U.S. patent number 3,815,681 [Application Number 05/354,965] was granted by the patent office on 1974-06-11 for temporarily plugging an earth formation with a transiently gelling aqueous liquid.
This patent grant is currently assigned to Shell Oil Company. Invention is credited to Edwin Allen Richardson.
United States Patent |
3,815,681 |
Richardson |
June 11, 1974 |
TEMPORARILY PLUGGING AN EARTH FORMATION WITH A TRANSIENTLY GELLING
AQUEOUS LIQUID
Abstract
A permeable earth formation is temporarily plugged by contacting
it with a substantially homogeneous liquid mixture of an aqueous
solution of a metal that precipitates as a gel-forming gelatinous
metal hydroxide, a pH-increasing reactant that reacts at a selected
rate to cause the precipitation, and a pH-decreasing reactant that
reacts at a selected slower rate to subsequently dissolve the
precipitate.
Inventors: |
Richardson; Edwin Allen
(Houston, TX) |
Assignee: |
Shell Oil Company (Houston,
TX)
|
Family
ID: |
26945418 |
Appl.
No.: |
05/354,965 |
Filed: |
April 27, 1973 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
256507 |
May 24, 1972 |
|
|
|
|
62931 |
Aug 11, 1970 |
|
|
|
|
Current U.S.
Class: |
166/281;
166/280.1; 166/292; 166/254.1 |
Current CPC
Class: |
C09K
8/5045 (20130101); E21B 43/267 (20130101); E21B
43/261 (20130101) |
Current International
Class: |
E21B
43/267 (20060101); E21B 43/26 (20060101); E21B
43/25 (20060101); C09K 8/504 (20060101); C09K
8/50 (20060101); E21b 033/138 (); E21b 043/26 ();
E21b 043/27 () |
Field of
Search: |
;166/281,292,294,295,254,280 ;61/36R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Novosad; Stephen J.
Parent Case Text
RELATED PATENT APPLICATION
The present application is a continuation-in-part of patent
application Ser. No. 256,507 filed May 24, 1972, now abandoned
which was a division of patent application Ser. No. 62,931 filed
Aug. 11, 1970, (now abandoned).
Claims
What is claimed is
1. A process for temporarily plugging a permeable earth formation,
which comprises:
compounding an aqueous liquid solution, of from about 0.1% by
weight of a saturated solution of each of (a) at least one salt of
a polyvalent metal that is soluble in an aqueous liquid of pH from
about 2 to 7 and precipitates as a gelatinous metal hydroxide when
the pH of the aqueous liquid is increased to from about 7 to 10 (b)
at least one water-soluble, water-reactive reactant which increases
the pH of the aqueous liquid and causes said precipitation and (c)
at least one watersoluble, relatively slowly water-reactive
reactant which yields a water-soluble acidic product that decreases
the pH of the aqueous liquid and causes the dissolution of the
precipitated metal hydroxide;
adjusting the relative amounts and rates of each of said
pH-increasing and pH-decreasing reactants and reactions by
coordinating the types and amounts of said reactants so that the
aqueous solution first gels and becomes immobile, as the pH
increases to a value at which a gelatinous metal hydroxide is
precipitated, and then breaks and becomes a mobile fluid, a the pH
decreases and the precipitate is dissolved;
permeating an earth formation with said aqueous solution before the
occurrence of said precipitation;
maintaining the fluid substantially static within the earth
formation until the precipitation occurs; and k
after the occurrence of said dissolution of precipitated metal
hydroxide, displacing fluid from the so-treated earth
formation.
2. The process of claim 1 in which:
the permeated earth formation is an upper zone of a multiple zone
well, and
fluid is circulated within the well while said upper zone is
plugged with the precipitated metal hydroxide.
3. The process of claim 1 in which:
the permeated earth formation is the formation adjacent to at least
the most permeable one of a series of substantially adjacent
perforations through the casing of a well,
after said precipitation of metal hydroxide, but before said
dossolution of metal hydroxide, the precipitated hydroxide is
displaced from the perforated portion of the casing, and
at least one additional portion of said transiently gelling fluid
is injected into the earth formation adjacent to any of said
perforations through which such fluid will flow in response to a
pressure that exceeds the pressure at which the preceding portion
of said fluid was injected but is less than the fracturing pressure
of the surrounding earth formations.
