Abstract:
Various apparatuses and methods to traverse an undersea topographic feature ( 12 ) with a subsea pipeline ( 18 ) are disclosed. The apparatuses and methods of the present invention accomplish this task through the use of a concentrated buoyancy scheme ( 10 ). The invention disclosed can allow more efficient and cost effective traversal of hostile terrain for subsea pipelines at great depths while minimizing the risk of rupturing the pipeline ( 18 ) or negatively impacting the surrounding undersea environment.

Description:
BACKGROUND OF THE INVENTION 
   The pursuit of petroleum products in deep waters has revealed an underwater world completely different from a level or gradually sloping seabed. Far off the coast, unlike relatively featureless continental shelves where most offshore oil and gas has been historically developed, the deep-water ocean bottom has hazardous topographic features that can compromise pipelines and subsea structures. These topographic features include enormous basins, domes, valleys, cliffs, canyons, and escarpments. 
   An escarpment, or scarp, is a steep slope or cliff formed by erosion or faulting. The Sigsbee Escarpment, for example, is the largest in the Gulf of Mexico and lies beyond the edge of the continental shelf thousands of feet below the sea surface. The Sigsbee Escarpment encompasses drops of hundreds to over a thousand feet and extends for hundreds of miles. Between the Sigsbee Escarpment and the continental shelf exists a region called the continental slope. Because of the randomness and variability of the salt and sediment deposits, the topography of the continental slope is a complex landscape with many scarp-like features. 
   This complex topography is a significant challenge to laying subsea pipelines across these regions. The abrupt changes in the slope across such topographic features and escarpments can cause pipelines crossing them to bend sharply. This bending leads to ovalization of the pipeline cross section which may cause the pipeline to buckle and collapse. Long free spans exceeding the stress and vortex induced vibration fatigue limits of the pipeline can also result from seabed irregularities associated with these topographic features. 
   Subsea pipelines are most often used to transport production fluids from offshore facilities to land or to other offshore facilities. Such fluids include, but are not limited to, gases (methane, ethane, etc.) liquid hydrocarbons, additives (diluents added to heavy fluids or corrosion control additives), or any mixture thereof. Many issues arise with respect to the laying of subsea pipelines including countering the subsea currents, traversing the varying topography, and the complexity of the installation process itself. Existing solutions for spanning the treacherous topographic features described above can be too costly, risky, environmentally destructive, or result in other hazards. 
   Existing solutions include re-routing pipelines through existing valleys or canyons where the slope is more gradual, drilling subsea conduits, and blasting or trenching the undersea topography to provide a better support profile for the pipeline. The re-routing option can be time consuming and expensive because it requires a longer pipeline. The trenching, blasting and drilling options can have a negative impact on the undersea environment and sea life and can likewise be very costly. Other options, including the installation of rigid pilings and framework to support pipeline spans have been tried on smaller scale installations, but would be very costly on longer spans. 
   Undersea pipelines are crucial to the low cost delivery of production fluids (hydrocarbons) from offshore facilities to land or to other offshore facilities. If pipelines are not available, the hydrocarbons must be transported via tankers or some other means to the coast. Pipelines are generally considered lower risk than tankers because there is significantly less risk of maritime collisions and there are fewer exchanges (platform to tanker; tanker to shore facility) of the hydrocarbons. The hazardous topography of the continental slopes increases the risk (through stresses and failures) that leaks may occur. A solution that safely allows pipelines to traverse hazardous topography in a manner that is cost effective and environmentally responsible would be highly desirable. 
   BRIEF SUMMARY OF THE INVENTION 
   The deficiencies of the prior art are addressed by methods and apparatuses to elevate a subsea pipeline section using concentrated buoyancy to facilitate the traversal of steep underwater slopes, hazardous topographic features, and other varied irregularities on the seabed. 
