Patent Publication Number: US-2007114026-A1

Title: Method and apparatus for extracting gas hydrate deposits

Description:
BACKGROUND OF THE INVENTION  
      Natural gas hydrate deposits are known to exist in numerous regions in great quantities in the world and contain many times the known producible reserves of conventional natural gas. Natural gas hydrates are crystals of principally methane within a lattice of water molecules and are formed naturally under conditions of low temperature and high pressure. The deposits can generally can be reached using conventional well drilling and well completion technology. However, heating and disassociating such deposits to release the trapped natural gas is a problem.  
     SUMMARY OF THE INVENTION  
      According to one aspect of the invention, there is provided a method of extracting natural gas from a deposit of natural gas hydrates, said method comprising supplying water to said deposit of said natural gas hydrates, heating said water supplied to said deposit of natural gas hydrates and flooding said deposit of said natural gas hydrates to disassociate said natural gas hydrates in order to recover said natural gas and the water from said disassociation of said natural gas hydrates, said natural gas and said water migrating from said deposit of natural gas hydrates to an area of lower pressure being production casing.  
      According to a further aspect of the invention, there is provided apparatus for heating a deposit of gas hydrates to disassociate said gas hydrates and obtain natural gas comprising a reactor module located within casing of a heating well, a water injector to supply water to said reactor module and a heater within said reactor module to heat said water supplied to said reactor module and to inject said heated water into said deposit of gas hydrates.  
      According to yet a further aspect of the invention, there is provided a method of heating a deposit of natural gas hydrates comprising positioning an induction tool in downhole well casing and generating an induction flux in said tool to excite and heat said well casing and said deposit of natural gas hydrates. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      Specific embodiments of the invention will now be described, by way of example only, with the use of drawings in which:  
       FIG. 1  is a diagrammatic layout illustrating the overall technique for extraction of the natural gases from the natural gas hydrate formation; and  
       FIG. 2  is a diagrammatic plan view of a plurality of injector and heating wells drilled about the boundaries of a natural gas hydrate formation.  
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENT  
      Referring now to the drawings, a natural gas hydrate formation is generally illustrated at  100 . The formation may be located at relatively shallow or relatively deep depth and conventional well drilling and well completion is sufficient to reach the formation  100 .  
      A production well  101  is drilled and put into operation using conventional technology. A horizontal portion  102  extends into the gas hydrate formation  100  and a perforated production liner  103  is installed at the retrieval area of the natural gas hydrate formation  100 . A pump  122  is located downhole in the production well  101  for the purpose of pumping the water produced from the disassociation of gas hydrates to the surface  111 . Natural gas from the dissociated hydrate flows to the surface within the production casing where a compressor (not illustrated) is located to compress and transport the recovered gas.  
      A second drill hole, namely an injection and heating well is generally illustrated at  104 . It extends from the surface  111  substantially vertically in a vertical portion  112  and terminates at the end of a horizontal portion  113 . A water injection unit  120  and a water tank  121  are located on the surface  111  and act to provide water and a polar solvent such as methanol or ethylene glycol solvent for injection into the injection and heating well  104 . The use of solvent prevents the re-association of the water and the natural gas into hydrates causing blockage of production.  
      A reactive module according to the invention is generally illustrated at  114 . It is located within the horizontal portion  113  of the heating and injection well  104 . The reactive module  114  takes the form generally illustrated in U.S. Pat. No. 6,384,389, the contents of which are incorporated by reference. The reactive module  114  has a hollow bore and in a first embodiment, it is inductively powered; that is, it projects electromagnetic flux outwardly to optimally heat the steel well casing  123  of the injection and heating well  104 . A hydraulic pump  124  is provided within the reactor module  114  which hydraulic pump  124  utilizes a motor driven piston contained within a cylinder. The hydraulic pump  124  provides pressure to a bladder  130  which seals the reactor module  114  within the well casing  123  as will be described. Telemetry and control electronics are provided within the reactor module  114  to monitor various sensors and transducers embedded within the reactor module  114  which sensors and transducers are used to measure process variables such as downhole temperatures and pressures, as well as to control actuation of the reactor module  114 , the hydraulic pump  124 , the bladder or seal  130 , the fluid removal pump  122  and the methanol injection process taking place in the water injection unit  120 . A DC to AC inverter is provided to supply power to the reactor module  114 .  
