Abstract:
The present invention is a device suitable for capture and containment of oil and gas wells following blowouts or other catastrophic failures, including those in submarine environments, and methods for its construction. The present invention provides a structurally-robust repair collar with integrated locking elements capable of engaging a riser pipe assembly, and an internal structure allowing in situ formation of an impermeable permanent seal through the introduction of liquid concrete into the device. The repair collar can provide means for attaching valves and various other downstream components in order to return pre-blowout functionality to the repaired riser, including oil recovery and flow control capability.

Description:
PRIORITY CLAIM 
       [0001]    The present application claims benefit under 35 USC Section 119(e) of U.S. Provisional Patent Application Ser. No. 61/364,901 filed on Jul. 16, 2010: The present application is based on and claims priority from this application, the disclosure of which is hereby expressly incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a device adapted to repair a undersea well-head riser apparatus in the event of damage to an undersea riser connecting an undersea well to a surface floating oil platform rig. 
       INTRODUCTION 
       [0003]    Devices for extracting oil from beneath the ocean floor are well-understood in this art of repairing risers after a blowout. A representative system is described by Kortla et al. in U.S. Pat. No. 7,779,917, which issued on Aug. 24, 2010. Kortla describes a subsea connection apparatus to allow connecting a surface blowout preventer stack and riser to a subsea wellhead and further provides context of the current level of understanding in the art. The present invention makes reference to the environment and devices described by Kortla and incorporates the patent in it entirety as if fully set out herein. Other representative teachings include an apparatus and method for killing or suppressing a subsea well described by Fontana et al. in U.S. Pat. No. 6,179,057 issued on Jan. 30, 2001: The present invention makes reference to the environment and devices described by Fontana and incorporates the patent in it entirety as if fully set out herein. 
       The Problem: 
       [0004]    As the oil industry has faced accelerated depletion of onshore and shallow water oil resources, attention has turned increasingly to deepwater production to alleviate the shortfall. At the same time, global oil consumption is expected to rise for the foreseeable future, particularly with the rapid increase in use by emerging economies, with projections of global demand reaching 115 million barrels per day (Mbd) by 2030. The U.S. claims about 5% of the world&#39;s population, yet as a nation it now consumes a disproportionately large share of global oil production, roughly 25% of the 86 Mbd recovered. Possessing only about 2% of the world&#39;s proved oil reserves, or 21 billion barrels (much of it offshore within the Gulf of Mexico), at the present production rate of 7.5 Mbd, U.S. reserve life is now only 8 years. 
         [0005]    To meet rising global demand, exploration and production (E&amp;P) spending has grown dramatically in recent years, from $200 billion in 2000 to $450 billion in 2009, in order to locate and exploit the increasingly remote and technically challenging remaining resources. Despite the fact that production from deepwater resources typically recovers less than twenty percent (20%) of the reserve find, projections show that within a few years, global offshore oil production could equal total oil output from Saudi Arabia, the world&#39;s largest oil producer. 
         [0006]    In addition to this, climate change is opening Arctic resources worth trillions of dollars (including oil, natural gas, and methane hydrates) to recovery efforts far more quickly than projected. As much of these resources are located offshore, recovery from incidents resulting in loss of well containment could be severely impacted by seasonal sea ice accumulation and lack of response access. Of particular concern are unconstrained, protracted releases of methane gas from the vast stores which underlie substantial portions of the Arctic basin in both gaseous and hydrate form. Recent research indicates that abrupt climate change could be triggered by the release of even a small fraction of the methane stored within the East Siberian Sea Shelf alone. 
         [0007]    As demonstrated by the environmental and economic devastation caused in the Gulf of Mexico by the blowout of the Macondo 252 (MC252) well and sinking of the Deepwater Horizon (DH) exploratory drill rig in Spring of 2010, and disclosed in related Congressional testimony, the oil industry is far more capable at accessing these remote resources than in containing a damaged deepwater well when extreme incidents do occur, whether through negligence, human error, or simple mechanical failures. This event, therefore, is most appropriately viewed not simply as an anomaly, but a reminder of the potential magnitude of damage posed by future incidents resulting from these trends if left unchecked, particularly through the development of appropriate response technologies. 
