bridge and the beginning of raising of the crown assembly. 
           [0045]      FIG. 8E  shows further raising of the crown assembly. 
           [0046]      FIG. 8F  shows the crown assembly raised. 
           [0047]      FIG. 9A  is a front view of a derrick according to the present invention. 
           [0048]      FIG. 9B  is a front view of a crown assembly of the derrick of  FIG. 9A . 
           [0049]      FIG. 9C  is a front view of the derrick of  FIG. 9A  with the crown assembly lowered. 
           [0050]      FIG. 10A  is a front view of a drill ship according to the present invention with a derrick according to the present invention. 
           [0051]      FIG. 10B  is a side view of the derrick of  FIG. 10A . 
           [0052]      FIG. 10C  is a partial view of the derrick of  FIG. 10B  showing the crown assemblies lowered. 
       
    
    
       [0053]    Presently preferred embodiments of the invention are shown in the above-identified figures and described in detail below. Various aspects and features of embodiments of the invention are described below and some are set out in the dependent claims. Any combination of aspects and/or features described below or shown in the dependent claims can be used except where such aspects and/or features are mutually exclusive. It should be understood that the appended drawings and description herein are of preferred embodiments and are not intended to limit the invention or the appended claims. On the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims. In showing and describing the preferred embodiments, like or identical reference numerals are used to identify common or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
         [0054]    As used herein and throughout all the various portions (and headings) of this patent, the terms “invention”, “present invention” and variations thereof mean one or more embodiment, and are not intended to mean the claimed invention of any particular appended claim(s) or all of the appended claims. Accordingly, the subject or topic of each such reference is not automatically or necessarily part of, or required by, any particular claim(s) merely because of such reference. So long as they are not mutually exclusive or contradictory any aspect or feature or combination of aspects or features of any embodiment disclosed herein may be used in any other embodiment disclosed herein. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0055]      FIG. 1  shows a typical prior art drill ship S with a deck K on a hull H. One or more cranes C are on the deck K. An upright derrick D is mounted on the deck K. 
         [0056]      FIG. 2  shows a floating system  10 , e.g., in one aspect, a drill ship, according to the present invention with a deck  12  on a hull  14 . A derrick  20  according to the present invention is mounted on the deck  12 . The derrick  20  has a crown assembly  40  and an associated (optional) motion compensator  40   a  releasably and movably connected to a top part  22  of the derrick  20 . Movement apparatus  11  (shown schematically) selectively moves the crown assembly  40  and the motion compensator  40   a  down to reduce the overall weight of the derrick  20 . The movement apparatus  11  may be any apparatus disclosed herein. 
         [0057]    As shown in  FIG. 3A , in an embodiment  10   a  according to the present invention the derrick  20  has a plurality of crossmembers and braces  23 . A pipe handling system  60  connected to the derrick moves pipe, e.g. drill pipe. A guide rail structure  66  connected to the derrick  20  guides a top drive system TDS (shown schematically,  FIG. 3B ) within the derrick. A support  9  is pivotably secured to the derrick  20  with pivoting arms  9   a  so that the top drive TDS is movably downwardly out of the way of the crown assembly  40 . 
         [0058]    A crown assembly  40  has crown sheave  40   s  and a base  42  which is movable by movement apparatus  11   a  (shown schematically) within the derrick  20 . 
         [0059]    Initially, e.g. as shown in  FIG. 3A , the crown block assembly  40  with the compensator  40   a  projects beyond the top part  22  of the derrick  20 . As shown in  FIG. 3B , the crown block assembly  40  and compensator  40   a  have been lowered to a lower position within the derrick  20 . 
         [0060]    In one particular aspect, the derrick  20  (including the crown block assembly and compensator) is 201 feet 8 and 11/16 inches in height as shown in  FIG. 3A ; and, in the crown-block-assembly-lowered position of  FIG. 3B , the overall height is 171 feet 8 and 11/16 inches—a difference of 30 feet. In one such aspect, the crown block assembly  40  etc. weighs about 150,000 pounds so that lowering the crown block assembly  40  etc. as shown results in a significant lowering of the center of gravity of the drill ship  10 . 
