Abstract:
An apparatus for reducing the load applied to a rig. The rig is positioned over a well, with the well having a tubular string disposed therein. A landing string is connected to the tubular string such as casing, production and/or testing assemblies. The apparatus comprises a floatation module attached to the landing string and a clamp for clamping the floatation module onto the landing string. In one embodiment, the floatation module comprises a tubular sleeve having a buoyant material applied thereto. The tubular sleeve includes slots. The clamp may contain a set of dies adapted to engage the slots of the tubular sleeve. A method of landing a work string into a sub-sea well head from a floating drilling rig is also disclosed, wherein a marine riser connects the rig to the sub-sea well head.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a floatation module and method of using the floatation module. More particularly, but not by way of limitation, this invention relates to a floatation module and method for safely reducing the rig hoisting requirements to run tubular strings into sub-sea wells and well bores. 
   As the energy industry continues to search the globe for hydrocarbon reservoirs, the search has increasingly focused in the world&#39;s oceans. Economical hydrocarbon reservoirs are increasingly being discovered and developed in deep water tracts located in remote and exotic places on the planet. Floating drilling platforms, such as mobile offshore drilling units (MODU&#39;s), are anchored in water depths of more than 9,200 feet and are dynamically positioned in water depths greater than 10,000 feet. 
   In combination with this deep water drilling, the actual wells drilled are in increasingly deeper water in order to penetrate commercially feasible hydrocarbon reservoirs. Hence, these wells can exceed 34,000 feet in depth. The equipment required to safely drill ultra deep water wells is large, extremely heavy, and difficult to safely handle. As understood by those of ordinary skill in the art, the lifting and lowering capacity of the drilling rigs, including MODU&#39;s, are loaded to the maximum safe working loads. 
   For instance, if an operator is running a casing string into a well bore to a sub-sea wellhead, the operator is required to lift out of the casing slips then lower that proper amount of casing. However, the operator will also be required to pick-up and lower a landing string in combination with the casing, and wherein the ultimate length of the landing string will be basically equal to the distance between the rotary table and sub-sea well head at the sea floor. Therefore, the combined weight of the casing string and the landing string could push the safe hoisting and drill pipe slip&#39;s capacity of the MODU to its maximum designed safe working loads. 
   The landing string is specifically designed to provide the very high tensile strengths (now rated to 1,500,000 lbs. working load) to safely land out casing in the sub-sea well head. As the water depth increases, the length and weights of the landing string increase proportionateley. Existing MODU&#39;s are now operating at or near their maximum hoisting capabilities with loads of 1,500,000 to 2,000,000 pounds. Casing loads of 1,500,000 pounds translate to dynamic loads of 1,750,000 lbs or more (depending on hole condition, fluid characteristics, casing designs, friction) when picking up out of the slips. In some cases, this exposes the entire load path/hoisting system (top drive, subs, crown sheaves, derrick, slips and brakes) to maximum loading. 
   Numerous problems involving drill pipe slip crushing and catastrophic slip failures have occurred which have required new heavier designs that even now barely meet load requirements. Loading the hoisting system to the maximum of its design creates several safety concerns including, but not limited to: special landing strings being designed that are heavier wall, which further exacerbates the load handling requirements; rig hoisting system capability to safely handle extreme loads (static/dynamic); the rig&#39;s capability to safely apply over-pull in tight hole conditions; the requirement of inspection of hoisting and braking system prior to the job; and dynamic loads which reach and/or exceed safe working capabilities. 
   A prior art technique, known as floating, is sometimes used to reduce casing loads during running. The floating technique entails running the casing without completely filling the entire length with fluid, therefore establishing buoyancy due to the air inside. This presents several concerns for operations, equipment, and the health and safety of the rig crew. For instance, some of the problems encountered include: extremely high differential pressures on float equipment; failure of float equipment could cause immediate overloading of rig hoisting system caused by loss of buoyancy, which would be catastrophic; well control and/or stuck pipe due to swabbing or suction if floats fail; casing collapse; and, removal of air in casing effects circulation and cementation of the casing. 
   Therefore, there is a need for an apparatus and method for running and landing casing from floating drilling platforms. There is also a need for a device and method that can reduce the rig hoisting requirements to safely run casing strings from floating drilling platforms. These as well as many other needs will be met by the invention herein disclosed. 
