Well comes under suspicion in West Divide Creek gas seep
A gas well that was inadequately sealed could have been the source of a natural gas seep in West Divide Creek, industry officials say.Owned by EnCana Oil & Gas (USA) Inc., the Schwartz well stands about four-fifths of a mile from where natural gas was found bubbling up in the creek March 30. Joel Fox, an engineer for EnCana, said it is possible that the Schwartz well bore may have conveyed natural gas from a shallow, non-productive gas deposit to a natural fissure or fault, which gave the gas an avenue to the surface in the form of seeps.Fox, team leader for EnCanas South Piceance Group working in the Dry Hollow area south of Silt, said his company is trying to determine the source of the seeps by process of elimination. The Schwartz well was one possibility the company has studied. He insists that the idea is very speculative at this time.Cement disappeared into fissureAn unusual circumstance caused the company to pay special attention to the Schwartz well.When gas wells are drilled into rock and lined with steel casing, the space between the rock and the steel casing is filled with cement. This is done by pumping the cement down through the casing under pressure, so that it is forced back up around the casing, all the way back to the surface. This process is called squeezing.After the Schwartz well was drilled, cement was forced in from top to bottom, Fox said, although some wells are often just sealed off near the top to protect groundwater, and near the bottom to isolate the natural gas. The Schwartz well extends 6,514 feet below the ground.The drill rig was removed Feb. 9, Fox said. It wasnt until Feb. 15 that a crew discovered the cement, which at first came to the surface, had somehow fallen. The crew used an acoustical tool to find the top of the cement, and discovered it had sunk to 3,460 feet below the surface.Sometime between when the drilling rig moved off and when the completion rig moved on, Fox said, we lost some cement. A huge amount of cement, in fact, had disappeared. Fox guesses it may have flowed back down the well bore into a fissure or fault in the surrounding rock.The cement may take 12 hours or longer to harden, he said, so it had plenty of time to drain into a fissure before it cured.Well completed with hydraulic fracturingAt a depth of 3,460 feet, the sealed part of the casing was still well above the level of the Williams Fork formation, the tightly packed sand layer roughly 6,000 to 7,000 feet below the surface, where EnCana is finding commercially rewarding quantities of natural gas. So the company decided to go ahead with completion procedures. Completion includes perforating, or making holes in the well casing at the depth of the gas-bearing layer, followed by hydraulic fracturing.Once a gas well is drilled, crews often fracture the sandstone of the gas-bearing formation in order to free the gas to flow into the well. This is done by pumping water or other substances into the well at high pressure. Coarse sand suspended in the water keeps the fracture open once the water drains away.Schwartz well could be source of gasNatural gas was found to be seeping out of the ground and the streambed in West Divide Creek on March 30 by landowner Steve Thompson. Area residents soon began to question EnCana and the Colorado Oil and Gas Conservation Commission, the state agency charged with regulating the gas drilling industry, as to what had gone wrong to create the seep.Fox said its conceivable the Schwartz well could be the cause of the seep. The gas could be coming from a higher sandstone formation called the Wasatch, which contains natural gas, but not in commercially useful concentrations.The section of the bore that was not sealed with cement could have conveyed natural gas, between the steel casing and the rock, from the Wasatch formation to a fissure or fault at a different level, Fox said. It could have been the same gap into which some of the cement disappeared, or a different one.If theres any gas in the Wasatch that you dont have covered with cement, it could have migrated up to the surface, Fox said.Remedial work isolates suspect wellOn April 5, EnCana subcontractors did what Fox calls a remedial squeeze job on the Schwartz well. The well was cemented from top to bottom.If that was the source of the seep, weve taken that well out of the equation, Fox said. EnCana squeezed the nearby Brown well too, although there were no signs of a problem there, he said.It may be some time before it is known whether the Schwartz well was causing the seep, and it may never be known.Gas from the seep was tested for a chemical profile, or signature, and compared with gas from the Williams Fork formation. It was found to be identical. But no samples of gas from the Wasatch formation are available, Fox said, because it is not commercially extracted. And that might not be conclusive evidence.Theres a good chance that gas in the Wasatch has the same signature as the Williams Fork, Fox said.Although EnCana proceeded with its fracturing process before the well bore was fully sealed, there was no risk involved, said Walter Lowry, EnCanas director of community and industry relations.The engineers concluded that there was enough cement to isolate the fracture, and it was deemed safe, Lowry said.Moreover, Fox said, salty water used in fracturing would probably have been found in the creek, if fracturing had created a pathway from the bottom of a nearby well to the seep. Contact Jeremy Heiman: 945-8515, ext. firstname.lastname@example.org
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