Note: Descriptions are shown in the official language in which they were submitted.
J~K/las
A-71728
. ~
--1--
-THERMAL ACIDI2ATION AND RECOVER~
PROCESS FOR-~ECOVERING VISCOUS PETROLEUM
.
The government of the United States of America has
rights in this invention pursuank to Contract No. ET-C-03-
2046 awarded by the U.S. Energy Research and Development
Administration (now Department of Energy).
BACKGROUND OF THE INVENTION
This invention relates to a method for conditioning a
subterranean formation containing clay..particles creating
adverse permeability effects around a well bore communicating
from the surface of the earth to the formation in order to
increase the recovery of heavy viscous hydrocarbon materials,
such as petroleum crude oil or synthetic fuels. The presence ~:
of clay particles.may create adverse permeability effects in
the formation and particularly around the well bore by swell-
ing if water-sensitive clays, particle plugging by dispersal
of clay fines or by p~rticle invasion of such fines. Such
effects reduce permeability of the formation both to fluids
injected for stimulation of production of viscous hydrocarbons
and to the production of the hydrocarbons themselves
There are many methods known in the art for injecting
thermal energy into a formation for the purpose of reducing
the viscosity of heavy viscous petroleum crude oil so that
it may.be recovered. Such meth~ds are usually classified as
"thermal.drive", "single well thermal injection" or the
like. Thermal drive processes basically involve injecting
. --2
thermal energy, usually from steam boilers or in situ com-
busti.on, into an oil-bearing formation by means of an injec-
tion well, driving the petroleum towards one or more adjacent
producing wells and recovering the petroleum thr~ugh the
producing wells ~ingle well thermal injection processes
usually involve injecting thermal energy into the oil-
bearing formation by means of an injection well and subse-
quently withdrawing the resulting heated petxoleum through
the same well. Such single well thermal injection processes
are also commonly referred to as "huff~and-puff" processes.
There are, of course~ many modified versions.of these basic
techniques known in the art which employ a wide variety of
thermal energy agents, such as hot water, in situ combustion
gases, steam, heated condensable and non-condensable gases,
and the like.
Although many thermal injection rnethods have been
useful under certain conditions, there are many formations
known to contain large volumes of heavy viscous petroleum ,
from which the petroleum has not been economically and
efficiently recovered by the employment of any known thermal
injection technique. By way of example, there are many
formations located throughout the United States, particularly
throughout southern Illinois, western Missouri, southeastern
Oklahoma, and southern Kansas, saturated with heavy viscous
crudesl e.g., having viscosities greater than 200 centipoises
and/or API gravities below about 22 (both at 60 F), which
have not been recovered in economic quantities by employment
of conventional recovery techniques. Additionally, previous
attempts to increase the recovery of such heavy crudes from
such formations by the employment of known thermal injection
processes, especially direct single well steam injection,
have been substantially unsuccessful. As known, one of the
primary problems in attempting.to recover such viscous
crudes from such formations is that the formations have such
low relative permeabilities to oil and water that thermal
energy cannot be injected into the formations at economic
injection rates. In fact, there are many formations which
have such low relative permeabilities to oil and water that
, , ~ ~ . . . . , , -
--3--
33~
they will not accept su~ficient quantities of thermal energy
by the employment of known injection processes at any
injection rate~
A recent patent discloses a method for enhancing petro-
leum production in such formation. For example, U.S. Patent
No. 3,993,135 discloses a method comprising initially.heating
a well bore penetrating the formation and surrounding sub
terranean strata with a thermal ~apor stream containing
combustion gases and superheated steam until sufficient heat
is imparted.thereto to,permit the therm,al vapor stream.to be
injected,into the,formation at a desired high.~njection
rate. The, well,bore,.and.surrounding strata are heated by-
continuously inject,ing the thermal ~apor. stream.:into ~he
well and,simult,an,eously.venting a portio,n of the vapor
, 15 strea,m from the well at the surface to remove condensed
liquids formed,from,,w~ile-heating the.well-bore..and.formation
...... . . . . . ... . .. . .. .. .. .. .
face. The heated flu~d,ls,then inje,c.ted.directly into the
formation at a des~red h~gh.l~jection.rate untll.the.orma-
tion and v,iscous pe,trole,um c~ontained therein.are heated and
....
