A method of plugging holes, in particular the plugging of drill
holes in the earth. The method utilizes a tubular capsule filled
with coarse ground sodium bentonite. The capsule, when inserted
into the hole, sinks through any mud or slurry material within the
hole to rest at the bottom of the hole. If the hole is filled with
overly dense material, a rod may be used to force the capsules to
the bottom of the hole. The capsule is constructed of a water soluble
material and includes a plurality of slots cut along its exterior
wall to facilitate expansion and to allow liquid to easily permeate
the container. A plastic cap on its upper end allows rods to be
forced thereagainst to push the capsule downward without puncturing
the capsule. Alternatively, layers of sand may be interspersed with
layers of bentonite nodules.
What is claimed is:
1. A method for plugging a drill hole having an opening at a surface,
comprising the steps of:
introducing coarse ground chemically unaltered sodium bentonite
nodules into the hole;
retarding an expansion rate at which said bentonite nodules expands
to set said expansion rate at a rate that provides a predefined
time period for said bentonite nodules to reach a bottom of the
hole before expanding to a plugging state at which swollen bentonite
nodules plug the hole; and
once said bentonite nodules reach the bottom, allowing said bentonite
to expand to said plugging state to plug the hole.
2. A method according to claim 1, wherein said hole is at least
200 feet deep, said retarding step enabling said bentonite nodules
to expand at a rate at which said nodules sink through at least
100 feet of liquid before increasing 100% in volume.
3. A method according to claim 1, wherein said hole is an oil well
drill hole lined with a casing, said introducing step filling a
portion of said casing with bentonite nodules.
4. A method according to claim 3, further comprising the step of
filling a void about an exterior of an upper portion of said casing
with said bentonite nodules.
5. A method according to claim 1, further comprising the steps
filling a bottom portion of the hole with a layer of bentonite
filling an intermediate portion of the hole with a layer of non-bentonite
6. A method according to claim 1, further comprising the step of:
alternately staging multiple layers of bentonite nodules and sand
within the hole.
7. A method according to claim 1, further comprising the step of:
covering said bentonite nodules in the hole with a layer of material
to resist upward migration of said bentonite nodules during expansion.
8. A method according to claim 1, wherein said retarding step reduces
said expansion rate below an expansion rate of finely ground bentonite
particles having a diameter no greater than 3/8 inches.
9. A method according to claim 1, wherein said retarding step includes
forming bentonite nodules have a diameter of at least 7/8 inches
before introducing said nodules into the hole.
10. A method according to claim 1, wherein said retarding step
includes placing said bentonite nodules in a water soluble capsule,
and introducing said capsule into the hole, said capsule partially
shielding said nodules from liquid within the hole for a predefined
time, during which said capsules sink to the bottom before exposing
the nodules entirely to liquid.
11. A method according to claim 1, further comprising the steps
placing said nodules in a sealed canister which isolates said nodules
from liquid within the hole;
lowering said canister into the hole to a desired depth; and
discharging said nodules from said canister.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to filling or plugging
of drill holes. In particular, the present invention relates to
an improved method for plugging an abandoned drill hole within the
earth and for maintaining the plug integrity indefinitely.
2. Description of the Related Art
It has been well known to provide deep (on the order of several
hundred feet) drill holes within the earth for a variety of purposes.
Such holes are typically formed during a standard oil well drilling
operation. The drill hole is formed and then lined with a casing.
The drill hole passes through several compositions, such as hard
compacted soil, clay, loose sand, and other typical geologic material,
in addition to one or more water bearing layers. Such water bearing
layers may represent a saline water source or a fresh water aquifer.
Once an oil reserve is exhausted, the oil well hole is abandoned.
If left unattended, gases and fumes escape through the hole into
the atmosphere. Further, the casings erode and crack, thereby causing
damage to the aquifier levels and the like.
In particular, a fresh water aquifer may "leak" downward
through the casing and hole into a fracture or uncharged zone, causing
loss of water from the aquifer. A drill hole extending between a
saline water source and a fresh water aquifer may allow commingling
of these water supplies, damaging both. Additionally, contamination
from the surface may cause damage, such as surface rain water passing
downward through the hole and casing into a fresh water aquifer.
To overcome these problems it has been known to plug the casings
and drill holes with concrete. However, concrete has proven less
than effective in maintaining the integrity of the seal throughout
the casing over long periods of time. First as the concrete dries,
it contracts thereby separating (pulling away) from the casing.
Second, as the concrete ages it cracks. These age cracks and contractions
during curing produce voids within and about the concrete which
allow gases to escape and allow contamination of the water level.
Hence, concrete plugs have met with limited success.
In the past, finely ground chemically unaltered sodium bentonite,
has been proposed for filling shallow holes of up to 30 meters or
100 feet deep. Heretofore, a system or method has not been proposed
which effectively utilizes sodium bentonite to fill holes several
hundred feet deep, such as oil well holes. A report entitled "Axial
Shear Strength Testing of Bentonite Water Well Annulus Seals"
by Fred Lee Ogden and James F. Ruff published by Colorado State
University, 1989, discusses the use of bentonite as an annulus sealant.