       Current State-of-the-Art: 
       [0008]    The capture techniques employed in response to the Deepwater Horizon incident are in many ways similar to those employed three decades earlier in the relatively shallow (162 ft. seafloor) Ixtoc 1 blowout off the coast of Mexico (prior to the Deepwater Horizon, or “DH”, blowout, the largest in the Gulf). In this earlier incident, four pound steel and lead balls were initially forced down the wellhead, but were ejected by the high-pressure oil and gas leak. Following this, a funnel-like device nearly 40 ft. in diameter and 18 ft. tall known as the “Sombrero,” was deployed to the site and placed over the wellhead. Capturing little of the spewing oil during its two months of use, the device was eventually abandoned before a relief well ended the spill 290 days after the blowout, with more than 3 million barrels of crude pouring into the Gulf. 
         [0009]    When the DH drill rig sank, the riser pipe extending from the rig to the seafloor 5,000 ft. below had collapsed and buckled at an expected point, immediately above the wellhead Blowout Preventer (BOP) structure on the seabed. Initial containment methods, ranging from hoods to inserted pipes, focused on leaks along the collapsed riser pipe and particularly its severed end on the seafloor. Each method failed to capture significant portions of the spill, due in part to blockage issues resulting from methane hydrate formation, an issue common at these depths and temperatures with methane/water interaction. 
         [0010]    A subsequent back-fill of the well known as “top kill” was then attempted, an unprecedented procedure in which heavy drilling mud was forced into the wellhead assembly in an attempt to overcome the flow of the lower-density crude oil and drive it back down the well casing. This was to be followed with concrete to form a permanent plug in the upper portion of the casing. In addition to this “top kill” operation, which introduced 30,000 barrels of drilling mud into the wellhead, a “junk shot” of golf balls and other debris was also forced into the spewing well in an effort to slow the flow. After several days&#39; effort, these procedures were deemed unsuccessful and terminated. 
         [0011]    As a result of these failures, approximately six weeks into the incident response, cut and shear operations were performed on the riser immediately above the BOP in order to provide a seat on the cut pipe to form a “seal” within a containment cap in yet another unprecedented tactic. With several caps of various sizes manufactured to provide one with an optimal seal for the resulting cut, the final condition of the sheared riser pipe stub at the BOP provided only modest capture capability, while continuing to be plagued with hydrate blockage issues. 
         [0012]    With worldwide attention directed to the DH incident, a variety of alternative containment techniques were suggested. The vast majority failed to take the fundamentals of the extreme environmental conditions at the wellhead into consideration, including the above-mentioned hydrate formation, extreme pressure, ocean currents, and limitations of the remotely operated vehicles (ROV&#39;s) performing all seafloor tasks of deployment and maintenance. 
         [0013]    The various state-of-the-art technologies deployed in the months following the Deepwater Horizon (DH) seafloor blowout had minimal success in capturing the escaping crude, typically required continuous monitoring and fine-tuning, and at 2½ months into the incident, could capture less than half of the projected daily output from the spewing wellhead. In addition, methanol and oil dispersants injected at the blowout capture site, combined with the seawater contamination, rendered the captured oil largely non-viable for refinement, and therefore much of this oil (as well as all of the captured methane) was flared (burned) for disposal on site. 
         [0014]    At present, the only existing technique for positively containing a deepwater blowout has required use of a relief well to “bottom kill” the original well. In this method, a second drilling operation is undertaken sometime following a blowout incident with the intention of running a new well parallel to the original well casing, then diagonally to form an intersection of the two wells. Upon interception, drilling mud and concrete are forced down the relief well to permanently isolate, or kill, the erupting well from the reservoir below. 
         [0015]    Under the best-case scenario, the first of two relief wells directed at killing the DH blowout will have taken more than three months to make a first attempt at interception. As the process is by necessity protracted, a number of factors can significantly hamper the success of this containment method, including drilling delays due to extreme weather, as well as issues similar to those leading to the initial blowout. Under arguably more-favorable conditions, the 2009 Montara blowout off the Australian coast, was finally contained with a relief well on the fifth drilling attempt after leaking oil for 2½ months, despite being in much shallower seas (250 ft. vs. 5,000 ft. for the DH) and with a shallower intercept target depth (1.6 miles vs. 3.4 miles, respectively). 
         [0016]    Thus, there remains a need for a device that can quickly repair a riser blow-out. 
     
    
     
       DRAWING 
         [0017]      FIG. 1  is a front cross section of the device according to the present invention. 
           [0018]      FIG. 2  is a partial side view of an alternative coupling mechanism for use with the present invention. 
           [0019]      FIG. 3  is a partial side view showing a damaged riser assembly. 
           [0020]      FIG. 3A  is a top view of the damaged riser assembly of  FIG. 3 . 
