Note: Descriptions are shown in the official language in which they were submitted.
~ 21~3~9
TI~T-~ OF T~E INVE~IQN:
Process and Apparatufi for the Recovery of
Hydrocarbons from a Hydrocarbon Deposit
',~CT10~' 8 C02RECT10~ O~ INV~NTO~; . ~ .. ..
5EE CERTIFIC~ Roger M. Butler ...
~OR.~tCTlON -- AR~ICLE~
VO.R C~IIFICAT
FIELD ~F THE INVhrllTION
Thi~ invention rel~te6 to processes ~nd
apparatus for the recovery of hydrocarbon~ from
hydrocarbon depo~its.
rl4.~h ~ UIII~ AJID SUM~R~ OF THE INUENTIOJI
~ a~y heavy oil re~ervoir6.. in Canada,
particulary in ~lberta and Saskatchewan, are thin and
underlain ~y extensive aquifer6. Bottom water
frequently limits the performance o~ primary ~nd
therma~ recover~ methods used in the recovery of oil.
Pr~mary production of oil i8 often hampered ~y rapid
water coning, and economic recoverie6 are limited to
about 1-5% of the original o~l in place.
In the inventor~s p~ior Uni~ed States patent
no. 4,344,485, there i8 described a thermal method for
the enhanced p~o~uction of heavy oil6, known ~8 eteam
aseis~ed gravity drainage (SAGD). ~cco~ding to that
method, heated fluid is in~ected into a depo~it ~rom
an injection well drilled into the deposit and another
well, thermally connected to the injection w811, i6
u~ed for the prod~ction of oil. ~owever, thermal
me~od~ for the enhanced production of oil can be
inefficient and unecono~ical due to excessive vertical
heat lo~ses, thin pay zones, high water cut~ a~d steam
scavengin~ ~y bottom water zone6.
21083~9
Underlying zones of high water saturation
are al80 common in bitumen reservoirs for example in
the Peace River, Cold Lake and Athabasca formations of
Alberta, Canada and in heavy oil r~ervoir~ 6uch as
tho~e in the Lloydmin3ter area of CAn~d~. Fluids
injected into ~uch re~ervoir~ tend to migrate through
the path of lea~t re~i~tance, i.e., vla the bottom
water zone, re~ulting in low recoveries and poor ~weep
efficiencie~. Pilot or -commercial thermal recovery
operation~ in the~e re~ervoirs are e~ther con~idered
unsuitable or their location i5 cho~en to maximize net
pay thiGknesR and to r;n;r;2e bottom water thickness.
As a result, unt11 now re6ervoirs with an underlying
~quifer have been o~ a lower co~~ercial value to
operators because of low productiYities and high wat~r
cuts.
By contra6t, the inventor has now developed
~ proce~ that uses saturated hydrocarbon 601vent
vapour (typically ethane or propane) in conjunction
with horizontal wells ~o mobilize and recoYer VifiCOU8
oils and bitumens from hydrocar'oon depo~its in which
the bottom wate~ zone (~quifer) i~ used to deliver the
~olvent vapour to the ~ase of the re~ervoir. A
hydrocarbon 601vent ~n thc vapour phase is preferably
injected at reservoir temperature into an aquifer
underlying the deposit. The hydrocar~on ~olvent vapour
i~ essentially insoluble in water, while strongly
~oluble in oil,~with the consequence that there are no
heat or material los~es to the water layer.
FurthPrmnre, the water in the bottom water zone will
be mobiltzed and underride the lighter diluted oil and
assist in moving it towards the produc~ton well.
~ he in3ection of h~drocarbon vapour i~to
~ottom water re~ervoi~s i~ believed to be a cost
~ 21D83g9
e~fect; ve ~olution that L~LOVe8 chances for an
eco~omic re~urn. What i~ a disadvantage for SAGD,
namely bottom water, become~ an advantage for the
present proce~ u~ing hydrocarbQn vapour injection
into an aqui~er.
Another advantage of the present invention
i8 that he~t 106se6 to the reservoir rock and
overburden are typic~lly negligi~le. This makes the
process attractive for low porosity and/or thin
reservolrs a6 well a8 for thicker, higher porosity
reservoir~. The inven~ion may also have application
in fractured, and/or vuggy, low poro~i~y rocks.