   One embodiment of the invention is an apparatus that includes a subsea pipeline to carry fluids from a first to a second location and at least one concentrated buoyancy device. The pipeline extends from a first section, to the concentrated buoyancy device, and then to the second section with the buoyancy device providing a connection between the first and second pipeline sections. The concentrated buoyancy device can be one or more devices, either cylindrical, rectangular, profiled, H-shaped, or other configuration and/or can be an integrated buoyancy device. Optionally, a mooring system to secure the concentrated buoyancy device in a particular location can be employed. If employed, the mooring system can include one or more pilings (either suction, driving, or any other type of piling known to those skilled in the art) and one or more mooring lines connecting the pilings to the concentrated buoyancy device. The mooring system can exist either proximate to the first section of pipeline, the second section of pipeline, or midway between both sections of pipeline. Optionally, a flexure control device including, but not limited to a stress joint, a flex joint, a swivel, or an anchor can be employed either at the first or second sections of pipeline to prevent pipeline from over stressing or otherwise being damaged. If present, the flexure control device can be offset from a cliff edge of the topographic feature, depending on if a more favored formation is present elsewhere. 
   One method for traversing an undersea topographic feature with a subsea pipeline includes installing a plurality of pilings (either suction, driven, or any other type known to those skilled in the art) on the sea floor where a concentrated buoyancy device is desired. Using mooring lines attached between the pilings and the buoyancy device, the buoyancy device is winched down to its desired location where first and second sections of pipeline are subsequently attached thereto. Installing a jumper section, to span the buoyancy device and connect first and second pipelines, completes the traversal. Optionally, remotely operated vehicles and surface towing vessels can be used to stabilize the buoyancy device and pipeline sections during the installation process. 
   A second method for traversing an undersea topographic feature with a subsea pipeline includes connecting a first buoyancy device to a first section of pipeline and a second buoyancy device to a second section of pipeline. The first section of pipeline (with attached first buoyancy device) is then laid before the topographic feature, and the second section of pipeline (with attached second buoyancy device) is laid after the topographic feature. The buoyancy devices can then be winched together to create a single unified buoyancy device and a jumper connected across the buoyancy device to connect the first and second sections of pipeline. Optionally, remotely operated vehicles may assist in connecting the jumper line from the first section of pipeline to the second section of pipeline. Also, fluids may be added (or taken away) during the winching process of the two buoyancy devices to allow buoyancy devices to sink into a desirable position as they are winched together. 
   Finally, an assembly to connect a first pipeline segment to a second pipeline segment according to the second method summarized above can include a pair of buoyancy devices, each with a latching mechanism, a pulley mechanism, and a hinged basked. The hinged baskets are configured to receive and retain the pipeline segments in a hinged arrangement, one that allows the pipeline segments to swivel when so received. The pulley mechanism assists the winching process by allowing tension cable to be routed from a first winch, to the first buoyancy device, to the second buoyancy device, and on to a second winch. As the tension cable is pulled by the two winches, the two buoyancy devices are winched together. The latching mechanism is configured to latch the pair of buoyancy devices together permanently (or at least semi-permanently) when the winching process is complete. Finally, the pair of buoyancy devices is configured to receive a jumper line to connect the first and second segments of pipeline together. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more detailed description of the embodiments of the present invention, reference will be made to the accompanying drawings briefly described below. 
       FIG. 1A  is a schematic representation of a concentrated buoyancy pipeline system in accordance with the present invention. 
       FIG. 1B  is a close up representation of a buoyancy device of the concentrated buoyancy pipeline system of  FIG. 1A . 
       FIGS. 2A–2J  are schematic representations of pipeline spans crossing a topographic feature and having a concentrated buoyancy system in accordance with embodiments of the present invention. 
       FIGS. 3A–3H  are schematic representations of a method used to deploy a concentrated buoyancy pipeline in accordance with an embodiment of the present invention. 
       FIGS. 4A–4D  are schematic representations a second method used to deploy a concentrated buoyancy pipeline in accordance with an embodiment of the present invention. 
       FIG. 5A  is a side view schematic drawing of a buoyancy apparatus for use with the method described by  FIGS. 4A–4D  in accordance with an embodiment of the present invention. 
