Section 18

Well Construction Report

A Water Well Record should be prepared for each well that is drilled (see Appendix F). The record is used to guide future drilling, to ensure that the well screen extends across the appropriate thickness of the aquifer and that the well casing/screen has been lowered to the bottom of the hole. It is also useful if there is ever a need to conduct repairs on the well in the future.

Well records document details of drilling a borehole and completing a well. Well records should include the driller's description of: the geologic character of each formation; the depth at which changes were observed; the thickness of the various formations; the drilling speed; the depth to water or where water appears to have been reached; the depth at which drilling was stopped.

Drillers should collect representative samples at measured depths and at intervals that will show the complete lithologic character of the borehole. Formation samples should be collected at 1.5 m (5 ft) intervals and at every change in formation materials. Collected samples will consist of muddied cuttings produced by the action of the drill bit.

Awareness of changes in drilling action is vital in compiling an accurate and informative log. Observations made by the driller should be included in the log because the drilling action and penetration rate indicate the character of the formation and especially the depth at which a formation change is encountered (Driscoll, 1986). Therefore, the person making the log must pay close attention changes in drilling fluid level, to the motion of the rig and to the noise made by the rig.

When drilling with the LS-100, the drilling action in clay or shale will be smooth. An occasional "chatter" (drill bit and pipe rapidly shaking/jumping a little) or temporary reduction in penetration rate may indicate scattered gravel in clay and glacial till or concretions in shale. Continuous chatter usually indicates sand and gravel formations or sandstone. Smooth drilling with rapid penetration occurs in layers of fine sand (Driscoll, 1986). Silt and clay is less than 0.08 mm dia, fine sand 0.08-0.43 mm, medium sand 0.43-2.0 mm, coarse sand 2.0-4.8 mm and fine gravel 4.8-19.0 mm (Unified soil classification system).

The value of a systematic record of the drilling time for each drill rod is sometimes overlooked. Each significant change in drilling speed indicates a difference in the material being drilled. The top, bottom, and thickness of each formation can be approximated from drilling speed (Driscoll, 1986); Factors other than formation character also affect the drilling rate. These include weight on the bit, sharpness of the bit, diameter of the hole, type of bit, velocity through the nozzles in the bit and speed of rotation (Driscoll, 1986).

For example, weight on the bit increases as the hole is deepened and additional drill pipe is added, thereby increasing the penetration rate. While interpretation of the time log is a relative matter, the gradual increase in weight on the bit does not seriously affect the usefulness of the results.

References

Driscoll, F. (1986) Groundwater and Wells, St. Paul: Johnson Division