An aquifer at the bottom of the reservoir
creates a laterally exte~ding communication path that
distributss ~aturated hydrocarbon vapour underneath
the deposit to mobilize the oil. In the presence o~
an a~uifer, in situ mixing of hydrocarbon solvent and
oil may be further enhAnced by the stir~ng action of
~ater oozing through the porous sand. ~y in;ecting
the saturated hydrocarbon 501~ent vapour below the oil
sand~ i.e. within the underlying aquif~r, advantage i8
taken of ~oth the percolation of the water that
carr~es along the ~aturated vapour and of the gravity
sc~r~tion of the lighter hydrocarbon which tende to
form rislng solvent ch~hers in the underbelly of the
oil sand payzone thue diluting and draining the oil.
The invention may also provide in-situ upgrading and
de~etallizing the bitumen. A high production ra~e m~y
be o~t~ined o~ oil that i~ lighter and of higher
quality than the original crude oil. In addition, it~
r~fi n; ng iB simpler.
As opposed to spreading solvent chambers ~as
~or example whe~ a liquid ~olvent iB injected from
vertic~l well into a reservoir~, where the oil
~i~83~9
production rate dec~ea~e~ when a no flow boundary has
been reached, the ~ertical rise of ~ol~ent chambera in
accor~ance with the present invention occur6 at a
con6tant rate. The presence of an aquifer i~
therefore bene~icial a~ it ~u,~ote6 the ~ormation of
a continuou~ ~lan~et o~ riBing 801~ent vapour cha~bers
or fingers which re~ult~ in a more complete contact of
hydrocarbon vapour with the oil depo~ita, in a faster
and more steady production rate and in a higher
ultimate reco~ery.
There i~ therefore provided in one a6pect of
the invention 8 method for~ he recovery of
hydrocarbo~6 from a hydrocarbon deposit having an
aquifer at the ba6e of the depo~it, the method
comprising the steps of injecti~g a hydrocarbon
solvent in the vapour phase into the aquifer to
mobilizc hydrocsrbons in the hydrocarbon depo~it; and
producing mobilized hydrocarbons from the hydrocarbon
deposit . --
Preferably the mobilized hydroc~rbon~ are
produced from ~he aguife~, and ~he hydrocar~on solvent
i8 in~ecSed along one or more-pr0dominantly hor~zontal
injection wells in the aquifer that are ~paced from
and alternate with the production well or ~ell~.
The hydrocarbon solvent i~ preferably a
hydrocarbon solvent ~elected from the g~oup con6ts~ing
of ethane, propane, and butene.
Preferably, a first -horizontal well iB
drilled int~ the aquifer to be used for injectio~ of
the vapour, and a second horizontal well i~ drilled
into the aquifer to be u~ed for production of oil.
After inltlal in~ection of the hydrocarbon sol~ent
v~pour into the equifer, a commu~ication path ~s
2~ ~83~
established between the first horizontal well and the
second horizontal well. . . .
In another aspect of the invention, there i8
provided apparatus for the recovery of hydrocarbon~
from a hydrocarbon deposit having an aguifer at the
ba~e of the depo it, the apparatus including a ~ource
of hydrocarbon ~olvent ~apour; at least a first-and
prefer~bly ~everal in3ection wells drilled into the
aquifer, the in~ection wells having a portion open to
10 fluid c~ ni catio~ with the aqui~er; ~nd at least a
first production well and preferably ~everal
production wells drilled into one of the nquifer and
the deposit, and spaced horizontally from the
injection wellr the production well~ each including a
pump for pumping oil from the well. The ln~ection
wells and produc~ion wells preferably lie parallel to
each other, spaced apart and alternate. A solvent
recovery 6y6tem i~ also preferably connected between
the injection well~ and production wells. The
injectlon and production well~ preferably have a
~ub~tant-ial portlon lying hor~zontally in the aqu;fer.
The aquifer may be created by initial
hydraulic fracturing of~the ba~e of the deposit,
preferably by injection o~ water or ~ther suitable
fracturing fluid into ~he base of the depo~it.