   SUMMARY OF THE INVENTION 
   An apparatus for reducing the load applied to a rig. The rig being positioned over a well, with the well having a tubular string disposed therein. A landing string is connected to the tubular string, such as casing or production equipment. The apparatus comprises a floatation module attached to the landing string and a clamp means for clamping the floatation module onto the landing string. Also included is engagement means, located on the floatation module, for engaging with the clamp means. 
   In one preferred embodiment, the floatation module comprises a tubular sleeve having buoyant material applied thereto. The engagement means includes slots formed in the tubular sleeve. In the most preferred embodiment, the tubular sleeve is constructed of aluminum and the buoyant material comprises a foam bonded to the aluminum sleeve. 
   Also in the most preferred embodiment, the tubular sleeve comprises a first cylindrical half body pivotly attached to a second cylindrical half body. The clamp means further includes a first shell attached to a second shell, and wherein said first shell and said second shell are pivotly attached to form a cylindrical member. The clamp means may further comprise a first set of dies adapted to engage the slot of the first tubular. 
   In one embodiment, a second floatation module is attached to the landing string and wherein the clamp means further comprises a second set of dies adapted to engage a slot located in the second floatation module. In the preferred embodiment, the first shell comprises a latching rod and the second shell comprises a latching protrusion and wherein the latching rod is configured to engage the latching protrusion in order to latch the first shell and the second shell together. 
   A method of landing a tubular string, such as casing or production equipment, into a sub-sea well head from a floating drilling rig onto a sub-sea well head is also disclosed, wherein a marine riser connects the rig to the sub-sea well head. In the preferred embodiment, the tubular string is a casing string. The method comprises running the casing string into the marine riser, and connecting a casing hanger to the casing string. Next, a landing string is attached to the casing hanger. A floatation module is connected to the landing string. 
   The method further includes lowering the landing string through the marine riser so that the weight of the tubular string being lowered into the marine riser is reduced. The casing hanger can then be landed into the sub-sea well head. 
   In one preferred embodiment, the floatation module comprises a tubular member having a buoyant material bonded thereto, a slot formed within the tubular member, and engagement means for engaging with the slot and the step of attaching the floatation module to the landing string includes attaching the engagement means with the slot in order to clamp the floatation module with the landing string. Also, the engagement means may comprise a die member and wherein the step of attaching the engagement means further includes engaging the die member into the slot. 
   An advantage of the present invention includes an apparatus and method that safely reduces rig hoisting requirements. Another advantage is that the invention is safer than prior art methods and devices. Yet another advantage is that an operator can install floatation modules before going to the rig site, or can install at the rig site. Another advantage is the modularity of the invention. For instance, an operator can install several floatation modules per joint of pipe, or alternatively, the operator can space out floatation modules in a predetermined sequence along the entire length of the landing string in order to effect the desired amount of buoyancy. 
   A feature of the invention is that the buoyancy material, such as syntactic foam, is bonded to a sleeve, such as an aluminum sleeve. Another feature is that the sleeve consist of two cylindrical halves that are latched together to form the floatation module. A feature is the clamp means for clamping the halves together. Yet another feature is that the sleeve can contain engagement means that comprises slots. Another feature is that the clamp means includes dies that engage with the slots thereby holding the sleeves about the landing string. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of the floatation module of the present invention in the open position. 
       FIG. 2  is an isometric view of the clamp means of the present invention in the open position. 
       FIG. 3  is an isometric view of the clamp means seen in  FIG. 2 , with the clamp means in the closed position. 
       FIG. 4  is an isometric exploded view of the floatation modules about a joint of landing string. 
       FIG. 5  is an isometric assembled view of the floatation modules of  FIG. 4  shown clamped about a joint of the land string. 
       FIG. 6  is a schematic view of the floating platform lowering a tubular string into a well in accordance with the teachings of the present invention. 
       FIG. 7  is a sequential schematic view of the floating platform seen in  FIG. 6  wherein the tubular string has been lowered to a predetermined depth. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , an isometric view of the floatation module  2  of the present invention in the open position will now be described. As seen in  FIG. 1 , the floatation module  2  contains a first half cylindrical sleeve  4  and a second half cylindrical sleeve  6 . A cylindrical member is formed when the first half cylindrical sleeve  4  and second half cylindrical sleeve are joined together. In the most preferred embodiment, the first half tubular sleeve  4  and the second half tubular sleeve  6  are constructed of aluminum. 