       FIG. 5B  is a top view schematic drawing of the apparatus of  FIG. 5A  whenever the halves  402 A,  402 B have been drawn together. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Referring initially to  FIGS. 1A and 1B  together, a schematic of a concentrated buoyancy pipeline system  10  is shown. System  10  is shown traversing an undersea scarp  12  and extends from the top  14  of scarp  12 , across a slope  15 , to a bottom  16  of scarp  12 . System  10  includes a length of pipeline  18  in a bell-shaped configuration as it traverses scarp  12 . While a scarp  12  is shown, it should be understood to one of ordinary skill in the art that various other topographic obstructions and hazards including, but not limited to, basins, domes, valleys, cliffs, and canyons, may be traversed without departing from the spirit of the invention. 
   To traverse scarp  12 , a concentrated buoyancy assembly  20  is located approximately mid-span along pipeline  18  to make it positively buoyant. Buoyancy assembly  20  desirably includes a buoyancy device  22 , a profiled surface  24 , and one or more tethers or mooring lines  26 ,  28  to secure concentrated buoyancy assembly  20  in place. Optionally, pipeline connectors  30 ,  32  can be used to help maintain pipeline  18  upon concentrated buoyancy assembly  20 . Optionally, flex or stress joints  38 ,  40  may be used to control the stress on pipeline sections  34  and  36 . Pipeline  18  includes section  34  extending from top  14  of scarp  12  to buoyancy assembly  20  in a catenary-like suspension. At buoyancy assembly  20 , pipeline  18  can curve around buoyancy device  22  at profiled surface  24  and continue via second section  36  in a catenary-like suspension to bottom  16  of scarp  12 . Optionally, connectors  30 ,  32 , retain pipeline  18  on concentrated buoyancy assembly  20  and prevent slippage therefrom. 
   Referring generally to  FIGS. 2A–2J , several concentrated buoyancy systems in accordance with the present invention are shown.  FIGS. 2A–2J  are merely schematic in nature and are solely for the purpose of detailing particular configurations available to one practicing the present invention. No specific material or component requirements are to be inferred from viewing these schematics. Furthermore, the reader is not to assume that  FIGS. 2A–2J  are drawn to any particular or consistent scale.  FIGS. 2A–2J  are merely to show various configurations and embodiments that are possible and are not drawn to reflect relative stress conditions of the pipeline systems disclosed therein. While various alternatives are shown for buoyancy devices, it should be understood that one of ordinary skill in the art could use such devices interchangeably. For example, buoyancy devices shown in  FIGS. 2A–2J  are shown as cylindrical ( FIG. 2B ), rectangular or profiled ( FIG. 2A ), or integral ( FIG. 2D ) to the lower portion of pipeline  18 . In any pipeline installation, the selection of the buoyancy device to be used will depend on the conditions of the installation location and the budgetary concerns of the operating company among other factors. Furthermore, it should be understood by one of ordinary skill that additional tethers (not shown) can be secured to the pipeline and/or buoyancy device to further stabilize the various embodiments of undersea pipelines shown in  FIGS. 2A–2J . These tethers, while not deployed as primary structural support for pipeline installations, offer secondary support in resisting the displacement of pipelines  18  that may result from undersea currents or installation conditions. These tethers, if used, are installed and secured using methods and apparatuses well known to one skilled in the art. 
   Referring generally now to  FIGS. 2A–2D  several embodiments for concentrated buoyancy pipeline suspension systems are shown. The schemes detailed in  FIGS. 2A–2D  are optionally deployed in situations where a bending control device with an anchor device ( 54 ,  64 ,  74 ,  84 ) is able to be optionally located in the immediate vicinity of the top  14  of scarp  12  and this type of installation is feasible where the formation at top  14  of scarp is sufficiently stable to allow such a bending control and/or anchor device to be permanently mounted. For those circumstances where the formation at top  14  of scarp  12  is not known to be sufficiently stable enough to support such a device, schemes detailed in  FIGS. 2E–2J  may instead be used. The schemes of  FIGS. 2E–2J  all allow the anchor and/or bending control devices to be located away from a cliff edge  14 A at the top  14  of scarp  12 . 