Past usage of bentonite is explained in a report entitled "Experiments
in Subsurface Applications of Bentonite in Montana" by John
Wheaton, Steve Regele, Bob Bohman, Dave Clark and Jon Reiten, published
by Montana Bureau of Mines and Geology, 1994. Both of the foregoing
reports are incorporated herein by reference.
A first and simple method for placing the bentonite in a shallow
hole without a casing is to simply pour a small granular form of
dry bentonite (i.e., less than 3/8" in diameter) into the drill
hole from the surface. The bentonite falls downward through the
drill hole, filling the hole from the bottom upward. However, where
the drill hole passes through unconsolidated material, such material
may form a cave in at the sides of the drill hole, forming a plug
at a position spaced above the bottom of the hole. In such cases
the small granular bentonite will simply fill the hole from the
plug upward and not pass downward to the bottom of the hole to fully
plug the hole. Additionally, it is not possible to pour bentonite
in the foregoing manner into drill holes passing through high volume
artisan flows, or in drill holes using a dug pit (i.e. where a bentonite
slurry has been employed to maintain wall integrity in the hole).
When the small or finely ground bentonite of 3/8" in diameter
is poured into the hole, it begins to expand when exposed to water.
The conventional finely ground pouring method is adequate for shallow
holes since the bentonite sinks to the bottom of the hole before
a significant amount of swelling occurs. However, if bentonite is
poured into deep oil well holes, the hole may contain several hundred
feet of water.
In general, high-grade and low-grade bentonite chips fall at an
average velocity of 1.0 ft/sec. Smaller bentonite granules of 3/8"
in diameter or less have more surface area per unit weight, and
therefore fall at a slower rate. This is due to the fact that smaller
bentonite granules are typically less dense than larger chips. For
instance, a bentonite granule with a diameter of 3/8" may have
a volume of 0.5 cm.sup.3 and weigh 1.01 grams, while a bentonite
chip with a 3/4" diameter weights 3.65 grams and has a volume
of 1.50 cm.sup.3. In this example, the smaller granule has a density
of 2.02 gr/cm.sup.3 and the larger chip has a density of 2.43 gr/cm.sup.3.
Further, once hydration begins, the density of the granule decreases
as the granule swells. Similarly, the fall velocity of the granule
in water decreases at a rate of about 0.009 ft/sec per minute of
fall. For instance, a granule having an initial fall velocity of
just under 1 ft/sec, after 44 minutes of exposure to water, with
fall at approximately 0.6 ft/sec. As the granule absorbs water,
its density decreases approaching the density of water further slowing
the fall velocity. These factors prevent small granules from effectively
being used to plug deep holes with several hundred feet of water
The conventional form of bentonite poured into shallow holes is
formed of small granular particles having a diameter of no greater
than 3/8 inches. Such small material has proven ineffective when
poured into holes having high fluid flow rates therethrough and
when poured into deep holes retaining a high liquid level (i.e.,
a long distance between the hole bottom and liquid level). As the
small granular material passes through the liquid, it begins to
hydrate and swell. Granular bentonite having a diameter of no greater
than 3/8 inches swells quickly and reaching its liquid limit (i.e.,
the saturation point of the bentonite). If the bentonite swells
beyond its liquid limit, the bentonite turns to a slurry state.
At the liquid limits, the bentonite lacks sufficient additional
swelling ability to achieve seal within the hole. Hence, conventional
small granular material is ineffective for filling deep holes. Additionally,
the conventionally sized granular bentonite falls through the liquid
in the hole in an unconcentrated state. Each granular particle is
afforded a large portion of the cross-sectional area of the hole
within which to expand. Sodium bentonite will continuously expand
until it is restrained by its surrounding environment or starved
for water. Once the bentonite expands to a size several times its
dehydrated size, the conventionally sized bentonite granule loses
its solid structure and turns to a slurry liquid state. Once sodium
bentonite hydrates to the point that it turns to a slurry liquid,
the granule becomes ineffective at plugging holes.
Past systems that use the conventional sized bentonite particles
have prevented degradation to this slurry state by filling the hole
with dehydrated granular particles before each individual particle
is allowed to expand substantially. To do so, the granules are poured
into shallow holes or holes having very little liquid standing therein.
In shallow holes, conventionally sized particles collect in the
bottom of the hole before expanding substantially. However, when
conventionally sized granular bentonite is poured into deep holes
and through deep liquid levels, each individual particle turns to
a slurry state before reaching the bottom of the hole and collecting
with the other falling particles.
