July 19, 2022
The entire service area of Corpian Well Drilling Inc. of Boscobel, Wisconsin, lies within the Driftless Area. The area was affected by glacial runoff as the glaciers melted. Water working through the underlying limestone eroded it through dissolution, creating a subterranean drainage system. The inundations carved out the region’s rivers and streams.
Drillers in this area never know when they will hit fractures, fissures, crevices, voids, or even caves on the way down through karst — only that they will hit them. They can be convinced they have found a solid rock at 91 meters (300 ft). They might case off at that point, only to lose circulation again 80 m (60 ft) past the end of the casing.
Mike Beinborn, a fifth-generation driller, and owner of Corpian Well Drilling, Inc, once lost a fully cased upper well to karst’s unpredictable strata. To ensure it wouldn’t happen again, he adopted a unique drilling method and will only use TH60 water well rigs for their reliability and the close support he gets from the manufacturer’s Milwaukee service center.
Beinborn received a call on a Sunday night from a livestock producer whose well had failed. Corpian’s TH60 was drilling there the very next morning. It was an emergency.
The 2014-model TH60 featured a Peterbilt 367 with a 600 hp (447 kW) Cummins ISX engine. The same engine powers drilling operations through a transfer case, supporting the rig’s 40,000-pound pullback capability, two-speed rotary head, 18,000-pound (80 kN) casing winch, and a 900 cfm / 350 psi compressor.
The rig’s size and handling characteristics allowed Corpian’s chief driller, Rick Kazda, to fit it between the landowner’s house and garage. Kazda leveled the rig and set it up to drill a pilot.
Drilling a pilot hole first is not the typical water well drilling method used elsewhere. Many drillers start with a wide-diameter hole, find the bedrock, case, grout, then drill the smaller production bore to the desired depth. Beinborn starts with the smaller bore in a method similar to exploration or definition drilling. Kazda located the competent bedrock first with the 6-inch bit and then continued drilling farther.
Kazda ran the hammer on about 250 psi (17 bar), injecting foam to help lift cuttings. He nursed the penetration rate, constantly adjusting to efficiently keep hammering as he felt his way through the strata. He went through 10.4 meters (34 ft) of loose rock and clay from the surface before encountering 53.6 meters (176 ft) of limestone and crevices. Then after 12 meters (40 ft) of soft sandstone, he hit soft shale prone to swelling and sloughing.
At 80.4 meters (264 ft), he found what he was looking for, hard shale. He continued to 104 meters (340 ft), assuring himself that he was in sound bedrock. He was ready to open the hole for surface casing.
Kazda tripped out to open the hole to 83 meters (273 ft), setting a 6-inch casing in the hard shale. Beinborn prefers the security of a 51-mm (2 in) grouted annulus, giving him a sound seal in the inconsistent formation.
Because the highly varied strata can throw off even a shallow well bore’s straightness, perfect concentric casing placement in wells as deep as 183 m (700 ft) is just too difficult. Beinborn sticks with a 2-inch annulus.
Kazda completed the 6-inch production bore to a total depth of 116 meters (380 ft). Once the water was flowing, and all looked good, he began grouting. When cement hits an unpredictable void and runs laterally, he has to call the state for permission to use bentonite to seal off the bad areas and continue grouting to the surface.