The little big drillMarch 8th, 2012 | Posted by in RD20
In western Wyoming, at 7,000 feet above sea level, there is a mesa of consolidated rock that holds gas in fissures in the formation. Unlike other formations, where the body of gas rests in softer formations capped off from the surface, this is tight in the rock. Drilling gas wells closer together allows drill crews to save time, while maximizing the gas recovery. Atlas Copco’s RD20 also helps speed the process because of its fast setup and ability to angle drill at a much shallower depth than big conventional rigs.
Another big advantage of placing wells close together is that it minimizes the impact on the environment. A conventional drill site would require 6 acres per drilled well. By putting 36 wells on one 40-acre site, the overall drilling footprint is greatly decreased. This means more than 150 acres are retained for animal habitat.
Discovered in the 1970s, the gas near Pinedale, Wyoming, proved difficult to recover. The formation held the gas so tightly that fracking only sealed up the formation tighter. In recent years with improved technology that includes directional drilling and the use of high-pressure epoxy sands that are “tougher” to hold the formations open, the natural gas is not only more accessible, but the wells produce at a much higher rate than the average well.
By placing multiple well heads on one pad just 10 feet to 16 feet (3 to 4.8 meters) apart, it’s possible to put dozens of wells in a small footprint. “We have drilled as many as 36 wells on one pad,” says Zane White, owner of White Mountain Drilling.
At one time, a particular play had more than 40 big conventional rigs working in the area. Today that number is just over 20. White Mountain operates two RD20 rigs to advance the drilling operation ahead of the conventional rigs. By drilling the surface hole in the 1,700-foot (518-meter) range, White’s fleet allows the big rig the ability to get to total depth faster. Wells in the area will ultimately go to 14,000- to 15,000-foot (4,267- to 4600-meter) depths.
The big advantage
Because a conventional drill needs pipe to add weight to the drill string, and the RD20 has hydraulic pull down, standard is 30,000 pounds (13.6 metric tons). A mud motor requires down pressure of 30,000 lbs of force to turn. Although White has added 10,000 pounds (4.5 metric tons) with additional hydraulics, the well drilled by an RD20 can begin to angle off from vertical sooner, or more shallow than a conventional rig.
This becomes critical when placing multiple well heads on such a small footprint. A conventional rig wouldn’t be able to turn until it reaches 300 feet (91 meters); an RD20 can begin to angle from vertical at 80 feet (24 meters). “We kick off from the surface at an angle; this little rig can do it from the beginning,” emphasized White. This is a huge advantage to maximize well production.
By setting the surface casing with the RD20, White’s drills increase overall well completion time. “We speed up the development of a pad enough that the customer can get one more well done in the same time,” says White. “We may cost a bit more per drilled foot, but at $3 to $4 million per completed well, we ultimately save the company money and time.”
From the surface
When White’s crew begins on the site, he preps the site and drills the mouse and rat holes if needed. His crews then begin drilling the surface holes. The area is covered with 50 to 100 feet (15 to 30 meters) of glacial till and overburden. When beginning the hole with the RD20, the crew can choose to go with DTH hammer drilling or tricone.
“We can make it happen with the tricone, but if we hit a boulder, which is very common, it is easy to change out to hammer drilling,” says White. White Mountain uses a 14¾” tricone bit to start the hole. “We started here on total air using auxiliary compressors when the water got too much [at one time the work was all vertical drilling]. Today everything is on fluid and mud motors for directional drilling,” says White.
White’s crew completes a well when they set the casing. Another contractor will come and concrete the well, making it ready for the conventional rig to “walk” over the prepared surface well. The conventional rig will continue with long pipe to total depth.
A well that’s drilled to depth can have multiple frac zones. The well on the job site discussed in this article has 23 zones. Between each zone 100,000 pounds (45 metric tons) of sand could be used to hold the well open. One well could have a million pounds of sand used in the fracking process. According to Zane White, a well has three phases of life.
The first phase is free flowing under natural pressure. The second phase involves water flooding to force hanging oil or gas from the zone. The third phase is CO2 injection. The global average is 0.5 to 1 million MCF per day. This play on the mesa of Wyoming that covers about 60 by 50 miles in area produces as much as 30 million MCF a day with little water.
The average is 9 million MCF per day. “I’m not aware of other gas plays like this. Most are unconsolidated whereas this rock is like granite – all the way to the bottom,” says White. The formation has had much to do with the RD20’s advantage at mesa, but it’s the increase in productivity that has really proven the RD20’s worth. The RD20 is a little drill in comparison to a conventional triple, and it has certainly proven itself as a big player in the world of big rigs.