Note: Descriptions are shown in the official language in which they were submitted.
CA 02567413 2006-11-09
TITLE
METHOD AND APPARATUS FOR EXTRACTING GAS HYDRATE DEPOSITS
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.
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SUNIlMARY 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
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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:
Figure 1 is a diagrammatic layout illustrating
the overall technique for extraction of the natural gases
from the natural gas hydrate formation; and '
Figure 2 is a diagrammatic plan view of a
plurality of injector and heating wells drilled about the
boundaries of a natural gas hydrate formation.
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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
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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 United States Patent 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
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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.
1
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
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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
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injection and heating well 112.
OPERATION
Using the downhole tooling previous,ly 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
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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
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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.