         [0061]      FIG. 4A  shows a system lob according to the present invention (like the system  10 ) in which a crown assembly  40   b  with a base  40   c  (see  FIG. 4B ) is movably mounted at the top of a derrick  20   b  of a drill ship with a motion compensator  40   d.  The crown assembly  40   b  with the compensator is lowered in the derrick  20   b  by a powered apparatus  30  with line  32  connected to the crown assembly  40   b  and passing over sheaves  33 ,  34 . The apparatus  30  reels in and pays out the line  32  to raise and lower the crown assembly  40   b  and the compensator. Optionally, two apparatuses  30  and lines  32  are used. 
         [0062]      FIGS. 5A and 5C  show a system  10   c  according to the present invention (like the system  10 ) with a crown assembly  40   e  and motion compensator  40   f  movable with respect to a top  22   c  of a derrick of a drill ship. Apparatuses  30   c  raise and lower the crown assembly  40   c.    
         [0063]    As shown in  FIG. 5A , the crown assembly  40   e  is at its highest position with respect to the top  22   c  of the derrick. Pistons  30   p  of the apparatuses  30   c  are retracted and lines  30   l  extend around piston sheaves  30   s  and derrick sheaves  30   d  and are secured to the crown assembly at points  40   p.    
         [0064]    As shown in  FIG. 5C , the pistons  30   p  have been extended resulting in lowering of the crown assembly  40   e  and the compensator with respect to the top  22   c  of the derrick. 
         [0065]      FIGS. 6A-6C  illustrate a system  60  according to the present invention which includes a derrick  62  on a drill ship (not shown). A top part  61  of the derrick  62  is pivotably mounted with pivot apparatus  64  to a lower part  65  of the derrick  62 . The top part  65  includes a crown assembly/compensator combination  68 . 
         [0066]    As shown in  FIG. 6B , a connection  66  has been released and the top part  61  has begun to tilt toward a support  67 . As shown in  FIG. 6C  the top part  61  (with the combination  68 ) has been tilted approximately ninety degrees and rests on the support  67 . This effectively reduces the overall height of the derrick  62  and, therefore, of the drill ship on which the derrick  62  is mounted; and also lowers the center of gravity of the drill ship. 
         [0067]      FIG. 7  shows a system  100  according to the present invention which has a crown assembly  140  at the top  112  of a derrick  110 . The derrick  110  is on a drill floor  114  on a main deck  116  of a drill ship  120  (shown partially). A racker  101  handles pipe in the derrick  110  and a top drive  102  on a carriage  103  is movable within the derrick  110 . A drawworks  106  has a fastline  105  which passes over crown sheaves  142 . A deadline  107  is on the other side of the derrick  110 . 
         [0068]    Jacking systems  130  operate on toothed pillars  144  (see also  FIG. 7A ) to lower and raise the crown assembly  140 . There are four pillars  144  and four jacking systems  130  (two shown,  FIG. 7 ). The jacking system  130  are supported by a platform  134 . 
         [0069]      FIG. 7A  illustrates the reduced overall height of the derrick  110  when the crown assembly  140  is lowered. The raised position (as in  FIG. 7 ) of the crown assembly  140  is shown in dotted lines in  FIG. 7B . The crown assembly  140  has been lowered a distance a. In one particular aspect, this distance is about 23 feet 7 inches (or about 6.9 meters). With the top drive  103  lowered, the crown assembly  140  can be lowered within the derrick  110  without having to remove or relocate any other major pieces of equipment. 
         [0070]      FIGS. 8A-8F  illustrate steps in the operation of a system  100  when the drill ship  120  approaches an obstacle (e.g. a bridge  150 ) under which it must pass. As shown in  FIG. 8B , the jacking systems  130 , working on teeth  144 t of the pillars  144 , has begun to lower a crown assembly  141  (like the crown assembly  140 ) down within the derrick  110 , as the drill ship  120  continues to move toward the bridge  150 . 