A second and more reliable method is to insert a conduit into the
drill hole and pass a slurry of bentonite through the conduit while
slowly withdrawing the conduit. For example, U.S. Pat. No. 5,013,191
to Kitanaka discloses a special auger which is rotated in the normal
manner to drill the hole, and then is fixed against rotation while
the bentonite slurry is passed through a central hole in the auger
and the auger is withdrawn. While this method is effective, it requires
the use of a special and expensive auger and is limited to shallow
An alternative slurry/conduit method consists of simply inserting
a standard 11/2 inch PVC pipe into the drill hole and passing the
slurry through this pipe. While this method does not require the
use of a special auger, if the hole has been plugged as noted above,
the method requires an initial step of drilling with an auger to
clear the plug prior to inserting the pipe. Again, this system is
limited to shallow applications.
Moreover, problems have been encountered with the above systems
when using a mixture of heavy bentonite gel water slurry. The slurry
mixture is used while drilling the holes to keep the walls of the
drill holes from sluffing inward, thereby avoiding the need to reconstruct
stuffed areas within the hole. After abandonment, the slurry stands
within the hole. The density of the slurry is sufficiently close
to the density of conventional granular bentonite which is poured
directly into the hole, that the slurry holds the granular bentonite
in suspension proximate the top section of the hole. Thus, when
the granular bentonite is poured into the hole, it does not sink
to the bottom, and thus does not plug the hole from the bottom up.
Moreover, the foregoing systems are ineffective when used with
wet auger drilled holes which utilize water injected from the surface
downward into the hole. While drilling the hole, the agitation of
the auger stem, when combined with the injected water, creates a
heavy native mud material that remains within the hole after drilling
is completed. The density of this mud is relatively high, with respect
to that of bentonite granular material, and thus holds the bentonite
granular material in suspension at the top of the hole.
Finally, in any plugging application (shallow or deep) utilizing
bentonite, the bentonite retains the ability indefinitely to expand
or contract depending upon its degree of hydration. Thus, the bentonite
remains in a swollen state to plug the hole so long as it remains
adequately hydrated. If the bentonite dries out, it contracts, thereby
compromising the seal within the hole. Therefore, it is necessary
to ensure that the bentonite is continuously and indefinitely exposed
to liquid or at least used in an application designed to prevent
liquid loss. Past shallow applications using fine bentonite have
failed to acknowledge or address this problem, in part due to the
fact that shallow holes are generally exposed to a natural water
table which provides a continuous source of liquid. Further, past
shallow fine bentonite applications utilize a column of bentonite
less than 100 feet long within a hole which does not necessarily
contain a casing. In these shallow applications, natural water from
the water table and run-off water from the surface provide adequate
and indefinite hydration of the entire bentonite column.
However, in deep holes much longer columns of bentonite are required.
Plus, when a hole casing is used, so long as it retains its integrity,
the interior of the column is isolated from ground water and underground
water tables. Hence, any bentonite within the column may dry out
and contract, thereby compromising the seal integrity.
A need remains within the industry for an improved method and apparatus
for plugging abandoned drilled holes. It is an object of the present
invention to meet this need.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of plugging
holes which is simple, inexpensive and effective.
Another object of the present invention is to provide such a method
which may reliably seal water supplies from contamination and loss
in holes passing into the earth.
Another object of the present invention is to provide such a method
which will clear any plugs from the hole and reliably pass plugging
material to the bottom of the hole.
It is a further object of the present invention to provide a plurality
of capsules containing bentonite chips, of which the capsules may
be dropped into a hole and ensured to sink to the bottom of the
It is a corollary object of the present invention to provide a
capsule which affords minimal interference with expansion of the
bentonite therein to fill the hole, such interference being minimized
through the inclusion of a plurality of slots cut through the outer
casing of the capsule which also function to maximize communication
between the liquid outside the capsule and the bentonite inside.
Another object of the invention is to prevent the bentonite, once
used to plug a hole, from dehydrating and compromising its sealing
A corollary object of the invention is to provide layers of sand
or gravel between layers of bentonite to retain moisture which maintains
the bentonite in an expanded state at all times.
These and other objects are achieved by a method of plugging holes,
in particular the plugging of drill holes in the earth. The first
method consists of inserting an auger, having a bit at the lower
end and a central rod about which is formed a helical land, into
the drill hole and rotating the auger to cause material to be conveyed
upward and out of the drill hole. As the auger is moved downward
this will cause any plugs or debris within the hole to be removed.