4. The process of claim 1 in which:
the permeated earth formation is one that forms the wall of a
fracture, and
said fracture is extended and propped while its walls are plugged
with said precipitated metal hydroxide.
5. The process of claim 1 in which:
the permeated earth formation is the most permeable portion of a
reservoir interval containing formations of different
permeabilities, and
a treating fluid is injected into said reservoir interval while the
most permeable portion is plugged with the precipitated metal
hydroxide.
6. A process for temporarily plugging a permeable earth formation
which comprises:
compounding a substantially homogeneous liquid consisting
essentially of an aqueous solution of a salt of a metal that
precipitates as a gelatinous metal hydroxide when the pH of the
solution is increased, a pH-increasing reactant that reacts at a
selected rate to increase the pH of the aqueous solution and cause
the precipitation, and a pH-decreasing reactant that reacts slower
than the pH-increasing reactant to subsequently decrease the pH of
the aqueous solution and cause a dissolution of the precipitated
metal hydroxide;
adjusting the compositions and proportions of said pH-increasing
and pH-decreasing reactants so that, at a given temperature, the
precipitation occurs within a selected time and forms a gel that
substantially immobilizes the liquid, the gel breaks after a
selected time, and the liquid becomes relatively mobile;
permeating at least a portion of the earth formation to be plugged
with the liquid before the gel has formed;
maintaining the liquid substantially static during the persistence
of the gel; and
after the breaking of the gel, displacing the liquid from the earth
formation.
7. The process of claim 6 in which a buffering agent is dissolved
in said aqueous solution.
8. The process of claim 6 in which said pH-increasing reactant is a
water-soluble material that reacts with water to yield an amino
group-containing material.
9. The process of claim 6 in which said pH-decreasing reactant is a
water-soluble ester that reacts with water to yield a water-soluble
acid.
10. The process of claim 6 in which the pH-increasing reactant is a
mixture of urea and an alkali metal nitrite.
Description
It is also related to the E. A. Richardson U.S. Pat. No. 3,614,985,
which describes an earth formation plugging liquid containing an
aqueous solution of a metal that precipitates as a gelatinous metal
hydroxide at a relatively high pH and a reactant that raises the pH
of the aqueous solution to cause the precipitation. The present
application relates to a relatively high pH and a reactant that
raises the pH of the aqueous solution to cause the precipitation.
The present application relates to a liquid in which such a metal
and such a pH-increasing reactant are combined with a pH-decreasing
reactant which lowers the pH of the aqueous solution and
subsequently causes a dissolution of the precipitated metal
hydroxide.
BACKGROUND OF THE INVENTION
This invention relates to temporarily decreasing the permeability
of a permeable material. More particularly, it relates to
temporarily plugging a permeable earth formation by an in situ
formation of a gel that subsequently reverts to a free-flowing
liquid.
SUMMARY OF THE INVENTION
The present invention realtes to temporarily plugging a permeable
earth formation. A transiently gelling liquid made up to contain a
substantially homogeneous mixture of an aqueous solution of a salt
of a metal which precipitates as a gelatinous metal hydroxide at
relatively high pH, a reactant that reacts at a selected rate to
increase the pH of the aqueous solution and cause the
precipitation, and a reactant that reacts at a relatively slower
rate to subsequently lower the pH of the aqueous solution and cause
the dissolving of the precipitated metal hydroxide. The
compositions and proportions of the pH-increasing and pH-decreasing
reactants are correlated so that, at a given temperature, the
precipitation occurs within a selected time and forms a gel that
tends to immobilize the solution, the gel breaks after a selected
period, and the solution becomes relatively mobile. At least a
portion of the earth formation to be plugged is permeated with the
solution before the gel has formed. The solution is kept
substantially static during the persistence of the gel and, after
the breaking of the gel, is displaced from the earth formation.
DESCRIPTION OF THE DRAWING
FIGS. 1 and 2 are schematic vertical sectional illustrations of two
stages of a workover operation in a dual completion well.
FIGS. 3 through 5 are similar illustrations of three stages of a
perforation cleaning operation.
FIGS. 6 through 8 are similar illustrations of three stages of a
hydraulic fracturing operation.
FIGS. 9 and 10 are similar illustrations of two stages of a
selective acidization of a relatively impermeable portion of a
reservoir interval.