         [0071]      FIG. 8C  illustrates the crown assembly  141  sufficiently lowered for the drill ship  120  to pass under the bridge  150 . 
         [0072]    As shown in  FIG. 8D , part of the drill ship  120  is still passing under the bridge  150  and the derrick  110  has already passed under the bridge  150 . The jacking systems  130  have begun to again raise the crown assembly  141  back to its position as in  FIG. 8A  before it was lowered. Continued raising of the crown assembly  141  is shown in  FIG. 8E  as the drill ship  120  continues to move. 
         [0073]    As shown in  FIG. 8F , the crown assembly  141  has been raised to its full upright position as in  FIG. 8A . 
         [0074]      FIG. 9A  illustrates a dual activity rig  200  on a drill floor  202  of floating well operations system  201  which may be a floating rig, vessel or ship and which, as shown in one embodiment in  FIG. 9A  is a drill ship. The rig  200  is used with respect to two (or more) adjacent wellbore locations W 1 , W 2  over which the drill ship  201  is positioned. 
         [0075]    The rig  200  has a derrick  210  with two crown assemblies  221 ,  222  both of which are on a base  230 . Movement apparatus  240  (which is shown schematically; may be any crown assembly movement apparatus disclosed herein) moves the base  230  and the crown assemblies  221 ,  222  down within the derrick  210 . 
         [0076]      FIG. 9C  illustrates a lowered position of the base  230  and crown assemblies  221 ,  222  within the derrick  210 . 
         [0077]      FIGS. 10A-10C  illustrate the application of the present invention to dual activity rigs, e.g. as disclosed in U.S. Pat. Nos. 6,068,069; 6,047,781; 6,085,851; 6,056,071; and 6,443,240—all incorporated fully herein for all purposes. 
         [0078]    A system  300  includes a drill ship  301 , a hull  309  and with a multi-activity derrick  340  which is located above a moonpool  334 . The multi-activity derrick  340  drawworks  341  (two present; one shown in  FIG. 10B ) with appropriate cable  344  and sheaves  346 ,  350  traveling blocks  352 ,  354  etc. The derrick  340  is on a drill floor  314 . 
         [0079]    First and second mini-derricks  332  and  334  on a base  336  are movable down within the derrick  340  by movement apparatus  360  (shown schematically; may be any movement apparatus disclosed herein for moving a crown assembly).  FIG. 10C  shows the position—in dotted line—of the mini-derricks once lowered within the derrick  340 . 
         [0080]    Other apparatus, equipment, and structure in the rig  340  which is not labeled or named is as in, e.g., U.S. Pat. No. 6,068,069. 
         [0081]    It is within the scope of the present invention to provide a derrick of any suitable height for a vessel or a drill ship, to provide a crown block assembly of any suitable height, and to provide structure and apparatuses for moving the crown block assembly or a crown block assembly and some support structure up and down to achieve a derrick height and/or a desired relocation of a vessel&#39;s or a ship&#39;s center of gravity. 
         [0082]    The present invention, therefore, provides in some, but not in necessarily all, embodiments a vessel or a drill ship with a selectively adjustable height and/or an adjustable center of gravity and a crown block assembly movably mounted in a derrick of the ship. 