   Referring specifically to  FIG. 2A , a general schematic for one embodiment of a concentrated buoyancy pipeline system  50  is shown. Buoyancy system  50  includes pipeline  18  extending from top  14  to bottom  16  of scarp  12  through a buoyancy assembly  52 . System  50  includes a flexure control device  54  at top  14  of scarp  12 . Flexure control device  54  may be a flex joint or a tapered stress control joint or any other known to those skilled in the art. Primarily, flexure control devices  54  act either to allow the stress-free bending of pipeline  18  or to reduce the amount of stress experienced by the pipeline  18 . Furthermore, flexure control device  54  acts as an anchor to resist displacement of pipeline  18  resulting from currents and other forms of loading. By adding flexure control device  54 , the likelihood of ovalization of pipeline  18  adjacent thereto is greatly diminished. 
   Buoyancy device  52  is shown in  FIG. 2A  as an un-tethered device but may be tethered if the installation so requires. Using this system, the weight of lower section  18 B of pipeline  18  can retain buoyancy device  52  in position. In this configuration, upper section  18 A of pipeline  18  is designed to form a catenary with suitable curvature distribution between flexure control device  54  and buoyancy device  52 . Lower section  18 B of pipeline  18  may either exist in a catenary-shaped position with its lower end tangential to the seabed (as shown schematically) or may depart from the seabed at an angle greater than zero through the addition of another anchor flexure control device  54  at bottom  16  of scarp  12 . This condition is referred to as taut and is shown by straight lines in the schematics. 
   Referring now to  FIG. 2B , an alternative embodiment for a concentrated buoyancy system  60  is shown. Pipeline buoyancy system  60  enables a pipeline  18  to extend from a flexure control device  64  at the top  14  of a scarp  12  to the bottom  16  of scarp  12 . Buoyancy system  60  includes a buoyancy device  62  tethered to a piling  66  by a tether cable  68 . Piling  66  may be constructed in any manner known to one skilled in the art, including, but not limited to, driven pilings, suction pilings, or other subsea anchors. Regardless of configuration, the purpose of piling  66  is to maintain a mounting fixed on the seabed to which buoyancy device  62  may be tethered to by tether cable  68 . In this embodiment, pipeline section  18 A extends from a flexure control device  64  to buoyancy device  62  in a catenary-like configuration. Pipeline section  18 B then extends from buoyancy device  62  down to scarp bottom  16  under tension roughly parallel with tether cable  68 . From scarp bottom  16 , pipeline  18  is able to continue on the subsea floor to its next destination. Particularly, buoyancy device  62  may contain features that ease the transition from catenary section  18 A to taut section  18 B through an angle of about 90 degrees at buoyancy device  62 . For example, pipeline sections  18 A,  18 B may terminate at buoyancy device  62  with a flexible, or rigid bent jumper (not shown) making the connection therebetween. Buoyancy device  62  of  FIG. 2B  is shown as a cylindrical buoy, but other designs known by one skilled in the art may be employed. 
   Referring now to  FIG. 2C , a second alternative embodiment of a concentrated buoyancy pipeline system  70  is shown. Pipeline system  70  includes a buoyancy device  72  tethered to piling  76  by tether cable  78 . Buoyancy system  70  enables pipeline  18  to traverse from a flexure control device  74  at top  14  of scarp  12  to buoyancy device  72  and then to bottom  16  of scarp  12 . Two suspended sections  18 A,  18 B of pipeline  18  are thus created, each of which is suspended in a catenary-like shape. Buoyancy device  72  is shown as a profiled buoy, one that allows pipeline  18  to curve easily and smoothly thereacross with minimal or no ovalization experienced by the cross-section of pipeline  18 . Alternatively, buoyancy device  72  may be constructed as an H-shaped, rectangular, or otherwise contoured buoyancy device, as would be appreciated by one of ordinary skill in the art. 
