Unexpected Challenges: Sand, Soil, Clay And Rock On 4600-Foot Bore

June 2011 Vol. 66 No. 6

Two-bore decision
Davidson explains factors that led to drawing up of the drill plan that called for completing two separate bores. “The installation plan intersected with a highway and continued beneath an environmentally sensitive expanse,” Davidson said. “The route had been pre-planned when we got it, so we walked the route to gauge the physical topography of the area. After completing a physical inspection, we felt two separate bores would be the best approach, especially since the distance under the environmentally sensitive area was so long. What we didn’t anticipate were the challenges we would encounter underneath.”

After a final evaluation of the soil profiles gathered by project owner Regency Energy, and a completion plan timeline firmly established, Davidson’s crew made equipment and tooling selections they felt would be most efficient to complete the job.

“Based on the length of the crossing and the specified pipe size, we felt the D500x500 was the best fit for the job,” Davidson explains. “Of the models in our fleet, it was best suited for both phases of the project, especially the long bore where we knew there would be environmental sensitivities to contend with.”

Within the first bore, a variety of soil conditions were encountered ranging from sand, hard clay and then some rock. These variations continued throughout the duration of the bore. The core samples showed a two-inch layer of rock but didn't offer any indication of the exact distance, width or depth of the formation. After drilling approximately 300 feet through the tough stuff, the initial soil profile changed abruptly, requiring Davidson’s crew to pull back and adjust their approach, and install a 6 3/4-inch mud motor with an 8 1/2-inch drill tooth bit. The mud motor was selected because of its effectiveness in navigating through harder formations.

"The mud motor is powered by your mud flow and is designed to cut through harder formations," Davidson explained. “The mud pressure makes the drill bit work better by allowing it to turn on the end. This proved to be a good decision as it allowed us to complete the project more efficiently and improved our production rate."

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