20, the visco,si,ty of the..hydro~arbons is reducedu.. Injection is
.. . . .. . .. .. . .. . .. .. .
then discontinued and the.he.ate.d crude is.produced through
the well. Surprisin,gly, and contrary to prior~attempts, a
.. . . . . . .. . . .. .. .. .. . . .. _ . . . . .
formation havin,g l,ow relative p.ermeabilities .to water and
oil will readily,a-ccept a the,rmal vapor stream containing
steam at hlgh injection rates wh.en .the heated fluid contain-
ing steam.is inje,cted in accorda.nce with the process of U.S.
. .
Patent No. 3,993,135. U.S. Patent 4,118,923 describes
apparatus particularly suited for. generating a thermal vapor
stream for use in the described method.
Best resul.ts are obtained wi.th the above process when
the heated fluid is.injected at the maximum in~ection rate
possible so.as to impart heat to the formation as rapidly as
possible. But it has now been found that the above process
cannot be applied ~o maximum efficiency in those ~ormations
which clay particles which cause adverse permeability effects
by swelling upon contact with water or being of such fine
particle size that the particles migrate through the forma~
tion ultimately plugging the formation. Injection of a
~ 3 ~
thermal vapor stre~m ~s clescribed i~ U.S. Patent 3,993,135
causes the fine particles to migrate through the ~ormation
to ultimately plug the formation. Where the clays are
water-sensitive, swelling occurs. Such swelling lo~ers the
already low permeability of such format:ions which lowers,
for practical purposes flow of the therrnal vapor stream into
such formations and greatly impeds the recovery of petroleum
from such wells. Additionally, when a continuous thermal
drive technlque is employed the presence of such clays within
the formation around the drive well impeds the ability to
drive the petroleum crudes from the field through the use of
the injection well. Examples of such clays which adversely
affect the permeability of such formation include, for example,
illite, smectite, bentonite and montmorillonite.
Traditional treatment of such formations with hydrogen
fluoride to dissolve the clay or with clay stabilizers has
proved unsuccessful, partly because of the difficulty of
removing carbonaneous materials, such as oil, from the clay
particles. The coating of crude oil prevents the hydrogen
fluoride from attacking and dissolving the clays. This result
is partly because hydrogen fluoride reacts with calcium,
magnesium and other metals contained in the formation to
form insoluble metal fluoride salts which are deposited
within the pores of the formation to further limit its
permeability. Attempts to solve this problem, such as des-
cribed in U.S. Patent 4,136j739 illustrate the difficulty in
treating formations with hydrofluoric acid and hydrochloric
acid to solve the problems created by clay particles which
adversely effect the permeability of oil-bearing formation.
These problems are compounded when heavy viscous hydrocarbons
are present in the formation. Further, conventional acidizing
with hydrogen fluoride is very corrosive and causes consider-
able damage to the well bore.
Treatment similar to that described in the prior art
was attempted where a liquid hydrocarbon, in this case
diesel fuel, was injected into the formatlon to attempt to
remove heavy viscous crude in the presence of such clay
particles to make them susceptible to treatment with hydro-
fluoric acid failed. No increased permeability was noticed.
3~
S~MMARY OF THE INVENTION
-
Applicant has now discovered a method by which the
problems created by the presence of clay particles which
adversely effect permeability in a format:ion containing
highly viscous hydrocarbon.materials such as petroleum crude
oils and synthetic fuels are solved, allowing the formation
to be stimulated by the injection of a thermal vapor stream
comprising steam and combustion gases, such as, for example,
carbon dioxide. The method of this invention comprises
initially injectin~ the ~thermal vapor stream through the
bore hole to clean- that part ~f the formation in the vicinit~
of the bore hole of hydrocarbon crude oil to expose the clay
particles; injecting v-aporized hydrochloric acid simul-
taneously with the thermal vapor s-tream until calciuml
magnesium and other meta}s., if present,.in-the formation
about the bore hole have.reacted to form water-soluble
chloride salts;-injectin~ vapor~zed hydrofloric acid simul~
taneously with the thermal-vapor stream until sufficient
amounts of the clay-in-the forma-t^ion about the bore hole
ha~e been dissolved by-the hydrofluoric acid; and, continu-
ing to-inject the thermal vapor -into the forma*ion until
suff-icient heat has -been imparted.thereto to permit the
petroleum therein to be.recovered at an improved recovery
rate. -.. . . ..