After the auger has been inserted to a sufficient depth the rotation
of the auger is reversed, and bentonite or other plugging material
is poured into the drill hole about the auger. The reversed rotation
of the auger will cause the plugging material to be conveyed downward
along the drill hole and compacted at the bottom. As the drill hole
is filled with compacted plugging material the auger is slowly removed
to form a consistent reliable plug of the plugging material. Alternative
embodiments are used to fill the hole, including the use of encapsulated
bentonite, large nodule sized bentonite and a hollow canister remotely
dumped into the hole. Also, the bentonite may be layered with sand
or gravel sections.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects and features of the invention noted above are explained
in more detail with reference to the drawings, in which like reference
numerals denote like elements, and in which:
FIG. 1 is a cross sectional view illustrating an abandoned drill
FIG. 2 is a cross sectional view illustrating the clearing of the
drill hole according to the present method;
FIG. 3 is a cross sectional side view showing the conveyance of
plugging material through the abandoned drill hole to fill same;
FIG. 4 illustrates an alternative embodiment in which capsules
are dropped into a drill hole to plug same;
FIG. 5 illustrates an application of the alternative embodiment
which uses a separate line to gauge and control the application
of capsules in overly deep holes;
FIG. 6 illustrates an exemplary cross-sectional side view of a
capsule according to the second embodiment;
FIG. 7 illustrates an alternative embodiment in which large nodules
of bentonite are poured into a drill hole;
FIG. 8 illustrates an alternative embodiment in which a large canister
is lowered into a hole and remotely opened to drop sodium bentonite
into the hole; and
FIG. 9 illustrates an alternative embodiment in which layers of
bentonite are separated by layers of sand or gravel.
BRIEF DESCRIPTION OF THE INVENTION
With reference to FIG. 1, there is shown a mass of material 10
having an outer surface 12. The mass 10 may be uniform, or formed
of a plurality of disparate layers. In the embodiment shown in FIG.
1, the mass 10 is the earth, and includes a plurality of layers
of geologic material formed in layers roughly parallel to the surface
12. For example, the upper surface 12 would be formed of soil with
the lower layers formed of shale, sand, limestone, and other typical
materials. Additionally, such layers may include one or more water
sources 14 such as a saline source or a water aquifer.
A drill hole 16 extends into the mass 10 from the surface 12. The
hole 16 extends through several of the layers, possibly including
one or more water source layers 14. As may be envisioned, where
the hole 16 passes through one or more of the water bearing layers
14, such water bearing layer is subject to contamination from material
falling into the hole 16 and from other water bearing layers 14,
and is also subject to loss due to flowing downward through the
hole 16 and into a fracture or uncharged zone, or of passing upwardly
and out of the hole 16 in the case of a high volume artisan flow,
all as indicated by arrows in FIG. 1. Another common feature of
such holes 16 is a plug formation 18. The plug formation 18 is formed
of a mass of material which has broken away from the side walls
of the hole 16 and has become interengaged to block the hole 16,
even though the remainder of the hole below the plug may be open.
As noted above, when the purpose of the hole 16 has been completed
the hole may be termed abandoned. For such abandoned holes it is
highly desirable to plug the holes, typically with bentonite (of
the type indicated above), to protect the water bearing layers 14.
To effect such a plugging there is introduced into the holes 16
a standard auger drill having at its lower end a bit 20, an elongated
central shaft 22 and a helically extending land formed on the exterior
of shaft 22. The shaft and land are formed in segments which may
be connected end-to-end to provide an auger drill of the proper
As is known in the art, the auger drill is rotated in the direction
of arrow 26 as it is forced downward into the hole 16 (or into the
solid mass 10 to form the hole 16) such that the helical lands 24
will engage the particulate material generated by bit 20 and convey
the particulate material towards the surface 12 with the side walls
of the hole 16 acting as a surrounding sleeve. Once upon the surface
12 the particulate material will fall from the helical land and
accumulate on the surface 12 adjacent the hole 16.
As may be readily envisioned from FIG. 2, the use of the standard
auger drill will clear any plug formations 18 present in the hole
16. Additionally, the auger drill is typically somewhat flexible,
such that it may more readily follow existing abandoned holes 16,
rather than drilling a separate or new hole. As such, continued
rotation and insertion pressure upon the auger drill will eventually
result in the drill extending the desired depth into the hole 16.
If desired, the auger drill may continue to be rotated without downward
pressure, such that all or most material engaged within the helical
land is transported to the surface 12. Once the desired amount of
particulate material has been removed from the hole and helical
land, rotation of the auger drill is stopped.
At this point the plugging material 28, preferably bentonite as
described above, is poured into the hole 16 at the surface 12 while
rotating the auger drill in the opposite direction, as indicated
by arrow 30. Due to the opposite rotation of the auger drill, the
helical land 24 will force material downward into the hole 16. Any
remaining material within the helical land and the plugging material
28 will be thus be conveyed downward. At the lower end of the helical
land this material will fall downward due to gravity.
As the bit 20 of the auger drill is adjacent the lower end of hole
16 due to the previous steps, and is preferably below any water
bearing layers 14, the remaining particulate material and the plugging
material 28 will be reliably displaced into the bottom of hole 16
below the water bearing layers 14. The process will continue, with
additional plugging material 28 falling below the auger drill, eventually
filling the volume below the auger drill. Continued rotation of
the auger drill and introduction of plugging material 28 will eventually
cause compaction of the plugging material for even greater reliability.
Once the volume below the auger drill bit 20 has been filled and
possibly compacted, the rotation in the direction of arrow 30, and
introduction of plugging material 28, is continued as the auger
drill is raised out of hole 16. This raising of the auger drill
may be at a slow continuous rate or may be in incremental steps.