DESCRIPTION OF THE INVENTION
The present invention is particularly useful in temporarily
plugging subterranean earth formations into which wells have been
completed. For example, in various well completion situations, a
multiple zone well may be equipped with a casing string which is
perforated in at least one upper and one lower reservoir interval.
In various operations in a multiple zone well; it is desirable to
vary the pressure of the fluid within the casing without causing
fluid to flow into or out of one or more of the reservoir
intervals. Such operations may involve fracturing the lower
reservoir interval by pressurizing the fluid in the casing,
cleaning the well by displacing sand or debris from below an upper
reservoir interval by circulating fluid through the casing to a
surface locations, or the like operations.
In other situations a well may be opened into a reservoir interval
that contains layers having different permeabilities. In the latter
situation it may be desirable to preferentially acidize or displace
residual oil from the least permeable one of such layers. A
preferential treatment can be accomplished by injecting a
transiently gelling fluid into the reservoir interval. In such an
interval most of the injected fluid tends to enter and penetrate
deepest into the most permeable layer. The so-injected transiently
gelling fluid is allowed to gel. Subsequently, a treatment fluid is
injected into the interval and is deflected, by the gel, into the
least permeable layer. The gel later reverts to a free-flowing
liquid.
The present transiently gelling fluids can also be used in well
testing and various other operations. For example, in one type of
injectivity profile well logging operation, a discrete slug of
relatively cool liquid is injected into a relatively hot reservoir
and measurements are made of the rate of the temperature recovery
in order to determine the injectivity profile of the reservoir. A
transiently gelling fluid of this invention can be advantageously
used as the liquid which is injected. It is adapted to gel, and
thus prevent the formation of convection currents during the
temperature recovery. It is also adapted to subsequently revert to
a free-flowing liquid. The present transiently gelling fluids can
also be used to temporarily plug or stabilize various permeable
materials, such as the sand of a foundry mold, or the like.
FIGS. 1 and 2 show a use of the invention in a workover in a well
completed into upper and lower zones of permeable earth formation.
Well borehole 1 contains cement sheath 2 and string of casing 3.
The borehole is opened into fluid communication with upper and
lower zones 5 and 6 of permeable earth formations by means of
perforations 7 and 8 through the casing and cement. In FIG. 1, a
tubing string 10 is equipped with a bottom cap 11 and a packer 12
and arranged for injecting fluid through the perforations 7.
Transiently gelling fluid 13, in its initial liquid state is
injected, as is indicated by arrows, into the region 14. A downflow
within the borehole is prevented by packer 12 and an upflow is
prevented by means of an additional packer (not shown) and/or by
maintaining a back pressure on the annulus within casing 3, (i.e.,
the space between tubing 10 and casing 3).
Transiently gelling fluid 13 is maintained static until it becomes
gel 16 (FIG. 2) comprising a precipitated galatmous metal
hydroxide. The gel is removed from the relatively large spaces
within the borehole by a procedure such as a fluid circulation with
an inflow through tubing 10 and an outflow through the annular
space between the tubing and the casing. Such a fluid circulation
disrupts the structure of portions of the gel that are contained in
the relatively large openings within the borehole, entrains the
gel, and conveys the entrained gel to a surface location. This
leaves the borehole open while the region 14, within the earth
formation 5, is plugged by gelatmous metal hydroxide gel 16. In the
relatively small pores within a permeable earth formation, the gel
16 is resistant to displacement in response to a relatively high
pressure differential.
In the operational stage shown in FIG. 2, tubing 10 has been
replaced by a string of tubing 17 which is extended to near the
perforations 8 leading into the lower zone 6 of permeable earth
formation. As indicated by arrows, fluid may be circulated, with an
inflow through tubing 17 and an outflow through the annulus between
that tubing and casing 3, to entrain and remove solid particles 18,
such as sand or debris. Such a fluid circulation is apt to involve
fluctuations, in the injecting and/or flowing pressures, which
could cause undesirable inflows or outflows of fluid through the
upper perforations 7. In using the present invention, such inflows
or outflows are prevented by the presence of gel 16 in the zone 14
around the perforations. The gel 16 subsequently reverts to a
free-flowing liquid that can be produced into the borehole or
displaced further into the formation where it does not interfere
with the operations of the well with respect to the upper zone.
