June 2011 Vol. 66 No. 6
Features
Unexpected Challenges: Sand, Soil, Clay And Rock On 4600-Foot Bore
When Gary Davidson, president and co-owner of DrillTech Inc., based in Clarksville, TX, reviewed the results of soil samples provided him by project owner, Regency Energy Partners, he felt confident the mainline natural gas pipeline project his company was hired to complete in Louisiana would be a fairly routine horizontal directional drill installation. At first glance, the only thing that Davidson felt may be somewhat of a challenge was the length.
Davidson, who has been involved with drilling and pipeline installations since 1991, founded DrillTech with friend and partner Lance Downs in October 2007. The company has enjoyed steady growth ever since, and currently employs more than 20 people. The installation contractor specializes in trenchless pipeline installations with the assistance of what Davidson credits as the staple of his fleet: a Vermeer D500x500 Navigator drill.
Based in Dallas, project owner Regency Energy Partners owns more than 5,200 miles of gathering lines, including an ownership interest in the Regency Intrastate Gas System, a 450-mile intrastate pipeline located in North Louisiana. Regency’s assets are located in some of the most prolific gas producing regions of the United States, including the Haynesville, Eagle Ford, Barnett, Fayetteville and Marcellus shales.
Regency operates significant gathering and processing assets in four geographic regions of the United States and contracts with producers to gather raw natural gas from individual wells or central delivery points that likely have multiple wells behind them. The wells are connected via gathering lines through which the raw natural gas flows to a processing plant, treating facility or directly to interstate or intrastate gas transportation pipelines.
The project Regency Energy awarded to DrillTech was located near Logansport, LA, in extreme western Louisiana, just a stone’s throw from the Texas/Arkansas border and was an extension of an existing 24-inch diameter mainline fed by the output of raw material from several wells.
The drill plan specified the pipeline be installed in two separate bores; the first, a relatively standard shot of 1,938 feet and the second spanning some 4,628 feet. It was the second shot that would present challenges for the DrillTech crew.
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.”
The DrillTech crew completed the first bore in relatively smooth fashion after eight days, realizing production rates that averaged 250 to 300 feet per hour after making some initial minor adjustments. After reaming the bore in stages using a variety of incremental size reamers — ranging from 18 to 36 inches in diameter — the hole was swabbed and 969 feet of the 40-foot sections of 24-inch pipe, already welded together and strung out on stretched rollers, was pulled back through the bore. The equipment was then repositioned for tackling the second, longer 4,628-foot bore.
Quick change
Soil samples through the environmentally sensitive area had been taken from the projected entry and exit points and lacked any detailed information about what would be encountered in between. The bore began with some clay, followed by areas of sand; nothing of critical significance or that was particularly challenging at the onset. Suddenly, however, things began to change as the operator sensed a dramatic shift in conditions.
“Having previously drilled in the area before on different jobs, we were suspicious there could be several changes in the terrain over the course of the 4,600-foot shot,” Davidson says. “As expected, we did encounter a lot of variation in formations that the soil samples didn’t show, many of which surprised us.”
“These conditions were something that we didn’t anticipate, so we had to go to a rock reamer to cut through the formation,” Davidson explains. “We didn’t realize from the soil samples there would be this much rock and didn’t have the appropriate tooling to get through it on site, so we had to order a split bit hole opener. Because we discovered this when drilling the pilot bore we got that rolling and the bit arrived in time and never caused production to be halted.”
With the split bit hole opener installed, drilling commenced as the drill rig was outfitted with the tooling required to tackle the rock. The pesky rock and unpredictable abrupt changes to alternating ground conditions consisting of sand and varying densities of clay made the second bore tough to navigate. It also reduced production rates and extended the duration of the second bore to more than five weeks. But all things considered, Davidson was satisfied with the overall results.
“The project certainly wasn’t without its challenges,” he recalls. “But with good equipment, the right tooling and the experience of our drill operators having previously completed jobs in similar conditions proved to be a tremendous benefit. I’ve been involved with jobs that didn’t go nearly as well as this, despite how complicated it was. I felt like DrillTech did everything properly, the way it should be done. The Vermeer drill performed beautifully and has been a good investment for us.”
There’s little doubt that the abruptly changing soil conditions encountered by the DrillTech crew on this installation was the greatest challenge, compounded by the lack of detailed sampling data that would have better prepared them for what to expect. That said, Davidson was emphatic about the crucial role that the experience of his drill operator played in successfully overcoming the challenges presented by conditions below the surface.
“Never underestimate the value of a skilled drill operator,” Davidson says. “It takes some time to learn and our operators have what it takes to overcome most any challenge the earth can dish out. Sure, it takes some time to learn, but experience is the best teacher. Anyone can learn to drive a car, but not everybody can drive a NASCAR car. The same can be said for horizontal directional drilling. Anybody can get up there and pull levers, but you want somebody aboard that drill who knows what he’s doing and is also safety conscience. Safety is among the most important attributes an operator can have and is always top of mind with all DrillTech employees.”
FOR MORE INFO:
DrillTech Inc., (903) 427-0836
Vermeer Corp., (888) 837-6337, www.vermeer.com
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