Regardless of the manner of raising, the overall rate should be
such that a sufficient amount of the plugging material 28 is deposited
along the hole 16, possibly with compacting as described above.
This process will continue until the hole 16 has been filled with
the plugging material 28 at least to a level above the water bearing
layers 14. Of course, this process could continue until the entire
hole 16 has been filled with plugging material 28, or at least substantially
filled such that plugging material may be introduced easily, without
voids, after total withdrawal of the auger drill.
As may be readily envisioned, the present method will reliably
remove any debris plugs from the hole, and will reliably place the
plugging material along the desired length of the hole 16, without
the need to remove the auger drill. The present method therefore
provides a high-quality plug without high labor costs and without
expensive specialized drills. However, in many situations augers
are not useful or necessary when plugging holes. FIGS. 4-9 is illustrate
alternative embodiments which may be used in place of an auger system,
such as for extremely deep holes and the like.
FIGS. 4-6 illustrate an alternative embodiment which utilizes a
plurality of capsules 50 (FIG. 4) to fill each abandoned hole 70.
The capsules 50 contain coarse ground sodium bentonite 55 and have
sufficient density to displace free standing material, such as water,
slurry and mud, within the hole. The capsules 50 sink through the
free standing liquid within the hole to assure that the capsules
(and thus the bentonite) fill the hole from the bottom up. The capsules
are inserted one after the other until the hole is filled to the
desired level. If the hole contains mud having a density greater
than that of a capsule 50, the user may push the bentonite capsules
through the mud with one or more interconnectable rods (not shown)
abutted against the rear surface of each capsule.
As shown in FIG. 6, each capsule 50 includes a liquid soluble exterior
cylindrical wall 52, such as one formed of cardboard, a water soluble
material and the like. The cylindrical wall 52 includes a plurality
of slots 54 cut therein. In the preferred embodiments each slot
extends in a direction substantially parallel to the longitudinal
axis of the cylindrical wall 52. In the preferred embodiment, the
slots 54 are aligned end to end with one another and separated via
spacing wall segments 56. The dimensions of the slots 54 and wall
segments 56 may vary, so long as adjacent ends 58 of slots 54 are-located
proximate one another and are separated by less than a maximum wall
segment distance 63. This maximum segment distance 63 is dictated
by the dimensions of the capsule and the structural integrity of
the material forming the wall 52.
By way of example only, if a cardboard wall 52 is included with
a thickness of approximately 1/4 inch, it is preferable to utilize
a segment distance 63 of no greater than two inches and preferably
less than one inch. When the sodium bentonite 55 expands, the wall
segments 56 fracture between adjacent slots 54 to minimize the confining
forces created by the wall 52 and to facilitate the expansion of
the sodium bentonite 55 within the hole. This fracture is illustrated
in FIG. 6 via the dashed line 60. Hence, the slots and wall segments
54 and 56 regulate the expansion rate to an extent. The slots 54
also provide a vehicle for allowing the liquid within the hole to
penetrate the capsule and hydrate the sodium bentonite 55.
As shown in FIG. 6, the wall 52 includes a lower end 62 which may
be tapered to form a point. This point may be formed by merely crimping
the cylindrical side wall at the lower end 62. The point enables
the capsule to propagate easily through the material within the
hole. A cap 64 is provided at the upper end of the wall 52 to close
the capsule 50. The cap 64 may be formed of plastic or a similarly
rigid material and is removable to facilitate filling of the capsule
with sodium bentonite. As shown in FIG. 6, a plurality of vent holes
61 are also provided within the cylindrical wall to prevent moisture
buildup within the capsule 50 during storage and to allow liquid
to enter and air to leave the capsule 50 when in use.
FIGS. 4 and 5 illustrate two alternative methods for inserting
the capsules 50 into a hole. FIG. 5 illustrates an extremely deep
hole 70, such as an oil well hole, containing water or a similarly
viscous liquid 71 up to a level 72. The liquid within the hole 70
has a density less than that of a capsule. 50 and thus the capsule
50 sinks through the liquid without assistance. While loosely poured
coarse bentonite may not have a density greater than certain liquids
71 in the hole, the weight of a capsule with the closely packed
bentonite therein affords such a density. Hence, the weight of the
capsule plus the weight of the bentonite therein overcome the frictional
forces exerted upon the exterior of the capsule by the heavy liquids
71, and the capsule 50 sinks.
FIG. 5 illustrates a relatively deep hole, such as 50 feet or greater,
with a liquid level 72 substantially below the ground level. In
this situation, it may be preferable to attach a wire line or twine
74 to the bottom most capsule and lower same into the hole 70 at
a controlled rate, thereby preventing the impact with the liquid
level 72 from breaking the capsule. A plurality of capsules 51 may
be inserted immediately after the lowermost capsule and piggybacked
downward into the hole. Optionally, piggybacking capsules need not
be formed with a tapered lower end. The line 74 also allows the
user to measure the depth to which the lowest capsule 50 sinks.
