U.S. patent number 3,559,737 [Application Number 04/726,720] was granted by the patent office on 1971-02-02 for underground fluid storage in permeable formations.
Invention is credited to Jack H. Heathman, James F. Ralstin.
United States Patent |
3,559,737 |
Ralstin , et al. |
February 2, 1971 |
UNDERGROUND FLUID STORAGE IN PERMEABLE FORMATIONS
Abstract
Fractures in caprocks of fluid storage reservoirs can be sealed
and flow barriers can be established at desired regions of porous
rocks by locally freezing the formation water to form an impervious
cryogenic structure and/or by forming gas hydrates by contacting
hydrate forming gases with formation water subjected to heat
removal therefrom and agitation, for the purpose of stored fluid
leakage control, increasing storage volume of limited reservoirs,
and formation of storage conditions in homoclines and
monoclines.
Inventors: |
Ralstin; James F. (Wichita,
KS), Heathman; Jack H. (Wichita, KS) |
Family
ID: |
24919735 |
Appl.
No.: |
04/726,720 |
Filed: |
May 6, 1968 |
Current U.S.
Class: |
166/281; 166/271;
166/305.1; 166/302; 405/56 |
Current CPC
Class: |
E21B
33/10 (20130101); E21B 33/138 (20130101); E21B
36/003 (20130101); B65G 5/005 (20130101) |
Current International
Class: |
E21B
33/138 (20060101); E21B 36/00 (20060101); E21B
33/10 (20060101); B65G 5/00 (20060101); E21b
033/138 (); E21b 043/26 () |
Field of
Search: |
;166/285,281,302,57,305,(305D),306,308,271 ;61/.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Novosad; Stephen J.
Claims
We claim:
1. A method for locally impermeating a naturally occurring
underground formation to be used for gaseous fluid storage having a
porous, permeable aquifer zone overlain by an impervious aquiclude
zone having a fracture therein or having an escape path thereunder
making such unsuitable for fluid storage, so that said aquifer zone
can be utilized for storage of fluids without said fluids escaping
from said aquifer zone comprising, subjecting said formation to a
coolant in the region of said fracture or escape path as the case
may be, thereby removing heat from said formation and forming a
barrier structure adjacent the area of said formation where said
formation is subjected to the flow of said coolant, thereby
providing a gaseous fluid storage reservoir.
2. The method according to claim 1 wherein said coolant is a
refrigerant which is substantially water immiscible, has a density
equal to or less than the density of water in said formation, has a
viscosity higher than the viscosity of said water in said
formation, is present in a liquid phase during injection into said
formation, and possesses a high heat conductivity.
3. The method according to claim 2 wherein said aquifer zone is
subjected to said refrigerant and said refrigerant is selected from
the group consisting of carbon dioxide, freon, and the like, said
refrigerant being continuously circulated down to said formation
and back to the surface, and said barrier is a cryogenic structure
formed in the area where said refrigerant is contacted with water
in said aquifer zone.
4. The method according to claim 2 wherein said coolant is directly
contacted with said formation.
5. A method for locally permeating an underground formation to be
used for fluid storage having a porous, permeable aquifer zone
overlain by an impervious aquiclude zone having a fracture and
water therein so that said aquifer zone can be utilized for storage
of fluids without said fluids escaping from said aquifer zone
comprising, subjecting said aquiclude zone to a refrigerant which
is substantially water immiscible, has a density equal to or less
than the density of the water in said formation, has a viscosity
higher than the viscosity of said water in said formation, is
present in a liquid phase during injection into said formation, and
possesses a high heat conductivity selected from the group
consisting of carbon dioxide, freon, and the like, thereby removing
heat from said formation and forming a barrier structure, said
barrier being an impervious structure formed where said refrigerant
is contacted with said water in said aquiclude zone thus sealing
said fracture in said aquiclude zone.