FIGS. 3 through 5 show a use of the present invention in a
procedure for cleaning each of a plurality of perforations that
open into a reservoir interval and being certain that each of the
perforations has been cleaned. A cased borehole 21 is opened into a
reservoir 22 through perforations 23 and 24. Such a casing is
preferably surrounded by a sheath of cement (not shown) with the
perforations being extended through the casing and cement.
In FIG. 3, a string of tubing 26 surrounded by packer 27 has been
installed with the packer set to plug the annular space between
tubing 26 and casing 21. In the illustrated stage of the operation,
the region 28 around perforation 23 and the region 29 around
perforation 24 have been plugged with a gelatmous metal hydroxide
gel 16.
During such a plugging operation, a slug of transiently gelling
fluid is injected, at a downhole pressure greater than the
reservoir pressure but less than the reservoir fracturing pressure.
Where one or a plurality of perforations (and/or the perforation
tunnels extending through a cement sheath) is relatively highly
permeable (e.g., perforation 23 is cleaner and more permeable than
perforation 24), most of the injected fluid flows through the more
permeable perforation and permeates a relatively large zone (e.g.,
zone 28) around the clean perforation with only a small zone (e.g.,
zone 29) being permeated around the less permeable perforation.
In FIG. 4, gel 16 is being removed from the borehole. Tubing string
26, with packer 27 unseated, has been extended to near the bottom
of the perforated interval. Fluid is circulated with an inflow
through tubing 26 and outflow through the annulus around it, as
shown by arrows. The circulating fluid breaks up the gel structure
and entrains the broken-up portions of the gel 16 where the gel is
unsupported in the relatively large openings existing within the
borehole.
In FIG. 5, the packer and tubing string have been relocated and
reset, in the positions shown in FIG. 3, and a second slug of
temporary gelling fluid 13 is being injected. During such an
injection, where a relatively large and relatively pressure
resistant plugged zone 28 exists around one perforation and a much
smaller plugged zone 29 (as shown in FIG. 3), exists around
another, two events tend to occur. First, no fluid injection occurs
at the injection pressure used in the prior injection of
transiently gelling fluid. Second, after the injection pressure has
been increased to a higher pressure (less than the fracturing
pressure), the small plug in and around a debris plugged
perforation (e.g., perforation 24) is displaced and fluid enters
the surrounding zone 31. If substantially no fluid injection occurs
at such an increased pressure, it is likely that (a) all
perforations were clean and were plugged around during a previous
injection of transiently gelling fluid or (b) the plugging material
in any perforations which are still plugged is embedded too firmly
to be removed without fracturing the reservoir. The gel 16
subsequently reverts to a free-flowing fluid that can readily be
displaced when the well is returned to normal operation.
FIGS. 6 through 8 show a use of the invention in forming, extending
and propping a fracture. In FIG. 6 a cased borehole 32 is opened
through perforations 33 into reservoir 34 which has some, but a
limited amount of, permeability. Such a reservoir may either be one
which tends to fracture horizontally (as shown) or one which tends
to fracture vertically. In the stage shown in FIG. 6, a fracture 35
has been formed, e.g., by injecting fluid through tubing 36
extended through packer 37, and is being held open by the pressure
of a transiently gelling fluid 13 that is flowing into the fracture
and the surrounding zone 38 as indicated by arrows.
In the stage shown in FIG. 7, the fluid injected into zone 38 has
been kept stationary until it formed gel 16 and the gel that formed
within the borehole has been removed. A fracturing fluid is being
injected as shown by arrows to form a fracture extension 39 from
which the fracturing fluid is leaking into the reservoir in the
zone 41. Leakage through the fracture walls near the reservoir is
prevented by the gel plug 16 in zone 38.
In the stage shown in FIG. 8, a granular fracture propping agent 42
is being pumped into the fracture as shown by arrows. The fracture
propping material suspending liquid leaks into the zone 41 and
displaces fluid from that zone into the expanded zone 43. Leakage
near the well is prevented by the gel 16 in the zone 38. The gel
facilitates the transporting of fracture propping material for a
relatively long distance within the fracture by preventing the
leakage into the fracture walls that tends to cause sand-outs or
depositions of the fracture propping material. The gel 16 in the
zone 38 subsequently reverts to a free-flowing fluid that is
readily displaced when the well is used for the injection or
production of fluid.