   A buoyant material will be bonded to the first half cylindrical sleeve  4  and the second half cylindrical sleeve  6 . In the most preferred embodiment, the buoyant material is a syntactic foam commercially available from CRP Corporation under the name Syntactic Foam. For instance, the  3  bonded foam, which is bonded to the sleeve  4 , is seen generally at  7 . 
     FIG. 1  also shows that the first half cylindrical sleeve  4  has means for engaging with a clamp, wherein the clamp will be explained with reference to  FIG. 2 . Returning to  FIG. 1 , for the first half cylindircal sleeve  4 , the engaging means includes slot  10  formed on a first end of the first half cylindrical sleeve  4 , and the slot  14  formed on a second end of the first half cylindrical sleeve  6 . For the second half cylindrical sleeve  6 , the engaging means includes slot  18  on a first end of the second half cylindrical sleeve  6 , and the slot  20  formed on the second end of the second half cylindrical sleeve  6 . In the most preferred embodiments, the slots are rectangular in shape.  FIG. 1  also shows a third half cylindrical sleeve  22  and a fourth half cylindrical sleeve  23 . 
   Referring now to  FIG. 2 , an isometric view of the clamp means  24  of the present invention in the open position is shown. The clamp means  24  contains a first half cylindrical shell  26  and a second half cylindrical shell  28  that pivotly attached via the hinge means  30 . In the preferred embodiment shown in  FIG. 2 , the hinge means  30  is a conventional type of hinge having a rod  31  extending through cylindrical bodies. 
     FIG. 2  also depicts that the clamp means  24 , and in particular the member  26 , contains a first die  32  and a second longitudinally spaced die  34 , wherein the dies are protrusions fixed on the inner portion of the shell  26 . The shell  28  contains the third die  36  and a fourth longitudinally spaced die  38 , wherein the dies are protrusions fixed on the inner portion of the member  28 . In the most preferred embodiment, the dies are rectangular, formed on the inner portion of the shells  26 ,  28 , and are configured to engage the slots formed on the sleeves of the floatation modules. 
     FIG. 2  also shows a pair of mounting brackets, namely mounting bracket  40  and mounting bracket  42 . The mounting brackets  40 ,  42  will have rods  44 ,  46 , respectively, that are pinned to the mounting brackets  40 ,  42 . The rod  44  is configured to cooperate and engage with the receiving bracket  48 , wherein the receiving bracket  48  is attached to the first half shell  26 . The recieving bracket  48  has the cavity  48   a  configured to receive the rod  44 . The rod  46  is configured to cooperate and engage with the receiving bracket  50 , wherein the receiving bracket  50  is attached to the first half cylindrical member  26 . The receiving bracket  50  has the cavity  50   a  configured to receive the rod  46 . The rod  44  will have nut member  52  that will engage external thread means on the rod  44 , wherein the nut member  52  will fasten the members  26 ,  28  together. Also, the rod  46  will have nut member  54  that will engage external thread means on the rod  46 , wherein the nut member  54  will fasten the members  26 ,  28  together. 
   Referring now to  FIG. 3 , an isometric view of the clamp means  24  seen in  FIG. 2 , with the clamp means  24  being in the closed position will now be described. It should be noted that like numbers appearing in the various figures will refer to like components. The members  26 ,  28  have been pivoted closed via the hinge  30 . The rod  44  pivots to engage the receiving bracket  48  within cavity  48   a , and the rod  46  pivots to engage the receiving bracket  50  within cavity  50   a . The nut members  52 ,  54  can then be turned to fasten the clamp means  24 . 
     FIG. 4  is an isometric exploded view of a plurality of floatation modules about a joint of landing string  62 . More specifically,  FIG. 4  shows a first floatation module  64  that consist of a first half sleeve  64   a  and a second half sleeve  64   b ; a second floatation module  66  that consist of a first half sleeve  66   a  and a second half sleeve  66   b ; and, a third floatation module  68  that consist of a first half sleeve  68   a  and a second half sleeve  68   b . The sleeve  64   a  has slots  70 ,  72 ; the sleeve  164   b  has slots  74 ,  76 ; the sleeve  66   a  has slots  78 ,  80 ; the sleeve  66   b  has slots  82 ,  84 ; the sleeve  68   a  has slots  86 ,  88 ; and, the sleeve  68   b  has slots  90 ,  92 . In the most preferred embodiment, the sleeves  64   a ,  64   b ,  66   a ,  66   b ,  68   a , and  68   b  comprise the aluminum sleeve with the bonded foam, as previously described. 