           [0021]      FIG. 4  is a top view of a damaged riser assembly highlighting typical interface locations for pre-load rams. 
           [0022]      FIG. 5  is front view of a basic repair collar according to the present invention. 
           [0023]      FIG. 5   a  is a top view of the repair collar of  FIG. 5 . 
           [0024]      FIG. 6  is a front cross section of the repair collar relative to a damaged riser assembly. 
           [0025]      FIG. 7  is a front cross section of the repair collar and damaged riser and shows one step of a method of repair according to the present invention. 
           [0026]      FIG. 8  is a front cross section of the repair collar and damaged riser and shows another step of a method of repair according to the present invention. 
           [0027]      FIG. 9  is a front cross section of the repair collar and damaged riser and shows another step of a method of repair according to the present invention. 
           [0028]      FIG. 10  is a front cross section of a radially-positioned internal gusset plate according to the present invention. 
           [0029]      FIG. 11  is a top view of the device of the present invention. 
           [0030]      FIG. 12  is side cross section of the device of the present invention and illustrates one step of a method of use of the present invention in a well-head repair operation to a damaged riser. 
           [0031]      FIG. 13  illustrates another step in the method of  FIG. 12 . 
           [0032]      FIG. 14  illustrates another step in the method of  FIG. 12 . 
           [0033]      FIG. 15  illustrates another step in the method of  FIG. 12 . 
           [0034]      FIG. 16  illustrates another step in the method of  FIG. 12 . 
           [0035]      FIG. 17  illustrates another step in the method of  FIG. 12 . 
           [0036]      FIG. 18  illustrates another step in the method of  FIG. 12 . 
           [0037]      FIG. 19  illustrates a step in another method of repair using the device of the present invention. 
           [0038]      FIG. 20  illustrates another step in the method of  FIG. 19 . 
           [0039]      FIG. 21  illustrates another step in the method of  FIG. 19 . 
           [0040]      FIG. 22  illustrates another step in the method of  FIG. 19 . 
           [0041]      FIG. 23  illustrates another step in the method of  FIG. 19 . 
           [0042]      FIG. 24  illustrates another step in the method of  FIG. 19 . 
           [0043]      FIG. 25  is an end view of a capture pin according to the present invention. 
           [0044]      FIG. 25A  is a left-side view of the pin of  FIG. 25 . 
           [0045]      FIG. 25B  is a top view of the pin of  FIG. 25 . 
           [0046]      FIG. 26  is a front cross section of a system for establishing lateral positioning of repair collar when first installed on target assembly according to another method of the present invention using a device according to one embodiment of the present invention. 
           [0047]      FIG. 26A  is a top view of the repair collar of  FIG. 26 . 
           [0048]      FIG. 27   a  is a top view of an outer dam according to an embodiment of the device of the present invention. 
           [0049]      FIG. 27   b  is a detail partial top view of the dam of  FIG. 27   a.    
           [0050]      FIG. 27   c  is a detail partial side view of the dam of  FIG. 27   a.    
           [0051]      FIG. 28  is a side cross section of a repair collar anchored to a damaged well riser. 
           [0052]      FIG. 29  illustrates one step of a repair method using the an alternative embodiment of a device according to the present invention. 
           [0053]      FIG. 30  illustrates another step of the method of  FIG. 29 . 
           [0054]      FIG. 31   a  illustrates another step of the method of  FIG. 29 . 
           [0055]      FIG. 31   b  illustrates another step of the method of  FIG. 29 . 
           [0056]      FIG. 32  illustrates yet another step of the method of  FIG. 29 . 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0057]    Possible embodiments will now be described with reference to the drawings and those skilled in the art will understand that alternative configurations and combinations of components may be substituted without subtracting from the invention. Also, in some figures certain components are omitted to more clearly illustrate the invention. 
         [0058]    While variations of details will be driven by the unique nature of each well recovery response and available target equipment, the preferred embodiment expressed in the deployment sequence shown in  FIGS. 12 through 18  onto target components based on the Deepwater Horizon MC252 wellhead, provides a general overview of components and features of the invention. Relative dimensions shown are general representations of structural elements only, and do not necessarily reflect specific engineering values, as variables may exist within the confines of each unique application. 
