Note: Descriptions are shown in the official language in which they were submitted.
CA 02254244 1998-11-20
METHOD A ~~ W FOR ENHANCED RECOVERY OF VISCOUS OIL
DEPOSITS
(Dm82,193)
Field of The Invention
This invention relates to oil field production apparatus and techniques, and
more
particularly, to such apparatus and techniques for use in the production Gf
extremely
viscous crude oil.
Background of Invention
It has been known to produce viscous crude oils in reservoirs by drilling
vertical
wells into the producing zone and then injectir g steam into the viscous c.
ude to increase
its mobility and reduce its viscosity. This steam injection has been done in
several
different ways. In one technique producing wells in the reservoir can be
cyclically steamed
by injecting steam down a vertical well into the production zone for a
relatively sort period
Gf tlme. I he '.'VCIi Is ti ie~ GIcCc:. Crl rrGdUCtiGn fCr c r c~a':i'vely
)CnCer pCriGd Cf t(t~ic c1d thlS
cycle repeated until the production becomes unprofitable.
Another technique which has been used to produce viscous crude reservoirs is
to
drill vertical wells in a geometrical pattern into the production zone and to
designate
~0 certain of these wells as injection wells. Steam is then continuously
injected into the
production zone via the injection wells in an attempt to drive the steam and
its heat to
move the viscous crude oil to the other vertical producing wells in the
geometrical array.
In the initial development of 2 reser voir gf viscous crude these descr ibed
methods
CA 02254244 1998-11-20 _
have worked well. Cver time however, the steam tends to cor'~~rea~te in the
upper portion
ef the producing zone. This, of course, does not cause heating of the viscous
cr ude in the
lower portion of the producing zone. The heavy crude saturated lower portion
or the
producing zone is not depleted as the high viscosity of the crude prevents its
easy
migration to the well bores of the producing wells. Thus large quantities of
potentially
producible crude oil can become otherwise not recoverable.
Brief Description of The Invention
In order to more efficiently heat and render mobile heavy viscous crude oils
throughout a thick production zone a horizontally oriented well is drilled
into the production
zone. Special apparatus according to the concepts of the invention is then
used to deliver
steam uniformly horizontally distributed to the production zone along the
entire length of
the horizontal portion of the well in the producing zone. This type of
delivery can prevent
steam migration into the underlying water zone or into the upper desaturated
portion of the
reservoir. Also by delivering t'~e steam uniformly along the entire horizontal
portion ef the
prceucing zone penetrated by the horizontal portion of the well, any potential
damage to
1 ~ a production liner in this horizontal bore is reduced. The special
apparatus comprises a
horizontal steam stinger made up of perforated production tubing which is
inserted into the
horizontal production zone liner. The perforations in the stinger_are sized
and spaced to
deliver a particular amount of steam equally along its length at a
predetermined pressure.
The stinger is provided with a sacrificial impingement strap at each
perforation to present
~0 direct impingement of live steam delivered by the stinger onto the
production liner. These
straps also assist in distributing the steam around the circumference of the
wellbore prior
CA 02254244 1998-11-20
to its entry through the liner into the production zone.
The apparatus and techniques of the invention are best understood by reference
to the following detailed description thereof, when taken in conjunction with
the
accompanying drawings, in which:
Brief Description of The Drawinos
Figure 1 is a schematic diagram of prior art technique showing in cross
section a
heavy cr ude production zone penetrated by a vertical well using steam to t-
~e~t the crude
oil;
Figure 2 is a schematic diagram showing in cross section a vertical well
penetrating
a heavy crude production zone which is also penetrated by a second, horizontal
well;
Figure 3 is a schematic drawing spewing in cross section a prior art steam
delivery
in a horizontal well in a heavy crude producing zone;
Figure 4 is a schematic drawing showing the steam stinger apparatus of the
present
invention in more detail; and;
Figure 5 is a schematic drawing acccrdine to concepts cf the present invention
showing a horizontal well using the steam stinger to uniformly deliver steam
along a .
horizontally drilled well in a heavy crude producing formation.
Detailed Description of The Invention
Referring initially to Fig. 1 a prior art heavy crude oil production zone
penetrated
by a vertical well is shown schematically. A well borehole 11 (vertical)
penetrates
producing oil sands 12 which are saturated with high viscosity heavy crude
oil. The
completion technique uses a slotted liner 17 below cemented casing 19 which
extends to
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CA 02254244 1998-11-20
the surface. A lead seal 18 isolates the producing sand 12 from ver<ical
communication.
A gravel pack 14 outside slotted liner 17 keeps loosely compacted formation
sand 12 from
gathering around the liner 17 slots and clogging the line slots. Steam is
injected into the
wellbore 11 frcm a tubing string 15 which goes to the surface. Arr ows 16A
indicate the
direction of flow or' steam as it exits the lower end 16 or' tubing string 15.
As discussed
previously) the application of steam via end 10 of tubing 15 is maintained for
a relatively
short period of time. This lowers the viscosity of the heavy crude and its
incr eaSad
mobility allows it to enter the wellbore 11 via the gravel pack 14 and slotted
liner 17. The
well is then placed on production until the flow or heavy crude falls too low.