6. A method for locally impermeating an underground formation to be
used for fluid storage having a porous, permeable aquifer zone
overlain by an impervious aquiclude zone so that said aquifer zone
can be utilized for storage of fluids without said fluids escaping
from said aquifer zone comprising, selectively hydraulically
fracturing said formation to establish flow channels of least
resistance in said formation, subjecting said formation to a
coolant thereby removing heat from said formation and forming a
barrier structure adjacent the area of said formation where said
formation is subjected to the flow of said coolant.
7. A method for locally impermeating an underground formation to be
used for storing hydrate forming gases having a porous, permeable
aquifer zone overlain by an impervious aquiclude zone so that said
aquifer zone can be utilized for storage of fluids without said
fluids escaping from said aquifer zone comprising, subjecting said
formation to cooled water, said water being contacted and admixed
with said hydrate forming gases, thereby removing heat from said
formation and forming a gas hydrate barrier structure adjacent the
area where said formation is subjected to the flow of said
water.
8. The method according to claim 7 which includes the step of
injecting a hydrate forming gas selected from the group consisting
of carbon dioxide, hydrogen sulfide, sulfer dioxide, natural and
manufactured gases having a high content of light parafinic
hydrocarbons, and the like, prior to the injection of said fluid to
be stored in said formation, admixing said gas hydrate forming gas
and said cooled water thus forming a gas hydrate barrier
structure.
9. The method according to claim 8 which includes admixing an
additive selected from the group consisting of alcohols, acetic
acid, and the like to said hydrate forming gas to accelerate
hydrate formation in said formation.
10. The method according to claim 9 wherein said cooled water is
continuously circulated down to said formation and back to the
surface thus maintaining cooled water within the formation at all
times.
Description
This invention relates to the underground storage of fluids. In one
aspect it relates to the underground storage of gaseous fluids. In
another aspect it relates to a localized in situ freezing process
whereby an impervious cryogenic structure is formed to seal
fractures in the caprock of a permeable formation containing stored
fluids. In another aspect it relates to a localized in situ
freezing process whereby an impervious cryogenic structure is
formed at a strategic location, to enlarge the available storage
volume. In yet another aspect it relates to a method of forming a
gas hydrate, in situ, in order to seal fractures in formations and
the like in the caprock to prevent the undesired migration of the
stored fluid out of the permeable formation. In another aspect it
relates to a method of forming gas hydrates within a porous
formation to enlarge the available fluid storage volume within the
porous rock.
In recent years much attention has been directed to underground
storage of fluids, especially to the storage of volatile fluids
such as hydrocarbon fuels. Due to the varying seasonal demands for
hydrocarbon fuels much work has been done in discovering methods of
storing these fuels. However, many of the prior art methods utilize
methods of forming caverns and the like by mining or dissolving a
cavity in a soluble strata. Such caverns are limited by size and
economics.
Other prior art methods have utilized surface reservoirs wherein
the fluids are stored within a vessel or reservoir having a cap or
cover over the reservoir. The fluids are then maintained at a
temperature sufficiently low so that the vapor pressures of the
fluids will not exceed pressures which the cap cover is designed to
withstand. For large volume storage such methods of utilizing
surface reservoirs are undesirable due to the expense in
constructing the reservoirs and the necessity of requiring a
portion of the surface of the land in order to provide for such
storage. Thus, means are constantly being sought whereby fluids can
readily be stored in natural formations of the earth which are
economical to use, and which will yield, on recapture, a desirable
quantity of the product stored within the formation.
Other prior art methods have utilized underground fluid storage
wherein the fluid is stored in large quantities of porous and
permeable rock at various depths beneath the surface of the earth.
Such underground storage is especially feasible in geographic areas
having depleted or semidepleted oil and gas reservoirs which can be
converted into fluid storage fields. In areas devoid of depleted or
semidepleted fields, aquifer/aquiclude systems associated with
structural and/or stratigraphic traps can be converted to fluid
storage reservoirs. These systems are called aquifer storage
facilities.