         [0059]    In a first preferred embodiment, for example, the embodiment depicted at least by  FIGS. 1 ,  5 ,  5   a , and  6 - 26   a , the present invention contemplates a well-riser repair collar for coupling to a wellhead riser having a wellhead riser flange.  FIGS. 2 ,  3 , and  4  illustrate a common wellhead riser having a flange. The present invention consists of a repair collar comprising an outer seal enclosure  2  coupled to an annular cap plate  4  and an inner flow enclosure  3 , which is also coupled to the annular cap plate. The annular cap plate defines a center, circular opening, which is intended and adapted to fit over the wellhead riser. Further, the inner flow enclosure and outer seal enclosure and annular cap plate cooperate to define an open-bottomed annular chamber. 
         [0060]    In this first preferred embodiment, the outer seal enclosure further comprises a means for mechanically capturing the riser flange. For example, as  FIG. 1  shows, the means comprises at least one capture pin  5   c , which is engaged under pre-load from at least one corresponding hydraulic ram  6  (see  FIG. 14 ). 
         [0061]    Further, the outer seal enclosure also includes an inlet aperture  19  adapted to direct a material, such as concrete, to the open bottomed annular chamber and an outlet aperture  20  adapted to enable other material, such as seawater, trapped gases including methane, or other fluids or gases or solids, to escape the open bottomed annular chamber—when the concrete is directed to the collar. It will be understood that the collar, cooperating with the wellhead riser flange to define a three-dimensional area—this area may not be water tight, but is well enough defined to enable a pouring of concrete into the collar between the outer and inner enclosures to seal the wellhead riser leak by using the wellhead riser flange as a bottom wall and the collar is fixed relative to and coupled with the wellhead riser by the means for mechanically capturing the riser flange, in this first embodiment, by a plurality of pins  5 . 
         [0062]    In an alternate embodiment, as  FIG. 2  illustrates, the present invention in a second preferred embodiment contemplates a means for selectively coupling the collar to a riser flange wherein the means consists of a mechanical grappler device  5   d , or preferably a plurality of annularly arranged grapplers. Each grappler is pivotably mounted to a portion of the collar, for example the grappler  5   d  couples to a ring extension on the outer seal enclosure. The outer seal enclosure can consist of an industry standard pipe  9  and flange, as would be well understood by those skilled in this art. The grappler  5   d  is configured to selectively engage the flange  1  on the wellhead riser by preload rams  6  in a conventional manner. 
         [0063]      FIG. 1  is a side view cross-section of the preferred embodiment, facilitating repair of a typical target assembly (based on the Deepwater Horizon MC252 wellhead riser flange). The target  1  has been mechanically captured via capture pins  5   c , which are engaged under pre-load from the hydraulic rams  6  via the ram pads  28  and target flange assembly  1 . Outer dam  7  has engaged the upper perimeter of the flange assembly, and the in situ formation of the concrete seal  8  is complete. Oil flow through the target and repair collar is continuous throughout the installation process. Following a brief concrete curing period, pre-blowout flow control and oil recovery capabilities are restored, with the addition of relevant downstream systems (pre-installed valves, quick-couple fittings, etc.) via an industry-standard mounting system  9 . 
         [0064]      FIG. 2  is a cross sectional view of an alternative collar according to a second preferred embodiment and shows at least one grappler  5   d  pivotably mounted to the collar at an exterior portion of the industry standard pipe  9  having a flange. 
         [0065]      FIG. 3  is a graphic representation of a typical wellhead riser flange assembly, such as a MC252, atop a seafloor-mounted Blowout Preventer (BOP) structure. Riser pipe  10  includes a portion that represents a buckled portion, which can occur from the sinking of a drill rig, such as the Deepwater Horizon in the Gulf of Mexico in 2010. The riser pipe can be cut via a remotely operated vehicle (ROV) using a diamond wire saw. If this cutting system fails, as it did in the Deepwater Horizon disaster, the riser can be sheared for removal from the BOP, resulting in a jagged contour. The severed riser stub  10  and BOP  11  are shown adjacent to the target mounting flange assembly  1 , with hardware  12  coupling mounting flange components. 
         [0066]      FIG. 4  shows potential locations for pre-load ram reaction  13  and outer dam contact  14  on upper flange of target flange assembly  1 , relative to hardware  12  and riser stub  10 . Potential contact points for capture pins  5  (not shown) are common to  13 , except on lower flange surface. 
         [0067]      FIG. 5  shows basic structure of the preferred embodiment, with outer enclosure  2 , inner enclosure  3 , and annular cap plate  4  generally located concentric to one another. Side view cross-section (left), and bottom view cross-section (right). 
