CA2502800C

CA2502800C - Enhancement of flow rates through porous media

Info

Publication number: CA2502800C
Application number: CA2502800A
Authority: CA
Inventors: Brett Charles Davidson
Original assignee: Wavefront Energy and Environmental Services Inc
Current assignee: Wavefront Energy and Environmental Services Inc
Priority date: 2004-03-31
Filing date: 2005-03-31
Publication date: 2015-06-16
Anticipated expiration: 2025-03-31
Also published as: GB2412675B; GB0506521D0; GB2412675A; CA2502800A1

Abstract

Especially in loose soils, driving a drive-point apparatus into the ground can create a leakage path in which liquid injected out into the ground tends not to spread laterally but to squirt upwards towards the surface; a packer is provided, to seal between the tube of the drive-point apparatus and the ground material. The prevention of such leakage is especially important when the injection is being done by cyclic pulsing, especially by out-and-back surge-pulsing.

Description

Title: ENHANCEMENT OF FLOW RATES THROUGH POROUS MEDIA
[001] This invention relates to injecting a liquid from a borehole into the surrounding ground material. This may be done, when, for example, it is desired to inject and distribute a remediation substance into a contaminated aquifer. The invention addresses the special problems that can arise when the borehole is made by a drive-point apparatus.

[002] The present invention is a development of the technology as described in CA-2,232,948, to which attention is hereby directed.
GENERAL FEATURES OF THE INVENTION

[003] In the apparatus for adding a liquid into porous ground material, of the invention, the preferred features are:
- the apparatus includes a drive-point structure, which is capable of being driven, from the surface, into the ground;
- the drive-point structure includes a tube, comprising a tube wall, which defines an interior chamber;
- the apparatus includes a source of a liquid, the source being located at the surface, and includes a means for transferring the liquid therefrom into the chamber;
- the tube wall includes an exit port, through which the chamber is in liquid transfer communication with the ground material outside the apparatus;
- the apparatus includes an expandable packer, and a means for expanding same;
- the packer is of annular configuration, and is located radially outside the tube wall, between the tube wall and the ground material;
- the packer is located above the level of the exit port;
- the packer is effective, when expanded, to exert pressure inwards against the tube wall and outwards against the ground material; and - the structure and arrangement of the packer, when inflated, is such as to provide a seal between the tube wall and the ground material, thereby to inhibit the passage of liquid upwards towards the surface from the exit port, outside the tube-wall.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[004] By way of further explanation of the invention, exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which:
Fig I is a sectioned side view of an apparatus for injecting liquid into the ground, including a first drive-point apparatus.
Fig 2 is a sectioned side view of an apparatus for injecting liquid into the ground, including a second drive-point apparatus.
Fig 3 is a sectioned side view of an apparatus for injecting liquid into the ground, including a third drive-point apparatus.
Fig 4 is a sectioned side view of a first above-ground portion of an apparatus for injecting liquid into the ground.
Fig 5 is a sectioned side view of a second above-ground portion of an apparatus for injecting liquid into the ground.
Fig 6 is a sectioned side view of a third above-ground portion of an apparatus for injecting liquid into the ground.

[005] The apparatuses shown in the accompanying drawings and described below are examples which embody the invention. It should be noted that the scope of the invention is defined by the accompanying claims, and not necessarily by specific features of exemplary embodiments.

[006] Diameter is at a premium in borehole engineering. Where the job can be done with smaller-sized boreholes, smaller size is preferred. In the smaller sizes of borehole (i.e less than about ten cm diameter, and preferably less than five cm) drive-point technology is favoured. In the slim drive-point apparatuses, it is not practical to provide down-hole pistons, cylinders, power actuators, valves, and the like, and so all, or most, of the machinery and mechanism has to be provided at the surface.