FIGS. 9 and 10 show the use of the invention in a process for
selectively acidizing a layer of lesser permeability within a
reservoir interval that contains layers of different
permeabilities. As shown in FIG. 9, the well contains a perforated
casing 44, a tubing string 45, and has been pretreated by injecting
a transiently gelling liquid and allowing it to form a gel 16
within the portions 48 and 49 of the reservoir formation. The
reservoir interval includes oil sand layers 46 and thief zone layer
47. Since the oil sands are less permeable than the thief zone,
they are permeated and plugged only to the depths 48, which are
small relative to the depth 49 of the plugging in thief zone
47.
In the stage shown in FIG. 10, an acidizing fluid 51 is being
injected as shown by the arrows. Such an acidizing fluid can be
substantially any relatively strong mineral and/or organic acid
formulation, such as the acidizing fluids conventionally used for
increasing the permeability of an earth formation. The acidizing
fluid can be prevented from rising within the annulus between
tubing 45 and casing 44 by maintaining back pressure by means of
surface located equipment or downhole packers (not shown). The
pressure at which the acidizing fluid is injected exceeds that used
to inflow the transiently gelling fluid but is preferably less than
the reservoir-fracturing pressure. A so-pressurized injection of
fluid tends to displace portions of the relatively thin plugs in
zone 48 without displacing the relatively thick plug in zone 49. As
acidizing fluid 51 flows through the gelled metal hydroxide in
zones 48, it tends to dissolve the plugging material and most of
the acidizing fluid tends to be guided around the undisturbed plug
in zone 49 into the relatively impermeable oil zones, as indicated
by the arrows. The undisplaced and undissolved portions of the gel
16 subsequently revert to a free-flowing liquid.
The transiently gelling fluid of the present invention can comprise
substantially any relatively homogeneous liquid mixture that is
adapted to penetrate into the pores of a permeable earth formation
and contains an aqueous solution of at least one multivalent metal
that precipitates as a gelatmous metal hydroxide at relatively high
pH, at least one pH-increasing reactant which reacts at a
relatively rapid rate to form at least one alkaline material that
increases the pH of the aqueous solution and at least one
pH-decreasing reactant that reacts more slowly to form at least one
water soluble acidic material that decreases the pH of the aqueous
solution. The transiently gelling fluid can be a clear solution, a
micellar dispersion, or an emulsion containing a dispersed phase in
which the particles are sufficiently small and mobile to move
through the interstices within a permeable earth formation.
The aqueous liquid solution of a metal which precipitates at
relatively high pH in the form of gelatmous metal hydroxide can
comprise a solution of substantially any salt of such metal which
is soluble in an aqueous liquid having a moderately low pH and is
precipitated from an aqueous solution of a moderately higher pH.
Such salts are preferably soluble in a pH range of from about 2 to
7 and precipitated at a pH from about 7 to 10. The preferred salts
are typified by the chlorides, nitrates, acetates, etc., of metals
such as chromium, aluminum, iron, copper, bismuth, or the like.
A pH-increasing reactant suitable for use in this invention can
comprise substantially any water-soluble compound or mixture which
reacts in contact with water to produce at least one water-soluble
alkaline reaction product and increases the pH of the water.
Suitable materials include water soluble amides of carbamic acid,
such an ammonium carbamate, carbamic acid halides, N-alkylamides,
urea, salts of cyanic acid, such as alkali metal cyanates,
cyanamide, etc. Urea and potassium cyanate are particularly
suitable reactants that increase the pH of an aqueous solution by
producing ammonium hydroxide at rates which are suitable for use at
temperatures commonly encountered in subterranean earth
formations.
Where desirable, a buffer system, such as a dissolved mixture of a
weak acid and its salt of a strong base, can be used to facilitate
and/or control the adjustment of the pH of the solution. For
example, a substantially equal molar mixture of acetic acid and
sodium acetate will maintain a pH of from about 4.5 to 5.0 as long
as both components are present. Such a mixture can be used to
extend the time required for the ammonia released by the hydrolysis
of urea to raise the pH of the solution. The first portions of the
ammonia are used up in depleting the components of the buffer and
the attainment of the pH at which the metal hydroxide is
precipitated is delayed by the time required to overcome this
effect.
