Apparatus and method for plugging voids in a ground stratum

Apparatus and method of filling voids in a ground stratum in the vicinity of a well bore are enclosed. The apparatus is a self-contained device and, for example, it can be placed in the well bore in the vicinity of the voids to be plugged by dropping the apparatus down a drill string. Once in place it will automatically respond to the well pressure to provide the required plugging. To accomplish this the apparatus includes precursors of polymers such as precursors of polyurethanes, epoxy type polymers, polyesters or other polymers which are released from the apparatus and flow into the voids.

This invention relates to drilling oil and gas wells or pipelines through 
voids in ground strata, and in one of its aspects, to a method and 
apparatus for filling voids in ground strata in the vicinity of a well 
bore hole. In another aspect it relates to a self-contained device for 
responding to a surrounding pressure to provide a plugging medium. 
In drilling oil and gas wells, drilling muds are circulated under pressure 
to lubricate and cool the drill bit and to carry away cuttings. Losses of 
drilling mud or other drilling fluid may occur as the result of various 
underground voids such as cracks, holes, fissures in the geographical 
formations, water sands, or any other structure that would permit the loss 
of drilling mud, and this phenomenon is generally referred to as "lost 
circulation". When sufficient lost circulation occurs to impair the 
drilling operation, drilling generally halts until the sources of the lost 
circulation can be plugged. 
Lost circulation has been a long standing problem. In the past, the primary 
approach to solving lost circulation has been to pull the drill string and 
then plug the hole in the vicinity of the voids with a substance that can 
be handled in a liquid state until it is in place and which will then 
harden in place, such as concrete or polyurethane foam. Once the plugging 
substance has hardened, it is then drilled through. A major problem with 
such approaches, in addition to the lost drilling time and costs 
associated with pulling the drill string, has been keeping the plugging 
substance in a liquid state until the substance is in place. One method of 
using polyurethane foam for plugging voids was to mix the precursors of 
the polymeric system on the surface and rapidly force the foam downhole by 
pressure or by a plug which is generally known as a "pig". This process is 
very costly, necessitating a standby crew and equipment on a constant 
basis. In premixing the foam producing materials at the surface, a 
retarding agent can also be included allowing more time to get the 
premixed foam into place, as shown in U.S. Pat. No. 3,379,253, issued to 
Chism. Another approach is to pump the different required chemicals down 
separate pipes so that they mix forming the stable foam in the vicinity of 
the voids as shown in Chism and in U.S. Pat. No. 3,637,091, issued to Lee, 
but this approach requires the lowering and withdrawing of large amounts 
of special equipment into the bore hole. Withdrawing the special equipment 
from the bore hole once the foam has begun to solidify can be difficult or 
even impossible. 
It is thus an object of the present invention to provide an apparatus for 
plugging voids in a ground stratum which is self-contained, not requiring 
other equipment or elaborate procedures for its use. 
Another object of the present invention is to provide an apparatus and 
method for plugging voids in a ground stratum which permits the plugging 
substance to be positioned adjacent the voids to be filled while it is 
still in a liquid state. 
Another object of this invention is to provide an apparatus and method of 
plugging voids in a ground stratum in the vicinity of a well bore during a 
well drilling operation without the necessity of pulling the drill string. 
Another object of this invention is to provide such an apparatus and method 
which is relatively inexpensive to manufacture, can be easily stored until 
useage, and which can be used in the field without the necessity of highly 
trained personnel or expensive or elaborate equipment. 
In accordance with these and other objects of this invention, which will be 
apparent from consideration of this specification and the appended claims, 
the present invention provides a self-contained, sealed cartridge with 
separate chambers for containing the precursors of a polymeric system. The 
cartridge is designed so that the precursors are kept separated until it 
is in the vicinity of voids in a ground stratum which cause loss of 
circulation. When the cartridge reaches the vicinity of the voids to be 
plugged, the pressure about it causes a breakdown of the structure 
separating the precursors, allowing the precursors to mix, and as the 
precursors mix, the resultant foam is released from the cartridge into the 
voids to be plugged where it solidifies. 
