Hard rock island

March 8th, 2012 | Posted by in TH60

Texas drilling company looks to the Atlas Copco TH60 as the latest in rig technology to get it through various formations.

Virdell Drilling Inc. is an example of a company that has adapted as technology has evolved to take advantage of the latest tooling. Many drillers who have been around a while can relate to this family’s story – and appreciate how far modern hard rock drilling has come. After looking at the black and white photos dropped by the drill site by family patriarch Taylor Virdell Sr., Taylor Virdell Jr., current head of the family business, reminisced with his father about the days when Taylor Sr. and the Virdell family elders, great grandfather James Sr. and grandfather James Jr., would drill sun up to sun down penetrating just 12 feet (3.6 meters) in the hard rock with cable-tool rigs.

Back in those days they drilled an 8-inch (20 cm) hole just because the heavier tooling got better penetration than lighter bits. Virdell Drilling has been serving central Texas since 1900. Central Texas has a lot of fast-drilling limestone with good fragmentation and water flow, but not in the Llano area near Fredericksburg, which is at the heart of Virdell Drilling’s working territory.

Today the man at the controls of the company’s new Atlas Copco TH60 is the fifth-generation family driller, Caleb Virdell. The Precambrian metamorphic formation near Llano contains hard abrasive granite, chert, gneiss and quartz. Caleb can hammer drill 12 feet (3.6 meters) in roughly 15 minutes – the depth that took his forefathers a full day to reach.

Virdell Drilling switched to a TH60 after first purchasing a T3W in 2006.

The Virdell family’s rig technology has evolved from cable tools to top head rotary drives and so has the family’s way of servicing rigs. Just as most vehicles today need a technician to spot issues, Virdell says, “I’m not an electrician or computer technician. Venture and Atlas Copco have been real good for us. We are with Atlas Copco today because of our relationship with Venture and their dependable support system. If we need anything we can call Venture and they are here right away.”

The company also works with Venture to support their tooling needs. The company purchases new Atlas Copco Secoroc Fusion DHD60 down-the-hole hammers, and also works with Venture to turn over the hammer casing and other hammer servicing. Each well in this area is developed open-hole to depth with a 6-inch DTH hammer. It’s finished with an 8 3/4-inch surface hole and 6-inch PVC casing sealed in place.

To do this, the crew drills to depth with the 6-inch hammer then goes back in the hole with an 8 3/4-inch hole reaming bit on 6-inch hammer. Regulations require the hole must be sealed from surface contaminants to 25 feet (7.6 meters). Once the hole is reamed and cased to the required depth, the crew goes back in with the 6-inch hammer and drills another few feet to remove all cuttings that have fallen to the bottom. Then they thoroughly flush the hole, giving the customer clean water. Virdell says 200 feet (61 meters) is as deep as they’ve been in this area and most wells won’t go deeper than 160 feet (48 meters).

Great drilling depths are achieved with Atlas Copco's TH60.

“We never know what the ground will be like in this area,” says Virdell. He has seen both solid granite with no fissures and well fractured ground with ample water. Today the well is drilled in a slight depression in an open pasture. Virdell thinks this depression may offer the possibility of a broken up formation below.

This location was the choice of the customer, who had the site selected by a person using a divining rod, also called “witching.” If no water was found Virdell had decided to try a spot about 50 yards (46 meters) up the hill where he had discovered “an obvious fault” and geologically upset ground with large broken rock exposed to the surface. Virdell says they have had lots of rain, which makes it hard to know if they will get a true look at where the ground water will flow in dry times.

Virdell says he would be happy with 2 to 3 gallons per minute (gpm) in this area. Many local residences use a tank to store groundwater because the flow rate is so low.

Choosing the right rig

This is the second Atlas Copco drill Virdell Drilling has run. The first was an Atlas Copco T3W purchased in 2006. After Virdell took a closer look at the features he needed the most, he decided on a TH60 for the most recent purchase. After years using a rig with a deck engine, Virdell says, “I really like how clean and wide open the deck is on this rig – it’s so uncluttered.” The TH60 is built on a Peterbilt 367 truck that features a 600 hp Cummins engine.

Power is important for drilling, but also is necessary to navigate the terrain. This area is known as one of the most beautiful parts of Texas, which is also called Texas’ Hill Country because of its often steep and continuously wavy landscape. “We can climb the hills around here and not even have to shift down. You just put it on cruise control. This is a real truck!” emphasizes Virdell.

Open deck space on the TH60 also helps keep the rig clean. Driving to well site locations for the company often includes moving through forested areas. Virdell says cleaning the mess from the deck of the T3W takes too much time and also adds time when servicing the components.

Heavy rains have made it difficult to reach some drill locations. Without portable fiberglass mats the rig buried to the axles.

Although he changed some time ago, Virdell has used 4½-inch drill pipe in the past, but switched to 3½ inch and found it beneficial. In the past the company drilled more municipal wells that were larger diameters. Now that they consistently drill 6-inch wells, he thinks the 3 ½-inch pipe allows for better flushing of the annulus when gravel or larger chips come from the well. On the well discussed in this story, at 90 feet (27 meters) a heavily fractured zone produced cuttings over an inch in diameter.

For Caleb Virdell, speed is the big advantage with the new TH60. He can trip from the hole much faster and the winch operates faster. His father Taylor agrees with that comment and adds idling while tripping – at a faster speed – also reduces fuel consumption. “Working faster at an idle, that’s where you see fuel savings.”

Today the well has reached 120 feet (36 meters) with the best flow coming from the fracture at 90 feet. The well produced 12 gpm after flushing the hole clean. Sampling the water, it showed 520 ppm of total dissolved solids. As a comparison, at 2,000 ppm Virdell says the water tastes salty. He says the lowest they’ve seen is 250 ppm, which is like rain water.

After 110 years Virdell Drilling has come a long way.Taylor wants to continue to provide the best service he can for his customers, which includes using the most advanced drills available.

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