Method and device for sealing boreholes

Abstract

A device and method for sealing boreholes. Typically, a seismic test hole is sealed by covering a topping plug with water expansible material, such as bentonite, which seals the hole once it expands on exposure to water or moisture. The present invention provides a method and a device for sealing seismic holes, the device comprising a generally tubular water permeable sleeve filled with water expansible aggregate.

Description

FIELD OF THE INVENTION

[0001] This invention relates to the sealing of boreholes, for example seismic boreholes, to prevent contamination of groundwater by water or debris from the surface.

BACKGROUND

[0002] In seismic exploration there is a requirement to seal boreholes after drilling in order to prevent contamination of groundwater and to prevent hydraulic communication between aquifers. As well, it is important to close up such holes to prevent injury to animals or people who may not see the holes.

[0003] After a seismic borehole is drilled, a topping plug is placed in the hole. A sealing material is added on top of the topping plug and soil and topsoil is replaced on top of the sealing material. Bentonite is often used as the sealing material since it expands when water is added.

[0004] However, bentonite is usually packaged in large bags making it heavy and difficult to pour. The bentonite can spill on the ground near the borehole and therefore, is wasted and must be cleaned up. It is also difficult to ascertain how much bentonite was poured into the borehole.

[0005] Another method used to seal boreholes involves pouring concrete over the topping plug. The same problems that occur with bentonite can occur with concrete, namely spillage and not knowing how much concrete was used. Spilled concrete is also messy and difficult to clean up.

[0006] This invention overcomes the problems identified with the prior art by providing pre-measured amounts of water-expansible aggregate, such as bentonite, in a water permeable sleeve that is easy to handle and insert into the borehole. The sleeve that contains the aggregate prevents spillage.

SUMMARY OF THE INVENTION

[0007] In a broad aspect, this invention provides a device for sealing a borehole comprising: a generally tubular water permeable sleeve, said sleeve being closed at both ends, and water expansible aggregate, said aggregate located within and contained by the sleeve, said sleeve generally of a size and stiffness to maintain its shape when filled with said water expansible aggregate to permit insertion into a borehole and allow expansion of its contents on exposure to water.

[0008] In another aspect, this invention provides a method for sealing a borehole using the device as described in the first aspect consisting of: plugging the hole with a topping plug; sliding said device into said borehole; and exposing said device to water whereby said aggregate matter expands and seals the hole on exposure to water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 depicts a perspective view of a preferred embodiment of the invention.

[0010] FIG. 2A is a longitudinal sectional view of a borehole containing a preferred embodiment of the invention, before the aggregate has absorbed any moisture.

[0011] FIG. 2B depicts a longitudinal sectional view of a borehole containing a preferred embodiment of the invention, after the aggregate has expanded.

[0012] FIG. 3 depicts a longitudinal sectional view of a borehole filled with three of the sealing devices as provided by a second embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] In the preferred embodiment of the invention depicted in FIGS. 1, 2A and 2B, the borehole sealing device 1 consists of a mesh sleeve 2 made from polypropelene which is filled with crushed bentonite 3. The mesh sleeve 2 is closed at both ends with metal fasteners 4.

[0014] The sleeve 2 is generally tubular in shape after it is filled with the aggregate 3. The diameter of the sleeve 2 is somewhat less than the diameter of the borehole 7, and of suitable length.

[0015] The material from which the sleeve 2 is made must be of suitable stiffness such that the generally tubular shape is maintained after it is filled with the aggregate so that it can slide into the borehole. At the same time, the material must allow water to flow through it to the aggregate and permit the aggregate to expand. A material that allows expansion in the horizontal plane of the generally tubular shape while at the same time tending to restrict longitudinal expansion is preferred. The sleeve 2 must be constructed from a material strong enough not to tear when filled with the aggregate 3 either during handling or insertion into the borehole. A mesh material of suitable stiffness and strength and with suitable sized openings is preferred.

[0016] Polypropelene mesh is durable even at cold temperatures and will resist tearing before the sealing device 1 is installed in a borehole. Polypropelene mesh is available in the form of a sleeve in a variety of weights and diameters, and of indefinite lengths. A polypropelene mesh sleeve material is selected of suitable diameter and weight. The diameter will be less than the diameter of the borehole 7 after the mesh sleeve 2 is filled with aggregate 3. The strength is sufficient to prevent tearing and the stiffness of the mesh will be sufficient to maintain the generally tubular shape after filling with the aggregate 3. It is important that the mesh sleeve 2 does not bulge unduly under the weight of the aggregate 3, so that it can slide into a borehole 7.

[0017] Once the device is installed, the mesh sleeve 2 has no further function. However, it must allow the aggregate matter to expand across the diameter of the borehole in order to seal it. The polypropelene mesh 2 used in the preferred embodiment is flexible enough to allow for such expansion. An added advantage of polypropelene mesh sleeves is that they are already commercially available in a variety of sizes. However, any material that meets the requirements of holding the aggregate 3, maintaining its size and shape, allowing water to penetrate and allowing the aggregate 3 to expand can be used. Examples of materials that could be used are suitable plastic mesh, such as polyethylene or nylon, or wire mesh.

