Water Well Journal
Issue link: http://read.dmtmag.com/i/465664
When the target indicates the bore- hole is drifting from plumb, the driller can pull back and re-drill that section of the borehole and get it back into plumb. Careful attention paid to the straight- ness of the borehole every hundred feet will help to keep a well straight. Work- ing the borehole while drilling the pilot borehole, or working with the reamed borehole before installing the casing, gives the contractor a much better chance of having a completed well that meets post-construction alignment standards. Intense Accuracy Gyroscopic deviation survey tools can also be run in open boreholes when- ever there's a need to either hit a target at depth, or construct a very plumb well. Gyroscopic deviation tools are typically more accurate, but they're typically run by outside wire line service contractors who have these special tools. These gyroscopic-driven tools are so- phisticated and may seem to be expen- sive. But when compared to the cost of re-drilling a well, they're good insur- ance for reaching your desired outcome. The gyroscopic deviation tools col- lect and store digital data while they are being run that allows the wire line con- tractor to construct pictorial representa- tions of the data in various formats. Two examples of the presentations available from a survey of a completed well are shown. Figure 3 shows the plan view of deviation from the starting point at the top center of the well to the bottom center of a 1004-foot, 16-inch- diameter well. Figure 4 is view of deviation from plumb of the same well in vertical north-south section. This well is documented by the gyroscopic to be 0.78 feet out of plumb at the total depth of 1004.53 feet. Water well contractors can use a col- lection of tools and devices in their at- tempt to drill a straight or nearly plumb well into which they endeavor to install a well casing as nearly plumb as possi- ble. Their choice of tools may depend upon a number of factors, including their personal experience in their market area. Plumbness and alignment are not al- ways so important for a domestic well, but it can be for public supply, indus- trial, agricultural, and other high capac- ity efficient water wells—especially those to be equipped with a line shaft turbine pump. Here, plumbness and especially alignment can be critically important. STRAIGHT WELLS from page 21 waterwelljournal.com 22 March 2015 WWJ Figure 1. A Totco tool drops a plumb bob down a well toward a target to determine if the well is drifting from plumb. Figure 2. An indentation near the middle of the Totco target from the dropped plumb bob shows this target is straight and plumb. Figure 3. A gyroscopic deviation survey tool's plan view of deviation from the starting point at the top center of the well to the bottom center.