[007] Fig 1 shows an apparatus for effecting a small-diameter borehole, having a drive-point configuration. Here, the apparatus is driven down into the ground, either by simple pressing or by the use of a hammer, rather than by rotary drilling. (The manner of driving the apparatus into the ground is conventional, and is not described herein.) Drive-point devices are especially suitable for use in ground materials (soils) of an easily-penetrable nature, such as gravels or tills, and are suitable for use at depths of e.g ten metres, and rarely more than thirty metres.

[008] The apparatus 21 in Fig 1 includes a drive-head 23, and a tube 25. The wall of the tube 25 defines an interior chamber 27, which extends to the surface. An exit port, comprising several through-holes 29, communicates the chamber 27 with the ground material 30 outside the tube.

[009] At the surface, injecting and pulsing machinery 32 is provided. Various arrangements can be used for effecting pulsing, of which three are illustrated (diagrammatically) in Figs 4,5,6.

[0010] A packer 34 is incorporated into the apparatus 21.
During driving, the packer 34 is uninflated, and resides in a recess 36 in the wall of the tube 25. When the apparatus has been driven to its desired working depth, as shown, now the packer 34 is inflated.

(0011] One manner of inflating the packer 34 is for the packer to include a mass of e.g bentonite, which swells upon contact with water. The bentonite may be arranged to be in contact with a hole in the tube 25, whereby, when water enters the chamber 27, the water contacts the bentonite, and causes it to swell.
Alternatively, it can be arranged that water present in the surrounding ground material contacts the bentonite, and causes it to swell. Of course, the designer should see to it that the swelling of the bentonite is delayed to the extent that no significant swelling occurs actually during driving.

(0012] Generally, it is not possible later to remove a bentonite packer. Similarly, a packer made of concrete generally cannot be removed. If it is desired to deflate the packer, the packer can be made as an inflatable bag, and a pipe connects the bag to the surface, and the inflation/deflation is effected and controlled from the surface, in the manner well-known to designers of down-hole packers.

[0013] The drive-point apparatuses are used generally in the looser, shallower, ground materials. Although these soils are horizontally stratified, and can be resistant to vertical movement of the liquid, it sometimes happens that the action of driving the drive-point device into the ground can create what almost amounts to an open conduit, around the device, caused by disturbing the ground. In that case, when the liquid is injected from the exit port, the liquid tends simply to leak upwards, by squirting back up to the surface, around the outside of the device, up the said annular conduit created by the loosened soil material.

[0014] If that happens, the desired lateral (radial) spreading of the injected liquid, over a large radial area, can be significantly spoiled. It is recognised that this tendency for the injected liquid to squirt upwards may be alleviated by providing the packer 25 around the drive-point device, just above the exit port 29 that provides liquid-transfer communication between the tube 25 and the ground formation. The presence of the packer has been found very effective in ensuring the injected liquid spreads laterally into the formation, rather than upwards towards the surface.

[0015] Fig 2 shows a different kind of drive-point apparatus, which includes an inner tube 41 and an outer tube 43. The inner tube 41 is fixed to the drive-point 23, while the outer tube 43 can slide axially relative to the inner tube 41. The outer-tube 43 engages a driving shoulder 45 on the drive-point 23 during driving, but when the drive-point has reached its working depth the outer tube 43 is withdrawn upwards, which exposes a bottom portion of the inner tube 41. This bottom portion is perforated, at 29, to form an exit port from the interior chamber 27, whereby liquid can be injected from inside the inner tube 41 out into the surrounding ground material.

[0016] Packer 47 prevents the injected liquid from passing upwards, i.e from passing upwards between the inner and outer tubes, and from passing upwards around the outside of the outer tube 43. The packer 47 is inflated after the outer-tube 43 has been withdrawn upwards. The packer 47 may be of bentonite which is inflated by contact with water, or the packer may be inflated by a pipe from the surface.

[0017] As shown in Fig 3, in some cases the ground strata include a layer 50 of loose soil near the surface, with a layer 52 of denser soil below. Now, it may be simple to provide a large-diameter hole 54 in the loose soil, while the narrower drive-point hole 56 is made in the denser material underneath. It can be effective to place the packer 58 in the looser ground, i.e in the larger diameter portion 54 of the borehole.