   Referring now to  FIG. 2D , a third alternative embodiment of a concentrated buoyancy pipeline system  80  is shown. Pipeline system  80  includes an integral buoyancy device  82  tethered to a piling  86  by a tether cable  88 . Buoyancy system  80  allows pipeline  18  to traverse from flexure control device  84  at top  14  of scarp  12  to buoyancy device  82  and then to bottom  16  of scarp  12 . As noted above, buoyancy device  82  is shown as an integral buoyancy device and is optionally integrated with bottom section  18 B of pipeline  18 . As a result, buoyancy device  82  is more rigidly connected to pipeline section  18 B than to first section  18 A, which is subsequently connected to buoyancy device  82  to complete the span. Pipeline sections  18 A,  18 B assume catenary-like geometries through their spans. Pipeline section  18 B may assume a more gradual curve than span  18 A due to buoyancy device  82  and pipeline section  18 B being rigidly connected and towed out as a single unit. 
   Referring generally now to  FIG. 2E , a general schematic for a concentrated buoyancy pipeline system  90  is shown. Buoyancy system  90  includes pipeline  18  extending from top  14  to bottom  16  of scarp  12  through a buoyancy assembly  92 . System  90  includes a flexure control device  94  located away from the cliff edge  14 A at top  14  of scarp  12 . In this embodiment, the location of flexure control device is farther back on top  14  of scarp  12 , away from cliff edge  14 A to avoid uncertain or undesirable conditions at edge  14 A. 
   Buoyancy device  92  is shown in  FIG. 2E  schematically without tethers but may be tethered if the installation so requires. Using this system, the weight of section  18 B of pipeline  18  retains buoyancy device  92  in position. In this configuration, upper section  18 A of pipeline  18  is optionally taut between flexure control device  94  and buoyancy device  92 . Lower end  18 B of pipeline  18  may either exist in a catenary-shaped position (as shown schematically) or may be taut through the addition of another anchor flexure control device  94  at bottom  16  of scarp  12 . 
   Referring now to  FIG. 2F , a fourth alternative embodiment of a concentrated buoyancy system  100  is shown. Pipeline buoyancy system  100  enables a pipeline  18  to extend from a flexure control device  104  at the top  14  of a scarp  12  to the bottom  16  of scarp  12 . Flexure control device  104  is shown set back from a cliff edge  14 A of scarp  12  in order to avoid unknown or undesirable conditions at edge  14 A. Buoyancy system  100  includes a buoyancy device  102  tethered to a piling  106  by a tether cable  108 . Piling  106  may be constructed in any manner known to one skilled in the art, including, but not limited to, driven pilings, suction pilings, or other subsea anchors so long as a mounting fixed to the sea floor for buoyancy device  102  is provided. 
   In this embodiment, pipeline section  18 A extends from a flexure control device  104  to buoyancy device  102  in a catenary-like configuration. Pipeline section  18 B then extends from buoyancy device  102  down to scarp bottom  16  roughly parallel with tether cable  108 . From scarp bottom  16 , pipeline  18  is able to continue on the subsea floor to its next destination. Optionally, buoyancy device  102  may contain features that ease the transition from catenary section  18 A to pipeline section  18 B through an approximately 90 degree angle at buoyancy device  102 . For example, pipeline sections  18 A and  18 B may rigidly terminate at buoyancy device  102  with a flexible, or rigid bent jumper (not shown) making the connection therebetween. Furthermore, buoyancy device  102  of  FIG. 2F  is shown as a cylindrical buoy, but other buoyancy device designs known by one skilled in the art may be employed. 
   Referring now to  FIG. 2G , a fifth alternative embodiment of a concentrated buoyancy pipeline system  110  is shown. Pipeline system  110  includes a buoyancy device  112  tethered to piling  116  by tether cable  118 . Buoyancy system  110  enables pipeline  18  to traverse from a flexure control device  114  at top  14  of scarp  12  to buoyancy device  112  and then to bottom  16  of scarp  12 . Two suspended sections  18 A and  18 B of pipeline  18  are thus created, each of which is suspended in a catenary-like shape. Buoyancy device  112  is shown as a profiled buoy, one that allows pipeline  18  to curve easily and smoothly thereacross with minimal or no ovalization experienced by the cross-section of pipeline  18 . Alternatively, buoyancy device  112  may be constructed as an H-shaped, rectangular, or otherwise contoured buoy, as would be appreciated by one of ordinary skill in the art. As with the system  100  of  FIG. 2F  detailed above, pipeline buoyancy system  110  of  FIG. 2G  employs a flexure control device  114  that is located away from cliff edge  14 A of scarp. As mentioned above, this configuration (as well as all other embodiments shown in  FIGS. 2E–2J ) can be advantageous in circumstances where the composition or condition of the formation at or near the edge  14 A is either unknown or not conducive to the placement of flexure control device  114  thereupon. 