BRIEF l:!--CC~TPTION OF ~u~ DR~WIlIGS
There will now be de~cribed a preferred
emb~diment o~..the invention r with refe~ence to the
drawing~, by way of illustr~tion, in which like
num~r~l~ denote like e~ement~ and 1n which:
Fig.~1-is a ~chematic section through a
hydroc~rbon deposit ~howing the injection of a
hydrocarbon ~olvent vapour. in an aquifer underlying
~ 2~ 08~49
the deposit and the recovery of hydrocarbons fro~
another point in the aqui~er;
Fig. 2 ie a schematic section sho~ing a~
array of para~lel horizontal well~ in an aquifer below
a hydrocarbon depo~it with alternating well~ used for
vapour lnjection and hydrocarbon recove~y;
Fig. 3A i3 a ~chemat~c showing an exemplary
horizontal production well for.use in implementing the
method of the invention;
Fig. 3~ i6 a schematic showing ~n exemplary
hor~zontal inject~on well for use in implementlng t~e
method of the invention;
Fig. 4 is a schematic showing apparatu~ for
implementin~ the method of the ~Lvention including an
array of . parallel well~ drilled from an underground
tun~el;
Fig. 5 iB a schematic showing finger8 of
propane vapour ri~ing into bitume~ in a hydrocar~on
depo~it, with diluted deasphalted bitumen falling
cou~ter~urrently ~o as to drain to a horizontal
production ~ell;
Fig. 6 iB a fluid flow schematic ~howing a
closed loop extraction proces6 for u~e with the
invention;
. .~ig. 7A is a grAph showing the result o~
applying the method of the invention to a model of a
P.eace River ~nA~) bitumen deposit; and
Fig. 7B i6 a graph showing the result of
appl~ing the method of the invention to a model of a
~0 Lloydmlnster (Canada~ heavy oil depo~it.
Ta~I~n n_8~P~PTION 0~ rn~ EMPODIMENTS
A hydroca~bon deposit 10 cont~; n; ng high
vi~cosity hydrocar~ons ~uch as heavy crude oil or
~ 21~831~
bitumen i8 illuatrated in Fig. 1 including a reservoir
cap 12 and main re~ervoir 14 lying in.a permeable
fQ~mat~on or forma~ions below the reservoir cap 12. A
permeable layer forming ~n aquifer 16 underlies the
main reservoiF 14. The deposit 10 i8 bounded .from
below by a lower boundary 18. Overburden 22 above the
depoBit 10 i8 also illus~rated along with under~urden
24 below the depo~it lO..The depo~i~ 10 is exempla~y:
not all deposits will ha~e thi6 ~tructure. As for
exa~ple there may be no overburden, but a further
hydrocarbon depo~it. However, an aquifer 16 i8
req~ired at the b~se of the depo6it for the operation
of the invention. Th~ a~uifer 16.may be naturally
formed but the permeable layer may be created by
hydraulic fracturing, as discu6eed below, of the
fo~mation at the ba~e of the deposit 10. The aquifer
16 must be ~ufficiently permeable that injection of
hydrocarbon solvent into the aquifer re~ults in
mobility of the hydrocarbon solvent an appreciable
distance .laterally (suf~tcient - for production
purpose~) into the a~ui~er.unde~.the res~rvoir 14.
AB illuatrate~ ln Figs. 1 and 3B
particularly, a horizontal injection well 26 is
drilled into the deposit 10 using known te~hn;ques,
preferably with a 6ignificant length of well 26 lying
horizontally in the permeable layer 16. Significant or
~ub~tantial in this context mean~ 10 m or more,
preferably over.100 m, for example 1 km. That part of
the well 26 lying in the p~rmP~hle layer 16 ie open ko
the depo~it .10 Cuch as by perforation of the well
~ubing a~ shown at 28. The horizontal.portion of.the
well ~6 may be a~ long as feasible.
A horizontal production well 32, with tubing
34 and ca6ing 36, ~ 8 also drilled u~ing conventional
2~d~3~
techni~ues into the deposit 10, and extend~ laterally
into the permeeble layer 16 a~ lllu~rated
particul~rly in Fig~. 1 and 3A. A ~ lficant length
of the production well 32 lying horizontally in the
per~e~hle layer 16 i8 open, as for example by u~ing a
610tted li~er: in portion 38 o~ the well, to the
depo~it 10. A pump 42 i~ located in t~e inclined
portion of the well 32. The pump 42 may be for example
a conventional suc~er rod reciprocating pump (a~
illustrated with ~uc~er rod 44), rotary po~itive
displacement pump, electrically driven pump, or other
suitable pump. The pump 42 pumps production oil from
the casing 36 up the tubing 34 to the surface where it
iB produced in convent~onal manner. ~ illu6trated in
Fig. 2, the injection well~ 26 and pro~uction well~ 32
are preferably sp~ce~ approximately parallel to each
other and alternate with each other.