[0018] Where the packer is located around the outer tube 43, a seal 60 should be provided between the inner tube 41 and the outer tube.

[0019] In Fig 3, an inflation/deflation pipe 61 connects the packer 58 to the surface. Alternatively, in place of the inflatable packer 58, the loose or open space around the apparatus may be filled with concrete, bentonite, etc. In that case, again, the intention would be that the apparatus remain in the borehole permanently.

[0020] As discussed in the above mentioned CA-2,232,948, lateral penetration into the surrounding ground of an injected liquid is hugely enhanced by the procedure of slosh- or surge-pulsing. Here, a coherent body of liquid outside the borehole is caused to slosh or surge back and forth by alternately injecting liquid from the borehole and then sucking it back into the borehole. When this out-and-back pulsing is repeated, cyclically, over a prolonged period of time, the coherent body may be found to extend many tens of metres laterally from the borehole.
Furthermore, the portion of the aquifer in contact with the coherent surging body of water gradually becomes homogenised, and its porosity and permeability are improved. Even when the injection is pulsed, but without the reversal of flow that characterises surge-pulsing, the improvement in lateral penetration distance can be very worthwhile, as compared with just a steady application of a pressure head. The enhanced lateral penetration arising from pulsing is especially vulnerable to being spoiled by the escape of injected liquid upwards around the drive point apparatus. Therefore, it is especially important to include the packer when pulsing is being done.

[0021] Injecting a remediation substance, whether dissolved or suspended in water, or itself a liquid, evenly and thoroughly over the whole area around the borehole, is one of the desired effects of surge-pulsing. That effect would be spoiled by the upwards leakage, and it is such upwards leakage that is prevented by the presence of the packer, as described.

[0022] In Fig 4, a piston 65 floats up/down in a cylinder 67.
Compressed air is supplied via a valve 69, which drives the piston 65 down and forces liquid from inside the inner tube 41 out into the ground formation. For the return stroke, the valve 69 is simply exhausted. Now, the porosity of the ground formation being of a resilient nature, liquid will flow back into the inner-tube 41, through the perforations 29, due to that resilience. Make-up liquid is added, to suit, through supply port 70, which is fed from a suitable reservoir.

[0023] Whether the injected liquid will flow back into the borehole when the driving pressure is released depends on the porous elasticity of the ground. Often, ground material (especially at shallow depths) is quite resilient in this sense, whereby a return flow of liquid back into the borehole happens when the piston is released, even if the piston is not mechanically drawn back.

[0024] Operating a pulse-generating piston can be useful in homogenising the ground around the borehole, even if the liquid does not return on the piston upstroke. For example, a steady positive pressure may be maintained at the liquid supply from the reservoir, whereby the pulsing action does create cyclic variations in flowrate, but does not cause the flow to actually reverse during the upstroke. Especially when the ground is barely saturated, this pulsing-without-reversing, though not as highly effective as pulsing-with-reversing, still can be effective to fill the interstitial pores and spaces more completely than simply injecting the liquid under pressure, and can be effective to advance the saturation more as a flat front than as a fingered front.
=

[0025] Also, even if the situation is such that the favoured surge- or slosh-pulsing (i.e pulsing-with-reversing) can be achieved eventually, it might be necessary first to go through a pulsing-without-reversing stage. Then, gradually, as coherence of the injected body of liquid is procured, pulsing-with-reversing takes over, leading to the great increases in saturation capacity, and improved homogeneity, of the ground.

[0026] If there is to be any chance of flow reversal during the upstroke, of course the (pressurised) supply of make-up liquid should be interrupted during the upstroke, using the valve 70.

[0027] Especially at greater depths, often there is not enough porosity resilience, and the piston must be mechanically drawn back on the return stroke. This can be done using compressed air, from the surface, as shown in Fig 5. Apart from the forced withdrawal of the piston, the Fig 5 apparatus operates similarly to the Fig 4 apparatus.