         [0068]      FIG. 6  shows basic structure of  FIG. 5  installed on target flange assembly  1 . When installed, two concentric chambers are formed within the confines of the present invention, with the outer enclosure  2 , inner enclosure  3 , and annular cap plate  4  working in conjunction with the flange assembly  1  and riser stub  10 , to create an inner (flow) chamber  15  and an outer (seal) chamber  16 . The flow chamber  15  provides a pathway for oil/gas to flow from the wellhead, through the repair collar, and subsequently to additional flow control and oil recovery components. The seal chamber  16  provides for in situ formation of an impermeable concrete seal. Operational plumbing components providing access for various materials into, and out of, chambers  15  and  16  include a liquid concrete inlet system  19 , a fluid removal vent  20 , and an optional methanol inlet  21  for mitigation of methane hydrate formation (during initial installation process, when applicable). 
         [0069]      FIG. 7  shows continuous oil flow through the target flange and riser assembly ( 1 ,  10 , and  11 ) during in situ formation of the preliminary concrete seal  8  from liquid concrete inserted through inlet  19 . A moderate vertical overlap between the inner enclosure  3  and riser stub  10  provides an upper limit for formation of this preliminary seal, as shown. The addition of a deformable lower edge (not shown) on inner enclosure  3  can maximize this overlap by allowing limited contact with target assembly hardware  12  or other target features, without jeopardizing capture pin  5  function. An annular outer dam  7  ( FIG. 10 ) prevents liquid concrete from escaping the enclosure through the gap between flange assembly  1  and outer enclosure  2  while the preliminary concrete seal sets. 
         [0070]      FIG. 8  shows preliminary concrete seal  8  set, vent  20  allows purging of outer seal chamber of fluids (water, oil and methanol), while secondary (final) concrete enters through inlet  19 . Upon concrete flowing from vent  20 , concrete flow is terminated, and secondary concrete is allowed to set, forming final seal and structural reinforcement of repair collar. 
         [0071]      FIG. 9  shows the addition of an extension skirt  23  to the lower perimeter of outer enclosure  2 . This skirt, fabricated through water-jet (or similar) cutting of plate material, or through a rolling process, provides additional depth for capture pin  5  lateral bore holes  22 . 
         [0072]      FIG. 10  shows additional components of the preferred embodiment. Radially-positioned internal gusset plates  27 , provide structural reinforcement (to  2 ,  3  and  4 , respectively), allow concrete flow and concrete reinforcement, and can provide touchdown stops for the repair collar during initial installation. Radially-positioned external gussets  26 , while not essential to each application, can provide additional support to the outer enclosure and top cap plate. Capture pins  5  lock repair collar to target assembly. A cable (not shown) passing through each of the capture pin handles  24  can provide a simple unified engagement feature in which an ROV can extend all capture pins simultaneously into position (in drawstring fashion) below the target flange assembly upon installation, while allowing unimpeded pin movement for final adjustments or retraction as necessary. Retaining guides  25  prohibit capture pin removal during deployment, and maintain proper pin orientation (with profiled pins,  FIG. 26 ) relative to flange surface during engagement. In the preferred embodiment, pre-load hydraulic rams  6  (a minimum of 3, when used), produce force against the upper target flange surface in order to remove slack from capture pins, the equivalent of providing torque-induced load to threaded fasteners. Pre-load force can also be produced by partially choking the flow of oil from the well riser via a downstream valve body, utilizing the subsequent pressure differential in conjunction with the relatively-large effective area within outer enclosure  2 , target flange assembly  1 , and cap plate  4  to supplement, or completely replace, the pre-load rams  6 . Pre-load rams can be mounted either within the seal chamber  16  as shown in this preferred embodiment, or external of the device enclosure. In the preferred embodiment, in addition to the previously described function, pre-load rams engage an outer dam component  7  which seals the gap between outer enclosure  2  and target flange assembly  1  via a deformable or elastomeric material, in order to prevent excessive concrete loss during sealing process. An industry-standard riser and mounting flange complete the preferred embodiment, allowing for pre-installation of subsequent equipment, including valves, quick-couple connectors, etc. 
         [0073]      FIG. 11  provides a top exterior view of the invention&#39;s preferred embodiment. Features visible include radially-positioned capture pins  5  and pin handles  24 , capture pin bore skirt  23 , outer enclosure  2 , and external gussets  26 . An industry-standard mounting flange and pipe assembly  9  for installation of subsequent components, together with hardware holes  9   a  and flow passage  9   b , are also visible. 
         [0074]      FIG. 12  through  FIG. 18  shows the sequence for installation of the preferred embodiment onto the target assembly. 