Once the capsule 50 has sunk to the bottom of the hole, the user
cuts the line 74.
In an alternative system, with holes having a higher liquid level
72 and when the user need not measure the depth to which the capsule
50 sinks, the line 74 is omitted. Instead, the capsule 50 is simply
inserted into the hole and allowed to sink through the material
76 in the hole 70. If the material 76 has a density greater than
that of the capsules 50, the user may insert one or more rods into
the hole to push downward upon the top end cap 64 of each capsule
to force same to the bottom of the hole 70.
Once the capsules 50 are inserted into the hole, the water soluble
exterior wall 52 begins to deteriorate rapidly. Simultaneously,
the walls 52 and slots 54 allow liquid to enter the capsule and
initiate rehydration. As the walls deteriorate and the liquid seeps
through the slots 54, the water begins to hydrate the sodium bentonite
55. As the sodium bentonite 55 hydrates, it swells causing interior
pressure upon the cylindrical wall 52. This pressure causes the
fracture 60 between each of the slots 54 until each of the slots
54 in one line communicate with one another without any separating
wall segments 56. The wall 52 continues to deteriorate as the sodium
bentonite 55 expands until the sodium bentonite fills the entire
inside diameter of the hole 70 creating a solid plug which prevents
movement of the liquid within the hole.
Optionally, the slots 54 may be aligned in a staggered arrangement
about the perimeter of the cylindrical wall 52 while maintaining
wall segments 56 within the desired dimension between adjacent ends
58 of adjoining slots 54. As a further option, a plurality of rows
of slots 54 may be used and aligned about the perimeter of the cylindrical
Preferably, the sodium bentonite 55 is formed of coarse, dry, dehydrated,
ground chips having a dimension between 2 inches and 1/4 inch in
diameter, and optimally between 7/8 inch and 1 inch in diameter.
The coarse, ground bentonite 55 typically swells to between 12 and
15 times its original size once hydrated. The ability of the bentonite
to swell to this volume depends upon the availability of water and
the space within the hole. Under ideal hole conditions, the swelling
effect of the bentonite will create a pressure of up to 250 PSI
within the hole. This swelling effect will halt any water flow within
the bore hole thus providing greater protection for ground water.
In this manner, the sodium bentonite prevents the co-mingling of
various water sources, such as a saline water source with a fresh
water aquifier. The swollen sodium bentonite further prevents surface
contamination which results when water is allowed to flow downward
into a hole to mix with a fresh water aquifier. The sodium bentonite
further prevents the depletion of shallow aquifiers within the hole
via a fracture or uncharged zone.
It is preferable to use at least a 21/2 inch capsule in a 4 inch
casing, a 3 inch capsule in a 41/2 inch casing, a 31/2 inch capsule
in a 51/2 inch casing and a 5 inch capsule in a 7 inch casing.
FIG. 7 illustrates an alternative embodiment in which the sodium
bentonite is formed into large nodules that are poured into the
hole in a free format, such as from a sack, bag, bucket and the
like. The bentonite may be also discharged from a conveyor on a
storage truck and the like. The bentonite is formed from large nodules
having a predetermined minimum diameter of preferably at least 7/8
inches and optimally of at least 2 inch. By utilizing large nodules,
the material is afforded time to float or fall to the bottom of
the drill hole before expanding to the point at which it plugs the
Each nodule expands at a rate proportional to the percentage content
of liquid within the nodule. The rate at which a nodule absorbs
liquid is dependent upon its surface area. The rate of hydration
is related to the surface area of the nodule and to the volume of
the nodule. However, the volume and surface area of a nodule vary
with respect to nodule diameter at differing rates. Thus, when a
spherical nodule's diameter doubles, the surface area similarly
doubles, while the volume more than doubles. For this reason, as
a nodule's diameter doubles, the amount of liquid absorbed by a
nodule per unit time also doubles, while the volume of the nodule
more than doubles. As the nodule increases in volume, it requires
an equal increase in the amount of absorbed liquid to maintain a
particular hydration ratio. The ratio of nodule surface area to
nodule volume decreases as the nodule increases in diameter. Accordingly,
the rate of hydration decreases (as does the rate of expansion)
with increased nodule size.
As noted above, it is necessary that the nodules have a diameter
of at least 7/8 inches and less than 2 inches. A nodule with a diameter
of less than 7/8 inches hydrates and expands too rapidly to allow
the nodule to reach the bottom of a deep hole before plugging the
hole. By way of example, fine bentonite particles with a 3/8 inch
diameter may hydrate and swell to 10 times its original size and
turn to a slurry state in less than 15 minutes. Often drill holes
are several hundred feet deep with over a hundred feet of liquid.
Each nodule falls at a rate dependent upon the nodule's density
and the liquid's viscosity. However, generally the viscosities of
the bentonite and the liquids within the holes is such that a nodule
having a 3/8 inch diameter falls at a rate of 60 feet per minute.