Hydrocarbon solvent iB injected in the
vapo~ phase, preferably at or iu~t below the
6aturation point, into th~ perme~hle layer 16 to
mobilize at least a portion of the hydrocarbons in the
hydrocarbon deposit 10. The injection pre~ure iB
~elec~ed 80 that the hydrocarbon ~olvent i8 in the
vapour phase near its gaturation point. The closer to
the saturation point, the higher will be the
concentra~iou of diseolved ~olvent ~n the oil which
enh~nces mobilization of the oil- and, if enough
eolvent iB dissolved, then, particularly with propane
as the solvent, al80 the higher the precipitation of
asphaltenes. However, if too much ~olvent i8 dis~olved
in the reservoir, Ruch that there are region~ o~
e~sentially pure 601vent, then mixing of liquid
solvent with crude oi~ may cause ma8sive precipitation
of asphaltenes 2nd plugging o~ the reservoir. This i8
21~3~
avoided by analy~ing the produced fluid~ and
controlling the rate of injection of solvent vapour to
maintain a ~a~get conce~tration of ~olvent in the
preferIed rsnge of 2 to 65% by weight, with be~t
result~ occurring in the range 15 to 50% by weight.
The de~ired pres~ure of the vapour chamber for a
re~ervo~r at a temperature of 20~C to 26~C and ~olvent
such a~ propane ifi in the order of 90 to 130 p~ig and
for ethane is in the range 490 to 550 p~ig. Vapour
pre~eure table~ for the oolvent being used, such as
~re well known in the art, may be u6ed to help
determine the a~lu~llate pre~oure range to operate
in, glven the re~ervoir temperature. Allowance should
al~o be ~ade for the 6mall rise in temperature of the
re~ervoir, perhaps ~e much a~ 5~C, a~ solvent vapour
dis~olve~ in the crude oil. In practice the
concentration of ~olvent di~solved in the crude oil
and the pre~ure are controlled by controlling the
rate of injection of the sol~ent into the aquifer.
Upon injection of the hydrocarbon sûlvent
into the pe~eable l~yer 16, the hydrocarbon Rolvent
spreads acro~s the are~ below the depo~it 10 on eith~r
side of the horizontal in~ection well 26. Vapour
ri~es, becau~e of gravity, acro~o thi~ area and
penetrates the overlying reservoir where it dilutes
and deasphalts the oil. Asphaltenes which separate
from the oil remain in the bulk of the reoervoir. The
vapour rise~ as a multitude of finger~ 46 into the
reservoir a6 illustrated in Fig. 5, mobilizing the
h~drocarbon in the re~ervoir 14 ~nd dilute~ bLtu~en or
heavy crude oil falls countercurrently to the
hydrocarbon ~olvent a~ indicated by the arrow~ 48. At
the interface between the hydrocarbon solvent vapour
~ 210~3~g
and the oil, the v~pour condenses into the oil,
mo~llizing it, and warming it up 0 - 5 ~C.
The d$1uted hydrocarbon in the deposlt i~
heavier. than the vapour and flow~ ~under~ gravit~
toward~ the production well 32, a~ i~dicated by the
arrou 52 whera the mobilized hydrocarbon~ are produced
from the hydrocarbon depo6it. The interface between
oil and vapour ri~es ~teadily until the supply of oil
has been exhau6ted, near the top of the re~ervoir.
A~ ;llu6trated in Figs. 2 and 4, it i8
prefer~ble that th~ hydrocarbon ~olvent- i8 injected
~long an nr~ay of.pre~om~n~ntly horizontal inject~on
wells 26 6paced from each other in the a~uifer and the
mobil;zed.hydrocarbon~ are p~od~ced along an array of
horizontal production well~ 32 spaced from each other
in the aquifer. The wells 26 and 32 may be drilled
from the 6urfsce (Fig~ . 1 and ~ or from a tunnel 44
(Fig. 4). Prefe~ably, the injection wells 26 and the
production well~ 32 ~lter~ate aa fihown in Fig. 4. It
~0 i8 po~sible that the in~ection well may be drilled
horizontally within the reservoir 14, rather than
wit~;n the aquifer but thi~ iB not preferred, as
production rate~ are believed to be reduced. In
addition, production could be obtMined fro~ vertical
well~, with a vert~cal injection well drilled into the
aquifer, or.any co~ination of vertical and horizontal
well6, 80 long a~.the~ are not 80 far spart that
cn n; cation cannot be establi~hed between them.
However, vertical well~ are consi~erably le88
30 efficient th~n horizontal well~ ~ince an important
a~pect- of the invention i~ the eetabli~hment of a
~olvent - oil interface that extend~ over a ~ide are~.
The horizontal injection and production
wells may be drilled in staggered rows, ~uch that a
2 1 ~
11 .
row of injection wells ly~ng more or le~s i~ line with
each other i5 parallel to a row of production well6 in
line with ea~h other, with adjacent injection well~
and production wells overlapplng each other. Various
other arrangement~ of injection and production wells
may be used.