[0028] Fig 6 shows a set-up in which pulses are created without the use of a mechanical piston. Here, air pressure is built up in an air chamber 74. When the valve 76 is opened, this pressure is dumped into the inner-tube 41, which causes the liquid in the inner-tube to pass out into the surrounding ground through the exit port. At the end of the expulsion, the excess air pressure in the inner-tube is released at the valve 78, and a fresh charge of make-up liquid is admitted through the valve 70. Liquid depth sensors, pressure sensors, etc, may be provided and used for timing the sequence of valve openings and closings, as required.

[0029] The described ways of initiating the movements of liquids should not be regarded as exhaustive, and other effective ways of creating the pulses are within the competence of skilled designers of down-hole machinery. For example, a piston can be driven by means of an electric actuator, which has the benefit of being highly controllable as to speed, acceleration, stopping points, etc.

[0030] The problems addressed by the apparatus as described herein arise mainly in the looser ground materials. The tighter (less permeable) ground materials tend to close tightly against the wall of the tube of the drive-point apparatus, and the tendency of liquid to leak upwards, around the tube, is minimal in tight soils.
Also, the loose soils, in which the problem occurs, tend to be near the surface, i.e at shallow depths, which is the area of preference for usage of the drive-point type of apparatus.

[0031] Thus, the invention preferably is used when the permeability, or hydraulic conductivity, of the ground is looser than about 0.1 cm/sec. The hydraulic conductivity of the ground is measured as the velocity of the liquid, in cm/sec, through the ground, per unit of imposed pressure gradient. The imposed pressure gradient is actually dimensionless, in that it is measured as a drop of so many cm of pressure head, per cm of length along the direction of the velocity. A permeability of 0.1 cm/sec is associated with fine silt or till. The clays, generally, are so tight that no steps need be taken to prevent upwards leakage. The 9a invention is suitable for use with very loose soils, such as large-grained gravels.

[0032] The packer itself takes up some annular space even when uninflated, and the uninflated packer should not be the radially-outermost component of the drive-point structure, or it might be damaged by contact with the ground material as the structure is driven downwards into the ground. Thus, preferably, the drive-head 23 is of a greater diameter than the overall diameter of the uninflated packer.

Claims

Claim 1. Apparatus for adding a liquid into porous ground material, wherein:
[2] the apparatus includes a drive-point structure, which is capable of being driven, from the surface, into the ground;
[3] the drive-point structure includes a tube, comprising a tube wall, which defines an interior chamber;
[4] the apparatus includes a source of a liquid, the source being located at the surface, and includes a means for transferring the liquid therefrom into the chamber;
[5] the tube wall includes an exit port, through which the chamber is in liquid transfer communication with the ground material outside the apparatus;
[6] the apparatus includes an expandable packer, and a means for expanding same;
[7] the packer is of annular configuration, and is located radially outside the tube wall, between the tube wall and the ground material;
[8] the packer is located above the level of the exit port;
[9] the packer is effective, when expanded, to exert pressure inwards against the tube wall and outwards against the ground material; and [10] the structure and arrangement of the packer, when inflated, is such as to provide a seal between the tube wall and the ground material, thereby to inhibit the passage of liquid upwards towards the surface from the exit port, outside the tube-wall.
Claim 2. Apparatus of claim 1, wherein the tube wall is liquid-tight, above the level of the exit port, in the sense of being free of through-openings through which the interior chamber could make liquid transfer communication with the ground material outside the drive-point structure.
Claim 3. Apparatus of claim 1, wherein:

