Note: Descriptions are shown in the official language in which they were submitted.
CA 02560354 2006-09-20
S'YS~ T1~OD. AND APPARA.'~IJS FOR AEGASSING TOOK FOR COAT BED
1VI~TSA1~TE GAS WELLS
BACKGROYJND OF TIE IIWENTION
1. Technical Field
[0001] The present inventioxl relates in general to sensitive fornaatioz~s
containing low pressure
gas, such as coal bed methane, and, in particular, to an improved system,
method, and apparatus
far a coal bed methane gas degassing tool.
2. pescription of the Xtelated Art
[OOOZj Subtexxanean deposits of coal contain substantial quantities of
entraitxed methane gas.
Limited production and use of methane gas from coal deposits has occurred for
many years.
Coal seams may extend over large areas of up to sevexal thousand acres, and
are fairly shallow in
depth, varying from a few inches to sevezal meters, singly or collectively in
layers.
[0003) After the well is drilled, surface casing is typically installed to a
nominal depth.
Production casing is then run i~aside the surface casing to the desired depth
of the well. The
lowermost joint o~ the production easing is sealed with a bridge plug as a
secondary seal against
gas leaks. The primary means o~ handling the gas during installation of the
production casing is
an inductor and flare, Which receives the gas via the annulus between the
surface and production
casiztgs. Aver the production casing is installed, the bridge plug 'vs drilled
out to initiate
production through the pxoductioo. casing, Although this design is workable,
an improved design
for sealing prod>xction casing during installation would be desirable.
,attorney oocxet No. v2oo5o28 (133s~sroa58B5)
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SU.~~12ARY OF TIE INVENTrON
[0004] One embodiment of a system, mefhod, and apparatus for a coal bed
methane degassing
tool is installed at the bottom of a first joint of production casing, As the
casing is lowered into
the well hole, the tool is fished to the top of the casing as more joints are
added. The pressure at
the tool may be recorded and logged. Any excessive pressure observed at the
tool may be bled
off by the tool, As more easiurg is tripped in, the tool is brought to the
top. Thus, at the end of
the run, a log of formation pressure is established. Reservoir engineers can
determine reserves in
coal bed methane wells drilled and completed with a reverse circulation center
discharge
(RCCD) process. The well is subsequently bled off and the tool is removed,
[000f~ Th.e foregoing and other objects and advantages of the present
invention will be apparent
to those skilled in the az~t, in view of the following detailed description of
the present invention,
taken in conjunction with the appended claims and the accompanying drawings.
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BRIEF DESCRIPTION OF TT» DRA~V'INGS
[0006] So that the manner in which the features and advantages of the
invention, as well as
others which ~c~rih become apparent are attained and can be understood in more
detail, more
particular description of the invention briefly summarized above nnay be had
by reference to the
embodiment thereof which is illustrated in the appended drawings, which
drawings form a part
of this specification. It is to be noted, however, that the drawings
illustrate only an embodiment
of the invention and therefore are not to be considered limiting of its scope
as the invention may
admit to other equally effective embodiments.
[0007] Figure 1 is a sectional side view of one embodiment of a downhole tool
constructed in
accordance with the present invention;
[0008] Fiiguxe 2 is a schematic view of a well utilizing the downhole tool of
Figure 1; and
[0009] Figure 3 is an enlarged schematic view of an upper portion of the well
of Figure 2
shown utilizing the downhole tool of Figure 1,
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DETAILED DESCRIPTION OF THE )1N'VENTXON
[0010] Referring to Figure 1, one embodiment of a downhole or degassing tool
11 is shown..
The downhole tool 11 comprises a body 13 having an axis 15, a plug shaft 17
including, in one
embodiment, a threaded end 19, A fishing shaft 21 is located opposite the
threaded end 19, arid a
bore 23 extends along at least a portion of the axis 15 from the threaded end
19. In the
embodiment shown, the plug shaft 17 has a diameter that is less than a
diameter of the fishing
shaft 21.
[0011] A plug 25, such as a cementing plug or slips, is mounted to the plug
shaft 17. The plug
25 is a device that fxictionally maintains a position of the entire assembly
within the production
casing. Other mechanical means for securing or locking the tool to the casing
also may be used.
The plug 25 has an outer diameter 27 for engaging and sealing against the
inner wall of
production casing, as will be described below. A nut 29 is fastened to the
threaded end 19 of the
plug shaft 17 for securing the plug 25 to the body 13. A shoulder 35 is formed
at an interface
between the plug and fishing shafts ~ 17, 2I, and the plug 25 is axially
restrained between the
shoulder 35 and the nut 29.
