CA2108349C - Process and apparatus for the recovery of hydrocarbons from a hydrocarbon deposit - Google Patents

Abstract

A method for the recovery of hydrocarbons from a hydrocarbon deposit overlying an aquifer, including injecting a hydrocarbon solvent in the vapour phase into the aquifer to mobilize hydrocarbons in the hydrocarbon deposit; and producing mobilized hydrocarbons from the hydrocarbon deposit. Mobilized hydrocarbons are produced from the aquifer, and the hydrocarbon solvent is injected along one or more predominantly horizontal injection wells in the aquifer that are spaced from and alternate with the production well or wells. The hydrocarbon solvent is a hydrocarbon solvent selected from the group consisting of ethane, propane, butane. Apparatus for the recovery of hydrocarbons from a hydrocarbon deposit overlying an aquifer, includes at least a first and preferably several injection wells drilled into the aquifer, the injection wells having a portion open to fluid communication with the aquifer; and at least a first production well and preferably several production wells drilled into one of the aquifer and the deposit, and spaced horizontally from the injection well, the first production well including a pump for pumping oil from the well. The injection wells and production wells preferably lie parallel to each other, spaced apart and alternate. A solvent recovery system is also preferably connected between adjacent injection wells and production wells. The injection and production wells preferably have a portion lying horizontally in the aquifer. The aquifer may be created by hydraulic fracturing of the base of the deposit.

Description

~ 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 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 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 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~

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.

Claims (23)

1. A method for the recovery of hydrocarbons from a hydrocarbon deposit having an aquifer at the base of the hydrocarbon deposit, the method comprising the steps of:
injecting a hydrocarbon solvent in the vapour phase along a predominantly horizontal injection well into the aquifer to mobilize hydrocarbons in the hydrocarbon deposit; and producing mobilized hydrocarbons from the hydrocarbon deposit.

2. The method of claim 1 in which the mobilized hydrocarbons are produced from the aquifer.

3. The method of claim 1 in which the hydrocarbon solvent is injected into a pre-existing aquifer.

4. The method of claim 1 in which the mobilized hydrocarbons are produced along a predominantly horizontal production well in the aquifer.

5. The method of claim 4 in which the hydrocarbon solvent is injected along an array of predominantly horizontal injection wells spaced from each other in the aquifer and the mobilized hydrocarbons are produced along an array of horizontal production wells in the aquifer, and the production and injection wells alternate.

6. The method of claim 1 further including initially creating an aquifer at the base of the hydrocarbon deposit by:
hydraulic fracturing of the hydrocarbon deposit to create a horizontal fracture in the hydrocarbon deposit; and injecting water into the horizontal fracture.

7. The method of claim 1 in which the hydrocarbon solvent in the vapour phase is injected into the hydrocarbon deposit at about the hydrocarbon deposit temperature.

8. The method of claim 3 in which the hydrocarbon solvent is injected along an array of predominantly horizontal injection wells spaced from each other in the aquifer and the mobilized hydrocarbons are produced along an array of horizontal production wells in the aquifer, and the production and injection wells alternate.

9. The method of claim 1 in which the hydrocarbon solvent is selected from the group consisting of ethane, propane and butane.

10. The method of claim 1 further including injecting the hydrocarbon solvent into the aquifer along with a diluent gas that is less soluble in the hydrocarbon deposit than the hydrocarbon solvent.

11. The method of claim 1 in which the solvent vapour is dry.

12. The method of claim 1 further including producing free gas along with the mobilized hydrocarbons.

13. Apparatus for the recovery of hydrocarbons from a hydrocarbon deposit having an aquifer at the base of the hydrocarbon deposit, the apparatus comprising:
a source of hydrocarbon solvent vapour;
a first injection well drilled horizontally into the aquifer, the injection well having a portion open to fluid communication with the aquifer and being connected to the source of hydrocarbon solvent vapour;
and a first production well drilled horizontally into one of the aquifer and the deposit, and spaced horizontally from the injection well, the first production well including a pump for pumping oil from the well.

14. The apparatus of claim 13 further including a solvent stripper connected between the first injection well and the first production well.

15. The apparatus of claim 13 further including a second injection well drilled into and lying horizontally in the aquifer spaced from the first production well, with the first production well located between the first and second injection wells.

16. The apparatus of claim 13 further including a gas recovery system attached to the production well.

17. A method for the production of hydrocarbons from a hydrocarbon deposit having a base, the method comprising:
drilling a first horizontal well into the base of the hydrocarbon deposit;
drilling a second horizontal well into the base of the hydrocarbon deposit spaced from the first horizontal well;
fracturing the base of the hydrocarbon deposit to form horizontal fractures extending between the first horizontal well and the second horizontal well;
injecting a saturated hydrocarbon solvent vapour into the base of the hydrocarbon deposit through the first horizontal well; and producing hydrocarbons from the second horizontal well.

18. The method of claim 17 in which the hydrocarbon solvent vapour is selected from the group consisting of ethane, propane and butane.

19. The method of claim 18 in which the hydrocarbon deposit is a bitumen deposit.

20. The method of claim 17 in which fracturing the base of the hydrocarbon deposit includes:
injecting a fracturing fluid into the base of the hydrocarbon deposit from the first horizontal well.

21. The method of claim 17 in which injecting a saturated hydrocarbon solvent vapour into the base of the hydrocarbon deposit through the first horizontal well includes initially injecting a mixture of the hydrocarbon solvent vapour and a diluent gas into the base of the hydrocarbon deposit.

22. A method for the recovery of hydrocarbons from a hydrocarbon deposit having a aquifer at the base of the hydrocarbon deposit, the method comprising the steps of:
injecting a hydrocarbon solvent in the vapour phase into the aquifer at about the hydrocarbon deposit temperature to mobilize hydrocarbons in the hydrocarbon deposit; and producing mobilized hydrocarbons from the hydrocarbon deposit.

23. The method of claim 22 in which the aquifer is pre-existing.