In the utilization of the underground storage facilities leakage
from the storage reservoirs to higher porous and permeable rock
beds frequently occurs through fractures or breaks in the caprock,
through nonsealing faults, and the like. Sometimes it is feasible
to collect leaking fluids from wells completed in the higher rock
beds and cycle the fluids back to the storage formation. However,
leakage control by fluid cycling is an economic burden on the
operation. Thus, other methods of fluid leakage control are highly
desirable.
Several methods for soil and porous rock impermeation are known in
the prior art wherein grout is employed to seal the fracture or
break in the caprock. However, the success of the grouting depends
on the complete invasion of the grout into the fracture channels,
pores, and pore channels of the rock body which is to be
impermeated. Due to the very nature of the rock structure a
complete invasion of the leakage channel by the grout is frequently
not achieved. Thus, the prior art methods which employ the grouting
technique many times are undesirable.
Even when a desirable fluid storage reservoir is located having an
anticlinal trap surrounded by structural conditions suitable for
fluid storage, the reservoir is frequently limited in storage
capacity by a saddle region or spill point. The capacity of such a
reservoir can be increased if gas migration beyond the saddle
region is prevented by regional impermeation of the storage
formation.
Further, frequently structural conditions favorable to fluid
storage cannot be found near population centers, even though
various porous and permeable rocks overlain by impervious
formations are encountered below the ground. Thus, it is very
desirable to provide a means to modify the underground structural
conditions so that a reservoir is formed which can be utilized for
the underground storage of fluids thus providing a supply source
near the population centers. Thus, it is highly desirable to
provide a method wherein the structurally high end of the porous
rock bed, the outcropping end, can be impermeated thus producing a
desirable reservoir for the underground storage of the fluid.
According to the present invention, a method is provided for
impermeating an underground formation for sealing fractures in the
porous rock and/or its caprock, by removing heat from the rocks and
the saturating water, thus causing the water to crystallize and
form a substantially impervious cryogenic structure.
Further according to the invention, a method of rock impermeation
and channel sealing is provided whereby the formation water is
cooled and contacted with a gas capable of forming gas hydrates so
that a substantially impervious rock hydrate structure is formed
thereby.
Further, a method is provided for sealing fractures and/or broken
formations in the upper impervious caprock covering a porous
geological structure by removing heat from the aquifer and/or
aquiclude water and thus producing localized cooling of the same so
that an impervious structure is formed which seals the broken or
fractured caprock structure.
Further according to the invention, a method is provided wherein
localized cooling of aquifer water is employed to form gas hydrates
in the rock pore spaces in order to employ the hydrates so formed
to seal the broken and/or cracked formations within the caprock
covering the desired storage area.
Further, according to the invention, a method is provided wherein
the heat flow through porous rocks and saturating fluids is
employed to initiate and maintain localized in situ freezing so
that the aquifer and/or aquiclude water is crystallized and an
impervious cryogenic structure is formed.
Further according to the invention, a method is provided whereby
the fluid storage capacity of the structure can be increased by
means of initiating and maintaining a localized in situ freezing
process whereby the water in the aquifer and/or aquiclude is
crystallized and an impervious cryogenic structure similar to a dam
is formed across the saddle region of the structure.