         [0083]    The present invention, therefore, provides in some, but not in necessarily all, embodiments a system for well operations, the system comprising a floating system, the system having: a hull; a deck on the hull; a derrick on the deck, the derrick having a top and a top portion; a crown assembly on the derrick; the crown assembly movably mounted to the derrick for movement with respect to the top portion of the derrick to reduce overall height of the derrick. Such a system may one or some, in any possible combination, of the following: the system is one of a vessel, drill ship, semi-submersible rig, floating jack-up rig, and floating rig; wherein the system has a center of gravity and the crown assembly is movable to lower the center of gravity; well operation equipment connected to the derrick, the well operation equipment movable to facilitate lowering of the crown assembly past the well operation equipment; wherein the crown assembly is lowered between twenty feet and fifty feet below the top of the derrick; wherein the crown assembly is lowerable within the derrick; motion compensation apparatus connected to the crown assembly and lowerable therewith; movement apparatus connected to the crown assembly for lowering the crown assembly with respect to the derrick; wherein the movement apparatus is one of powered apparatus with reeled lines connected to the crown assembly; powered piston-cylinder apparatus; and a toothed-pillar jacking system; wherein the crown assembly is a first crown assembly, the system further having the derrick being a dual activity derrick structure, the first crown assembly connected to a lowerable with respect to the dual activity derrick structure, a second crown assembly connected to and lowerable with respect to the dual activity derrick structure, and movement apparatus for moving the crown assemblies with respect to the dual activity derrick structure; and/or the crown assembly includes a base, the base receivable within the derrick. 
         [0084]    The present invention, therefore, provides in some, but not in necessarily all, embodiments a system for well operations, the system comprising a floating system, the system having: a hull; a deck on the hull; a derrick on the deck, the derrick having a top and a top portion; a crown assembly on the derrick; the crown assembly movably mounted to the derrick for movement with respect to the top portion of the derrick to reduce overall height of the derrick; the system one of a vessel, drill ship, semi-submersible rig, floating jack-up rig, and floating rig; wherein the system has a center of gravity and the crown assembly is movable to lower the center of gravity; wherein the crown assembly is lowered between twenty feet and fifty feet below the top of the derrick; wherein the crown assembly is lowerable within the derrick; movement apparatus connected to the crown assembly for lowering the crown assembly with respect to the derrick; and wherein the movement apparatus is one of powered apparatus with reeled lines connected to the crown assembly; powered piston-cylinder apparatus; and a toothed-pillar jacking system. Such a system may one or some, in any possible combination, of the following: the crown assembly may be a first crown assembly, and the derrick may be a dual activity derrick structure with the first crown assembly connected to and lowerable with respect to the dual activity derrick structure and a second crown assembly connected to and lowerable with respect to the dual activity derrick structure, and movement apparatus for moving the crown assemblies with respect to the dual activity derrick structure. 
         [0085]    The present invention, therefore, provides in some, but not in necessarily all, embodiments methods for reducing derrick height of a derrick of a system for well operations, the system being a floating system, the method including: activating a movement apparatus of a system, the system as any disclosed herein; and moving a crown assembly of the system on a derrick with the movement apparatus to reduce derrick height. In such methods there may be motion compensation apparatus connected to the crown assembly, the method further including lowering the motion compensation apparatus with the crown assembly; and/or the crown assembly may include a base, the method including lowering with the movement apparatus the crown assembly and the base within the derrick. 
         [0086]    In conclusion, therefore, it is seen that the present invention and the embodiments disclosed herein and those covered by the appended claims are well adapted to carry out the objectives and obtain the ends set forth. Certain changes can be made in the subject matter without departing from the spirit and the scope of this invention. It is realized that changes are possible within the scope of this invention and it is further intended that each element or step recited in any of the following claims is to be understood as referring to the step literally and/or to all equivalent elements or steps. The following claims are intended to cover the invention as broadly as legally possible in whatever form it may be utilized. The invention claimed herein is new and novel in accordance with 35 U.S.C. §102 and satisfies the conditions for patentability in §102. The invention claimed herein is not obvious in accordance with 35 U.S.C. §103 and satisfies the conditions for patentability in §103. This specification and the claims that follow are in accordance with all of the requirements of 35 U.S.C. §112. The inventors may rely on the Doctrine of Equivalents to determine and assess the scope of their invention and of the claims that follow as they may pertain to apparatus not materially departing from, but outside of, the literal scope of the invention as set forth in the following claims. All patents and applications identified herein are incorporated fully herein for all purposes. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function. In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.