Abstract:
A device including a tank adapted to be arranged on a sea bottom having a filling opening is provided. The tank includes an inflatable bladder with an elongated shape, made from a flexible material, provided with the filling opening at one end and equipped with connecting members. At least one cable extends over at least the largest length of the bladder and is connected thereto by the connecting members. The present invention is applicable to the treatment of uncontrolled eruptions of offshore oil wells.

Description:
[0001]    Priority is hereby claimed to FR 10 59974 filed on Dec. 1, 2010, the entire disclosure of which is hereby incorporated by reference herein. 
         [0002]    The present invention relates to an underwater hydrocarbon storage device, of the type comprising a tank adapted to be arranged on a sea bottom and provided with a filling opening. 
         [0003]    The invention applies to hydrocarbon recovery on an uncontrolled oil and gas eruption site. 
       BACKGROUND 
       [0004]    A recent accident in the Gulf of Mexico revealed the difficulty of controlling and stopping an erupting underwater oil well, when a confinement system cannot maintain the pressure from the well. Furthermore, in such a situation, capturing and bringing up the fluid is pointless without adequate support on the surface, while the surface means necessary to treat an oil effluent are difficult to mobilize quickly on-site. 
         [0005]    U.S. Pat. No. 7,448,404 describes a storage device. However, it involves a heavy rigid structure, difficult to deploy quickly and requiring dedicated vessels, which are generally not available on the site of an offshore oil accident. 
       SUMMARY OF THE INVENTION 
       [0006]    An object of the present invention provides an underwater hydrocarbon storage device that is inexpensive and can be deployed easily and quickly on a vessel of opportunity, of the towboat type, generally able to be mobilized in one or two days. 
         [0007]    The present invention therefore provides capture and storage on the sea bottom, at a significant depth, of erupting fluid for a period of several days to several weeks, or more, while waiting to be able to process it on the surface. 
         [0008]    The present invention provides an underwater hydrocarbon storage device, of the type comprising a tank adapted to be arranged on a sea bottom and provided with a filling opening, characterized in that the tank comprises an inflatable bladder with a very elongate shape provided with the filling opening at one end and equipped with connecting members to at least one cable and at least one cable extending over at least the largest length of the bladder and connected thereto using said connecting members. 
         [0009]    According to other features of this device, the device may include one or more of the following features: 
         [0010]    the bladder comprises a plurality of compartments secured to each other and communicating with each other by passages; 
         [0011]    the bladder comprises at least two longitudinal portions extending on either side of a cable and folded one on the other in the standby position of the bladder; 
         [0012]    the bladder comprises a central portion bordered by two cables and framed by two side portions folded on the central portion in the standby position of the bladder; 
         [0013]    the device comprises frangible connections for keeping the bladder in the folded position; 
         [0014]    the device comprises a drum on which each folded bladder is wound in the standby position; 
         [0015]    the bladder is equipped, on its upper surface, with at least one connector, and the device also comprises a compensating balloon adapted to be connected to said connector; 
         [0016]    the filling opening of the bladder is equipped with a funnel open downwardly; 
         [0017]    the or each cable is provided at each end with a connector for connecting to another cable; 
         [0018]    the device comprises a series of connections adapted to connect the or each cable to moorings; and 
         [0019]    the device comprises chains adapted to be connected to the or each cable. 
         [0020]    The invention also provides an installation for capturing and storing hydrocarbons escaping from an underwater well, characterized in that it comprises a plurality of storage devices as defined above, the tanks of which are arranged around the well; and a device for capturing and distributing hydrocarbons escaping the well. The device includes a bell, means for positioning the bell above the well and transfer means for selectively connecting the apex of the bell to the filling opening of any one of the tanks in a fluid manner so as to transfer the fluid into that opening. 
         [0021]    In one embodiment, the transfer means comprise a pipe provided at its free end with an upper orifice adapted to be arranged under the funnel of each bladder. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    One embodiment of the invention will now be described in light of the appended drawings, in which: 
           [0023]      FIG. 1  is a planar view of a storage device according to the invention; 
           [0024]      FIGS. 2 to 5  are cross-sectional views along lines II-II to V-V, respectively, of  FIG. 1 ; 
           [0025]      FIG. 6  diagrammatically illustrates, in side view, a drum on which a bladder is wound as shown in  FIGS. 1 to 5 ; 
           [0026]      FIG. 7  is a cross-sectional view along line VII-VII of  FIG. 6 ; 
           [0027]      FIG. 8  is a partial top view of the subject matter of  FIG. 7 ; 
           [0028]      FIG. 9  diagrammatically illustrates the placement of the bladder on a sea bottom; 
           [0029]      FIG. 10  shows a similar illustration of consecutive bladders on the sea bottom; 
           [0030]      FIGS. 11 to 13  diagrammatically illustrate the maintenance in position of a bladder on the sea bottom; 
           [0031]      FIG. 14  diagrammatically illustrates, in planar view, the arrangement of multiple similar bladders around an underwater wellhead experiencing an uncontrolled eruption; 
           [0032]      FIG. 15  shows a bell for capturing and distributing hydrocarbons escaping the well; 
           [0033]      FIG. 16  is a planar view of the object of  FIG. 15 ; 
           [0034]      FIG. 17  diagrammatically illustrates the recovery of a filled bladder; and 
           [0035]      FIG. 18  is a corresponding detail view. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    The storage device shown in  FIGS. 1 to 5  essentially comprises an inflatable bladder  1  made up of a suitable material, in particular an elastomer or a polyurethane, possibly reinforced with a geotextile layer. Said bladder comprises, with its accessories that will be described below, a tank R. 