The pH-decreasing reactant can be substantially any relatively
slowly reacting material (preferably a water-soluble material)
which yields a watersoluble acidic product that decreases the pH of
an aqueous liquid. The relative amounts and rates of each of the
pH-increasing and pH-decreasing reactants are adjusted by
coordinating the types and amounts of such reactants so that the
aqueous solution first gels and becomes immobile, as the pH
increases to a value at which a gelatmous metal hydroxide is
precipitated, and then breaks and becomes a mobile fluid, as the pH
decreases and the metal hydroxide is dissolved. The concentration
of the respective metal salt and pH-increasing and pH-decreasing
reactants can be varied over relatively wide limits. Such
concentrations can range from as little as about 0.1 percent by
weight to an amount (which may be as high as from about 30 to 50
percent) that forms a saturated solution. Suitable pH-decreasing
reactants are exemplified by the hydrolytically-reactive
halogenated organic compounds described in the solvolysis
acidization process U.S. Pat. Nos. 3,215,199; 3,297,090; and
3,307,630; esters such as esters of water-soluble organic or
inorganic acids, such as formic acid, acetic acid, chloroacetic
acid, acids such as phosphoric, sulfuric, nitric, etc., with
water-soluble alchols, such as methyl, ethyl, propyl, or the like
reactants.
Relative to the plug formation and plug dissolution reactions the
pH-triggered transiently gelling fluids of the present invention
are uniquely advantageous. During the plug formation, the viscosity
and flow properties of the fluid remain substantially unchanged
while the pH is slowly increasing. When the precipitation inducing
pH is reached, substantially all of the dissolved metal becomes
insoluble in substantially all of the aqueous liquid. The change
from a free-flowing liquid to an immobile gel is relatively sudden.
During the plug dissolution, the rigidity and insolubility of the
gel remain substantially unchanged while thhe pH of the aqueous
liquid component is slowly decreasing. When the metal dissolving pH
is reached, substantially all of the precipitated metal hydroxide
become soluble in substantially all of the aqueous liquid
component. The change from an immobile gel to a free-flowing liquid
is both relatively sudden and complete.
The transiently gelling liquids of the present invention are
characterized by certain readily determinable properties. These
properties can be evaluated from test tubes by visual observation.
In general, a test solution is placed in a test tube, sealed and
immersed in a water-bath. Time is taken as zero at the moment of
immersion in the bath, without allowance for warm-up At intervals
the contents of the tube and the following observations are
made.
1. IPT (Initial precipitation time). A transiently gelling fluid of
the present invention is usually a clear, water-white solution,
having a density and viscosity approximating that of fresh water.
At the time its components are mixed in the laboratory or blended
in a field operation, such a solution has a pH of from about 3 to
6. The reaction of typical pH-increasing reactants, such as the
hydrolysis of urea and KCNO, cause the pH to rise until a gel
forms, at a pH of about 6.5. The time, at a given temperature
required to form the gel is referred to as IPT. The gel usually
forms relatively quickly. The solution usually remains clear until
the gel forms. The pH of the gelled liquid continues to rise until
the pH-increasing reactant is spent. 2. GBT (Gel Break Time). When
the pH-increasing reactant is essentially spent, the rate of its
production of base becomes about equal to the rate of production of
acid by the pH-decreasing reactant, such as a hydrolyzing ester or
organic cloride. The pH of the liquid thus becomes steady and
eventually begins to drop as the rate of the base production
continues to diminish due to the continued depletion of
pH-increasing reactant. At a pH of about 6.5, the gel begins to
break as a large unit, even though many large patches of gel may
still be present as well as some individual suspended solid
particles. The Time at a given temperature required for the gel to
start breaking is referred to as GBT. Thus, the GBT contains the
IPT plus a period of time during which the solution or
precipitate-containing liquid was firmly gelled.
3. CT (Clear Time). The breaking of the gel does not immediately
produce a clear solution. A clearing of the solution is usually
appreciable by the time the pH drops to about 5.0. This time is the
CT. A typical solution exhibits a relatively slow transition from a
gel to a thick solution, to a thin milky solution, to a hazy
solution, to a dilute colloidal solution, and, finally, to a clear
water-white solution free of any visible suspended solid.