Where mobile, fine clay particles are present, a known
clay stabilizer may be added with any of the injection steps
after the crude oil has been cleaned from the clay particles
to further assist in curing the problem converted with
particulate migration.
Injection of hydrogen chloride and hydrogen fluoride
sequentially, o.r simultaneously after some initial HC1
injection, as a vapor at high temperatures insures that the
formation about the bore hole may be properly conditioned
for a distance.of at least five feet of the bore hole to
eliminate the problems caused by clay particles ~hen the
thermal vapor stream is employed to stimulate production of
the viscous petroleum contained therein.
3~
BRIEF DESCRIPTION OF ~E DRAWING
The drawing is a schematic drawing, partially in cross-
section, of a section of the earth, illustrating a well bore
penetrating a petroleum-bearing formatiorl and another means
at the surface for introducing a thermal vapor stream into
the well and formation. The drawing also illustrates a
means for introducing and vaporizing hydrogen chloride and
hydrogen fluoride with the thermal vapor stream, as well
as the s'abilizing compound, if desired, into the well and
formation in accordance with the method of the invention.
In the drawing the casing is partially broken away in order
to show the details of one embodiment for in~ection and
vaporizing hydrogen chloride and hydrogen fluoride simul-
taneously with the injection of the thermal vapor stream.
15 DETAILED DESCRIPTION OF THE INVENTION
It will be understood that the instant invention may be
employed for the recovery of substantially any type viscous
hydrocarbon materials, such as crude petroleum oil or synthe-
tic fuel from substantially any type of subterranean formationcontaining clay particles which adversely effect the perme-
ability of the formation. One of the primary advantages of
this invention is that it provides for the injection of a
thermal vapor stream containing combustion gases and steam
at high injection rates thereby permitting the formation to
be heated to a predetermined desired level at which the
cxude oil will be flowable in relatively short periods of
time. However, the instant process is particularly useful
for recovering heavy viscous crudes; e.g., those having
viscosities greater than 200 centipoise (at 60 F~ and/or
API gravities (at 60F~ of about 22 or below, from subter-
ranean formations having low relative permeabilities to
water and oil and containing water-sensitive or fine, mobile
paxticulate clays.
More specifically, the instant method is useful for
recovering such highly vis~ous crudes from a formation
where the low permeability of the formation is due, at least
-7-
in part, to the swelling of w~ter-sensitive clay p~xticles
which, when contacted with the thermal vapor stream, exp~nd
to inhibit the migration of the thermal vapor stream into
the formation at distances more remote from the well bore
or where mobile, fine clay particles migrate and plug the
formation.
Many of such viscous crude-bearing formations having
low relative permeabilities to oil and water are well-known,
and are usually located within the range of from about 500
to about 2,000 ~t. below the earth's surface. I~cluded
among such formations, by way of example, are those of
Pennsylvanian san~stone,-such as--Bartlesville sandstone of
the Cherokee group, which are known to-be located throughout
southern Illinois, western Missourij southeastern Kansas and
northeastern Oklahoma. ,$uch format,ions often contain about
10~ to 16% of troublesome clay particles.
The pr,acti,cç of t,hls,inv,ention can be most easily
understood by reference to the drawingO As illustrated, a
producing formation l0-bearing heavy viscous petroleum is
penetrated by ,a, well 11 which has--been-dr~lled from the
surface of-,the earth-12~ -The we,ll 11 has preferably been
completed in a conventional manner and includes a string of
casing 13 set within a-well bore 14 to,the petroleum-bearing
.. .. . .. . . .
formation-10 and supported by-a cement sheath 15. The well
bore 14 has penetrated the petroleum-~earing formation and
has been drilled to near the bottom of-the desired formation
injection zone. ,The well bore 14 may be left open as in an
open hole completion or a,screen or slotted liner or perfora-
ted casing (not shown) may be set in the well-bore lower end
14a to support the,walls of the well bore 14 Of course, the
casing may be set all the way throuyh the formation, cemented
and perforated.