As the nodule swells its density decreases, further educing its
fall velocity. Such nodules require several minutes to reach the
hole's bottom. Accordingly, 3/8 inch nodules swell and plug the
hole before reaching the bottom or turn to a slurry state otherwise.
Nodules having a 7/8 inch or greater diameter swell at a much slower
rate. Nodules with a 7/8 diameter also decrease in density (with
swelling) at a slower rate due to the larger volume, thereby allowing
the nodules to reach the bottom before plugging the hole.
Nodules according to the present invention preferably have a maximum
diameter of no greater than 3 inches and optimally no greater than
2 inches. Optimally, a combination of nodules, having varying diameters
between 1 inch and 2 inches, are used. Nodules between 1 and 2 inches
will fall through liquid for at least 1/2 hour without excess swelling
(i.e., increasing by less than 30% in volume) which is sufficient
to reach the bottom of any hole. By way of example, it is desirable
to arrest the rate of expansion to less than a 50% increase in volume
after exposure to liquid for 30 minutes, and optimally less than
FIG. 8 illustrates an alternative embodiment in which a hole 100
is lined with a casing 102. Such holes may be several hundred feet
deep. The hole 100 includes an inner diameter which is larger than
the outer diameter of the casing to form an annulus void 104 about
the casing. The upper portion of the hole includes a cement liner
106 formed against the inner diameter of the hole.
The lower end of the casing 102 includes perforations 108 which
allow the product of interest to enter the interior 103 of the casing
and to be pumped therefrom during production.
As a further alternative embodiment, a canister 110 may be provided
which is cylindrical in shape and hollow. The canister stores a
large quantity of sodium bentonite either loose or in capsule form.
The canister is air tight and water tight. A cable or hose 112 is
attached to the upper end of the canister in order to allow users
to lower the canister into the casing to a desired depth. Once the
canister 110 is lowered to the desired depth (which may be above
or below the water level 114), the user remotely opens the bottom
end 116 of the canister. The bottom end 116 is hingeably mounted
to the canister and may be open via an electronic solenoid or a
mechanical lever, either of which are remotely activated by the
user at the top of the hole. Once the door 116 is opened, the sodium
bentonite 118 falls from the bottom of the canister and collects
at the bottom of the hole. By using an air tight and water tight
canister 110, the sodium bentonite is isolated from exposure to
the liquid until the canister is at a desired depth. This depth
may be immediately adjacent the bottom of the hole. If the canister
110 is lowered to the bottom of the hole, a variety of sodium bentonite
sizes may be utilized, ranging from an extremely small granule to
large nodules. In the embodiment of FIG. 8, the size of the granule
is not critical when the canister 110 is lowered to the bottom of
the hole prior to subjecting the sodium bentonite to the liquid.
However, if it is preferable to maintain the canister 110 at a great
distance above the bottom of the hole and even above the water level,
then it is necessary to use larger diameter nodules of sodium bentonite
(as discussed above in connection with FIG. 7) in order to allow
the nodules to reach the bottom of the hole before turning to a
slurry state or swelling to such a degree as to plug the hole.
As is understood in the industry, the casing, hole and liner arrangement
illustrated in FIG. 8 is commonly encountered. This casing and liner
alignment may be utilized in cooperation with any of the above discussed
During operation, it is often desirable to perform several pre-plugging
and post-plugging steps to facilitate the use of sodium bentonite.
As is well known in the industry, many types of drill holes such
as oil wells and gas wells are lined (once drilled) with a casing
(as shown in FIG. 8). Product is pumped through the casing perforations
during production. The outer diameter of the casing is slightly
smaller than the inner diameter of the hole. Initially, a wire line
is lowered down to the bottom of the hole to determine whether the
casing is entacted and to locate the water level. Next, a packing
is lowered into the hole to a position immediately above the perforations.
The packing forms an air tight seal with the wall of the casing.
The casing integrity is tested by applying high pressure air (e.g.,
500 PSI) to the hole and determining whether this pressure is "bled
off" through cracks in the casing. If the casing holds the
air pressure, then the casing wall is air tight from the packing
to the top of the hole. If the casing wall is air tight, then sodium
bentonite only need be loaded to a desired point above the perforations
(approximately 100 feet above the perforations). If the casing integrity
is bad and it is unable to sustain the high pressure casing test,
then a bridging plug is set below the hole and a 100 foot sodium
bentonite plug is displaced above this point. By filling the hole
100 feet above the bridging plug with sodium bentonite, cracks in
the casing are sealed and the potential for water migration within
the hole arrested.
Once the casing is tested, the sodium bentonite is added by one
or more of the foregoing manners to the desired level. The sodium
bentonite is allowed to expand and seal the hole. Thereafter, the
seal is tested by again pressurizing the hole (e.g., to 500 PSI)
and determining whether the pressure is maintained. Next, an additional
portion of sodium bentonite is added at the top of the hole about
the outer perimeter of the casing into the annulus void between
the production casing and surface casing. This additional portion
of sodium bentonite seals the outer region surrounding the casing.