Drawings accompany and are a part of this disclosure. These
drawings depict preferred specific embodiments of the underground
storage in permeable formations of the invention, and it is to be
understood that these drawings are not to unduly limit the scope of
the invention. In the drawings,
FIG. 1 is a plan view of a portion of the ground surface intended
to illustrate the manner in setting out a method of this invention
in preparing for the construction of a flow barrier in a porous and
permeable formation or to repair fractures or breaks in its
caprock;
FIG. 2 is a cross section of the surface of the earth taken along
the line 2-2 of FIG. 1 illustrating the application of the method
of this invention to form a flow barrier to enlarge the fluid
storage area of an underground structure and to seal fractures or
breaks in the caprock above the formation being employed for fluid
storage;
FIG. 3 is a cross section taken along the line 3-3 of FIG. 1
illustrating the formation of a barrier according to the present
invention;
FIG. 4 is a cross section taken along the lines 4-4 of FIG. 1
illustrating the sealing of a fracture system in the caprock and
the like above the formation being employed for fluid storage;
FIG. 5 is a cross-sectional view of the earth depicting a typical
homocline showing the formation of storage conditions by local
impermeation methods of the present invention;
FIG. 6 is a cross section of the earth of a typical anticline
showing the use of directionally drilled wells for in situ
formation freezing and/or for forming a hydrate according to the
present invention;
FIG. 7 is a structural contour map of a typical anticline showing
the placement of gas hydrate flow barriers to seal fractures in a
caprock and to enlarge a reservoir by the formation of a damlike
barrier in the storage formation;
FIG. 8 is a schematic cross-sectional view illustrating a heat sink
well means employed by the process of the present invention;
FIG. 9 is a schematic cross-sectional view of a refrigerant
circulation system used according to the process of the present
invention.
In the following is a discussion and description of the invention
made with reference to the drawings whereupon the same reference
numerals are used to indicate the same or similar parts and/or
structure.
The discussion and description is of preferred specific embodiments
of the new process of our invention for forming formations of our
invention for storing fluids underground, and it is to be
understood that the discussion and description is not to unduly
limit the scope of the invention.
Referring now to FIG. 1, a plan view of a portion of the ground is
illustrated having contour lines 11 which indicate a saddle region
12 across which a barrier structure, 14, is to be constructed and a
crest region 16 which has a fracture system or breaks therein which
is to be sealed by local impermeation 17. In preparation for
building barrier 14 in saddle region 12 the present method can be
applied by drilling and completing a series of wells 18 at suitable
intervals so that wells 18 form a line which transverses the saddle
region 12. The bottom portion of wells 18 are positioned within the
aquifer zone which will be discussed in detail hereinafter.
Likewise, in preparation for the forming of impervious structure 17
to seal the fractures or breaks in the caprock covering the crest
of the anticline 16 the present method may be applied by drilling
and completing a series of wells 19 at suitable intervals so that
wells 19 form a line which approximately follows the system of the
fractures or breaks in the caprock. The bottom portion of wells 19
are positioned in the caprock in the immediate vicinity of the
fractures or breaks in the caprock as will be discussed
hereinafter.
Referring now to FIG. 2 a cross-sectional view of the ground taken
in lines 2-2 of FIG. 1 is illustrated. Underground structure or
formation 21 is shown comprising an aquifer zone 22, such as
sandstone, having an aquiclude zone 23, or a caprock zone, such as
limestone, positioned on top of aquifer zone 22. Likewise, a
sufficiently impervious lower layer aquiclude zone 24, such as
dolomite, is positioned below aquifer zone 22. Aquifer zone 22 is
the prospective fluid storage formation. However, it should be
understood that other types of impervious substances can make up
the impervious zones which are positioned above and below aquifer
zone 22. Other types of impervious materials which can serve as the
caprock which covers the prospective storage formation are well
known in the field of geology.
An aquifer as used herein is defined as a water-bearing bed of
stratum of underground porous and permeable rock, sand, or gravel.
In order for the formation to serve as a reservoir for fluid
storage use, such as gas storage, the aquifer must be overlayed by
beds of a sufficiently impervious aquiclude or caprock through
which stored fluids cannot escape.