         [0037]    The bladder  1  has a very large length and is made up of three juxtaposed strings  2  of compartments  3 . All of the compartments  3  communicate with each other, so that the bladder can be completely inflated from a filling opening  4  provided at one of its ends, visible in  FIG. 16 . The opening  4  is equipped with a funnel  104  open downwardly. 
         [0038]    Each compartment  3  is connected by welding and/or sewing to the adjacent compartments by flat strips  5 , at certain points of which communication passages or tunnels  6  with large diameters are provided. 
         [0039]    As is well known, offshore eruptions are generally made up of a mixture of oil, gas and water at a high pressure (around 100 to 300 bars) and high temperature (around 50 to 80° C.). Upon cooling in contact with the sea water and due to the relaxation, the viscosity of the oil increases and it can even congeal; the gas, in the presence of water, can form hydrate crystals (similar to ice crystals) that tend to plug the channels or channel constrictions. As a result, the diameter of the passages  6  is chosen to be large enough to prevent any risk of plugging by the hydrates. 
         [0040]    As an example of dimensions: 
         [0041]    the central string  2 A is slightly wider than the side strings  2 B: around 10 m versus around 8 m; 
         [0042]    all of the compartments  3  have the same length, comprised between 8 and 10 m; 
         [0043]    the bladder comprises thirty regions of three compartments, that is a total length of about 250 to 300 m; 
         [0044]    once inflated ( FIGS. 2 to 5 ), the thickness of the bladder is comprised between 3 and 5 m; 
         [0045]    the passages  6  have a diameter of about 1 m or more. 
         [0046]    Thus, the storage capacity of a bladder  1  is in the vicinity of 100,000 barrels (15,900 m 3 ). 
         [0047]    The bladder is completed by valve bridges  7  arranged under the two longitudinal strips  5  at a rate of two valve bridges per compartment  3 . The valve bridges  7  are formed by strips made of the same flexible material as the bladder and welded/sewed thereto by their ends. A cable  8  is slipped into each series of valve bridges and protrudes at each end of the bladder, where it is provided with a connecting tip  108  ( FIGS. 9 and 10 ). 
         [0048]    The bladder is also completed by a small number of connectors  9  arranged on the upper surface of compartments  3  neighboring the ends of the bladder. 
         [0049]    The total mass of such a bladder and its two cables is in the vicinity of 135 tons. 
         [0050]    To store the bladder and place it on standby, the two side strings  2 B thereof are folded on the middle string  2 A ( FIGS. 7 and 8 ), and are maintained by frangible connections  11  ( FIG. 8 ). Thus, the two cables  8  are visible on each side. The assembly is then wound on a drum  12  ( FIG. 6 ). 
         [0051]      FIGS. 9 to 11  illustrate the placement of the bladder  1  on a sea bottom  13  at a great depth (typically 1,000 m or more). 
         [0052]    The drum  12  supporting the bladder  1  is placed onboard a towboat  14  or another easily available vessel. The onboard mass is in the vicinity of 170 tons, which makes it possible to load it with handling means commonly available in an oil port. 
         [0053]    A mooring  15  is arranged at a suitable location on the bottom  13 , said mooring being connected to one end of two parallel initiation cables  16  each provided with connecting tip  116 . 
         [0054]    The bladder  1  is lowered, under the effect of its own weight, to the mooring  15 , and each of its cables  8  is connected to the free end of the corresponding cable  16  by a ROV (Remote Operated Vehicle) using the tips  108  and  116 . 
         [0055]    Then ( FIGS. 11 and 12 ), side moorings  17  are arranged on either side of the bladder and are connected to the two cables  8  by lightened towing chains  18 , at chosen spaces along the bladder. 