      The downhole tooling used to install and operate the reactor module  114  includes centralizers (not illustrated) to maintain the reactor module  114  centrally located within the injection and heating well  113  as is known and the reactor module  114  is supported by tubing (not illustrated) supplied from the topside tube spool as is also known. The tubing incorporates a high pressure tube for the supply of solvent, a fluid extraction tube for extraction of fluids, a power cable and a data telemetry cable all as is known. The topside tubing spool will further include the necessary electrical and fluid slip rings to interface the downhole tool with the topside subsystems used to process the downhole data.  
      A power control unit(PCU) (not illustrated) controls three phase power to high voltage DC power to be supplied to operate the reactor module  114 . The PCU provides an operator interface and the control logic.  
      The gas extraction system used by the production well  101  enhances the separation of the natural gas from the water flowing from the production well  101 . The gas extracted from the gas hydrate formation to the surface  111  is then compressed for storage and/or transport.  
      A fluid separator subsystem (not illustrated) separates water and solvent fluid pumped out of the production well  101 . The water is collected for recycling to the solvent mixing systems, with excess water going to disposal. Recovered solvent plus the addition of any required make-up is mixed with water to an optimal concentration and re-injected into the injection and heating well  112 .  
     OPERATION  
      Using the downhole tooling previously described, the reactor module  114  is deployed to its initial operating position within the horizontal portion  113  of the injection and heating well  104 . The operation of the hydraulic pump  124  is initiated and the bladder or seal  130  is inflated in order to provide a pressure seal between the reactor module  114  and the casing  123 . The reactor module  114  is powered on to heat the well casing  123  and the injected solvent/water mixture causing the hydrate within the gas hydrate formation to disassociate into a two phase gas and fluid mixture. Hot water permeates the formation causing the hydrates and water to migrate to the lower pressure perforated production liner  103 . Water within the casing is pumped to the surface  113  by pump  122 . Solvent is injected into the water being supplied to the injection and heating well  104  from injection unit  120 . The injected solvent/water mixture may be partially or completely vaporized by the heat generated by the reactor modules thus forming a high pressure vapor “cloud” which emanates from the injection liner  131 . The vapor “cloud” expands the heating zone further into the gas hydrate formation  100  which contributes further to the disassociation of the gas hydrates resulting in increasing amounts of natural gas being passed to the low pressure zone of the perforated production liner  103  and into the production well  101  where it passes to the surface  113 .  
      The reactor module  114  is moved along the horizontal portion  102  of the heating and injection well  104 . Prior to movement, the bladder or seal  130  is deflated to allow for movement of the reactor module  114  and when the new operating position of the reactor module  114  is reached, the bladder or seal  130  is inflated to provide a new seal between the reactor module  114  and the casing  123 . As the movement of the reactor module  114  takes place, the heated zone within the gas hydrates formation is increased and expanded to disassociate the gas hydrates and thereby to contribute to more complete natural gas flow to the production well  101 .  
      While the reactor module  114  has been illustrated and described in a horizontal portion of the injection and heating well  104 , it is apparent that the benefits of the invention would also apply equally to the reactor module  114  being deployed in a vertical well or a slant well. Thus, the reactor module  114  may be deployed and operated in an injection and heating well of virtually any configuration.  
      Many further modifications in the invention will readily occur to those skilled in the art to which the invention relates and the specific embodiments described herein should be taken as illustrative of the invention only and not as limiting its scope as defined in accordance with the accompanying claims.