A schematic of a typical well is attached. The 12” pump housing casing is set
from ground level to a depth of 150m. This is sufficient depth to install pumps
to depths >120m. if required. The 12” casing is attached to 10” casing by a
concentric reducer. The combined 12” and 10” casing is run to a depth just
above the aquifer as identified from the geophysical log. When the casing
string is in position, it is cemented in the hole using the inner string cementing
method. A conceptual drawing of this is also attached. One of the advantages
of this method is that the casing string is completely and reliably cemented
from casing shoe to surface. This protects the casing from corrosion and
blocks any movement of water between aquifers of different depths. Once
cemented in place, the casing shoe is drilled out and the hole cleaned to the
depth required to install the stainless steel pipe and screen assembly. After
installation, the riser pipe from the 8” screen is sealed between the 10” casing
and 8” stainless steel pipe with a rubber K-packer. We have found that
attaching the stainless steel section directly to the mild steel casing results in
a weak point due to galvanic corrosion. This method does away with the need
for welding or threading and thus removes a potential failure point.