The well 11 also;includes a string of tubing 17 disposed
within the casing 13 and the well bore 14 extending through
the formation 10 thereby forming annular space 18. Prefer-
ably, the tubing 17 extends downwardly to near the well bore
lower end 14a. A conventional sealing device ~not shown~ is
provided adjacent the top of the well head 19 to seal off
~ 3 ~ 3~ ~
the casing annulus 18 ~nd maintain pressure within the wellO
In an optional embodiment to be discussed subsequently, a
second short length of supplemental tubing 37 is included
within the tubing 17 and forms a second annulus ~0 there-
with. Tubing 37 extends partially the length of tubing 17,terminates in opening 37a and is held in place by centralizer
39 which has openings therein (not illustrated~ to allow
fluid flow in tubing 17 pass centralizer 39. ~ conventional
sealing device 38 is provided at the top of tubing 17 to
seal off the second annulus 40 and maintain pressure within
the well.
In the first step of the method of this invention the
formation face lOa and suxrounding strata adjacent the well
bore 14 is preliminarily "preconditioned" to clean or remove
viscous crude, paraffins, or other hydrocarbonaceous materials
adhering to the particles of the formation - including clay
particles contained therein - which could restrict flow of
the thermal vapor stream into the petroleum-bearing formation
10 .
In the first step in carrying out the method of the
invention the well bore 14 and surrounding strata through
which the well 11 extends to and through the formation 10 is
initially heated by injecting a thermal vapor stream contain-
ing combustion gases and superheated steam; i.e., particularly
carbon dioxide and superheated stoam, into the annulus 18
through a valve-controlled pipe 20. The heated therm~1
vapor stream travels down the annulus 18 where part of it
contacts and penetrates the formation face lOa and surround-
ing strata adjacent the well bore 14 while the remainder
enters the open end 17a of the tubing 17, causing the thermal
vapor and any condensed fluid as well as any hydrocarbona~
ceous material removed from the formation about the bore
hole to pass upwardly through the tubing 17 where it is
vented into suitable collection means (not shown) at the
surface through a suitable venting means 23 connected with
the surface end of the tubing 17, such as by pipe 22. The
venting means 23 include a means for controlling the pressure
in the tubing, such as a valve, restriction orifice, auto-
matic operating valve or a combination of such devices.
3~
1 This pressure controllin~ means 23 is preferahly instal.led
between the end of the pipe 22 and a valve 21.
~ f desired, the -thermal vapor stream may be injec-ted
into the tubing 17, such as through piping 24 connected
therewi-th and vented at the surEace :Erom the annulus 18 by
appropriate ven-ting pressure controlling means 25 mounted with
pipe 26. Ilowever, annulus injec-tion and venting through
the tubiny 17 for hea-ting and cleaning the well 11, the
casing 13 and surrounding strata is preferred~
The injection of the thermal vapor stream into the
well 11 contacts the tubing 17, casing 13 and the formation face
lOa may cause, depending upon the ormation tempcrature,
substantially simultaneous condensation of condensable fluids,
e.g~, steam, in the thermal vapor stream which may collect
in the wcll bore 1~. If the rate at which the flui.d condenses
in ~he we:Ll bore 1~ :is greater than the ra-te which the
formation can accept at the injection pressure employed,
the well bore 1~ starts to accumulate fluids usually at the
bo-ttom l~a. As these fluids accumulate they reduce the area
of the Eorma-tion injection zone which in turn reduces the
injection rate oE the hea-ted fluid into the formation. As this
condition continues, the l.evel of condensed fluids can rise
to a level in the well bore 1~ and formation 10 where it
effectively seals o:Ef the entire formation injection horizon
and the maximum injection ra-te of the heated fluid into
the formation may drop to near zero.
However, by simultaneously venting, as described
previously and taugh-t by U.S. Patent 3,993l135, the injected
thermal vapor stream at the surface throuyh the pressure
3~ control means 23 any condensed liquids formed and collected in
the well bore 1~ are forced into the tubing 17 through its
3~
open lower end 17a and are forced or lifted towards the
surface. The simultaneous venting step thus sweeps the condensed
li~uids from the wel.l bore 14 thereby eliminati.ng -the
aforementioned blockage problems.