   Referring now to  FIG. 2H , a sixth alternative embodiment of a concentrated buoyancy pipeline system  120  is shown. Pipeline system  120  includes an integral buoyancy device  122  tethered to a piling  126  by a tether cable  128 . Buoyancy system  120  allows pipeline  18  to traverse from flexure control device  124  at top  14  of scarp  12  to buoyancy device  122  and then to bottom  16  of scarp  12 . As with the immediately preceding embodiments, flexure control device  124  is located away from cliff edge  14 A of scarp  12  in order to avoid unknown or undesirable formation conditions at edge  14 A. Buoyancy device  122 , shown in this embodiment as an integrated buoy, is optionally integrated with bottom section  18 B of pipeline  18 . As a result, buoyancy device  122  is more rigidly connected to pipeline section  18 B than to first section  18 A, which is subsequently connected to buoyancy device  122  to complete the span. Pipeline sections  18 A,  18 B assume catenary-like geometries through their spans. Pipeline section  18 B may assume a more gradual curve than span  18 A due to buoyancy device  122  and pipeline section  18 B being rigidly connected and towed out as a single unit. 
   Referring now to  FIG. 21 , a seventh alternative embodiment of a concentrated buoyancy pipeline system  130  is shown. Pipeline buoyancy system  130  is analogous to buoyancy system  110  of  FIG. 2G  with the exception that subsea piling  136  and tether  138  are located at the top  14  of scarp  12 , rather than at the bottom  16 . Nevertheless, buoyancy system  130  includes a profiled buoyancy device  132  tethered to subsea piling  136  by tether cable  138 . Buoyancy system  130  allows pipeline  18  to traverse from flexure control device  134  at top  14  (but away from cliff edge  14 A) of scarp to buoyancy device  132  and then to bottom  16  of scarp  12 . 
   Referring now to  FIG. 2J , an eighth alternative embodiment of a concentrated buoyancy system  140  is shown. Pipeline buoyancy system  140  is analogous to buoyancy system  120  of  FIG. 2H  with the exception that subsea piling  146  and tether  148  are located at the top  14  of scarp  12 , rather than at the bottom  16 . Nevertheless, buoyancy system  140  includes an integrated buoyancy device  142  tethered to subsea piling  146  by tether cable  148 . Buoyancy system  140  allows pipeline  18  to traverse from flexure control device  144  at top  14  (but away from cliff edge  14 A) of scarp to buoyancy device  142  and then to bottom  16  of scarp  12 . 
   Referring again to  FIGS. 2I–2J  together, buoyancy systems  130 ,  140  are desirable for installations where the location and installation of anchor piling  136  and  146  is more feasible or cost effective at the top  14  of scarp  12  rather than at the bottom  16 . For example, the change in depth between top  14  and bottom  16  of scarp may be so much that it is cost prohibitive to install pilings  136  and  146  at the extended depth at the bottom  16 . Furthermore, because an operation to install flexure control devices  134  and  144  at top  14  of scarp  12  must already be performed, it may be desirable to also install pilings  136  and  146  in a proximate location. Finally, whereas the formation at top  14  of scarp  12  may be too loose or silty to properly retain flexure control devices  134  and  144 , such formations may be optimally structured for the installation of a suction or driven pilings  136 ,  146 , thereby making such installations beneficial. 