         [0075]      FIG. 12  shows present invention on final approach to the target assembly ( 1 ,  10 , and  11 ), with radially-positioned approach guides  32  assisting alignment process. Capture pins  5   a  are in retracted position, retained by retaining guides  25  via pin handle  24  tabs. Outer dam  7  is in receiving position (raised), as are pre-load rams (not shown). Internal gussets/touchdown pads  27  in this application will contact target assembly flange between flange hardware. Pre-installed valves (not shown) mounted to repair collar&#39;s discharge flange  9  remain open to provide free flow of oil from target assembly  1  through repair collar during installation process ( FIGS. 1 ,  7 , and  8 ) 
         [0076]      FIG. 13  shows preferred embodiment internal gussets  27  resting on target assembly flange  1  (shown without hardware for clarity). Outer dam  7  remains disengaged from target, while capture pins  5   a  remain retracted. 
         [0077]      FIG. 14  shows target and repair collar rotated to reveal one of multiple pre-load rams  6  (minimum of 3, when used), which remains in retracted position, along with outer dam  7 . Capture pins  5   b  are now extended below target flange. 
         [0078]    The process of extending capture pins can be performed through direct action on each pin, or through a unified process for simplicity and expediency, such as use of a common “drawstring” cable routed through the capture pin handles  24 , or other appropriate means. 
         [0079]      FIG. 15  shows a bottom view of the repair collar and target flange assembly  1 , as a cross-section of outer enclosure  2 , pin bore extension skirt  23 , and radially-positioned capture pin bore holes  22 . Capture pin  5  is shown removed from repair collar (shown for detail only, as pins are retained during deployment process), capture pins  5   b  are extended below target flange assembly  1 , and pin  5   a  remains retracted. In the preferred embodiment, capture pins engage target assembly in oriented to target assembly hardware  12  for optimum contact. 
         [0080]      FIG. 16  shows pre-load rams  6  extended to raise repair collar and subsequently engage capture pins  5   c  against target flange assembly  1  lower surface. Outer dam  7  is engaged against perimeter of target flange  1 , forming a general seal in preparation for primary concrete insertion. 
         [0081]      FIG. 17  shows capture pins  5   c  engaged on target flange assembly, pre-load rams extended to remove mechanical slack from capture pins, and primary concrete seal  8  setting. Concrete is inserted via inlet plumbing  19  ( FIG. 6 ). The concrete, being of greater density than seawater, oil, or methanol, settles to the surface of the target flange assembly  1 , also being contained by outer enclosure  2 , outer dam  7 , and target riser stub  10 . Depth of primary seal is limited by elevation of target riser stub  10 . Following insertion, primary concrete seal  8  is allowed to set, terminating cross-contamination of oil with other materials (seawater, methanol, etc.). 
         [0082]      FIG. 18  shows secondary (final) concrete insertion  8   a  atop previously-set primary concrete seal  8 . Vent  20  ( FIG. 6 ) allows water, oil, methanol and other material to be replaced by concrete within seal chamber  16  ( FIG. 6 ). Concrete flow from vent  20  verifies completion of concrete insertion. Upon setting, primary and secondary concrete ( 8  and  8   a ) form an impermeable seal to the environment. This concrete matrix is reinforced by target assembly hardware  12  and internal gussets  27  ( FIG. 3 ), with optional enhancement by rebar, etc. (not shown). Repair is now complete, with pre-blowout flow control and oil recovery capabilities available (within limits posed by upstream and downstream components). As the effective area subject to hydraulic pressure from the wellhead is limited by the internal dimensions of inner enclosure  3  ( FIG. 6 ), forces exerted on the repair collar via flow control, etc., are only slightly higher than those imposed on original well equipment, and remain well within limits of repair collar structure. 
         [0083]      FIG. 19  through  FIG. 24  show a repair sequence similar to that shown in  FIG. 12 through 18 , though with a secondary embodiment based on a single-flange target riser assembly  1   a.    
         [0084]      FIG. 19  shows repair collar approaching target assembly flange  1   a  with capture pins  5   a  retracted. Annular reaction plate/dam assembly  29  is retained within repair collar via hardware  36 , or similar. 
         [0085]      FIG. 20  shows repair collar landing on target assembly  1   a . Annular reaction plate/dam assembly  29  engages upper surface of target flange assembly  1   a , and moves upward within repair collar to provide vertical clearance for extending capture pins  5   a  below target flange. 