EXAMPLE 1
An aqueous solution containing about 2 grams of KOCN per 100 cc is
blended with an equal amount of an aqueous solution containing
about 4.41 gram per 100 cc of AlCl.sub.3 .sup.. 6 H.sub.2 O and
29.4 cc per 100 cc of a 3% aqueous solution of ammonia. A 100 cc
portion of that blend was mixed with 6 cc of ethylformate and 2 cc
of an aqueous 3% ammonia. This yielded a transiently gelling
solution having a pH of about 5.7 and containing a ratio of
equivalents of pH-increasing reactant to pH-decreasing reactant of
about 0.3. At about 140.degree.F, this solution exhibits an IPT of
5 minutes, a GBT of 3 hours, and a CT of 6 hours (at which the pH
is 4.5).
EXAMPLE 2
A transiently gelling solution was prepared as described in Example
1, except that a 100 cc-portion of the blend of pH-increasing
reactant and metal salt solutions was mixed with 4 cc of
ethylformate, 2 cc of ethyl acetate, and 4 cc of a 3.7 percent
hydrochloric acid. This yielded a transiently gelling solution
having a pH of about 4.9. at 140.degree.F, this solution exhibited
an IPT of 20 minutes, a GBT of two hours, and a CT of 8 hours (at
which time a faint haze was apparent).
EXAMPLE 3
A transiently gelling solution was prepared substantially as
described in Example 1 except that the KOCN reactant was replaced
by urea and the blend of the pH-increasing reactant and
metal-containing solutions was mixed with ethyl alcohol. At about
190.degree.F. the resultant transiently gelling solution exhibited
an IPT of 2 hours, a GBT of 2 days, and a CT of greater than about
6 days (relative to a solution containing only a faint haze).
EXAMPLES 4 AND 5
An oil-in-water emulsion containing, respectively, about 2 cc of
allyclchloride, 0.3 cc anionic surfactant (Triton GR-7, available
from Rohm and Haas), and 1 gram KOCN per 100 cc of water, was
blended with an equal amount of a metal salt - containing aqueous
solution of the type described in Example 1. The blending provided
a transiently gelling liquid of the present invention in the form
of an emulsion. The results of testing that liquid at two different
temperatures are indicated in the Table I:
TABLE I ______________________________________ Example T.degree.F
Test IPT min. GBT min. CT (estimated as allyl chloride obscures)
______________________________________ 4 160 (1) >19 62 93 min
(pH=5.1) (2) 24 45 81 min (pH=5.0) 5 140 (1) 63 262 406 min
(pH=5.35) (2) 56 175 329 min
______________________________________
EXAMPLE 6
The results of measuring the viscosity as a function of time during
the course of a gel-break cycle, in order to illustrate the type of
changes occuring in a transiently gelling liquid of the present
invention, are indicated in Table II. Since such a gelled system is
highly non-Newtonian, the viscosity values are a function of
arbitrary conditions of measurement and the numerical values have
only a qualitative significance. An aqueous solution containing
about 1 gram KOCN per 100 cc was blended with a metal
salt-containing solution as described in Example 1. A 100 cc
portion of the blend was mixed with 5 cc methylacetate and 0.2 cc
aqueous 3% ammonia. This yielded a transiently gelling solution
having a pH of about 5.3. The viscosity, with time, at
140.degree.F, is indicated in Table II:
TABLE II ______________________________________ T, Time Viscosity
at t=t minutes Viscosity at t=0 pH Notes
______________________________________ t= 0 1.00 5.3 solution
clear-water-white 5 1.00 clear 7 1.00 clear 10 1.03 hazy 15 3.1
smokey 16 6.0 weak gel 21 5.1 6.4 good gel -- IPT 30 4.5 good gel
65 5.1 good gel 185 5.5 7.3 good gel 365 6.8 good gel 395 7.8 good
gel 500 7.2 good gel 680 6.6 good gel 1,200 (1 day) 3.7 good gel
1,700 3.6 breaking -- GBT 2,000 4.5 smokey 2,600 (2 days) 2.3
smokey 4,000 (3 days) 1.86 smokey 4,700 (31/2 days) 1.65 smokey
5,500 (4 days) 1.29 smokey 6,900 (5 days) 1.03 colloidal -- CT
8,500 (6 days) 1.03 colloidal 10,000 (7 days) 1.00 5.2 colloidal
______________________________________
From the above data it is obvious that a sudden rise in viscosity
occurs between 10 and 15 minutes after immersion in the bath. At 21
minutes a good gel was noted, giving the indicated IPT value. The
solution remains at a high viscosity until about 1,200 to 1,700
minutes has passed, giving a GBT of 1,700 minutes. A slow drop
continues until t = 6,900 minutes, when essentially the original
viscosity is reached. However, the pH does not go low enough to
give a clear solution as dispersed colloidal solids too fine to
settle are noted in the solution. It is not expected that particles
this fine will cause formation damage in a subterranean
reservoir.
