From a practical standpoint, the biggest difference between vertical and horizontal drilling is in the stresses imparted to the casing during installation.
Vertical wells are completed by lowering a free-hanging string of casing into an oversized, ideally straight borehole. Unless the well is very deep, the casing is mostly subjected to minor compressive stresses during installation. Casing breakage during installation seldom occurs.
In contrast, horizontal wells require long strings of slotted or perforated casing to be dragged into a borehole that has deliberate bends and compound curves. Skin friction against the borehole invert and sides is relatively high and the tensile strength of plastic pipe may easily be exceeded by the drill rig’s pullback capacity.
A successful installation begins with a pilot bore that is as straight as practicable, minimizing bends. DTD personnel then select a reamer size that is appropriate for the soil conditions, casing diameter, and intended well use. One or more reaming passes may be performed using a variety of use-designed cutting tools, all combining a combination of mechanical and fluid cutting with drilling fluid used to circulate drill cuttings from the borehole. In general, tools that employ compaction to enlarge the borehole are avoided to minimize formation damage.
The selection of the proper casing for your installation depends on a variety of factors, including chemical compatibility, and several physical properties including tensile strength. High density polyethylene (HDPE) and high carbon steel are frequently installed. Stainless steel is also specified, but carbon steel may often be substituted (depending on the project) with significant cost savings and no decrease in performance. Call DTD for specific casing recommendations and design services.
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