Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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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.
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[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
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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
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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-
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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
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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
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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
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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
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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.
