Wells – Processes – Producing the well
Patent
1987-02-09
1988-10-25
Suchfield, George A.
Wells
Processes
Producing the well
166 68, 166 69, 166227, 166228, 166242, 210170, 2104163, 21049701, E21B 4308, E21B 4312
Patent
active
047796820
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for the grit-free withdrawal of water from a well and also to a device suitable for this purpose.
BACKGROUND OF THE INVENTION
A known method for the withdrawal of water uses a vertical double tube, uniformly provided with openings, via which water is drawn off by means of a subaqueous pump (or other withdrawal device). However, this method only provides a rather low withdrawal capacity if it is required that the water withdrawn shall be grit-free, i.e. if sand particles above a critical grain size are not also to be drawn off from the surrounding water-bearing stratum.
This method with the device, the so-called suction current collection (SCC), is known from German Offenlegungsschrift 2,401,327. According to the latter, the so-called collection element of the SCC consists of two coaxially disposed tubes of different diameter with uniform transverse slots over the variable length, the hollow cylindrical gap between the two tubes being filled with a fine-grain granulate. This construction is intended to achieve the result that the horizontal approach velocity at the critical point R.sub.K (FIG. 1) is approximately constant over the entire effective vertical length of the collection element, the so-called drainage length L.sub.E. As measurements have shown, a uniform horizontal approach velocity over the entire drainage length cannot be achieved with the collection element known from German Offenlegungsschrift No. 2,401,327. For a uniform approach velocity at the critical point R.sub.K (FIG. 2) over the drainage length of the collection element this has the result that for a certain delivery rate a certain quantity of fine-grain sand particles is still entrained and consequently drawn off.
It is therefore the object of the invention to provide, for a certain delivery rate, a method for the grit-free withdrawal of water from a well and also an associated device, and in doing this at the same time to reduce further the energy consumption compared to conventional water delivery without SCC as a result of a still lower groundwater depression in the well area.
SUMMARY OF THE INVENTION
The measures provided according to the invention result in the particular advantage that a uniform flow profile over the drainage length is produced for a certain delivery rate at the point R.sub.K (FIG. 2) and consequently no sand particles above the critical grain size are drawn off. in addition, the drive power required for the pump used is lower than for the conventional SCC according to German Offenlegungsschrift No. 2,401,327 since the mean approach velocity in the water-bearing stratum is lower and the collection element consists only of a transversely slotted, thin-wall single tube with as large a diameter as possible, which tube therefore produces no appreciable loss in pressure in the radial direction across the wall.
According to an advantageous embodiment of the invention, a uniform flow profile at the point R.sub.K is achieved by keeping the product of the length element .DELTA.x, the flow velocity V.sub.ssc(x) into the slots in the wall of the collection element (slot velocity) and the relative, i.e. referred to the area of the length element .DELTA.x of the SCC, water passage area (x) (relative slot area .DELTA. slot factor) constant over the entire drainage length of the SCC. That is to say that the same partial water quantity .DELTA.V flows radially into the SCC through each element of length .DELTA.x of the drainage length L.sub.E. In flow science terms this can be explained by the fact that the radial pressure drop across the SCC wall decreases in a specified manner from top to bottom, and consequently the flow velocity in the water passage areas which is proportional to this pressure drop also becomes correspondingly less from top to bottom. In order, therefore, to achieve delivery rate .DELTA.V=constant, the relative water passage area has therefore to become increasingly larger from top to bottom (FIG. 3).
An absolutely uniform flow profile at the point R.sub.K (FIG. 2) wo
REFERENCES:
patent: 2019418 (1935-10-01), Lang
patent: 4014387 (1977-03-01), Fink
patent: 4624319 (1986-11-01), Van Der Borght
Kabelwerk Eupen AG
Suchfield George A.
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