   Also shown in  FIG. 4  are the clamp means. The clamp means  94  will engage the floatation module  64 , and in particular, the slots  70 ,  74  via the dies of clamp means  94 . The clamp means  96  will engage the floatation modules  64  and  66 , and in particular, the slots  72 ,  76  and slots  78 ,  82  via the dies of clamp means  96 . The clamp means  98  will engage floatation modules  66  and  68 , and in particular, the slots  80 ,  84  and slots  86 ,  90  via the dies of clamp means  98 . The clamp means  100  will engage the floatation module  68 , and in particular the slots  88 ,  92  via the dies of clamp means  100 . 
   The landing string  62  has box end  104  and a pin end  106 . It should be noted that while three floatation modules have been shown, the actual number placed per joint can vary. In fact, with some landing strings, it is possible to alternate the placement of the floatation modules amongst various joints. The actual number, length of the floatation modules, thickness of the buoyant material, etc. will depend on specific design criteria. Many design criteria can be considered, such as the amount weight reduction required, rig space, etc. 
   Referring now to  FIG. 5 , an isometric assembled view of the floatation modules of  FIG. 4  shown clamped about a joint of the landing string  62  will now be described. More specifically, the floatation module  64  has been engaged to the landing string  62  via the clamp means  94  and clamp means  96 . The floatation module  66  has been engaged to the landing string  62  via the clamp means  96  and clamp means  98 . The floatation module  68  has been engaged to the landing string  62  via the clamp means  98  and clamp means  100 . Hence, the buoyant landing string  62 , as seen in  FIG. 5 , and can now be run into the marine riser using convention means known to those of ordinary skill in the art. 
   In  FIG. 6 , a schematic view of a floating platform  110  lowering a tubular string  112  into a well  114  in accordance with the teachings of the present invention will now be described.  FIG. 6  shows a surface casing  115  already cemented into place in the earth&#39;s surface, as understood by those of ordinary skill in the art. The tubular string  112  being lowered, in one preferred embodiment, will be a casing string  112 , and the floating platform  110  will contain a drilling rig  116 . The drilling rig  116  will contain a hoisting system that includes the block  118 . A sub-sea well head  120  is position on the ocean floor, and wherein a marine riser  122  extends from the sub-sea well head  120  on the ocean floor to the floating platform  110 . It should be noted that the tubular string  112  can also be, in one embodiment, a production assembly for producing hydrocarbons or a testing assembly for testing the well. 
   The method of landing a casing string  112  into a sub-sea well head  120  from the floating platform  110  includes running the casing string  112  into the marine riser  122  and connecting a casing hanger  124  to the casing string  112 . A casing hangar  124  is a device that serves to land and anchor to the casing string inside the sub-sea well head  120 . Casing hangers are commercially available from FMC Inc. under the name casing hangers. 
   The method further includes attaching the landing string  126  to the casing hanger  124 . As noted earlier, the landing string  126  is a tubular member that is used to lower into proper position a down hole component, and wherein the down hole component may be a casing string, bottom hole assembly containing a measurement while drilling tool with bit and mud motor, production and testing assemblies, etc. The landing string  126  may be referred to sometimes as a work string. In some embodiments, the landing string  126  is a specially designed and/or sized drill pipe. 
   The method includes connecting a buoyancy module, such as the floatation modules  64 ,  66  and  68  noted in  FIG. 4 , to the landing string  126 . The operator would thereafter lower the landing string  126  (containing the floatation modules) through the marine riser  122 . Since the marine riser  122  will have a fluid therein, the weight of the tubular string  112  being lowered into the marine riser  122  will be reduced, according to the teachings of this invention. Next, and as seen in  FIG. 7 , the casing hanger  124  can be landed into the sub-sea well head  120 . A plurality of floatation modules, including  130 ,  132 ,  134 ,  136 , are shown clamped about the landing string  126 . Hence, the casing string  112  has been lowered to a predetermined depth safely by reducing the rig hoisting requirements. 
   Although the present invention has been described in terms of specific embodiments, it is anticipated that alterations and modifications thereof will no doubt become apparent to those skilled in the art. It is therefore intended that the following claims be interpreted as covering all such alterations and modifications as fall within the true spirit and scope of the invention.