The thermal vapor s-tream is prefe:rably continuously
injected and simul.taneously vented until the well and sur-
rounding subterranean strata are heated sufficiently to
substan-tially eliminate condensation of the heated fluid
within the well 11 or at least reduce the amount of conden-
sation to a level which the formation will accept without
causing the aforementioned blockage problems. The time
requirecl will. vary widely, depending upon well location, dep-th,
and surrounding strata temperatures, types oE strata, etc.
and 3 S best determined emperically, such as by direc-tly
injecting thc thermal vapoxs into the formation by discon-
tinuing venting and observing whether a desi.red high formation
injection :rate can be maintained.
The thermal vapors may be injected into the well 11
at any desired rate to impart heat through the well and surround~
~ ing subterranean strata. However, it is preEerred to emplo~
the ma~imum injection rate possible so as to impart heat as
rapidly as possible~ Such maximum in]ection rates may be
obtained by emp:Loying an injection pressure practiceable below
the -fo.rmation frac-ture gradient pressure which may be. readily
de-termined, if desired, by known techni~ues. More specifically,
i.t is preferred to employ an injection pressure within the
range of Erom about 200 to about 1500 psig ~14 ~o about 105 kg/
cm2 gauge). Again, such injeetion procedure is described in
U.S. Patent 3,993,135.
Further, the thermal vapor stream is vented at the
surface at a rate sufficien-t to keep the gas velocity in tubing
--10--
.
3~gD
1 17 high enough to lift any condensed liquids formed and
collec-ted in the well bore 1~ -towards the sur:Eace so as to
keep i-t substantially Eree o:E liquids while maintaining
substantially full pressure on the forma-tiorl. This may be
readily accomplished by the employment o:E the aforementioned
appropriate ven-t pressure con-trol means at the surEace, such
as a valve, restric-tion orifice or like devi.ce in -the conven-
tional manner to provide a gas velocity in the tubing within
the range of from abou-t 10 -to about ~0 ft./sec. (3 to about
1~ 12 meters/second).
During the above-mentioned injecting and venting
the hea-ted fluid through the well 11 the formation face lOa
adjacent the well bore lower end 14a is conti.nuous:Ly exposed
directly to the heated fluid, -thereby gradually increasing
its temperature and the temperature of the heavy viscous
petroleum therein~ This "pre-conditioning" of the adjacent
formation face cleans the. well bore 14 ana formation face lOa
of viscous crude, paraffins, or materials which could tend
to rest:rict flow of the -thermal vapors into the petroleum-
2~ bearing formation 10. It also exposes the clay particl.eswhich adversely eEfects permeability and ma~ces them suscep-tible
to fur-ther treatment.
The thermal vapor stream preferably employed to heat
and clean the formation face of the well 11 and surrounding
sub-terranean strata is usually a mixture of superheated steam
and combustion gases essentially free of solid carbonaceous
particles. Such a mix-ture of s-team and combustion gases are
preferably produced as described in V.S. Patents 3l993,135,
3,948,322 and ~,718,925. Any process and apparatus known in
the ar-t can be employed for injecting such steam-gas mix-tures
with a mix-ture o:E carbon dioxide and steam ~eing particularly
- useful.
~L31~3~
It is preferrecl to employ a steam-gas mixture which
is produced by initially burning a hydrocarbon ~ue], such as
diesel oil, ga~o~ine, hea-ting oil, natural gas, propane,
bu-tane, lease crude, e-tc. in the presence of subs-tantially
stoichiometric ~uan-tities o-E pressurized air under relatively
high pressures, e.g., within the range of from about 200 to
about 1500 psig and contacting the resulting pressurized
combustion gas stream with water as described in the
a~oremen-tioned paten-ts. ~s illustra-ted in the drawing, this
may be carried out by simultaneously injecting a hydrocarbon
fuel :Erom a suitable fuel storage supply 30 and a pressurized
stream of air produced by a suitable air compressor 31
through suitable piping 32 ancl 33 respectively, into a
pressurized combustion chamber 34 specifically designed ~or
high pressure combustion, such as the one described in U.S.
Patent 4,118,925, wherein the fuel is burned under high
pressure. The quantities o~ Euel and pressurized air are
regulated to provide essentially complete combus-tion in the
pressurized combustion chamber 34, resulting in a pressurized ;~
-lla-
-12-
combustion ~as stream essentially free of solid carbonaceous
particles, e.g., soot.