Referring now to FIG. 2 in conjunction with FIG. 1, aquifer zone 22
is overlain by impervious aquiclude zone 23 and underlain by
impervious aquiclude zone 24 and is associated with a
doubly-plunging asymmetrical anticline. The anticline considered
for fluid storage joins a larger anticlinal structure through
saddle region 12. However, the anticline has a limited storage
capacity because its structural closure is limited by saddle region
12. Further, aquiclude zone 23 has a localized fracture system 26
near its crest, and thus allows fluids stored therein to readily
escape and as such is highly undesirable. Fracture system 26 near
the crest of aquiclude zone 23 can be discovered by geophysical
and/or nonsteady water pumping tests, tracer surveys, and the like
which are well known. Once fracture system 26 in aquiclude zone 23
is discovered fracture system 26 must be sealed if the reservoir is
to be utilized for fluid storage in aquifer zone 22. Likewise, it
is desirable to form an impervious structure, such as barrier 14,
across saddle region 12 to prevent the movement of stored fluids
from passing beyond the saddle region of the formation and thus
increase the storage capacity of aquifer zone 12. Thus, by the
method of the present invention of utilizing in situ freezing to
crystallize the aquiclude water to seal the flow channels of
fracture system 26, fluids stored within aquifer zone 22 are
prevented from escaping through the fracture system. Likewise, by
crystallizing aquifer water within saddle region 12 an impervious
wall structure, such as barrier 14, is formed and the movement of
stored fluids is restricted thus enlarging the capacity of aquifer
zone 22 so that a larger volume can be utilized for the storage of
fluids therein.
Referring now to FIG. 3 in conjunction with FIG. 2 the method of
forming the barrier 14, across saddle region 12 of underground
formation 22 will be discussed. A plurality of wells 18 are
completed in aquifer zone 22 and used as lower temperature heat
sinks relative to the surroundings in order to crystallize aquifer
water and form a cryogenic structure 14 in aquifer zone 22 up to
the desired distance away from each of wells 18. Such can be
accomplished by pumping a coolant, such as a refrigerant, down to
the bottom of wells 18 by pump units 27. As is readily apparent,
the barrier 14 is constructed by in situ crystallizing of the
aquifer water in aquifer zone 22. Cryogenic rock-water structure 14
prevents fluid migration beyond saddle region 12 and thus increases
the storage capacity of aquifer zone 22 by lowering the extreme
spill point of the formation. Thus, it is readily apparent that
without the use of cryogenic barrier 14 fluid storage in aquifer
zone 22 is confined, as viewed from the top, within contour lines
260 (see FIG. 1) wherein contour line 260 denotes points on the top
of aquifer zone 22 equidistant and vertically from a reference
plane, such as sea level, measured in feet. However, with the
formation of cryogenic barrier 14 the capacity of formation 22 is
increased by extending the gas-water interface to contour line 300.
Thus, by employing the method of forming an in situ cryogenic
barrier across the saddle region of the formation the total fluid
storage capacity of the aquifer zone is greatly enlarged.
Referring now to FIG. 4, in conjunction with FIG. 2, the method of
sealing fracture system 26 in aquiclude zone 23 will be discussed.
A plurality of wells 19 are completed in aquiclude zone 23 which
overlays aquifer zone 22 which is to be utilized for fluid storage,
such as natural gas storage. When fracture system 26 is found to be
present in aquiclude zone 23, and it is desired to utilize aquifer
zone 22 for natural gas or other fluid storage, fracture system 26
must be sealed. Wells 19 are set a desired distance apart and are
positioned so as to substantially follow the line of fracture
system 26. When wells 19 are completed a coolant, such as a
refrigerant, is pumped down the wells by pump units 27. The
refrigerant cools the formation and the aquifer and aquiclude water
is frozen in situ thus forming a cryogenic structure 17 which seals
fracture system 26 and thus prevents the stored fluids from
escaping aquifer zone 22 through fracture system 26.
Referring now to FIG. 5, structural formation 29 which can be
modified by the present invention and thus made into a suitable
fluid storage reservoir is illustrated. In this situation the
present invention involves the establishment of favorable storage
conditions in porous, permeable formation 31 of a homocline or
monocline in which successively younger rock strata dip away from a
central uplift, and in the case of a homocline are gently curved in
a direction perpendicular to the direction of the dip. When such a
formation as formation 29 is overlain by a successively impervious
formation 32, a cryogenic structure 14 can be developed in
permeable formation 31 by completing a plurality of heat sink wells
18 at a desired vertical distance from the surface of the ground so
that a refrigerant can be pumped into wells 18 by pump unit 27 and
thus cool the formation and crystallize the water to seal the
outcropping or upper end of permeable formation 31. Depending upon
the degree of dip, the thickness of permeable formation, and the
fluid storage capacity desired it may be desirable and necessary to
locate geological conditions where the permeable bed is also
underlain by an impervious formation, such as formation 33.