Finally, an end cap is sealed over the opening.
In all of the foregoing embodiments, it is necessary to control
the ratio of the volume of bentonite versus the volume of hole.
If too little bentonite is added it turns to a slurry state before
the hole walls arrest its growth at a solid state. It is desirable
to fill a hole with at least 40% by volume of dehydrated sodium
bentonite in order that it may react with the remaining 60% by volume
of water within the hole.
When estimating an amount of necessary bentonite, 2-3 inches of
additional expansion must be accounted for in order to allow for
casing failure. When the casing fails, the bentonite expands to
the inner diameter of the hole. The sodium bentonite previously
stored in the hole further swells and is able to fill this additional
2-3 inches in diameter since liquid is present in the hole thereby
causing the bentonite to swell no matter how much time has past.
If a plastic capsule is used, it will prevent hydration of the
bentonite until the capsule reaches the bottom and dissolves. The
plastic capsule may be formed with an accelerator additive to increase
the dissolution rate of the plastic.
In the canister embodiment of FIG. 8, pressurized air or water
may be added to the full canister to force the bentonite out of
the canister when the door is opened.
FIG. 9 illustrates an alternative embodiment which may be utilized
with any of the preceding methods for plugging shallow or deep holes.
The embodiment of FIG. 9 is set forth in connection with a deep
hole, such as several hundred feet deep as used with oil wells.
FIG. 9 illustrates a hole 200 lined with a casing 202. The upper
portion of the hole 100 includes an inner diameter which is larger
than the outer diameter of the casing to form an annulus void 204
about the casing. The upper portion of the hole 200 includes a liner
206 formed against the exterior diameter of the void 204.
According to this embodiment, layers of sodium bentonite 210 are
injected into the hole according to the preceding methods. The layers
of sodium bentonite 210 are separated with layers of sand 212, gravel
or a similar liquid retaining or porous particulate material. To
form this layered structure, a lowermost section of sodium bentonite
is introduced into the hole (according to one of the preceding methods)
until it reaches a desired depth 215. Thereafter a portion of sand
is poured into the casing 202 to a depth 217. This process is repeated
alternately pouring bentonite and sand into the hole until the hole
is filled. As illustrated in FIG. 9, the thickness of each layer
may be varied depending upon its location within the hole and other
factors. Once the casing 202 is completely filled with bentonite
and sand layers, the void 205 about the exterior of the casing 202
is similarly filled with layers of bentonite 211 and sand 204. Within
the void 205, the bentonite 211 and sand 204 are repeatedly layered
until the void is filled.
Optionally, sand may be omitted and a similar type of material
substituted therefore, so long as the material exhibits a liquid
retention characteristic and delivers this liquid as need to adjacent
bentonite layers. By layering sand and bentonite in this manner,
each layer of bentonite is continuously and indefinitely exposed
to water which is stored within the adjacent sand layers. Hence,
liquid retained within the sand layers prevents the bentonite layers
215 from dehydrating and contracting, thereby maintaining a seal
within the casing 202.
The sand layers further function to prevent overexpansion of the
bentonite layers. As explained above, when bentonite is exposed
to water, it hydrates and swells, up to 10-12 times its original
volume. However, when bentonite expands to this volume, it liquifies
and loses its structural integrity, thereby losing its ability to
seal. Hence, when the bentonite over expands, it weakens its sealing
ability as a plug.
If left unattended, the bentonite 211 within the voids 205 about
the upper portion of the casing 202 would continue to hydrate until
it liquified or turned to a slurry state. However, expansion of
the bentonite along the column is arrested by covering each layer
of bentonite 211 with a layer of sand 216. The sand exerts downward
pressure upon the bentonite with sufficient force to counteract
the expansion forces of the bentonite, thereby arresting expansion.
Hence, the sand limits upward migration of the bentonite, thereby
directing the bentonite to expand laterally against the walls of
the casing 202 and liner 206. The foregoing effect of the sand upon
the bentonite layers occurs throughout the hole and throughout the
The combination of layered sand and bentonite functions to produce
downward hydrostatic pressure within the hole to prevent gases and
fluids from entering the well hole and the casing. In this manner,
the inventive combination of sand and bentonite plugs the drill
well hole and indefinitely maintains a seal.
From the foregoing it will be seen that this invention is one well
adapted to attain all ends and objects hereinabove set forth together
with the other advantages which are obvious and which are inherent
to the structure.
It will be understood that certain features and subcombinations
are of utility and may be employed without reference to other features
and subcombinations. This is contemplated by and is within the scope
of the claims.
Since many possible embodiments may be made of the invention without
departing from the scope thereof, it is to be understood that all
matter herein set forth or shown in the accompanying drawings is
to be interpreted as illustrative, and not in a limiting sense.