If there i6 no pre-exlstlng aquifer
underlying the ~ain reservoir, under some condition~,
such ~ whe~e f~actures propagate horizontally, an
aquifer ~ay be initially created at the ba~e of the
hydrocarbon depoeit by hydraulic fracturing of the
rock a~ the ba~e of the hydrocarbon reser~oir. This
technique can bc u~ed ~or the recove~y of bitumen from
shallow deposit~ in the following manner.
Three parallel horizontal well~, such a~
wells 26 and 32 ~hown in Figs. 1 - 4, are drilled near
the base of a shallow bitumen deposit Euch as those in
AthAhn~c~, Alberta, C~n~a. The depth i~ chosen BO
that an operating pres6ure of the order of 100 psi can
be employed without d~srupture o~ the surface. A
depth greater than about 400 ~eet is ~atisfactory.
The depth i5 al~o chosen BO that when a hydraulic
fracture iB created within the reservoir, it become~
horizontal rather than vertical. It i~ well known to
those ~killed in the art that horizontal fractures
form at relatively shallow depth~ and that there i8 a
depth beyond which fractures tend to be vertical. The
exact depth at whi~h this transition occurs depend~
upon the in situ ~tres~e~ in the reser~oir body.
Typically the depth i~ about 1000 feet. Thus, in this
example, a depth of about 600-800 feet i~ chosen.
The central well of the three is u~ed as an
inj~ctor ~nd the two flAnking wells as producers. In
2~083~9
12
a larger project, many ~uch parallel wells could be
employed with alternat~n~ in~ector~ and producers.
The fir~ ~tage in the procee~, a~euming
that there i~ no natural aquifer in the re~ervoir,
involves the creation of a horizontal fra~ture
extending between the injector and the two producers.
This is created b~ injecting water or another
fracturing liquid at ~ high pressure into the
injection well. A fracture -opens up and the
producers, which are initial~y ~hut in, are opened
when the wellbQre pre~ure ri6es above the reservoir
pressure. Eowever, the well~ are throttled ~o a~ to
mai~tain a high pre6~ure in the wellbore. ~uring thi~
pha6e, the injection of water (or other fracturing
fluid) is co~tinued.
After the flow o~ ~ater ha~ been
e~tabli~hed, a mixture of propan~ and a les~ soluble
gas 6uch a~ natural gas or nitrogen is fo~ced into the
injector, -still maintA;n;ng a high pre~ure. The
composition of propane in the gaB i5 ChOBell ~0 that
th~ partial pre6~ure withln the mixture will be close
to, bu~ below the vapour pre~ure of propane at
reservoir temperature. Thi~ flow of gas i~ continued
until ~ significant volume of propane-diluted bitu~en
h~ been produced at each of the production welle.
During thi~ tLme, these wells are throttled BO that
the pressure in the fracture remain~ high to help keep
it open.
Once 6u~ficient bitumen h~s been produced to
indicate that a channel has ~een leached abo~e and, to
a les~er extent, below ~he fractu~e i~ the ~eservoir
~snd, then the pres~ure in the production wel~s i~
reduced gradually towards the normal operating
pres~ure; this ~hould be ~lightly be~ow the vapour
~ 21~8349
pre6sure of propane at the reservoir temperature. As
hss been described previously, this re~ervoir
temperature will tend, during the p~oce~s, to ri~e ~
few degrees centigrade because of the heat of solution
o~ the propane. A~ the preB~ure i8 allowed to faLl in
the production wells, ~o the pres~ure also falls in
th~ injector, and the compositIon of the injected
~luid is changed by gradually removing the injected
dlluent ga6 (eg. natural ga~ or n~trogen~ until pure
prop~ne i~ in~ected. At this polnt, there is a
continuous flow of- propane in the plane below the
reservoir ~nd the process can proceed as descr}bed
previously .
I~ summa~y, a horizontal, approximately
planar frscture, i8 created below the re~ervoir by
hydraulic fractur~ng, a m~xture of a low solubility
gas and propane is introduced into the fracture,
euff~cient bitumen is leached by the propane to create
a flow passage within the matrix above the fracture,
and the proce~s described previously i8 continued.
By u3ing cond~tion~ such as tho~e de~cribed
above, the pres~ure within the vapour chamber will be
less than that in the surrounding re6ervoir and, as a
result, there will be no te~ency for the valuable
v~pourized solvent t~ e~cape into the reservoir.