Referring now to FIG. 8, a schematic of the proposed heat sink
wells 18 and 19 employed according to the present invention are
shown. A suitable refrigeration system, such as a vapor compression
refrigeration system, can be used to pump an appropriate
refrigerant such as a freon, CO.sub.2, liquified petroleum gas
(LPG), and the like, down an insulated tubing 34, to produce a
cooling effect to freeze the water of the aquifer surrounding the
well bore. When the refrigerant reaches the last joint of tubing 34
it is throttled by a throttle means 36, so that some of the
refrigerant flushes into vapor during the throttling process. The
remainder of the refrigerant evaporates inside the bottom section
of casing 37 by extracting heat from the rock matrix and water or
ice in the pore spaces, and the evaporated refrigerant flows up
through the annulus between insulated tubing 34 and of the
insulated long string casing 37, and enters compressor 38 as a
saturated or superheated vapor at low pressure. Following
compression it rejects heat in a condenser and begins its cycle
down tubing 34 again. The string of casing 37 is preferably
thermally insulated from the formations above the storage formation
by an insulation material, such as an organic or inorganic liquid,
and the insulation material is placed between the long string of
casing 37 and short strings of outer casing 39 above packer 41 but
below Christmas tree 42. Low temperature resistant high strength
cement 43 is employed to bind the casing strings to the formation
through the caprock and the storage zone. The annular space between
the overlying beds and the outer casing string is filled with
casing pack material 44 which are well known in the drilling art
and as such are believed sufficiently well known. Surface conductor
casing 46 is cemented with low temperatures being considered. In
some areas intermediate strings of casings may be necessary and in
others it may be possible to eliminate the outer string of casing
completely and insulate only the long string of casing from
formation by using low conductivity casing packs above the cement
top. However, such will vary widely depending upon the area wherein
the formation is located, the depth of the formation, and the type
of the formation.
The spacing and the number of wells 18 and 19, the refrigerant type
and circulation rates, the duration of time for the propagation of
approximately egg-shaped water crystallization and final merging
into an impervious cryogenic rock-water structure, depend upon a
multitude of factors, such as chemical, mechanical,
thermoproperties of the formation, and the in situ water,
structural conditions, formation temperature, formation pressure,
and the like. Obviously, the method of porous rock freezing
requires close welded spacing, such as measured in tens of
feet.
Referring now to FIG. 6 a plurality of wells 47 are illustrated
which have been drilled by a directional drilling process in order
to provide greater contact area between the formation of interest
and heat sink wells 47. However, the use of directionally drilled
wells 47 will depend upon the depth of the formation and its
structural attitude. Thus, the decision to employ direction
drilling in order to provide heat sink wells would depend on the
circumstances throughout the reservoir being prepared.