The pressurized combustion ~ases, usually having a
temperature within the range of from about 2,000~ to about
4,000 ~, is th~n passed into a steam ~enerator 35 where it
is contacted with water provided through suitable piping 36
to form steam. The resulting mixture of combustion gases
and superheated steam forming the thermal vapor stream, can
then be injected into the well annulus 18 through piping 20
or into the well tubing 17 through piping 24 under any
pressure within the range of from about 200 to about 1500
psig, depending upon the formation fracture pressure gradient
to enter the formation at a temperature within the range of
from about 550 to about 700F. The temperatures stated are
illustrative, with the important consideration being that
the thermal vapor stream enters the formation with super-
heated steam. At such temperatures and pressures, the
thermal vapor stream is injected into the well 11 for heating
it and the surrounding strata, described hereinabove, or
directly into the formation at steam~gas injection rates
within the range of from about 200,000 to about 2 million
standard cubic feet per day (scfd) and heat injection rates
within the range of from about 20 million to about 250
million BTU heat per day.
In accordance with the inventive method, after the sur-
rounding strata is sufficiently heated and the clay particles
substantially cleaned of hydrocarbaneous materials, vaporized
hydrochloric acid is injected simultaneously with the thermal
vapor stream through the well bore and thereafter vaporized
h~drofluoric acid is injected simultaneously with the
thermal vapors. This injection allows for solubilization or
stabilization of the clay particles which would, without
this treatment, adversely effect the permeability of the
formation.
With reference to the drawing, acid injection may be
accomplished by adding it directly to the supply line 24
through which the heated fluid is injected into the well.
After that, the acid added to the supply line will vaporize
-13-
3~
as a result OI contact with the heated fluid. This method
is not preferred because it exposes the mild steel of the
supply line to the corrosive effect of the acid. The acid
in the vapor phase is less corrosive than its liquid counter-
part. Thus it is preferred to vaporize the acid prior toits admixture with the heated fluicl. This may be accom-
plished by employing hydrogen chloride or hydrogen fluoride
gas rather than aqueous solutions of these acids. In this
event, it is merel~ necessary to inject the hydrogen chloride
or hydrogen fluoride,directly into the thermal vapor injection
line 24. Upon mixture.~ith the thermal vapors, the hydrogen
chloride or hydrogen fluoride will become heated to the same
temperature of the thermal vapors. It is important to avoid
corrosion that the tempe,rature,of the mixture of thermal
15 ~ vapors and the acid mix,,ture be,,a,bove the . ~ at which the
~' hydrogen chloride or.hydrogen fluoride, as the case may be,
will condense. , .. -.- .. : . . .
Alternately, an aqu.,eous-ac,id solution may be heated tp
vaporization in a heater-43,-prior-to injection via conduit
46 into tubing.17 where-it heçomes mixed with the thermal
vapor, which is simultaneously injected into tublng 17.
This,method requires a heater 43 constructed of a corrosive
resistant metal. - , -
In a preferred methpd of acid injection, the heat value
of the therrnal fluid i,s utilized to vaporize an acid solutionand raise it to a sufficient temperature such that the
mixture enters the formation at-a temperature above the dew
point of the mixture. In this embodiment, acid solution i.s
pumped from reservoir 47 or 48 to supplementary tubing 37.
Supplementary tubing 37 is constructed of a corrosive resis-
tant steel such as.Hastelloy B~ Simultaneously with the
injection of acid solution through supplementary tubing 37,
thexmal vapors are being injected into tubing 17 and passing
down annulus.40 in a heat exchange relationship with supple-
mentary tubing 37O Tubing 17 and supplementary tubing 37
form a heat exchanger in which acid flowing through supple-
mentary tubing 37 becomes vaporized prior to passing through
opening 37a where it becomes mixed ~ith the thermal vapors
in one preferred embodiment of this invention.
~ -14~
3~
Sufficient h~drochloric acid is injected into the
formation surrounding the bore hole in order to react with
such calcium and magnesium compounds as may be contained in
the formation to form water soluble metallic chlorides. '~he
hydrogen chloride treatment when such compounds are present
prepares the formation for hydrofluoric acid injection. If
hydrofluoric acid were injected without pxior hydrochloric
treatment, the hydrofluoric acid would react with the calcium
and magnesium, if present in the formation, to form insoluble
metallic fluorides which would deposit within the pores of
the formation and impair its permeability. rrhe amount of
hydrochloric acid needed can be readily determined by core
analysis of the formation.