Rather, bitumen under preesure wlll tend to flow
to~srds the extraction chamber, albeit very slowly.
The hydrocarbon solvent is tsken from the
group of light hydrocArbons, such as ~thane, propane,
butane or other low boiling point hydrocar~on~,
h~logen sulphide, and other materials hsving suitsble
vapour pressure characteristic~ and ~olvency, as well
a~ their mix~ure8. Hyd~carbon ~olvent in thi6 context
does not nece~sarily mean that the ~olvent is a
~ 2108349
14
hydrocarbon, but that the ~olvent i~ capable of
dis~olving hydrocarbons. However, propane and ethane
and their corresponding ~lefin~ are ~ref-er~ed.
A recovery and recycling eyetem for the
hydrocarbon ~olvent vapour i8 illustrated
~chematically in Fig. 6. The ~ystem is compoeed of
in}ection well 2~, produc~ion well 32, 801~ent
stripper 66 connected between the wells 26 and 32, a
gae recovery system 62 and.a make-up ~olvent source
56. In~ectlon well 26 i~ drilled into the depo~it and
iB fed by solvent vapour line 54 from a solvent source
56, or by recycled ~olvent from etrlpper 66 depending
on the amount of eolveLt recycled and the in~ection
requiremcnt~. The hydrocarbon solvent vapour ie
injected into the aquifer by the well 26 with pres~ure
controlled by the pressure of 301vent eource 56. The
preesure required to.rec~cle the ~olvent vapour arise~
from the action of pump 42. Mobilized production oil
i~ forced b~ the pump 42 of F~g. 3A through tubing 34
of the production well 32 28 indicated by the arrow
58.. Gan produced along with the oil flowe through the
annulue between ~he tubing 34 and caeing 3~ a~
indic~ted by the arrow 60 to a ga8 reco~ery 8y8tem 62
of conventional deeign. Removal of re6ervoir and some
chamber gas ie believed de6irable since it i8 believed
to aesist in keeping diluted bitumen flow channels
opeu. If the g~ i6 in rufficient volume, it-may be
desirable to 6epar~te the solvent vapour for
rocyclinq, but i$ not-, it may be flared or used for
fuel. Removal o~ gae fro~ the ca~lng preferenti~lly
removes more volatile ga6e~ euch as methane and carbon
diox~de. This helps maintain the purity of the
hydrocarbon ~olvent ~apour.
~ 2~0~34~
Liquid production under pre~sure ~rom pump
42 is pu~ped ~long line 64 to 601vent stIippe~ 66.
Heat from a ~urce 67 i8 applied to the production
liquid through reboiler 68. Oil i8 produced a~ong line
70 leading from reboiler 68, and ~olven~ vapour i8
returned along line~ 72 and 54 from the ~tripper 66
for injection into the depo~it through injection well
25 a~ required. The produced ~il will be ho~ and heat
may be recovered from the produced oil.
~0 Models of a bitumen depo~it in Canada ~Peace
River bitumen~ and a heavy oil depo6it ~Lloydminster)
were created to test the efficacy of the i~vention
with propane as the solvent. From pre~iou~ work by the
~nventor on liquid solvent re~overy system~ snd ~team
ass~sted gravity drainage-of heavy oil re~er~oir~, it
~ ~nown that the result~ from the models may be
extrapol~ed to the field.
~he experimental system consi~ted of a cell
~ade of reinforced phenolic re~in ~eet~ having
internal dimen~ions of 21.7 cm inside height, 6Q.80 cm
in~ide width and 3.4 to 3.5 cm ineide ~epth. The cell
Yolume of 5.15 1 wa~ filled with 30-50 mesh ottawa wet
~and, and represented a vertical cros~-section through
a re6ervoir pay zone with a horizontal injector and
horizont~l producer. In the experimental set up, a gas
recycle loop and vapour make up line;were included.
The main element of the recycle loop was ~ propane
etripper which heats up the propane-oil -production
liquid, boils off and recycle~ the ~aturated vapour
~n~ produce~ oil cont~in;ng small amounts o~ ~olution
gas. The solution gas ia separated from the dead oll
and cQllected above water in an inverted c~linder,
according to known techniqu~ eat for heating the
propane was provided by a boo~ter heater (for ~udden
....
~ 21083~
16 .
increa~es in propane t~ ~ ~rature as required during
s~art up) and a ~maller heater for temperature
maintenance. To prepare the cell ~or t~e experiment~,
water wa~ flrst in~ected into the cell and the~
partially di6pl~ced by oil or bitumen, ~uch that the
water had a depth of about 2.5 cm. Propane was then
in~ected into the water layer below the ~itumen.
