Time and Cost-Savings Achieved While Drilling in Hard Rock

Time and Cost-Savings Achieved While Drilling in Hard RockWhen Eastern Missouri Industries, a leading construction contractor and utility installation company, was tasked to install thousands of feet of water, sewer and other utility service lines for a privately owned and operated Luxury Christian Summer Camp in Patterson, Mo. — a remote part of the state — it went to Vermeer Sales and Service M.I. Inc. (Vermeer Midwest) for assistance to find a rock drilling solution to complete the job.

Because the project involved a significant amount of drilling in rock on the river crossings, Vermeer Midwest sales representative Tim Noltkamper contacted Carl Seeliger with Mincon for hard rock drilling solutions. Vermeer Midwest, located in Chesterfield, Mo., is a platinum distributor for Vermeer Mfg. The company is also a dealer for Mincon Hard Rock Drilling Systems.

Project Details
The profile of the job was to drill 300- to 400-ft shots in hard limestone to install 12- and 8-in. HDPE pipe. The maximum depth of the shots is 18 to 20 ft. The proposed tooling for the job was a Mincon HDD50 pilot hammer that drills a 5 ¼-in. pilot hole and a Mincon HDD80PR Pull Reamer with a 12-in. Pull Reaming Drill Bit and a 16-in. Pull Reaming Drill Bit. The tooling was used on a Vermeer D36x50 SII drill rig with a 1,350 cu ft feet per minute compressor with a maximum operating pressure of 350 lbs per sq in.

Once onsite, setup was completed to connect the compressor and water supply to the Support Station and then to the D36x50 rig. The HDD50 pilot hammer was connected to the drill pipe and torqued up and a full safety check was performed prior to starting up the compressor. The 300- to 400-ft pilot holes were completed in less than eight hours. The penetration rate for the pilot holes were between 15 to 20 minutes per 10-ft rod. The maximum steering was 3 to 3.5 percent per drill rod.

Time and Cost-Savings Achieved While Drilling in Hard RockCobble Challenges
When drilling commenced, it was discovered that there was about 30 to 40 ft of cobble at the beginning of the hole. The cobble presented a challenge, however, nothing that couldn’t be overcome. The same conditions were encountered at the exit side of the bore hole, which were similarly dealt with. Once the pilot hole was completed, the HDD50 was removed from the drill string at the exit side of the bore and replaced with the HDD80PR Pull Reamer with a 12-in. reamer bit. The hole was reamed out to 12 in. and then the HDD80PR was removed and a standard dirt head was installed to fish the drill pipe back to the exit side of the hole.

Once completed, the HDD80PR was re-installed with a 16-in. Pull Reamer Drill bit and reamed out. The penetration rate while pull reaming the hole was between 25 to 30 minutes per 10-ft rod. This rate slowed some when dealing with the cobble at the entry and exit sides. During all pneumatic drilling operations, approximately 2 gals per minute of water was used to keep the bore hole clean. The pilot hole and pull reamer bits were performing excellently and the wear due to the limestone formation was not excessive. The picture of the pull reamer bit (on  pg. 50) shows the bit with approximately 2,000 drilled ft of wear.

Due to the cobble at both the entry and exit sides of the shot, it was necessary to shore up the walls of the bore where the cobble was. This was done by fishing the drill pipe back to the exit side as carried out previously and installing a standard reamer and flooding the hole with approximately 500 to 1,000 gals of bentonite slurry, depending on the suspended solids being retrieved. Once completed, the hole was re-fished and the HDPE product was pulled through.

Project Completion
The finished bore took six days to complete, with the first day dedicated to the pilot hole. Days two through five were spent reaming the 12-in. and the 16-in. passes. The sixth and final day was spent completing the stabilization of the bore hole walls and pulling the HDPE product. Additional bores were completed in a similar fashion in six days or less.

“With the ability to pilot out and open the bore path up to 16 in. in solid hard rock in six days or less is a solution that Eastern Missouri Industries will benefit from,” stated Noltkamper. “We did have some chunk or small cobble type rock to fight through but even with that, the Mincon Hard Rock Drilling system, coupled to the Vermeer D36x50 SII, has been doing very well.”

The time-savings on the job by using the Mincon hard rock drilling system was estimated to be substantial. Typical penetration rates when using a low-flow mud motor can be 20 to 30 ft per day and similar when using a conventional reamer. The amount of bentonite slurry used on the job was also dramatically reduced. The low-flow mud motor and conventional reamer would typically use a maximum of 50 to 60 gals of bentonite slurry per minute.

Eastern Missouri Industries have been happy with the outcome of this project so far and the success and time-savings experienced with the Mincon hard rock drilling system. At the time of this article being written, the project is still ongoing.

Frank Purcell is vice president of Mincon Inc., which is based in Roanoke, Va.
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