In accordance with one aspect of the invention, a flexible or collapsible 
cartridge includes a plurality of storage chambers, each for containing a 
precursor of a polymeric system, and at least one mixing chamber. The 
precursors of the polymeric system are kept in their individual storage 
chambers until the cartridge is in the vicinity of the voids to be 
plugged, at which time the components are forced by pressure from drilling 
mud to enter the mixing chamber and mix, forming a foam which is then 
released from the flexible cartridge into the bore hole and the voids to 
be plugged. Once in the voids, the foam sets, hardening into a substance 
which is substantially impervious to the drilling mud so that drilling can 
be resumed. 
In accordance with another aspect of the invention, a cartridge includes a 
plurality of storage chambers each for containing a precursor of a 
polymeric system, at least one chamber for mixing the precursors, and 
plungers within the cartridge for transmitting increased pressures from 
outside the cartridge to the precursors of the polymeric system forcing 
the precursors into the mixing chamber when the pressure outside the 
cartridge is sufficiently great.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, a bore hole 10 extends into a stratum 12 with many 
voids, in this case fissures 14, which have been plugged in accordance 
with this invention with a polymeric foam 24. A drill bit 16 driven by a 
drill string 18 having a center bore 17 is used to drill the bore hole 10 
until it drills into the stratum 12 with fissures 14. In drilling through 
the other strata, drilling mud is circulated down through hollow drill 
string 18 through drill bit 16 to cool and lubricate drill bit 16 as it 
drills. The mud then goes back up the annulus 19 between drill string 18 
and a casing 20, as is well known in the art. By continuously circulating 
the drilling mud, adequate pressure is maintained to cool and lubricate 
drill bit 16 and to remove drilling waste from the vicinity of drill bit 
16. Once drill bit 16 drills into a stratum with voids in the stratum so 
that the drilling mud will flow into the stratum rather than back up 
through the annulus, circulation is lost, and drilling must cease. When 
the voids in a stratum which are causing loss of circulation have been 
plugged in the vicinity of bore hole 10 by foam 24 as shown in FIG. 1, and 
the foam has set, then drilling can be continued, drilling first through 
the foam in the well bore. The foam, which is substantially impervious to 
the drilling mud, then prevents further loss of circulation where it has 
been used. 
Referring now to FIGS. 2 and 3, a plugging material transporting, mixing 
and releasing apparatus 26 constructed according to this invention 
comprises a cartridge 28 made of a flexible, and preferably water-soluble, 
substance so that it will yield or collapse in response to increased 
pressure from outside the cartridge. The cartridge includes means for 
separating the precursors of a polymeric system such as storage chambers 
30 and 32, which are separated from each other by a wall or partition 31 
extending through the center of cartridge 28, a cylinder wall 33, and 
membranes 34 and 36 located at the lower portion of cartridge 28. Thus, 
when one precursor of a two precursor polymeric system is placed in 
chamber 30, the chamber in conjunction with membrane 34 completely 
encloses that precursor making it shelf-stable. Similarly the other 
precursor of a two precursor polymeric system is enclosed in storage 
chamber 32 which is closed at the bottom by membrane 36. The two 
precursors remain separate and stable until such time as the cartridge is 
to be used. 
Membranes 34 and 36 are preferably made of a flexible material, such as a 
thin rubber-like material, which can be readily ruptured by the pressure 
of the material in chambers 30 and 32 when the well pressure causes 
collapse of cartridge 28 as hereinafter explained. 
Cartridge 28 also includes a mixing chamber 38 formed by cylindrical wall 
33, membranes 34 and 36, and a rupturable membrane 40 at the bottom of 
cartridge 28 for mixing the precursors of the polymeric system. Mixing 
chamber 38 is separated from the storage chambers by membranes 34 and 36 
prior to their rupture. As noted, the outer wall 42 of cartridge 28 is 
made of a flexible material so that outside pressure on wall 42 will tend 
to collapse the cartridge and increase the pressure on membranes 34 and 
36. When sufficient pressure is applied to the outer wall of cartridge 28, 
membranes 34 and 36 will burst and fill mixing chamber 38 with the two 
stored precursors which begin to mix. As they mix the pressure in the 
mixing chamber increases until membrane 40 is ruptured and the foaming 
substance flows out of the chamber. 
Once the precursors of the polymeric system have begun mixing, they are 
forced out of the cartridge and into the well bore and the fissures to be 
plugged. Forcing the foam out of the cartridge can be accomplished in a 
number of ways such as including a blowing agent in one precursor, or 
mixing precursors which expand when mixing such as self-foaming 
precursors, or mixing components which expand when mixed with the water of 
the drilling mud or the formation. As used here, "precursor of a polymeric 
system" includes known blowing agents and catalysts. The foam can also be 
forced out of the cartridge with the force of the drilling mud as will be 
explained. 
The preferred method of using the present invention is to drop one or more 
cartridges which are cylindrically shaped and suitable for stacking down 
the drill string so that the cartridges 28 will stack one on top of 
another at the bottom of the drill string as shown in FIG. 4. A suitable 
number of cartridges may be determined by estimating the amount of foam 
which will be necessary to fill the voids which are creating the problem, 
though it may be necessary to limit the number of cartridges used at any 
one time due to the practicalities of forcing the cartridges and foam out 
of the drill string with the use of drilling mud. The volume expansion 
ratio for precursor to polyurethane foam for some precursors is in the 
range of 20 to 1. 
In employing this invention, drill string 18 is generally pulled up bore 
hole 10 until drill bit 16 is slightly above the stratum to be plugged, as 
shown in FIG. 4, and then cartridges 28 are dropped as described down the 
inside of drill string 18. After sufficient numbers of the cartridges have 
been dropped into drill string 18, drilling mud is forced down the drill 
string so that the pressure of the mud flow tends to both rupture the 
membranes and force the foam out through drill bit 16 and into well bore 
10. As shown in FIG. 4, pressure from drilling mud forced down drill 
string 18 onto cartridges 28 forces liquid state foam 24 into fissures 14, 
thus displacing any liquid such as water or drilling mud that might be in 
fissures 14. Sufficient drilling mud is forced down drill string 18 
through drill bit 16 to ensure that foam 24 does not set while in drill 
bit 16. Foam 24 is preferably substantially removed from drill bit 16, as 
shown in FIG. 1, before setting. 
Using the preferred method of this invention, it is especially advantageous 
to make the cartridges themselves of a soluble material such as water 
soluble cardboard or polyvinyl alcohol, hydroxyethyl cellulose, 
hydroxymethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose, 
polyethylene oxide, or other known water soluble materials suitable for 
making containers. Thus, once the drilling mud is forced down on top of 
the cartridges which are inside the drill string, the cartridges dissolve 
and can be forced with the foam through drill bit 16. Also, it is 
preferred that a retarding agent be added to the precursors (as is well 
known in the art) to ensure that the foam does not set until it has 
completely evacuated cartridges 28 and drill bit 16 and is in place in the 
voids to be filled. 
Referring now to FIG. 5, another embodiment 44 of the present invention is 
illustrated where storage chamber 46 is partially an extension of a mixing 
chamber 48, and a second storage chamber 50 is annular to the first 
storage chamber 46. As in the previous embodiment, the collapse of 
flexible container 52 in response to the down hole pressure causes the 
rupture of membranes 54 and 56 which had sealed chambers 46 and 50 
respectively. Once the precursors of the polymeric system begin mixing in 
mixing chamber 48, they then rupture membrane 58 and are released into the 
bore hole and fissures. 
In addition to the use of a collapsible cartridge other methods and 
apparatus can be used for transmitting the down hole pressures to the 
components of the polymeric system to cause the rupture of the membranes 
separating the precursors and allow the mixture of the precursors. One 
such apparatus uses plungers for transmitting the pressure from the 
environment about the cartridge to the precursors stored within the 
cartridge as shown in FIG. 6. The apparatus of this embodiment, referred 
to generally as 62, includes a rigid cartridge 64 with storage chambers 66 
and 68 with corresponding membranes 70 and 72 separating chambers 66 and 
68 respectively, until ruptured from a mixing chamber 78. A rigid plunger 
74 forms one end of chamber 66 and transmits pressure from outside 
cartridge 64 to the precursor of chamber 66. A ring-shaped plunger 76 
separates chamber 66 from chamber 68 and transmits pressure from the 
precursor in chamber 66 to the precursor in chamber 68 since an increase 
in the pressure on the outside of cartridge 64 is transmitted to the 
precursor in chamber 66 by plunger 74, and the increase in pressure that 
results in the precursor of chamber 66 will be transmitted to the 
precursor in chamber 68 through plunger 76. The increased pressure in the 
chambers will rupture membranes 70 and 72, thus allowing the precursors of 
the polymeric system to mix in mixing chamber 78. As the precursors mix in 
mixing chamber 78 and increase the pressure therein, membrane 80 will 
rupture and the mixed material will flow into the well bore and fissures. 
Thus, a self-contained cartridge with two compartments for a two-part, or 
two component polymeric systems such as polyurethane foam, expoxy foam, 
polyester foam, etc. or for solid polymeric systems has been described. 
The cartridge is remotely actuated as in down-hole oil and gas wells, and 
underground oil and gas pipe lines, by pressure. The pressure may be air, 
water, gas, oil, etc. The two component polymeric system is packaged in 
the two separate compartments, and most such systems will be shelf-stable 
for from six months to one year as a minimum. 
Besides the described use in plugging holes and fissures in drilling 
operations, the present invention has many other ramifications. In oil and 
gas wells, many times a certain zone must be plugged off, as when one of 
the productive zones no longer is producing, or is producing too much 
water or other unwanted product. The present invention is applicable in 
such uses. In oil or gas wells that are highly corrosive, many times the 
tubing will have holes due to corrosion which must be sealed off. In 
pipelines, for water, sewage, oil, gas, and other products, holes in the 
line due to corrosion must be sealed. The present invention is applicable 
for all these types of operations plus many others. 
Also, although it is preferred that the cartridge be made of water-soluble 
material, in a drilling operation, the cartridge is of such light 
construction that once the fluid components have been mixed and dispensed, 
the cartridge itself can be forced on through the ports or orifices in the 
drill bit and ground up into tiny pieces which are carried on with the 
drilling mud. In other instances , it may be desirable that the cartridge 
construction be strong enough that the empty cartridge may be pushed on 
through a pipeline, and be reclaimed intact on the other end, after having 
performed its function of sealing holes or leaks. 
It is understood, therefore, that these cartridges may be constructed of 
many different plastic materials so as to be very fragile, or very strong. 
It is even possible to construct them of steel or other metal if so 
desired, for some specific uses, where the cartridge may be used over and 
over again. 
Also, the polymeric materials to be utilized in such cartridges may be any 
type of thermosetting polymer, such as polyurethane, epoxy, polyester, 
urea-formaldehyde, phenolic, etc. where two or more components must be 
intimately mixed together in order to form a polymer. The polymer may be 
used as a solid material in uses where the end product must be very 
strong, or the polymer may be a foamed polymer of any given density. Such 
formulations are well-known in the art with all such thermosetting 
polymers. 
Cartridges may also be made of a water-soluble material if desired, such as 
ethylene oxide polymer, or polyvinyl alcohol polymer, or they may be made 
of an oil soluble polymer, such as styrene-maleic anhydride or other such 
polymer. They also may take many other forms other than described herein. 
From the foregoing it will be seen that this invention is one well adapted 
to obtain all of the ends and objects hereinabove set forth, together with 
other advantages which are obvious and which are inherent to the 
apparatus. 
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. 
As 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.