   Referring now to  FIGS. 3A–3H , a first embodiment of a method of deploying a concentrated buoyancy system  200  will be described. Referring initially to  FIG. 3A , the installation of buoyancy system  200  begins with the installation of suction pilings  206 A and  206 B (more pilings can be used based on need) at the bottom  216  of an undersea scarp  212 . Suction pilings  206 A and  206 B are installed using methods commonly known to those skilled in the art and are connected to small temporary buoyancy devices  220 A and  220 B (more buoyancy devices can be used based on need) at the ocean surface  222  by tethers  208 A and  208 B (more tethers can be used based on need). With buoyancy devices  220 A and  220 B, pilings  206 A and  206 B, and tethers  208 A and  208 B in place, a towing vessel  210  tows permanent buoyancy device  202  out to the location of scarp  212 . 
   Referring now to  FIG. 3B , buoyancy device  202  is attached to tethers  208 A and  208 B at ocean surface  222 . Once attached, vessel  210  releases buoyancy device  202  but remains in communication with a subsea winch or jack  226  through a cable  224 . Operators aboard vessel  210  then activate winch  226  to draw buoyancy device  202  into the ocean until it reaches the desired depth. Alternatively, buoyancy device  202  may be installed with less than its full buoyancy to make winching operation easier. Once buoyancy device  202  reaches desired depth, buoyancy device  202  can then be de-ballasted to attain full desired buoyancy. 
   Referring now to  FIG. 3C , a pipelay vessel  230  lays pipeline  218  as it approaches the location of buoyancy device  202 . A sub sea remotely operated vehicle (ROV)  228  is used to jettison small temporary buoyancy devices  220 A and  220 B from permanent buoyancy device  202  and its mooring lines  209 A and  209 B. 
   Referring now to  FIG. 3D , ROV  228  is piloted to attach pipeline  218  from pipelay vessel  230  to buoyancy device  202 . Towing vessels  210 A and  210 B connect to buoyancy device  202  with tension cables  232 A and  232 B to help prevent buoyancy device from moving while ROV  228  connects pipeline  218  to buoyancy device  202 . 
   Referring now to  FIG. 3E , pipelay vessel  230  begins laying second section of pipeline  218 B while towing vessel  210 A holds buoyancy device  202  with attached first section of pipeline  218  in place with tension cable  232 A. Second towing vessel  210 B can assist pipelay vessel  230  by securing tension cable  232 B to the free end of second section of pipeline  218 B while ROV  228  assists and pilots second section  218 B to buoyancy device  202 . A small temporary buoyancy device  220  can be attached to the end of second section  218 B to assist ROV  228  while cable  232 B winches section  218 B to permanent buoyancy device  202   
   Referring to  FIG. 3F , subsea ROV  228  secures free end of second pipeline section  218 B to buoyancy device  202 . Towing vessel  210  assists ROV  228  during this process by holding buoyancy device  202  in place with tension cable  232 . After ROV  228  connects pipeline section  218 B to buoyancy device, the ROV releases small temporary buoyancy device  220  for recovery at the surface  222 . Referring to  FIG. 3G , towing vessel  210  retains buoyancy device assembly  202  with tension cable  232  while pipelay vessel  230  continues laying second section  218 B of the pipeline. 
   Referring finally to  FIG. 3H , the pipeline is completed by connecting first section  218 A with second section  218 B by means of a jumper  240 . Ideally, jumper section  240  is installed by a pair of ROVs  228 A and  228 B, but may be installed by divers, undersea cranes, or any other techniques known in the art. Optionally, towing vessel  210  secures buoyancy device  202  in place through an attached tension cable  232 . This allows pilots of ROVs  228 A and  228 B to install the jumper with minimal movement of buoyancy device  202 . Following the installation of jumper  240 , the pipeline is ready for operation. 