[2] the drive-point structure includes a drive-head, which is positioned as a bottom-most component of the apparatus;
and [3] the drive-point structure includes a drive-strut, which is mechanically robust enough to transmit driving forces from the surface down to the drive-head.
Claim 4. Apparatus of claim 3, wherein:
[2] the apparatus includes an operable driving means, which is effective, when operated, to drive the drive-point structure, drive-head first, down into the ground; and [3] the driving means is effective, when operated, to drive the drive-point structure downwards, substantially without rotation of the drive-point structure.
Claim 5. Apparatus of claim 1, wherein the ground material in which the packer is located is relatively loose, having a permeability no tighter than 0.1 cm/sec.
Claim 6. Apparatus of claim 1, wherein the depth to which the drive-head of the drive-point structure is driven is no more than about fifteen metres.
Claim 7. Apparatus of claim 1, wherein:
[2] the tube of the drive-point structure includes an inner tube and an outer tube, and the outer tube is movable upwards axially relative to the inner tube;
[3] in a lowered position of the outer tube, the outer tube covers the exit port, and in a raised position of the outer tube the exit port is exposed to ground material around the drive-point structure; and [4] the apparatus includes an operable means, located at the surface, for raising the outer tube, which is effective, when operated after the drive-point structure has been driven into the ground, to raise the outer tube, and thereby uncover the exit port.
Claim 8. Apparatus of claim 1, wherein [2] the source of liquid includes a reservoir;
[3] the means for transferring the liquid from the source into the chamber is effective to place the liquid in the chamber at a substantial head of pressure; and [4] the means for transferring the liquid from the source into the chamber is effective to deliver the liquid into the chamber, and thence into the ground, at a sufficiently large volumetric flowrate of liquid as to saturate the ground material around the drive-point structure, and to keep it saturated.
Claim 9. Apparatus of claim 1, wherein:
[2] the apparatus includes an operable, powered, pulsing means, which is located at the ground surface;
[3] the pulsing means is effective, when operated, to periodically and cyclically discharge respective substantial charge-volumes of the liquid out of the chamber into the ground material around the drive-point structure.
Claim 10. Apparatus of claim 9, wherein the pulsing means includes:-[2] (a) a variable-volume chamber;
[3] (b) an operable, powered, means for forcefully reducing the volume of the variable-volume chamber, and for then enabling the volume to increase, on a cyclic repeated basis; and [4] (c) a port for admitting make-up volumes of liquid from the source of liquid; and wherein:
[5] the pulsing means is located at the surface; and [6] the apparatus includes a transfer conduit, for transferring liquid from the variable-volume chamber at the surface to the interior chamber located in the ground material.
Claim 11. Apparatus of claim 9, wherein the pulsing means includes:-[2] (a) a pressurisable chamber;
[3] (b) an operable, powered, means for increasing the pressure of a fluid in the pressurisable chamber, and for then enabling that increased pressure to dissipate, on a cyclic repeated basis;
[4] (c) a port for admitting make-up volumes of liquid from the source of liquid; and wherein:
[5] the pulsing means is located at the surface; and [6] the apparatus includes a transfer conduit, for transferring liquid from the pressurisable chamber at the surface to the interior chamber located in the ground material.
Claim 12. Apparatus of claim 1, wherein the packer is both inflatable and deflatable, and the apparatus includes a means for inflating and deflating the packer, which is located at the surface.
Claim 13. Apparatus of claim 1, wherein the packer contains a material, such as bentonite, that expands upon contact with water.
Claim 14. Apparatus of claim 1, wherein the packer comprises an annulus of concrete injected under pressure around the tube wall.
Claim 15. Apparatus of claim 1, wherein the exit port comprises several through-holes formed in the tube wall, and a protective screen physically prevents ingress of dirt into the interior chamber via the through-holes.
Claim 16. Apparatus of claim 3, wherein the drive-strut comprises the tube wall.
Claim 17. Apparatus of claim 1, wherein the tube wall, in the region of the exit port, has an overall diameter of no more than ten cm, and the drive-head extends down into the ground, from the surface, no more than thirty metres.
Claim 18. The use of the apparatus of claim 1 to inject a remediation liquid into a body of contaminated water in an aquifer.