[001Z] In one embodiment, the do~vnhole tool 11 also comprises a pressure gage
31 in fluid
communication with the bore 23 and extending from the fishing shaft 21, The
pressure gage 31
measures pressure in tl~e well downwell from the downhole tool 11. The
downhole tool 11 also
may comprise a safety relief valve 33 that is also in fluid comna~unieation
with the bore 23 and
extending from the fishing shaft 21. The safety relief valve 33 relieves
excessive pressure in the
well downwell from the downhole tool 11.
[0013] Referring now to Figure 2, one embodiment of a well system 41 for
accessing a
subterranean zone from the surface of the well. Iz~ the embodiment described
below, the
subterranean zone is a coal seam. It will be understood that other
subterranean formations and/or
low pressure, ultra-low pressure, and low porosity subterra~neau zones can be
similarly accessed
using the well system of the present invention to remove and/or produce water,
hydrocarbons
Attorney Docket No. V2005026 (1336.18-045865) -4~
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and other fluids in the zone, to treat minerals in the zone prior to mining
operations, or to inject
or introduce fluids, gases, or other substattces into the zone.
[0014] 'the well system 41 includes an entry well bore 43, well 45, one or
more articulated ~ovell
bores 47, a cavity 49, and a rat hole 51. Entry well bore 43 extends from the
surface 53 towards
the subterranean zone 55, Well 45 extends from the terminus of entry well bore
43 to the
subterranean zone 55, although well 45 zx~ay alternatively extend from any
other suitable portion
of entry well bore 43. Where there are multiple subterranean zones 55 at
varying depths, as in
the illustrated example, well 45 extends through the subterranean zones 55
closest to the surface
ixlto and through the deepest subterranean zone 55. At'ticulated well bores 47
may extend from
well 45 into each subterranean zone 55. Cavity 49 and rat hole 51 are located
at the terminus of
well 45.
[007.5] Entry well bore 43 is illustrated as being substantially vertical.
However, it should be
understood that entry well bore 43 may be formed at any suitable angle
relative to the surface 53
to accommodate, for example, surface 53 geometries and attitudes and/or the
geometric
configuration or attitude of a subterranean resource. 'Well 45 may be formed
to angle away from
entry well bore 43. It will be understood that well 45 may be formed at other
angles to
accommodate surface topologies and other factors similar to those affecting
entry well bore 43.
In addition, more than one well 45 may be formed at different angular
separations from entry
well bore 43.
[00J.6] As shown in Fig~,trc 3, the present invention also comprises a method
of installing a well,
such as a coal bed xn.ethane gas well. The method comprises drilling a well
bore; installing
surface casing 61 in the well bore to a nominal depth; positioning a downhole
tool 11 in an initial
joint 63 of production casing such that the downhole tool 11 seals against an
inner surface of the
initial joint 63 of production casing, 'Xbe downhole tool 1 l may be
positioned at a lower end of
the initial joint 63 of production casing. During installation of the
production casing, gas
pressure in the 'well may be handled via an inductor 64 or the like and
flared.
Attorney Docket No. V2005026 (133BJ&045865) -5-
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(0417] The method also comprises installing the initial joint of production
casing in the surface
casing 6T; fishing the downhole tool with a fishing tool 65 to an upper end of
the initial joint 63
of production casing adjacent a surface of the well; reading the downhole tool
11 (e.g., pressuxe
gage 31) at the surface of the well for a gas Formation pressure of the well
beneath the dovvnhole
tool 11; installing additional joints 67 of pxoduction easing in the surFace
casing to a desired
depth of the well; reading the downhole tool 11 for the gas formation pxessure
of the well during
the previous step; and bleeding off any excessive formation pressure (e.g., in
excess of 50 psi)
through the downhole tool 11 (e.g., safety relief valve 33) during preceding
steps.
[U018] While the invention has been shown or described in only some of its
forms, it should be
apparent to those skilled in the art that it is not so limited, but is
susceptible to various changes
without departing From the scope of the invention. For example, the gas
fortxiation pressure at
the downhole tool may be read remotely (e.g., by wire, transmitted sigxlal,
etc.) to eliminate the
need to manually xead the pressure gage at the surface of the well.
Attorney Docket No. V2005026 (1336JB-045865) -6-