Preferably a 35~/ by weight, aqueous solution of hydro-
chloric acid is used as a source of hydrogen chloride eventhough anhydrous hydrogen chloride gas may be used. The
rate of addition is adjusted such that about 5 to about 30
gallons of such 35~ solution is used per hour preferably
from about 5 to about 10 gallons per hour. Greater or
lesser amounts of hydrochloric acid may be used with the
heating time being varied accordingly.
The injection of hydrochloric as a vapor at elevated
temperatures above the dew point simultaneously with the
injection of the thermal vapor is important to insure that
the hydrochloric acid will be carried into the formation
adjacent the well bore for a distance of at least 5 feet.
The amount of hydrochloric acid necessary to treat the
formation around the well bore for the required distance of
at least 5 feet may readily be determined by determining the
calcium and magnesium content of the formation from a core
sample or samples of formation fluids. It is preferred to
employ an excess of hydrochloric acid to ensure that the
formation is properly preconditioned for the subsequent
hydrofluoric acid treatment.
After the hydxochloric acid injection, the well is
acidized with hydrofluoric acid in order to remove the
troublesome clay particles in that part of the formation
which surrounds the well bore 11. Hydrofluoric acid injec-
tion r,lay be accomplished in substantially the same manner,
and with the same te~perature requirements, as hydrogen
chloride injection. That is, the hydrofluoric acid may be
added as a gas to the heated fluid supply line 24 as an
aqueous solution, usually 70% by weight hydrofluoric acid,
which is vaporized in a heater 43 prior to injection, or
injected as an aqueous solution which is vaporized by in-
direct heat exchange with the thermal vapors in the same
manner as previously described which is simultaneously
injected into the well.
The hydrofluoric acid usually amounts to about 3%, by
~olume, of the amount of thermal vapor being injected.
Lesser amounts may be acceptable but would require addi-
tional time of injection and greater amounts may cause
corrosion and do,not normally,,result in significant reduction
in injection tlme. The preferred range is from about 2% to
about 6%. This,amount is easlly accomplished by injection
of from about 5 to about 30 gallons per hour, preferably
. .
from about 5 to about lQ gallons per hou,r, of a 70% weight
solution of aqueous hydrofluoric acid.
Injection o~ hydrofluoric acid as,a heated vapor simul-
taneously with the injection of the thermal vapors at tempera-
tures above the dewpoint of the,mixture insures that the
hydrofluoric acid will be carried into the formation surround-
ing the bore hole for a distance,of about 5 feet or more.
The hydro~luoric acid then reacts,with the clay particles of
the formation in the immediate vicinity of the well bore to
render them incapable of swelling. A surfactant may option-
ally be added to the hydrofluoric,acid to be injected to
increase the activity of such acid in its removal of the
clay particles.
In those formations where plugging of the pores within
the formation is caused by the migration of very fine clay
particles which are either,removed from the sandstone sub-
strate or are suspended in the pore volume fluids~ known clay
stabilizing compounds may be added J usually simultaneously
with hydrofluoric acid injection. This clay stabili~ing
compound added to the 70% weight solution of aqueous hydro-
fluoric acid in quantities of from about .003 ~allons to
-16-
~ 3 ~ 3~
about 0.5 gallons o~ cl~y stabilizing compound per ~allon
of 70~ by weight hydrofluoric acid with a rate of about 0.1
tQ about 0.30 gal. o~ clay stabilizing compound per gallon being
n
~c~. The acid stable organic clay stabilization com~
`:` 5 pound will attach itsel~ to these very fine clay particles
and rendex them in~obile; thus, preventing their migration
and subsequent plugging. Of course, once the clay particles
have been cleaned of the hydrocarbonaceous coating the
stabilizing additive can be used. One particularly useful
clay stabilizer is "Cla-Sta B" sold by the Halliburton Company
which is an aqueous solution of ammonium chloride containing
30% by weight of a quaternary polymer.