         [0086]      FIG. 21  shows pre-load rams  6  retracted, and capture pins  5   b  extended below target flange  1   a.    
         [0087]      FIG. 22  shows pre-load rams  6  extended, forcing reaction plate/dam  29  and target flange  1   a  to engage capture pins  5   c  and remove slack from these components. 
         [0088]      FIG. 23  shows primary concrete insertion (via plumbing  19 , shown in  FIG. 6 ), contained by annular reaction plate/dam  29  and adjacent edge seal  30 , outer enclosure  2 , inner enclosure  3 , and inner dam  31  (attached to reaction plate/dam  29 ). 
         [0089]      FIG. 24  shows secondary concrete insertion, following setting of primary concrete seal  8  ( FIG. 24 ). Repair is now complete, with flow control and oil recovery capabilities available (within limits posed by upstream and downstream components). 
         [0090]      FIG. 25  shows details of the preferred embodiment capture pin  5 . While a simple cylindrical pin is applicable for use with the repair collar (with low relative wellhead pressure, etc.), the increased contact surface area provided by a pin profile similar to that presented in  FIG. 25  (and  FIGS. 25A and 25B ) is preferable in many situations. Capture pin handle  24  provides features for interaction with a retaining guide  25  ( FIG. 10 ) for positive retention of the pins during deployment, and general pre-alignment of the pin profile with the target flange surface. 
         [0091]      FIG. 26  shows preferred embodiment of a system for establishing lateral positioning of repair collar when first installed on target assembly  1 , prior to pre-load and engagement of capture pins  5 . In this method, a pair of ramped spacers  17  are attached to the inner surface of the outer enclosure  2  during fabrication. These spacers are located approximately 120 degrees apart, and slightly below the touchdown point within the repair collar, as shown, providing increased lateral freedom of the repair collar until immediately prior to touchdown. As the capture and sealing features of the repair collar are enhanced with a relatively small lateral gap between the outer enclosure  2  and target assembly  1 , this additional freedom assists with installation. In the preferred embodiment, upon touchdown, a hydraulic ram  18  is activated, reacting via its plunger  18   a  (or other) to provide concentric alignment of the repair collar relative to the target assembly. This alignment assists with placement of dam  7 , and equalizes shear loads on capture pins  5 . A similar alignment process can be achieved without ram  18 , relying on ROV&#39;s for lateral force during capture pin pre-load. 
         [0092]      FIGS. 27   a ,  27   b , and  27   c  provide details of the outer dam  7  in the preferred embodiment. 
         [0093]      FIG. 27   a  shows a top view of the annular dam structure  7  which is dimensioned to travel in close proximity to the inner surface of outer enclosure  2 , near the target assembly  1  upper limit. While this dam can engage the target assembly independently (being either elastomeric or free-floating in nature), in the preferred embodiment, the dam  7  is actuated via the pre-load rams  6  in order to provide a positive seal. In this method, foot pads  28 , potentially contoured to provide optimized contact with the target assembly ( FIG. 4 ), are attached to the dam  7  in such a way as to allow the pre-load ram plungers  6   a  to transfer load to the target assembly and dam structure simultaneously. 
         [0094]      FIG. 27   b  shows detail of the dam  7 , foot pad  28  and pre-load ram plunger  6   b  interaction from the overview in  FIG. 27   a . Also shown is the outer enclosure  2  within which the dam structure  7  travels. 
         [0095]      FIG. 27   c  shows a detailed side view of the dam  7 , foot pad  28 , pre-load ram  6  and plunger  6   a , relative to one another and the inner surface of outer enclosure  2 . Also shown is a deformable seal  17   a  for limiting concrete loss during primary seal formation. This seal  17   a  can also be manufactured from elastomeric or deformable materials (metal, plastic, or rubber) in a range of shapes and styles to best suite environmental and function parameters. 
         [0096]      FIG. 28  shows the preferred embodiment of the repair collar anchored to target flange assembly  1 , with concrete seal formed, and repair complete. In addition, this drawing presents a typical configuration of downstream components pre-attached to the repair collar&#39;s optional industry-standard mounting flange  9  prior to deployment. Shown are a valve body  33 , and representative quick-release coupler  34 . Alternative options include hard-coupled risers, flow splitters (Y&#39;s, etc.) and multi-valve assemblies, among others, as required to restore flow control and oil recovery capabilities, as desired. As all embodiments of the present invention allow for use of industry-standard mounting systems (i.e. the mounting flanges shown), all of these options for restoring flow control and oil recovery capabilities pertain equally to all embodiments. 