[0018] Typically, about 20 inches of bentonite is used for closing seismic boreholes. Therefore, in the preferred embodiment the borehole sealing device 1, as shown in FIGS. 2A and 2B, would be approximately 20 inches long. Once installed within a borehole 7, the top of the device 1 would be being approximately 18 inches below the surface of the ground. However, the device can be made to various lengths depending on the needs of the user and can be used at any depth.

[0019] Crushed bentonite is used as the aggregate 3 in the preferred embodiment. Bentonite is commonly used in industry to seal seismic boreholes. Crushed bentonite works well with the polypropelene mesh sleeves because the bentonite chips are larger than the holes in the mesh, thus ensuring the bentonite remains within the sleeve 2. However, any suitable water expansible aggregate could be used in this invention, so long as the aggregate size is larger than any holes in the sleeve.

[0020] The sleeve 2 must be closed at both ends in order to contain the aggregate 3. This can be done in any suitable manner. The type of closure must be strong enough to hold the weight of the aggregate. Examples of methods of closing the sleeve include: cinching each end with tie wraps or crimps; folding and sealing the ends by heating or crimping; heat fusing the ends; or lacing across the ends. In the preferred embodiment, metal fasteners 4 are used to cinch the ends of the mesh sleeve 2. The fasteners 4 serve the purpose of holding the bentonite 3 within the sleeve 2 until at least after the device 1 is installed in a borehole 7.

[0021] Containing the pre-measured bentonite within the sleeve 2 eliminates the need for the user to pour estimated amounts of bentonite from heavy bags. The use of metal for the fasteners 4 has the added advantage that a metal detector can later be used to locate the sealed borehole at a later date if necessary. Often there is a requirement for seismic boreholes to be inspected but they are difficult to locate once they are filled. If a metal fastener or the other metal accessory is used on the sealing device 1, the inspector can use a metal detector to locate the boreholes.

[0022] To use the preferred embodiment of the present invention, a user slides the sealing device 1 into a borehole 7 after the topping plug 5 has been installed. Then, if desired, the remainder of the hole is filled with cuttings or other material 6. Water in the ground will cause the bentonite 3 to expand, thus sealing the hole. Later, if it is necessary to locate the hole 7, a metal detector can be used to detect the metal fasteners 4 used to close the ends of the sleeve 2 in the preferred embodiment.

[0023] The mesh sleeve 2 holds a measured amount of the water-expansible aggregate 3. Therefore, the user will know exactly the amount of the aggregate 3 placed into the borehole 7. The sleeve also provides a method of easily handling the aggregate 3 and eliminates the need of pouring it from a large bag into the borehole 7. Water or moisture can penetrate through the sleeve to the aggregate 3, thereby permitting the aggregate to expand and seal the borehole. The diameter of the sleeve is smaller than the diameter of the borehole, so that it slides easily into place before the aggregate expands and fits snugly after the aggregate has expanded. The sealing device 1 can be made to fit any size borehole.

[0024] In another embodiment of the invention shown in FIG. 3, more than one sealing device 1 can be placed into a borehole 7. According to this embodiment, any number of sealing devices can be stacked on top of each other. FIG. 3 shows three sealing devices 1 in the same borehole 7. The advantage of using more than one sealing device is that each sealing device can be made so that it is a weight and length that can reasonably be handled by workers who are sealing the boreholes. As well, the sealing devices 1 can be made to any size that is practical for shipping. In this embodiment, to achieve a seal of a desired length, a user inserts the number of sealing devices 1 needed to add up to the necessary length.

Claims

1. A device for sealing a borehole comprising:

a generally tubular water permeable sleeve, said sleeve being closed at both ends, and water expansible aggregate, said aggregate located within and contained by the sleeve, said sleeve generally of a size and stiffness to maintain its shape when filled with said water expansible aggregate to permit insertion into a borehole and allow expansion of its contents on exposure to water.

2. A device for sealing a borehole according to claim 1 wherein said sleeve is mesh.

3. A device for sealing a borehole according to claim 2 wherein said mesh sleeve is made of polypropelene.

4. A device for sealing a borehole according to claim 1 wherein said aggregate is bentonite.

5. A device for sealing a borehole according to claim 2 wherein said aggregate is bentonite.

6. A device for sealing a borehole according to claim 3 wherein said aggregate is bentonite.

7. A device for sealing a borehole according to claim 1 wherein at least one end of said sleeve is closed using a metal fastener.

8. A device for sealing a borehole according to claim 2 wherein at least one end of said sleeve is closed using a metal fastener.

9. A device for sealing a borehole according to claim 3 wherein at least one end of said sleeve is closed using a metal fastener.

10. A device for sealing a borehole according to claim 4 wherein at least one end of said sleeve is closed using a metal fastener.

11. A device for sealing a borehole according to claim 5 wherein at least one end of said sleeve is closed using a metal fastener.

12. A device for sealing a borehole according to claim 6 wherein at least one end of said sleeve is closed using a metal fastener.

13. A method for sealing a borehole using the device of claim 1 consisting of:

plugging the hole with a topping plug;

sliding said device into said borehole; and

exposing said device to water;

whereby said aggregate matter expands and seals the hole on exposure to water.

14. A method according to claim 13 whereby more than one device is slid into the borehole.