In accordance with the inventive method, after the well
11 and surrounding strata have been suficiently heated and
cleaned and the permeability has been increased by the treat-
ment described hereinabove, injection of the thermal
vapors is continued directly into the formation at the maximum
injection rate possible as described in the aforementioned
patents. Formation injection is then continued until suff~
cient thermal vapor has been injected to raise the formation
temperature sufficiently to permit the heated petroleum
to flow to the well bore 14 for recovery to the surface by
the employment of conventional production means. The injec-
tion necessary depends upon formation permeability, crude
viscosity, formation fluid composition and the like, all well-
known to those having ordinary skill in the axt.
In carrying out the inventive method, the thermal
vapors are continuously injected into the formation until it
has sufficiently heated the formation, usually about 150
millio~ BTUs. It is preferred to establish and maintain a
formation injection rate averaging at least 50 million BTU
per day and at least 500,000 scfd thermal vapor in order to
permit petroleum recovery as rapidly as practicable. However,
often times such injection rates are not obtained at initial
formation injection and oftentimes the ormation injection
rate diminishes below such levels before the formation has
bePn heated to the desired extent due to blockage problems
caused by condensed liquids forming and collecting in the
-17-
~3~133d3
well bore and adjacent injection zone of the fo~mation. It
is believed that this is cau~ed.by the well and ~urrounding
strata being insufficiently heated. However, it has been dis-
covered that this problem can be overcome by discontinuing
direct formatior. injection and further heating the well 11
and surrounding strata.by injecting and simultaneously
venting the steam-gas mixture through the wel~ as described
above. By alternating the well heating :injection and
direct formation.injection, the direct formation injection
rate is increased and stabilized. Also, the injection can
~e halted and the.formati.on allowed to "soak" with the
injected thermal vapors further improving permeability to
accept additional thermal vapor inj.ection.
Therefore, whenever the formation injection rate dimi-
nishes or is initially. established.at a rate below about 20
.
milltion BTU per day heat, preferably below about 50 million
BTU per day.heat, the alternate injection procedure may be
employed.
After the formation 10 has.been heated to the desired
extent, direct formation.injection is discontinued at the
surface and the heated,.now mobile petroleum is withdrawn
and collected at the surface through the well 11 by the
.. . .
techniques, such as natural flow, pumping, and the like, all
well-known in the art. If desired~ the formation may be
allowed to "soak" for a desired length of time prior to
petroleum withdrawal to allow the thermal vapor to dissipate
through the formation interstices, impart heat to the forma-
tion strata and petroleum and to allow the petroleum, in its
heated, more mobile state, to be easily removed from the
formation 10 through the well 11.
Into a well in southwestern Missouri containing a 21
API gravity crude was injected a thermal vapor stream prepared
as described in.U.S. Patent 4,118,923. A total amount of
about 300 million BTU were injected. Upon entering the
production cycle, only about 6 barrels of oil was recovered
per day for five days and the production dropped to near zero.
-18-
33~
It was attempted to acidize the well by cleaning clay
particles at normal ~eservoir temperatures (70-80 F~ with
diesel oil followed by injection of liquid 70~ HF to which
Cla-Sta B (The Hallibuxton Co.) had been added. ~ttempts to
stimul~te the ~ormation followed by the injection of thermal
vapors but no production of crude oil resulted.
The well was then treated by injecting sufficient
thermal vapors, carrying approximately 50 million BTUs of
heat at a temperature of from about 550-650 F and about 300
psig. Without ceasing the heat injection, over the next two
hour period, 55 gallons of 35% (wt) aqueous hydrochloric
acid was added to the thermal vapors. Then, over a two hour
period 55 gallons of 70% (wt) aqueous hydrofluoric ac:id was
added to the thermal vapor stream. One quart of Halliburton
Cla-Sta B was added to the hydrofluoric acid. After the
addition of the hydrofluoric acid was complete additional
thermal vapors were injected until a total of about 150
million BTU had been put into the formation. The well then
began production at a rate of about 35 barrels of oil per '
day. Another well in the same field and pay zone was
similarly treated and had a production rate as high as 60
barrels per day. Of course, in fields of this nature it is
well known that production falls off as the formation cools
and requires more heat injection. The period of time how-
ever can be as long as 4-6 months.
From the foregoing description, those skilled in the
art will be able to arrive at many variations of the same
without departing from the scope of the claimed invention.
