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Gillette Rancher Experiments with Reinjection
Click here to view drainage diagram. A local rancher’s aquifer recharge experiment mirrored the results of a Montana state study. Gillette Rancher Robert Brug determined 25 percent of his shallow gravel aquifer wells had the right rock type to accept water easily. His results were identical to a recent study conducted by the Montana Bureau of Mines and Geology, which found water replacement, or injection, was possible in 25 percent of the Powder River Basin. The Road to Replacement- From a Landowner’s Perspective Brug was having countless problems with short water supplies on his ranch. He couldn’t provide the yearling steers he was running with adequate water all of the time. He didn’t have enough water to support the grass he was grazing. To get the water supply he wanted, he had to do something. Because CBNG development began on his property, he was able to develop a potential solution due to the associated discharge water. “Landowners should have input and choices relating to use of the water,” Brug said. He did some research and checked around a bit, leading him to believe that if he could place the CBNG water into aquifers that were depleted years ago, he could maximize his water storage and available surface land. In collaboration with BJ Kristiansen, geologist and coordinator of the Coalbed Methane Coordination Coalition, Brug started experimenting with water replacement into alluvial sandstone formations in late 2005. So far, his results have the same success rate as a state study conducted by Hydrologist John Wheaton and Geologist David Lopez, both of the Montana Bureau of Mines and Geology. The Road to Replacement- From the State’s Perspective The state study was prepared for the Montana Board of Environmental Review and the Montana Department of Environmental Quality. The board wanted technical information from a neutral party to address rule changes that would require coalbed natural gas developers to either place the discharge water in deep aquifers by injection, or treat the discharge water, when injection was not technically feasible. Developers said injection was not a feasible alternative in most situations based on injection pilots and experiments done by a variety of different operators. Therefore, it should only be considered as one tool out of The Water Management Toolbox, and not the sole solution because it can’t be used all of the time. MT State’s Results The study found the only possibility for injection, or water replacement, is in one layer on the top of the Fort Union Formation. In this layer, only 25 percent is porous enough to accept water. Therefore, injection is only possible 25 percent of the time. They study also found it is extremely challenging. Landowner’s Results Brug and Kristiansen planned to pump water into four wells in the Fort Union Formation, all which were located on Brug’s ranch. They never tested one well because it was obvious from the start injection would not work, since the well had been unused for decades. Of the three wells they tested: one was questionable if it would ever accept water, one well accepted water poorly (at one to two gallons per minute), and one well accepted water at approximately six to seven gallons per minute. “I have worked in the Tongue River Member for over 30 years and I know the aquifer characteristics as well as anyone would,” Kristiansen said. “That which doesn’t produce a lot of water won’t take a lot.” Kristiansen explained two layers exist on top of the Tongue River Member. The topsoil is the first, followed by a gravel layer and then bedrock Kristiansen and Brug believe they can place discharge water into the gravel layer and it should hold the water. But they have also found challenges. Foremost, is figuring out a way to isolate the location of the gravel body so they can define the magnitude and storage capacity of the gravel. Despite the challenges, they will keep trying new methods, find out what works and what doesn’t and move forward – all in an effort to ensure Brug’s livelihood on the ranch.
More Challenges Come Along With Injection Understanding the difference between re-injection, injection and gravity flow methods is important because it helps explain some of the existing challenges and limitations. Re-injection is actually re-injecting water into the producing zone (the same zone that produced gas.) Injection happens further away and places water into different zones than it was removed from. Sometimes the water is piped to an entirely remote location and injected into an entirely different zone. Water replacement only requires the force of gravity and does not require additional pressure like injection or re-injection does. Experts say there are many reasons behind the challenges. Hydrologist Tom Osborne said the hydrology of the Fort Union Formation is not conducive to re-injection. He said it is difficult to find the sandstones. “By nature, the deposits are not predictable.” He said that since January 2000, only a small percentage of permitted injection wells actually reported achieving any amount of injected water. “The fact is, it has limited success.” Additional complicated issues exist. Dave Searle, with Marathon Oil, said “Injection will cause additional surface disturbance.” Kristiansen said, when the water is placed deep into the ground, it is not available for beneficial surface uses like stock watering. “This is also a major concern, as it defeats a beneficial purpose of why a landowner/ operator would choose to inject CBNG water.” He said another issue at stake is placing water of different quality into an aquifer, or mixing the water quality. For example, he said, sometimes the introduced water is better than the existing water in the aquifer into which it is being injected. Re-injection, injection, and water replacement are weighed down by numerous limitations and challenges but all three methods can work. This is why they should be considered as tools, out of approximately 30 tools, out of The Water Management Toolbox.
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