   Referring generally to  FIGS. 4A–4D , an alternative embodiment of a method of deploying a concentrated buoyancy pipeline system  300  to traverse an undersea scarp  312  will now be described. Referring initially to  FIG. 4A , buoyancy system  300  is optionally installed by laying pipeline sections  318 A,  318 B with buoyancy devices  302 A and  302 B already attached thereto. Buoyancy devices  302 A and  302 B are constructed so that they may be filled and drained of fluid to alter their buoyancy characteristics. As shown in  FIG. 4A , pipeline sections  318 A and  318 B with attached buoyancy devices  302 A and  302 B are optionally laid such that buoyancy devices  302 A and  302 B are close to the surface  322  and are proximate to one another. Pipeline sections  318 A and  318 B leading to and away from buoyancy devices  302 A,  302 B, respectfully, can be installed using methods already known to one skilled in the art. 
   Referring now to  FIG. 4B , a towing vessel  310  having two winches is moved into position over buoyancy devices  302 A and  302 B. A tension cable in three sections  332 A,  332 B, and  332 C is strung from a first winch  336 A, to buoyancy device  302 A, then to buoyancy device  302 B, and finally to second winch  336 B. Fluid/air lines  334 A and  334 B are also connected to the fluid inlets (not shown) of buoyancy devices  302 A and  302 B, respectively. Using this arrangement, winches  336 A and  336 B aboard vessel  310  can be operated to pull buoyancy devices  302 A and  302 B together. Simultaneously, fluid/air is added to or released from buoyancy devices  302 A and  302 B through fluid lines  334 A and  334 B to adjust the buoyancy in buoyancy devices  302 A and  302 B as needed. If all steps are coordinated properly, the buoyancy devices  302 A and  302 B terminating pipeline sections  318 A and  318 B will come together at the desired depth below waterline  322 . 
   Referring now to  FIG. 4C , buoyancy devices  302 A and  302 B are shown pulled together and at the proper water depth. Subsea ROVs  328 A and  328 B are then used to permanently secure the two buoyancy device halves  302 A and  302 B together so that they are inseparable and form buoyancy assembly  302 . 
   Referring next to  FIG. 4D , subsea ROV&#39;s  328 A and  328 B attach a jumper section  340  across both halves of unified buoyancy device  302  to make the completion between pipeline sections  318 A and  318 B. Towing vessel  310  assists ROVs  328 A and  328 B by holding buoyancy device  302  and jumper in place with tension cable  332  from water surface  322 . Once jumper connection  340  is made, the pipeline system  300  may now be used to flow petrochemicals therethrough. 
   Referring now to  FIGS. 5A and 5B , a buoyancy apparatus  400  capable of being deployed with pipeline system  300  is shown. Buoyancy apparatus  400  includes two buoyancy device halves,  402 A and  402 B, each having a respective hinged pipeline basket  404 A and  404 B, pulley system  406 A and  406 B, and latching mechanism  408 A and  408 B. Hinged pipeline baskets  404 A and  404 B retain and allow pipeline sections  418 A and  418 B to swivel as buoyancy devices  402 A and  402 B are manipulated. Pulleys  406 A and  406 B allow cables  410 A and  410 B run therethrough to move freely when tension is applied to them by winches for example,  336 A and  336 B of  FIG. 4B  on a vessel (for example,  310  of  FIG. 4B ) to pull buoyancy device halves  402 A and  402 B together as seen in  FIG. 5A . Finally, latching mechanisms  408 A and  408 B allow buoyancy device halves  402 A and  402 B to be permanently held together after they are winched together by cables  410 A and  410 B as seen in  FIG. 5B . Latching mechanisms  408 A and  408 B are of any configuration known to those skilled in the art, but are optionally constructed such that they may be activated by remotely operated vehicles (ROV&#39;s). 
   It should be understood by one of ordinary skill in the art that pipeline installations in accordance with the disclosed embodiments of the present invention are intended to be for permanent undersea pipeline installation. Other pipeline systems may exist to use buoyancy in the laying of subsea pipeline, but such systems are either temporary in nature or do not use concentrated buoyancy in their designs. 
   Numerous embodiments and alternatives thereof have been disclosed. While the above disclosure includes the best mode belief in carrying out the invention as contemplated by the named inventors, not all possible alternatives have been disclosed. For that reason, the scope and limitation of the present invention is not to be restricted to the above disclosure, but is instead to be defined and construed by the appended claims.