Then the cycle
is repeated by beginning another application of steam.
Cyclical heating such as described can cause the creation of a desaturated
steam
zone 13 which becomes largely depleted of movable hydrocarbon. This however,
leaves
the remainder of the oil sand 12 partially produced and still saturated with
heavy viscous
crude oil.
Referring now to Fig. 2, a wellbcre 21 similar to that e. Fig. 1 is shown and
using
the same completion technique with slotted liner 27, gravel pack 24 and tubing
siring 25.
Steam flows as indicated.by arrows 26A when applied from the end 26 of tubing
string 25,
and gradually creates a depletion of hydrocarbon, desaturated steam zone 23 in
production formation 22. In this c2se, however production sand 22 is also
penetrated by
a horizontal borehole section 21 A cf a second well. Borehole 21 A is lined
with a slotted
?0 liner 27A and has a tubing string 25A which extends to the surface.
Referring new to Fig. 3 a second c; ass sectional view shcws wellbore 21 A
(Fig. 2)
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CA 02254244 1998-11-20 ,
along a vertical section taken along the axis. Tubing string 25A and slotted
liner 27A are
as seen at right angles to the vie~N of Fig. 2. The slotted liner is isolated
by a lead seal 33
from vertical communication. Live steam is supplied via tubing 25A and exits
fr om its end
30. The steam flow is as indicated by arrows 31. Direct impingement of live
steam onto
liner 27A at the area numbered 32 can potentially cause erosion and collapse
0. the liner
27A, an undesirable condition. Also, using this technique the steams' heat is
concentr ated
in areas 34 and 35 ef formaticn 22, althcugh some heating does occur all along
the length
of the horizontal section of the wellbore 21 A. Sham and hot water condensed
therefrom
tend to migrate via area 35 to lower water sands 36. Steam also tends to move
vertically
upwardly through region 34 to the desaturated oil sand layer 23 of production
sand 22.
This configuration is an improvement over that of Fig. 1 alone, however, as
the horizontal
wellbore 21A tends to heat of more volume of the production zone 22.
Referring now to Figs. 4 and 5 the techr~icues and apparatus according to the
concepts of the invention are shown in mcre detail. ~, we!Ibore 81 has a
vertical pcrtien
which gees to the surface and a horizontal portion 61 A which penetrates a
long horizontal
1 ~ section of a producing sand 62. A slotted liner lines the horizontal
portion 61 A ef the
borehole 61. A tubing string 65 is run in from the sur'ace and, on the lower
end thereof
is plugged of' by a plug 65A. The length or tubing 65 above the plug 65A is
provided
along its entire horizontal por<ion with spaced apart drilled holes 70, each
of which is
covered with a sacrificial impingement strap 71. The straps 71 are or' a
carbon steel
.0 materiel and may be ceramic coated if desired. The straps 71 era welded to
the tubing 65
with an offset above each drilled hole 70 as s.~own in Fig. 5.
CA 02254244 1998-11-20
A steam generator source is Iecated at the surface and provides an input of
steam
into the tubing string 65. The steam travels down the tubing 65 to its lower
horizontal
portion where it exits via drilled holes 70. The sac. ificial impingement
straps 71 keep the
steam from directly impinging on the slotted liner 67 and thus prevent the
possible erosion
cf the liner 67. Based on experiment and experience it is k; own that about a
rate ef S
barrels of steam per day per foot of horizontal suction is desirable. Also
about 500 barrels
cr steam per acre foot is desirable V'Jith these as goals, and knowing the
tubing diameter
and steam delivery pressure, calculations allow the spacing and size of
drilled holes 70
to be made for a particular well. The drilled holes 70 and sacrif icial
impingement str ups
71 are usually symmetrically arranged along the tubing 65 and about its
circumference.
In practice a typical field procedure to run steam to a well using this "steam
stinger'
as described would be as follows.
(1 ) Pull the existing artificial lift equipment from the well.
(2) Run in on a tubing string the steam stinger designed for this well.
(3) Deliver the steam from the generatcr to the steam stinger via the
tubing string.
(4) Inject steam until the desired volume of steam is injected via the
stinger.
(5) Remove the tubing string and steam stinger; and
(6) Reinstall the artificial lift equipment into the well and place the well
back onto production.
This technique can be cyclically repeated when the produced volume of
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CA 02254244 1998-11-20
hydrocarbon fluid fails below an acceptable volume it the manner previously
described.
The use of the steam stinger as described distributes the heat from the steam
evenly along
the entire horizontal section of the well borehole. This causes heating of a
much larger
formation volume than heretofore possible which, of course, leads to
attendantly incr eased
mobility and volume of production cf the heavy, high viscosity crude oil from
the formation.
p The foregoing descriptions may make other equivalent embodiments and
techniques apparent to those of skill in the ar t. It is the aim of the
appended claims to
cover all such changes and modifications that fall within the true spirit and
scope of the
invention.
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