Referring now to FIG. 9 a refrigerant circulation system for
forming a cryogenic structure according to the present invention is
depicted when it is desirable to employ wider well spacing. A line
of refrigerant injection wells 48 and withdrawal wells 49 are
drilled into the aquifer or aquiclude zone where the water-rock
system is to be locally frozen. Injection wells 48 and withdrawal
wells 49 are cased through the formation of interest and perforated
selectively at a level corresponding to an approximately half way
point between the top and the bottom of the cryogenic structure to
be formed. By this limited entry perforation technique, selective
fracturing at each well, designated by numeral 51, flow channels 52
of least resistance are established between any pair of injection
wells 48 and withdrawal wells 49. The liquid refrigerant is pumped
by pump 53 through conduit 54 into tubing 56 of injection wells 48
and withdrawn by submergible pumps 57 located in each withdrawal
well 49 together with formation water. The liquid refrigerant and
the formation water is then pumped up tubing 58 and through conduit
59 and into pump means 53. The cycling of refrigerant through the
formation between the wells is first carried on without cooling and
heat rejection at the surface. The purpose of first cycling the
refrigerant through the formation without cooling is to saturate
flow channels 52 formed by hydraulic fracturing of the rock matrix
immediately surrounding the flow channels with refrigerant. During
the refrigerant circulation process at normal temperatures the
water cut of the refrigerant withdrawn from the formation will
steadily decline to a negligible level or it will stabilize. Water
is removed at the surface by separators, (not shown), and the
separated refrigerant is sent to a condenser to begin another
cycle. When the water cut stabilizes at a low value, the
refrigerant is gradually cooled at pump 53. The refrigerant picks
up heat from high temperature heat sources, i.e., the formation
rock matrix and water, while it flows through the channels of the
formation, and it rejects heat at the low temperature heat sink,
the surface separation and refrigeration systems. A refrigeration
plant such as a vapor pressure refrigeration plant can be employed
to cool the refrigerant circulating through the formation.
When the temperature of the refrigerant in the flow channels is
reduced below the freezing point of the formation water, the
cryogenic structure begins to form, and the interface between the
ice region and the cold water region propagates away from the flow
channels. Since the refrigerant saturates the flow channels but
does not freeze at the operating pressure and temperature of the
system, it continues to circulate between pairs of wells, such as
injection wells 48 and withdraw wells 49. Thus, the refrigerant
acts as a low temperature heat sink relative to the formation.
The refrigerant employed by the above-mentioned process can be any
suitable refrigerant which is known in the art. However, it is
preferred that the refrigerant selected be water immiscible having
a density equal to or slightly less than the density of the
formation water and a viscosity higher than the viscosity of the
formation water. Further, the refrigerant should be in the liquid
phase during its injection into the wells and its flow through the
formation and have high heat conductivity. The requirement of the
viscosity of the refrigerant being higher than the viscosity of the
formation water is a compromise between minimization of viscous
fingering and high pumping costs required to deliver the
refrigerant to the bottom of the input wells and thus into the
formation. The method of utilizing a series of refrigerant
injection wells and refrigerant withdrawal wells has a definite
advantage over the before-mentioned heat sink well method, wherever
applicable, in that the utilization of the refrigeration injection
wells and withdrawal wells provide greater area of exposure between
the heat source and the heat sink, and utilizes both conduction and
convection heat transfer principles.
Refrigerant injection wells 48 are equipped with insulated tubing
56 and are isolated thermally from the main body of casing 61 by an
organic or inorganic insulating material which is placed in the
annulus above the casing to tubing packer 62. Casing 61 is cemented
63 up to a desired point above the caprock, and the formation to
casing annulus above the cement top is filled with casing-pack
material of low heat conductivity 64. The surface conductor casing
and the intermediate strings of casing are not shown for the sake
of simplicity but are well known in the drilling art.
Refrigerant withdrawal wells 49 are also equipped with the
insulation lined tubing 58, submergible pumps 57, well control
equipment 66, and surface flow lines or conduits 59. Refrigerant
withdrawal wells 49 can be completed with one string of casing 67
cemented to the storage formation and the aquifer zone and isolated
from other formations by insulating casing-pack 68. Likewise, a
construction similar to the heat sink wells shown in FIG. 8 can be
used for increased protection from the possibility of leakage of
the circulating fluids and for providing better thermal insulation
from the strata above the storage formation and its caprock.
Intermediate and surface conductor casing strings are likewise not
shown for the sake of simplicity.
Following the stabilization of the water cut and the freezing of
the water surrounding the refrigerant flow paths in the formation,
one may remove the submergible pumps from the withdrawal wells, and
thus rely on the surface pumps, to circulate the refrigerant at
sufficient flow rate in order to maintain the cryogenic rock
structure so formed within the boundaries determined by design and
subsurface conditions.