Fig. 7A ~hows the re~ult~ o~ operation of
the invention.on a model of the Peace Ri~er bitumen
depo~it. The wet sand had an ab~olute permeability of
43.5 darcy, corresponding to 0.5 darcy vert~cal
permeAhility in the.field, 73.1~ oil saturation, 26.9
water ~aturation, and temperature o~ 22 - 26.5~C.
Propane was in~ected ~t a pressure of about 120 p5ig.
The ~cale~ of Fig. 7A ~how cumulative production of
oil in g~ams ver~es time in hour~. After an initial
perlod o~ 810w build up of vapour pre~sure w~thout
production, oil production of partially dea6phalted
oil began at a rate of 129.1 g/hr ~.~ndicated by arrow
A), correspondLng to field production of 1,088bbl/d
for a 30 acre field with a 1 km production well having
horizontal in~ector well~ on either sLde ~a3 in Fi~.
2), dropping to 3.44 g/hr or 50 bbl/d near completion
of drainage of the re~ervoir ~indicated by arro~ B~,
with initial viscosity at ~26,000 mPa.s at 20~
dropping to 1,900 mPa.6 at the end o~ the run. The API
g~vity of the produced bitumen showed.an increase o~
almo~t 6 degrees over itB initial value o~ 6.3~. Total
heavy metal..content (V+Ni~Fe) wa~ reduced from an
initial 31fi ppm to 128 ppm. Total recovery was about
70~, but this included a greater percent light
fraction6 a~ compared with the initial rese~voir. The
remaining 30% of gooey mater~al left behind a8
depo~lts in the re~ervoir had a much higher
2~08349
17
concentration of undesirable a~phaltene6 that contain
chemicall~ bonded heavy metal6 than with the original
crude. Water -was- lnitially produced be~ore oil
production started as oil diEp'laced water in the
aquifer. After oil break through, water produc~ion
cea~ed. Propane i~jection wa~ init~ally high with half
of all propane co~6umed during the fir~t hour a~ a
vapour chamber wa6 formed. An initial high vapour
consumption ~8 to be expected when an aqui~er is used
for injection o~ the vapour. ~apour in~ection mu~t be
at a controlled rate to prevent liquid conden~ation in
the c~ll a~ p~es~urized vapour ~r~nd~ lnto the cell.
Fig. 7B ~how6 re6ults of a ~im~lar model of
the application of the method of the invention to
Lloydminster heavy oil. The model was the s~me 29 with
the Peace River bitumen, only t,,he oil saturation of
the Lloydminster oil wa~ 75.94 with water saturation
at 24.1%. A similar production rAte of partially
de~sphalted oil (129.1g/hr corre6ponding to 1,088
bbl/d) was initially ~een ~arrow C), falli~g to
90bblJd near complete production (arrow ~)~ with
initial vi~cosity of 6 Pa.~ at 20~ C fallin~ to near
0.5 Pa.~ at 20~C near completion of production. The
total production wa~ 75% in 22 ~ield year~. The
25 similar produc~ion r~te for heavy oil as compared with
bitumen, which in this case iB 17 ~imes more vi~cous,
sugge~ts that the ~olvent i8 the deter~; ni ng factor
for ,the production rate, thereby indicating the
part~cular benefit of the invention for use with
bitumen.
Operat~on of the invention with the model of
Fig. 7B together with co-injection of water with
propane into the aquifer re~ulted in the ~ormation of
high vi~Gosity emul~i~ied oil which tended to negate
~, 210~34~
18
the benefit-of the reduction of viscosity due to in
BitU dea~phalti~g of the oil. The vi6co~ity of the
produced oil ranged fI~m 30 to 40,000 mPa. 8 with a
r~ of 60,000mPa.s, and the API g~avity dropped by
1-2 degree~. Production with co-injection of water
reached only 52% in 12 hour~ a~ compared with near 70%
fo~ production in 12 hour~ when water was not co-
injected with propane. It i~ there~ore believed that
~n~ection of dry solvent vapour is preferred.
In experimeuts ueing eth~ne lpre~sure about
500 p~ig)l similar producti-on ra~e~ were found, but
the ethane did not deaephalt ~he oil as effectively as
the propane. Co~r~rable pr~duction rates wer~ also
found when butane wa6 u~ed a~ the solven~ in
experiments carried ou~ in a similar but ~maller
apparatus.
