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Back to Glennallen well Rutter and Wilbanks goes for a second Ahtna sidetrack to test ’07 gas discovery Alan Bailey Petroleum News
In a new drilling initiative that Texas-based Rutter and Wilbanks hopes will finally vindicate its multiyear search for natural gas near Glennallen in Alaska’s Copper River basin, the company has re-entered its Ahtna No. 1-19 well, about 12 miles west of Glennallen and 180 miles northeast of Anchorage, to test a gas discovery that it made in the upper Nelchina sands when drilling the Ahtna 1-19A sidetrack in 2007.
“We’ve re-entered the well and we’re now at our previous kickoff point,” Bill Rutter Jr., the company’s vice president, told Petroleum News Aug. 31. Rutter said that drilling at Glennallen had started around Aug. 22 and that, if the drilling works out as planned, the drill bit should enter the gas reservoir in a few days time.
“By the end of the week or over the weekend we should be testing it,” Rutter said.
Using the same Schlumberger coiled tubing unit that Rutter and Wilbanks had used to drill the Ahtna 1-19A sidetrack, the company has augured down through the cement used to plug the well in 2007, clearing the cement out of the well casing and restoring the full diameter of the well bore in preparation for drilling a second sidetrack into the gas reservoir, to test the size and nature of the gas pool.
Perhaps 150 bcf Rutter said that he is fairly sure that there is 50 billion to 150 billion cubic feet of gas in the Ahtna prospect.
“We’ll probably have deliverability of 20 million to 30 million (cubic feet) per day,” he said.
And although there is a local market in Glennallen for the gas as a fuel for electricity generation, Rutter thinks that a find of this size would need a larger market, such as the sale of gas in Fairbanks.
However, success with the well is contingent on demonstrating that gas production would not be accompanied by excessive water production — high-pressure water that has in the past entered the well above the gas reservoir has plagued previous attempts at drilling. So, to stem the flow of water into the well drillers have used cement to “squeeze” the subterranean channel from which the water originates, and on Aug. 31 the drilling team was waiting to see whether the cement had successfully set, hoping that the setting would not be disrupted by water continuing to flow into the well.
“We believe we got a good squeeze. … The pressure kept going up, so we think we’ve gotten some resistance and that the cement will set,” Rutter said.
Once the cement has set, the drillers will perforate the well casing about 50 feet above the previous sidetrack point to determine whether the flow of high-pressure water into the well has ceased. And if the flow has stopped, the next step will be to cut open a new sidetrack window in the casing, and drill the new sidetrack, Ahtna 1-19B, into the gas reservoir, Rutter said.
Started 2004-05 The Rutter and Wilbanks Glennallen well venture originally started in the winter of 2004-05 when the company shot some seismic over a structure near an Amoco well drilled about 25 years earlier. And in 2005 the company drilled what should have been a straightforward exploration well, the Ahtna 1-19. The well was drilled to its target depth of 7,500 feet without apparently finding any gas. But because of a high pressure zone at a depth of 1,200 feet, the company had to use heavy drilling mud that damaged a potential gas reservoir partway down the well.
“We got 1,000 pound pressure at 1,100 feet,” Rutter later told Petroleum News. “In the annals of the oil business this is a very rare occurrence, almost impossible to comprehend.”
The reason for the high pressure seems to be recent uplift of deeply buried rocks along a fault — the rocks had been subjected to high pressure at depth and the pressure is still slowly bleeding off, Rutter said.
In the fall of 2006 the company made an unsuccessful attempt to penetrate the damaged section of the reservoir rock adjacent to the well bore, using a Cad Pressure Central snubbing unit.
“They got stuck again. … They couldn’t make the Perf Drill work; they couldn’t get more than 3 or 4 feet out into the formation,” Bill Rutter III told Petroleum News in October 2006. “It was an expensive experiment and it didn’t work. We’re coming back in the spring with a drill rig.”
Returned in 2007 The company duly returned in 2007 to drill the Ahtna 1-19A sidetrack well into the reservoir using the Schlumberger coiled tubing unit and in June 2007 announced the gas find in the upper Nelchina at a depth of 4,300 feet.
But the well was producing excessive amounts of water along with the gas, even though resistivity logs suggested that relatively little of this water originated in the reservoir. To determine whether gas could be produced viably and to better understand how much gas the reservoir contains, Rutter and Wilbanks decided that it would need to drill a second sidetrack. And so, after a two-year hiatus while the company tried to secure the use of a suitable drilling rig, drilling of that sidetrack is now under way.
“If I can get a rig that can re-complete the well I think we’ll have a gas discovery,” Rutter said in 2008. “We know how big the structure is. What we don’t know is how much of the structure has gas in it. Is it filled to the brim, or is it just up there in the very peak, because we drilled right on the top of the structure?”
So is this new drilling project the final, successful installment of a saga in which the initial estimated cost of $2 million had already ratcheted up to $20 million prior to bringing the coiled tubing unit back to the well site this summer? Rutter hopes so.
“It’s been one delay after another,” Rutter said. “I’ve made my reservations to go up there four times.”
Editor’s note: The Copper River Record contributed to this story
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