From the data presented above (and other data not given), a
tentative pH table may be set up as follows:
TABLE III ______________________________________ pH Range Solution
______________________________________ less than 6.5 and increasing
clear (low viscosity) greater than 6.5 and increasing gel forms
(viscosity increase) less than 6.5 and decreasing gel begins to
break (viscosity still to high) 6.5 and decreasing solution is
smokey-to-hazy-to colloidal (low viscosity) less than 5.0 and
decreasing clear (low viscosity)
______________________________________
EXAMPLES 7 - 18
Particularly suitable formulations of the present transiently
gelling fluids are exemplified by the urea and nitrite containing
solutions listed in Table IV. The advantages of a pH-increasing
reactant comprising a mixture of urea an an alkali metal nitrite
and preferred procedures for compounding and using such mixtures
are disclosed in the E. A. Richardson, R. F. Scheuerman patent
application Ser. No. 144,260 filed May 17, 1971; and those
disclosures are incorporated herein by reference.
Referring to Table IV, aqueous solutions of aluminum chloride,
sodium hydroxide, sodium or potassium nitrite and urea were blended
and mixed with 2-chloroethanol, substantially as described in
Example 1. The proportions used and the results of observing the
IPT and CT times at the indicated temperatures are listed in the
Table. It will be apparent that the relative proportions of the
reactants can be varied by significant amounts and such variations
can be utilized to obtain gel times and breakback times that are
delayed by selected amounts.
TABLE IV
__________________________________________________________________________
Example Al.sup.+.sup.3 M .sup.R NaOH .sup.R NO.sub.2 /R.sub.U
.sup.R CH.sub.2 ClCH.sub.2 OH Temperature IPT (Hours) CT
__________________________________________________________________________
(Days) 7 0.5 2.195 114/114 2 170 36 9 8 do. 2.17 do. 3 170 45 4.7 9
do. 2.18 1.578/1.105 3 do. 36 4.1 10 do. do. do. 4 do. 45 3 11 do.
do. do. 2 do. 38 .apprxeq.11.5 12 do. do. do. 4 180 32 2.2 13 do.
do. do. 3.0 180 32 2.6 14 do. do. do. 2.5 180 27.5 3.7 15 do. do.
do. 2.0 180 29.5 8.sup.+* 16 0.6 do. 4.0 170 20 3.3 17 do. do. 3.0
do. 20.8 5.0 18 do. do. 2.5 do. 19.5 5.2
__________________________________________________________________________
Al.sup.+.sup.3 M; molar concentration of aluminum ions (from
dissolved aluminum chloride) .sup.R NaOH, .sup.R NO.sub.2, .sup.R U
and .sup.R CH.sub.2 ClCH.sub.2 OH; ratio of moles per mole of
aluminum ions of, respectively, sodium hydroxide, nitrite ions,
urea, and 2-chloroethanol. * About 10% breakback in 8 days (when
the experiment was discontinued)
In general, a transiently gelling fluid of this invention (as
formulated for use in a subterranean earth formation having a
temperature commonly encountered in such formation) is exemplified
by an aqueous liquid solution containing from about 0.1 to 50% by
weight of each of: aluminum chloride, urea, and ethyl acetate. The
relative proportions are preferably such that the amount of urea is
at least the stoichiometric equivalent for increasing the pH of the
aqueous solution of the aluminum chloride to a pH at which aluminum
hydroxide is precipitated, and the amount of ethyl acetate is at
least the stoichiometric equivalent for reducing the pH of an
aqueous liquid containing the products of reaction of the aluminum
chloride and urea to a pH at which the precipitated aluminum
hydroxide is re-dissolved.
* * * * *