         [0056]    To dam an uncontrolled eruption of an offshore wellhead  19  ( FIG. 14 ), a plurality of bladders  1  are arranged radiating or “in petals” around the wellhead, with their filling ends situated on a circle  20  centered on the wellhead. The radius of the circle  20  is typically several tens of meters, for example 60 m. Of course, beforehand, the same number of turntables  12  as petals are placed onboard on the vessel  14 . 
         [0057]    To that end, when a bladder  1  has been completely unwound from the drum  12  temporarily motorized to power on and ensure the reversibility of the lowering operation; the following bladder is attached thereto using the tips  108  of four cables ( FIG. 10 ). When the first bladder has been completely placed on the bottom  13 , the following bladder is unhooked, and its lower end is moved to the mooring  15  associated with it. 
         [0058]    Then ( FIGS. 15 and 16 ), a hydrocarbon capture and distribution device  21  is lowered to the wellhead  19 . This device  21  comprises a bell  22  from the apex of which a rigid gooseneck  23  starts. The latter is pivotably mounted on the bell  22  using a swivel joint  24 , and its free end portion  25  is horizontal and provided on its upper generatrix with an outlet orifice  26 . Said orifice is situated at a distance from the wellhead  19  equal to the radius of the circle  20 . 
         [0059]    The bell  22  is kept in position using a positioner which may include several moorings  27  arranged in a circle around the wellhead and each connected to the periphery of the bell by a towing chain  28 . The bell can float or be weighed down, and in that case placed on a stabilizing structure (legs+cushion). 
         [0060]    In use, the orifice  26  is arranged under the funnel  104  of a first bladder  1  by a ROV. The oil-gas-water mixture leaving the wellhead at high pressure and high temperature is confined by the bell  22  and oriented into the gooseneck  23 . It emerges therefrom via the orifice  26  and thereby penetrates the bladder. The latter starts to inflate and deploy flat owing to the rupture of the connections. This inflation spreads from compartment  3  to compartment  3  as long as the captured mixture is not congealed. 
         [0061]    When the bladder is completely filled or stops filling, the ROV makes the gooseneck  23  pivot until the orifice  26  is located below the funnel  104  of the following bladder. 
         [0062]    For a leak of 100,000 barrels per day, one sees that each bladder can collect substantially one day of leakage, because when such a substantial flow rate, the cooling of the mixture is relatively slow. As a result, with fourteen bladders, it is possible to collect two weeks of fluid, which leaves the same amount of time to cover the well. 
         [0063]    If the flow rate is lower, each petal fills more slowly, and possibly incompletely due to the faster cooling of the fluid. 
         [0064]      FIGS. 17 and 18  illustrate the recovery of the bladders after they are filled. This recovery can occur several days, or even several weeks later, when a hydrocarbon treatment vessel  29  can be brought to a bottom  30  that is shallower (for example 100 m) in a neighboring region of the well  19 . 
         [0065]    To that end, each petal containing cold oil can be towed at a shallow depth in the “off-bottom tow” configuration. One of the difficulties in the recovery lies in the fact when that the oil is brought to a shallow depth, the gas relaxes, and part of the gas dissolved in the liquids leaves the liquid phase and takes up a more significant space. Thus, the passage from 1,000 m deep to 500 m deep results in a doubling of the gas volume. From 1,000 m to 100 m deep, the volume of gas is multiplied by 10, but from 1,000 m to the surface, it is multiplied by 100. 
         [0066]    That is why it is preferable to tow the bladders above the bottom  30  without returning them to the surface. 
         [0067]    To that end, a compensating balloon  31 , forming an attached bladder, is fastened on a connector  9  of the bladder situated close to the top point thereof. Chains  32  are fixed to the cables  8  in place of at least one portion of the moorings  15  and  17 , the assembly having an equivalent weight. The recovered mixture being lighter than water, the bladder stays at a small distance above the bottom  13 , as shown in  FIG. 18 . 
         [0068]    A towing chain  33  is then hooked to the bladder  1 , which is pulled by the vessel  14  while rising to the bottom  30 . During that movement, the spacing of the bladder above the bottom prevents any deterioration, and the gas that is freed and relaxes gradually fills the balloon  31 , facilitating the rise of the bladder. 
         [0069]    When the bottom  30  is reached, the bladder is stabilized using moorings  34 , and the vessel  29 , provided with oil treatment equipment  35  and a riser for the oil product  36 , is anchored nearby. The riser  36  is connected on a clip  37  situated at one end or in several locations of the petal to allow the light oil to rise naturally. A pumping system can also be lowered into the riser to activate the fluid. 
         [0070]    As will be understood, if the hydrocarbon leak is not controlled when all of the bladders are filled, it is possible to continue the recovery operation by moving the bladders away from each other in the manner indicated above and depositing new, empty bladders on the bottom  13 .