For t~e efficient oper2tion of the method of
the invention, it ~s desirable that the solvent vapour
~pread elong the aquifer at a rapid rate with ~ast
pressure-build up, such that the entire underbelly of
the reservoir i8 contacted almost simultaneou~l~. It
i8 preferable to ~n~ect the hydrocarbo~ solvent vapour
into the ~qu~fer at a rate such that the solvent
pa~sage in the aquifer i8 kept open. Ae liquid8 are
produced from the re~ervoir, additional propane mu~t
b~ ~dded to enBure 8 Continuous communication path
be~wee~ ~he well~. Th~ pressure for propane should be
kept in t~e r~ngH 90 to 130 p~ig. Thc solvent vapour,
a~ 0hown in Fig. 5, rises as finger~ with a more or
les~ con~tant rate of riBe. AE the inter~sce r~aches
the top of the payzone, the drsinage of oil ~10~B
signific~ntly. It is expected that high production
~ates can be expected until about 50-60~ of the oil i8
produced due to the e~fect of the rising 801vent
. .
~ 21D83g9
ch~ ~er, with a 6hQrp drop off thereafter when
dr~inage i8 due primarily due to gravity.
If the hydrocar~on ~olvent vapour i~ not
injected into the aqulfer at a ~ufficiently high rate,
the vapour will rise into the reservoir. ~erticall~
near th~ in~ection well and 6pread along the top of
the reservoir. While this will produce h~drocarbon
from the reser~oi~, production rate~ sre lower ~ince
there i8 le~ inter~acial..area avails~le for mass
transfer . - . ....... ..
~sing Darcy~ law ~d assuming comparable
diffusivitie~, d1ffu610n rates, porosity and oil
s~turation in the model and the ~ield ~believed to ~e
rea~ona~le aR~umptions~, it can be shown that:
(~/t~ p )~ kF
(H/ t~ M Hp k,~
where H i~ the height of the reservoir pay zone, t i~
tLme, ~ i~ the ~e_ ~-hility, ~nd F indicates the
paramete~ ~s a field parameter and M indicates model
parameter. ThiG equation ignore~. th~ e~fect~ o~
interfaci~l ten~ion snd capillary pre~ure. These
effecte can be important and tend to make rate~ in the
field higher ~han those predicted. From thi6 equation,
it follows that the model de~cribed above with a
payzone of 0.217 m at 43.5 darcy corresponds to an
l8.9m field payzone with 0.5 ~arcy vertlcal
perr.e-hility, and 1 model hour corre~pond~ to 0.866
field years. -In addition, the di~tance between
in~ector and producer, 6g.8 cm in ~he model,
correspond~ to 61 m in the field, for a pattern width
~dietance between injectors? of 122 m. Extrapo~ation
to the field al~o require6 multiplication by the
~ ~108~9
factor LF~LM where LF iB the length of the well in the
fleld ~assumed to be 1000 m) and LM i~ the length of
the model well (0.035 m). The calculated rate of 1,088
bbl~d corre~ponds to 50~ reco~ry in 3.g8 field years
aud i~ proport;on~J to the a6sumed vertical
perme~bility and the area of drainage. The flow rate
i~ determine~ largely by the 801vent. viscosity a~d
diffusivity ~ince the flow ta~es place largely at the
1nterface between t~e ~olvent and oil.
--Further modelling of solvent flow in an oil
re~ervo~r ~though without u8ing an aqui~er~ may be
found in Butler et al, "A New Proce~s ~V~P~X~ for
Recovering Heavy Oils using Hot Water and Hydrocar~on
Vapour" JCPT, Vol. 30, No. 1, pp. 97-106, Jan-~eb 1991
~nd ~u~ler et al,, ~'Recovery o~ Hea~y Oil~ U~ing
Vapour~zed Hydrocarbon Solvent~: Further Development~
of the VAPEX Process", J~PT, Vol. 32, No. 6, pp. 56-
62, June 19~3
The ~pacing between horizontal wells can b~
~0 adju~ted to achieve a drainage area with a required
oil production rate. Lower ~olvent pres~ure may lower
the oil production rate and -therefore extend
production lifetLme, though with lower API gravity oil
being produced. The limiting factor in the ~pacing of
wells i~ believed to be pres~ure and volume
r.equirement for establi~hing the initial communication
between adjacent well~, the rapid spread of the
solvent vapour.and the pumping capacity for propane
input and oil removal.
A per~on ~killed in the art could make
imm~terial modifications to the invention described
and claimed in thi~ pate~t without departing from the
e~ence of the i~vention.
