Wells – Packers or plugs – Expanded by confined fluid from central chamber – pump or...
Patent
1989-05-10
1991-09-17
Melius, Terry L.
Wells
Packers or plugs
Expanded by confined fluid from central chamber, pump or...
166203, 277 34, E21B 33127
Patent
active
050486055
DESCRIPTION:
BRIEF SUMMARY
This invention relates to packing-seals, of the kind that are used to isolate the various levels in a borehole. The boreholes in question are made in the ground, for example for the purpose of testing for contaminants that may be present in groundwater.
The general construction of such packing-seals, for use in a groundwater sampler, may be described as follows. The sampler itself includes a tube of PVC or other suitable material which is placed in the borehole. The tube contains one or several sampling ports, which are set at predetermined depths in the borehole.
Each sampling port is sealed off from the remainder of the borehole by respective packing seals, placed above and below the sampling port. The (vertical) distance apart of the packing-seals may range from a few centimeters to several meters.
Such packing seals have the requirement to be able to expand. When the tube is being lowered into the hole, the packing-seal must be clear of the walls of the borehole, whereas, once the packing-seal is in position at the correct depth, the packing-seal must expand into intimate sealing contact with the borehole wall.
In order that the packing-seal may be expandable, conventional packing-seals have been inflatable from ground level, or have been based on the use of a material, for example bentonite or Dowell Chemical Seal Ring Gasket (Trademark), which expands considerably when soaked in water.
Packing-seals may or may not be designed to be retrievable from the borehole.
Attention is now directed to the manner in which a packing-seal cooperates with the borehole. The borehole is drilled into the ground that is being sampled. It is normally the case that the type of ground from which the samples are to be taken is the kind that includes several different stratas, and various minor faults and pockets, because that is the kind of ground that is most apt to lead to the spreading of contaminants in the groundwater. Under these conditions, the packing-seal therefore is required to seal against what may be a very imperfect borehole-wall surface.
The requirements of the seal to provide a complete and reliable constraint against leakage of groundwater past the seal, on the other hand, are quite stringent. If the seal leaks, there is often no way of discovering the fact that the leak has occurred. The sampler apparatus continues to allow a sample of the water to be taken at the sampling port, and the analyst has no way of knowing that the water in the sample may have leaked in from a different depth.
This invention is aimed at providing, without undue expense, a packing-seal in which the analyst may have a high degree of confidence that the packing-seal is actually sealing, even though the analyst knows that the borehole wall surface may be imperfect due to fissures, faults, pockets, minor cave-ins, non-cohesive material, and the like, in the borehole wall.
Turning now to the physical construction of the packing-seal, hitherto. When the packing-seal has been of the kind that uses a water-expandable substance, such as bentonite, the bentonite is contained in the annular space between the PVC tube and a rubber sleeve. The rubber sleeve is secured to the PVC tube above and below the bentonite by means of clamps or end-grips. Between the end-grips, the PVC tube is provided with slots or holes so that the interior of the tube can communicate with the bentonite. Once the packing-seal is located in position, water is fed into the PVC tube from the surface, and this water flows out through the slots into contact with the bentonite, which consequently expands. The potentially-contaminated water that is to be sampled in the borehole must of course be kept sealed and separated from this water from the surface.
Bentonite, and other water-expandable materials, expand with a considerable force. If the borehole wall surface is strong, the bentonite is contained, and will be restrained from further expansion. But if the wall surface is locally very weak, or not present, the bentonite will continue to expand, with only the rubber sleev
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patent: 2781852 (1957-02-01), Rumble
patent: 3085627 (1963-04-01), Sodich
patent: 4310161 (1982-01-01), Streich
patent: 4406461 (1983-09-01), McGill
patent: 4544165 (1985-10-01), Coone
patent: 4838079 (1989-06-01), Harris
Belshaw Douglas J.
Cherry John A.
Johnson Paul E.
Kuryllowicz Peter F.
Toon Donald A.
Melius Terry L.
University of Waterloo
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