         [0097]      FIG. 29  through  FIG. 32  provide an overview of an alternative embodiment of the present invention, in which a simple, straight riser pipe is the preferred target for capture and containment by the present invention. 
         [0098]      FIG. 29  shows an embodiment of the repair collar on final approach to a simple, severed riser pipe stub  10 . The repair collar generally consists of an outer enclosure  2 , an inner enclosure  3 , an annular top cap  4 , and a capture mechanism ( 18 ,  37 , and  38 ). In this embodiment, the repair collar is elongated to provide additional contact area between the target riser pipe exterior and the concrete seal, as the reinforced concrete matrix will provide an impermeable seal for the hydrocarbon product, as well as carry an increased proportion of the axial load following completion of the repair. To facilitate these two roles, the inner enclosure  3  is perforated  3   a  circumferentially throughout its length, with the exception being the upper portion, in which the target riser pipe discharge will reside. These perforations  3   a  provide a flow path for the in situ formation of the concrete seal throughout the repair collar interior, and along the exterior of the target riser pipe  10 . In addition, these perforations  3   a  provide elements for engagement with the concrete matrix, coupling the repair collar to the target riser pipe  10  in order to resist axial loads. To maximize this effect, inner enclosure  3  is ideally dimensioned to provide only limited clearance to the outside of the target riser pipe  10 , while allowing for deformation of the riser pipe due to shearing operations, etc. Multiple clamping jaws  37 , actuated by hydraulic rams  18  or other means, capture the target riser pipe upon full insertion into the repair collar. These clamps, or separate mechanisms, provide a limited seal along the perimeter of the target riser pipe  10  in order to prevent excessive loss of liquid concrete during in situ formation of the concrete seal. Various plumbing features are included in this embodiment, including liquid concrete inlet  19  and vent  20 . Optional plumbing could include methanol inlet  21  (for mitigation of methane hydrates, when applicable), inlet for surface preparation chemicals, and others. 
         [0099]    In an alternative embodiment, the elongated repair collar as described in the above paragraph, in lieu of the circumferential perforations along its length, may include a plurality or a set of welded rings as a traction device for the concrete (as that was largely the function of the perforations in the above configuration, not for flow-through of concrete). Accordingly, the reinforced concrete matrix will provide an impermeable seal for the hydrocarbon product, as well as carry an increased proportion of the axial load following completion of the repair. 
         [0100]      FIG. 30  shows the repair collar fully installed on the target riser pipe  10 , with the riser pipe discharge in proximity to the top annular cap  4 , and lateral position guides  17  holding the riser pipe approximately concentric to the repair collar. Clamps  37  remain disengaged from the riser pipe. 
         [0101]      FIG. 31   a  shows side (upper) and bottom (lower) cutaway views of the clamp/dam mechanism of the repair collar prior to engagement. Clamp elements  37  and lateral rams  18  remain retracted to provide clearance for installation of the riser pipe  10 . 
         [0102]      FIG. 31   b  shows side (upper) and bottom (lower) cutaway views of the clamp/dam mechanism of the repair collar following installation onto target riser pipe  10  and clamp engagement. Clamp elements  37  have been engaged against target riser pipe  10  by hydraulic rams  18  plungers  18   a . These clamping elements capture the riser pipe and prevent initial axial travel, as well as provide a barrier against excessive loss of liquid concrete during formation of the concrete seal. Retainer flanges  38  above and below clamps  37  limit their travel to lateral motion only, and complete the dam preventing loss of concrete. 
         [0103]      FIG. 32  shows the repair collar installed and clamps  37  engaged on riser pipe  10 . Concrete has been inserted through inlet  19 , filling the void between the exterior of target riser pipe  10  and interior of outer enclosure  2 , with a lower limit set by clamp/dam mechanism  37  and  38 , and an upper limit established by position of the riser pipe discharge. As with all embodiments of the present invention, oil flow through target riser remains unimpeded throughout the installation process and in situ formation of the concrete seal. Following concrete cure, the non-perforated upper portion of the inner enclosure  3  provides a positive seal for the hydrocarbon product, while the perforated lower portion  3   a  enhances axial load carrying capacity for the repair collar. In order to maximize this capacity, the axial dimension of the repair collar could be substantially greater than that shown, dictated by load requirements, and limited principally by the target riser pipe  10  dimensions and condition. 
         [0104]    Although the invention has been particularly shown and described with reference to certain embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention.