AU739427B2 - Method of sealing a fluid passage - Google Patents

Description

I

k'IUU/U1 I 28(5/91 Regulatlon 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodiged: Invention Title: METHMOD OF SEALING A FLUID PASSAGE The following statement is a. full description of this Invention, including the best method of performing it known to us METHOD OF SEALING A FLUID PASSAGE The present invention relates to a method of sealing passages such as cavities, fissures and like formations as encountered, for example, in geological bodies for example in rocks surrounding mineshafts though the method may be applicable to sealing of passages in other situations.

From U.S. Patent No. 4296932 is known a method of sealing faults or like passages in geological bodies situated close to a mineshaft and like structures, wherein a sealing composition.comprising a rubber latex and a bituminous material is used to close the passage. Bituminous material is included in emulsion with the latex to prevent formation of a film in the latex when being injected. Such a film can form under, even low pressure and limits the depth of penetration into the fault. Such a film also can be easily broken due to the limited depth thereof.

However, it has been found that appropriate sealing of cracks may require injection of sealing composition at very high pressures, such as in excess of 10MPa and perhaps as high as 20 MPa. At these pressures, pure 00,0natural latex, being incapable of resisting hydrostatic pressure without setting and hence is unsuitable as it cannot be handled in the pumping equipment capable of achieving the required order of pressure.

Thus in these situations latex cannot be used, and the cost and sealing S..0 advantages that latex might enjoy in other situations is lost. Further, it is not S• desirable to use bitumen in such high pressure applications as it is a difficult material to pump and, is not of itself suitable as a sealing agent, even though it may promote coagulation of latex.

It is the object of the present invention to provide a method of sealing a fluid passage that enables employment of a latex based composition while reducing the problems experienced with the prior art methods employing latex as described above.

With this object in view the present invention provides a method of sealing a passage in a body, particularly a geological formation, with a sealing composition comprising substantially latex with selective additives whereby the said composition is pumped, at high pressure into said passage.

Generally, though it is not desired to hereby limit the definition of "passages", the passage may take the form of a cavity, fault, fissure or other formation through which fluid may travel to cause leakage and/or flooding. The above method is particularly applicable to sealing of fluid passages is geological formation surrounding mine shafts and other passages.

The sealing composition may contain additives which prevent setting of the latex and promote its flow properties at high pressures. Additives potentially suitable include extreme pressure additives, friction resistant additives, detergents and soap-like substances and plasticisers, advantageously in 10 admixture, especially of the soap-like substances and the plasticisers, to provide the necessary flow and friction resistant properties required for the latex composition to penetrate the fluid passage.

.i The additives individually or collectively are present in relatively low .i proportions within the latex composition and represent less than preferably 0.1 to of the total composition by weight.

Additives which may be employed to improve the flow properties, such as by viscosity enhancement, may be organic or inorganic in nature.

Suitable organic compound additives may be carboxylic acids, gums, polymers in particular acrylates, carbohydrates including, for example, proteins such as gelatin, polysaccharides or polysaccharide derivatives, particularly the alkyl cellulose family of polysaccharides. Low molecular weight, especially C1 to C3 alkyl, preferably saturated, but may alternatively be unsaturated, and methyl and ethyl cellulose, hydroxylated or carboxylated if desired, are suitable additives. Hydroxymethyl and hydroxyethyl cellulose (Walocel) is particularly preferred.

Other polysaccharides and polysaccharide salts that may be used include algins and pectins, alginates. Metal salts of polysaccharide derivatives, such as alginic acid, may be employed, if desired.

Also inorganic compounds may be included which, without limitation, include borates, silicates, hydroxides and, in particular, metal salts thereof.

Any of the above additives may be employed in admixture with the latex.

Such additives are advantageously hydrophilic and may be selected to achieve desired visco-modification effects, especially reduction with increased agitation.

The additive may be selected to form a gel with water present in the latex and/or impart thixotropic properties to the composition. Therefore, as the structure of the composition breaks down at a constant shear rate, a viscosity reduction is achieved.

The latex used may be an industrially type such as is readily available in Australia from a number of suppliers in various grades. Latex of purity greater than 50%, more preferably 60% particularly is suitable for use to prepare the sealing composition.

S. 10 In a preferred aspect, the method includes the step of introducing the sealing composition through a second passage intersecting the, generally fluid, passage to be sealed. The second passage is formed such that sealing composition is directed to the desired point of the passage to be sealed.

With respect to pumping equipment that may be used in carrying out the invention, there is made particular reference to reciprocating pumps of pressure capacity high enough to achieve the required pressures of injection, which though dictated by the structural integrity of the body to be sealed, will normally exceed 10MPa and are more likely to be in the range 12 to 18 MPa.

Cementation pumps may be especially suitable.

Such pumping equipment enables the desired control over introduction of the sealing composition to the leak passage to be sealed. The ability to employ conventional pumps, to introduce the latex composition to a fluid leak passage is a substantially important, and commercially advantageous, aspect of the presently proposed method, not previously achievable in the art to the best knowledge of the Applicant.

In particular, the ability to use a piston pump to deliver the latex into the leak passage improves penetration of the latex into the leak passages by a factor of 2 to 3, without the problem of formation of easily broken film or premature setting as experienced with prior art methods where pure natural latex is solely employed as a sealing composition.

The presently proposed method can effectively be used to seal fissures of narrow diameter, that can enable fluid ingress and leakage if not sealed, and without the use of very high pressure pump as was necessary previously.

The present invention has as an advantage the ability to employ latex compositions as sealing agents and the capacity to pump such compositions at high pressure to seal leaks, especially in geological formation.

The invention will be better understood from the following description made with particular reference to the accompanying drawing in which: Figure 1 is a schematic cross-sectional view of a body, such as a geological formation, containing a mineshaft having cracks requiring sealing, for example, there may be a problem with water leakage through cracks and fissures into a mine shaft or like structures. If allowed to proceed unchecked, the mine shaft could be flooded with serious consequences. Such problems have previously been discussed in Australian patent No. 534073.

As shown in Figure 1, water penetrates through a fissure in surrounding rock 32 at a level 32a below the area in which leakage occurs and passes through face 34 and cracks 30, and joints 30a in lining 31 to enter into the mine shaft. As most flows of water are likely to occur through cracks of larger cross section, it is desirable to seal cracks of large diameter prior to addressing leakage through smaller fissures or faults. In a preferred technique, a number of passages, in the example shown two passages, 38 and 40, are drilled through the lining 31 of the mine shaft to the fault below large cracks such as crack The sealing composition comprising substantially latex and an additive, as described below, is pumped into the fault via the lower passage 38 by means of a reciprocating pump of the kind form suitable for generating the high pressures required, for example a pump known in the pumping arts as a cementation pump.

The production of the substantially latex sealing composition used will be discussed further herein below.

It may also be found appropriate for an accelerator in the form of a dilute acid, for example hydrochloric acid, to be injected or pumped through an upper passage 40, i.e. downstream of the point where the sealing composition is injected, to promote coagulation thereof at an appropriate time not during pumping of the latex. Delay of coagulation may be affected by presence of alkaline substances, e.g. ammonia, ammonium hydroxide, to maintain pH above 7 during pumping as coagulation generally occurs at low pH.

An acidic additive is then introduced or incorporated within the composition to induce coagulation by reduction of pH. Metal salts of strong acids and weak bases may also be employed for this purpose. Chlorides, nitrates, sulphates of ammonia and other salts of alkali, alkaline earth, transition, light or other metals, in fine to coarse particulate form (1g to 1mm), may be especially suitable. The content of the "acidic" additive in the latex composition may be varied to achieve the desired coagulation properties.

S. 10 Particle size may be selected to achieve the desired result. Specifically, finely ground aluminium sulphate, thoroughly admixed with the composition, is a preferred coagulating agent. Concentration in the latex composition and aluminium sulphate particle size may be varied to attain desired coagulation timing. The concentration of the acidic additive may be up to 20%, but more preferably in the range 10 to 20% by weight of the latex composition.

Pumping at high pressure, in the range 12-18 MPa and higher will enable sealing of the large cracks. Smaller cracks may also be sealed in such manner though sealing efficiency will depend on the flow characteristics of the latex *...*composition and the pressure at which it is possible to present the latex composition to the cracks or fissures within the formation. If running water is present in the passage this may also have an effect for example by assisting sealing composition distribution.

If an accelerator is used, the volume of accelerator must be carefully controlled otherwise sealant may block entry passages such as 38 and before cracks are sealed. Any number of passages may be drilled through the mine lining into the faulty area to achieve the required sealing of leaks, fissures or like faults. Passages may be drilled in any pattern or formation to achieve sealing of leaks.

The latex composition includes additives of a nature to reduce coagulation during pumping to the desired site(s) and to increase the pressure resistance and friction resistance of the latex composition. Such additives may be present in a concentration of less than 1% by weight of the latex composition and preferably are in the range 0.1-1% by weight of the composition. The additives are pre-mixed, preferably in the dry state, and introduced to an industrially available latex of greater than 50% purity. In current practical usage, the latex was sourced from an Australian supplier at 60 to 80% purity. Natural or synthetic latexes may be employed optionally at higher purities, but this will be dictated by economics and it is to be remembered that it would be most advantageous to incorporate the additives above described in order to prevent the problems of coagulation which has been known to occur in methods according to the prior art. After mixing of the additives, conveniently available in a dry granular state, the additive mixture is introduced to the latex and mixed therein for a period of up to about 10 minutes. It has been found that a period of about 5 minutes is normally suitable. However, it is undesirable that the latex should not be subjected to any unnecessary heating and therefore prolonged mixing for a greater period may be disadvantageous. Foam generation, also 15 disadvantageous, may occur after prolonged mixing and this is ideally to be avoided.

Without wishing to limit the invention in any way, it has been found suitable to employ a mixture of a soap like substance and a plasticiser, such as a methyl hydroxyethyl cellulose cross-linked with glyoxal. An example of a soap-like substance is the proprietary product KT powder, which is essentially a soap powder. The methyl hydroxyethyl cellulose, cross-linked with glyoxal, is sold by Bayer Hodgsons Pty Ltd under the trademark Walocel XM40000-PFV under the MSDS reference 739808/01, the contents of which are hereby incorporated by reference. Compounds with like properties may be employed with advantage in accordance with the present invention. Special reference is to be made to the specification sheets for these materials supplied from Bayer to ensure that the materials are appropriately stored and handled both prior to and in the additive mixture. Both these additives are sourced from Bayer Australia Limited.

Materials with like properties to these additives may be employed.

Latex may be obtained in 210 kg drums and the additives may be sourced in a dry state in similar containers. The additives are mixed, for example in a screw mixer, prior to addition and mixture with the latex. It is undesirable that premixed additive be stored for any greater time than 2 months if efficacy is to be maintained.

In one example, prior to pumping into the formation as previously described, approximately 1260 kg (6 210 kg drums) of latex was mixed with an additive mixture comprising 3.2 kg of Walocel XM40000-PFV and 2.5 kg of KT powder. While this ratio of addition is ideally to be adhered to, it is possible that additions between 2-4 kg Walocel and 1-3 kg KT powder will provide some level of advantage in the application of the latex. After preparation, the modified latex composition may be pumped into the cracks as above described.

In a preferred embodiment, the composition is not pumped directly into the cracks through the passages 38 and 40 as shown in Figure 1, but the passage 38, or any further passages, may be drilled such as to have a larger diameter close to the mine shaft over a length sufficient to accommodate a packer. The packer is then brought into communication with the reciprocating pump via a valve means. The pump may then be actuated and the composition :i is pumped into the crack, fissure or similar fault until the desired pressure is attained. At this point the valve may be switched off and the pump 15 disconnected. The operation is then continued as many times as is necessary °ooo to achieve the required sealing of the faulty formation. Pumping of the latex composition at pressures of up to 10MPa was conducted without significant coagulation of latex on pump components. Tests have also been successful in pumping the latex composition at pressures up to 40 mpa in mines where the wall structure is of sufficient strength to withstand such pressure.

The person skilled in the art, reading the specification, will be aware that it is possible to use other additives and methods in accordance with the invention. Such additives and methods fall within the scope of the present invention.

Claims (17)

1. A method of sealing a passage in a body such as a geological formation with a seal composition including delivering under pressure into the passage an admixture of latex and one or more of the following components: a friction resistant material an extreme pressure additive a plasticiser the or each said component being present in quantities not greater than 1% by weight of the admixture, wherein at least one of the components is a i polysaccharide or a polysaccharide derivative.

2. A method of sealing a passage in a body such as a geological formation Swith a seal composition including delivering under pressure into the passage an admixture of latex and one or more of the following components: a friction resistant material an extreme pressure additive a plasticiser said components in total being present in quantities not greater than about 1% by weight of the admixture, wherein at least one of the components is a S. polysaccharide or a polysaccharide derivative.

3. A method as claimed in claim 1 or 2 wherein the components include detergents and/or soap.

4. A method as claimed in claim 1, 2 or 3 wherein the components include organic and/or inorganic origin viscosity enhancing materials.

A method as claimed in claim 1, 2 or 3 wherein the components include one or more of carboxylic acids, gums and polymers.

6. A method as claimed in claim 1, 2 or 3 wherein the components include at least one of the following: acrylates, and carbohydrates.

7. A method as claimed in claim 1, 2 or 3 wherein the components include gelatin.

8. A method as claimed in any one of claims 1 to 7 wherein the polysaccharides are selected from the alkyl cellulose family.

9. A method as claimed in claim 8 wherein the alkyl cellulose has a low molecular weight in the C, to C3 range.

10. A method as claimed in claim 8 wherein the alkyl cellulose is methyl cellulose or ethyl cellulose.

11. A method as claimed in any one of claims 8 to 10 wherein the alkyl cellulose is hydroxylated or carboxylated.

12. A method as claimed in any one of claims 1 to 11 wherein the components include at least one polysaccharide selected from the group consisting of hydroxymethyl cellulose, hydroxyethyl cellulose, and methyl hydroxyethyl cellulose.

13. A method as claimed in any one of claims 1 to 7 wherein the polysaccharides include algins, alginic acids, pectins and alginates.

14. A method as claimed in any one of the preceding claims wherein said components include borates, silicates, and/or hydroxides including metal salts thereof.

A method as claimed in any one of claims 1 to 14 wherein the latex is of a purity greater than

16. A method as claimed in any one of claims 1 to 14 wherein the latex is of a purity greater than

17. A method as claimed in claim 1 or 2 wherein the component or components are selected to impart thixotropic properties to the latex. DATED this 3 0 1h day of July 2001 *HYDROSEAL AUSTRALIA PTY LTD WATERMARK PATENT TRADEMARK ATTORNEYS 21 S FLOOR, "ALLENDALE SQUARE TOWER" 77 ST GEORGE'S TERRACE PERTH WA 6000