Referring now to FIG. 7, another embodiment of the present
invention will be discussed which also employs the removal of heat
from the formation and the formation water surrounding the area
wherein the in situ formed barrier is to be constructed in order to
seal a fracture in the caprock or enlarge the total area which can
be employed for storage of fluids by the continuation of a barrier
in the saddle region of the formation as previously discussed with
reference to FIGS. 1 and 2. Certain gases such as CO.sub.2,
H.sub.2S, SO.sub.2, and natural and manufactured gases consisting
chiefly of light parafinic hydrocarbons form solid gas hydrates
when the gases come into contact with water in sufficient amounts
when certain conditions as to temperature and pressure exist. It is
known that the gas hydrates are formed at temperatures above the
freezing temperature of the water.
Hydrocarbon hydrates are solid solutions of the hydrates of lower
hydrocarbons which are capable of forming hydrates. High velocity,
turbulance, pressure pulsations additives such as alcohol or acetic
acid, and inoculation of small hydrate crystals accelerates the
hydrate formation. It has also been found that the formation of gas
hydrates with ice proceeds at a negligible rate.
A local gas hydrate barrier to fluid flow can be developed in
porous and permeable bodies suitable for fluid storage by bringing
low temperature water into contact with a hydrate forming gas,
under favorable temperature, pressure and agitation conditions. For
example, the technique of impermeation by gas hydrate 71 can be
used to seal fracture system 26 in caprock 23 of underground
structure 21 shown in FIGS. 2 and 7, to form barrier 14 at
anticline saddle region 12, of aquifer zone 22. Likewise, gas
hydrate 71 can be utilized to form the flow barrier in porous beds
on a homocline or monocline (see FIG. 5). If the local impermeation
is not necessary until the stored gas approaches the zone of
leakage or spill, the gas front can be brought into contact with a
cold water zone maintained by circulating chilled water between
pairs of injection and withdrawal wells 48 and 49, respectively, so
that hydrates are formed in situ.
If the stored gas is one which does not form gas hydrates, or if
the local impermeation is to accomplished before the stored gas
approaches the leakage or spill zone, other gas, such as CO.sub.2
or light hydrocarbons can be injected into the formation through
additional injection wells to provide hydrate forming gas. These
gas injection wells are located between the approaching front of
the stored gas and the line of cold water circulation wells 48 and
49.
Injection wells 48 and withdrawal wells 49 for cold water
circulation can be similar to the refrigerant cycling system
depicted in FIG. 9 with the exception that the circulating
refrigerant is the formation water chilled at the surface and
hydraulic fracturing of the formation between the wells may or may
not be necessary. The circulation of the water at high rates
between the wells is for the purpose for creating agitation in the
formation in addition to the local cooling of the porous rocks and
the contents of its pores. Thus, by the cooling effect so created,
coupled with the agitation in the formation the gas hydrates of the
gas are formed. The steam-jet refrigeration techniques are
especially suitable to chill the water at the surface
facilities.
Thus, it is readily apparent that by utilizing the method of the
present invention of porous media impermeation by in situ freezing
of native or added water, and by gas hydrate formation desirable
results can be obtained wherein underground storage of fluids can
be achieved in prospective storage reservoirs with locally
fractured caprocks and/or limited by saddle regions. Likewise, the
method for sealing fractures and forming the barrier structure of
the invention is by no means limited to the control of leakage or
spill conditions in gas storage reservoirs. Rather, the method can
be utilized whenever and wherever porous and impermeable rocks are
to be locally impermeated to fluid flow and the economics and
technical feasibility of the application is ascertained.
Thus, the foregoing discussion and description is made in
connection with preferred specific embodiments of the method of
underground storage in porous media of the invention. However, it
is to be understood that the discussion and description is only
intended to illustrate and teach those skilled in the art how to
practice the invention and such is not to unduly limit the scope of
the invention which is defined in the claims set forth
hereinafter.
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