|Research to Enhance Oil and Gas Development and Environmental Protection on Federal Lands
DE-IA26-06NT15467/Task 5: Joint Montana Regional Coalbed Natural Gas Ground-Water Monitoring Program
The goal of the program is to support decision makers by providing scientifically sound, long-term data; descriptions of the ground-water systems in coalbed natural gas (CBNG) prospective and producing areas of Montana; and models of future conditions in these areas. Specific data that are required include water levels, aquifer physical characteristics, and quality of the ground water. Descriptions of ground-water systems are based on interpretations of these data; these descriptions include baseline conditions, CBNG changes, human-induced non-changes, recovery, and ambient seasonal patterns. Models will be developed to improve predictive abilities for future decisions. This monitoring is specifically required by the Montana CBNG environmental impact statement (EIS) and will facilitate development of CBNG resources by providing information that facilitates more-efficient permitting and higher public confidence in decisions.
Bureau of Land Management (BLM), Miles City Field Office, MT
U.S. Forest Service (USFS), Custer National Forest, Billings, MT
Montana Bureau of Mines and Geology (MBMG), Billings Office, MT
Monitoring activities include site maintenance. At wells that are within the areas influenced by CBNG production, wellheads that include valves and pressure gauges are being installed. These wellheads prevent escape of methane and provide safety by allowing field personnel to check for pressure before accessing the well. Fences are then built around the wells for protection. Well SL-4AC is shown below as an example.
Outside the areas influenced by production from Fidelity and Pinnacle fields in Montana, and Wyoming CBNG production, ground-water levels and spring flow show normal seasonal variations. Long-term precipitation trends are reflected in some ground-water levels. Precipitation for Sheridan, WY, is shown on the accompanying chart and shows increasing cumulative precipitation through the 1940s, which did not decrease until the late 1970s. Within the areas influenced by CBNG production, water levels continue to respond to water withdrawals:
- West of the CX field along Youngs Creek, water levels continue to show trends similar to those previously measured. At WR-24, the Canyon coal continues a slow decline. At CBNG02-2WC, the Carney coal has declined a total of about 9 feet. At CBNG02-RC the Roland coal, which is not being produced, declined about 9 feet but recovered 3 feet during 2006. East of the Decker East pit, the first indication of drawdown has now been measured at wells WRE-24, WRE-25, WRE-27, WRE-28, and WRE-29.
- East of the Tongue River, water levels in producing coalbeds continue to drop as CBNG influence is being detected. WRE-18 first recorded a water-level drop but has rebounded. Nearby well WRE-16, also completed in the Anderson coal, shows a drop but no recovery. Interburden wells and wells across fault lines from production do not indicate response to CBNG production (see WRE-19 and WRE-17).
- The gradient between the Tongue River Reservoir and the CBNG production areas continuous to increase, but at a slow rate (WRE-13).
- Wells southwest of Fidelity’s CX field continue to show a recovering trend. A number of CBNG wells were turned off due to poor gas production. The water level in well WR-34 increased about 2 feet during this quarter. Total drawdown at this well was 150 feet. Now the water level is about 40 feet below static conditions, or about 70 percent recovery in the 3 years since CBNG water production was reduced.
- State line wells in producing coalbeds north of Wyoming’s CBNG development are beginning to be impacted by development. At site SL-2, the water level in the Canyon Coal has dropped by 4 feet, while Anderson water levels are increasing, a fact which is not well understood. At site SL-3 overburden sandstone and Smith coal wells have not altered from baseline. Water levels at the Anderson Coal well have decreased by 4 feet, and the Canyon Coal has decreased by 80 feet.
- North of the Tongue River Dam at the Coal Creek field, water levels in the Wall Coal dropped 11 feet (CBNG02-4 site), since first signs of drawdown (April 26, 2005). The rate of drawdown decreased, then increased again. The changes in the rate of drawdown may relate to proximity to the Tongue River, changes in pumping scenarios, or a combination of both. The change in hydrostatic pressure in the Wall coal has not migrated vertically to the overburden sandstone wells.
- North of the Nance project on Hanging Woman Creek in Wyoming, the Anderson Coal water levels have dropped nearly 40 feet since CBNG production began (SL-4AC). The overburden coal water level (SL-4SC) originally dropped about 12 feet but has now increased to within about 8 feet of original levels. Since the water level rose during the fall and winter months while the producing coalbed showed decreasing water levels, it is felt that the drawdown in the Smith coal is not a direct result of CBNG production effects migrating vertically. A new domestic supply well was installed near this site and may have an effect on the Smith Coal water levels.
- Water quality samples were collected during this quarter, and results of samples collected during the third quarter of 2006 were received from the laboratory. In the Tongue River alluvial aquifer near the state line, from 1991 through 2006 there has been no change in the midst of CBNG discharge (WR-59). Water quality there is dominated by Mg-SO4 with a total dissolved solids (TDS) of 5,600 mg/L. North of the Tongue River Reservoir dam, the TDS level is 747 mg/L, with ions of Ca-HCO3 dominating. Near the Birney Day bridge, the TDS level is 1,764 mg/L with ions of Na-HCO3. The water quality samples appear to reflect very localized conditions. Based on the water quality results, at the Birney Day bridge sample the alluvium appears to be heavily influenced by discharge from the Knobloch coal subcrop. In the Powder River alluvium near the state line, the water quality has not changed since 2005, with a TDS concentration of about 2,830 mg/L being dominated by CaNa-SO4.
- Shallow overburden sandstone at WR-17A rose 30 feet in response to infiltration from a CBNG pond from 2000 to 2003. Use of the infiltration pond was discontinued in 2003, and now the shallow water table is down to about 8 feet above baseline and is continuing to drop (recovering). The TDS load increased initially from 2,567 mg/L to 3,516 mg/L in 2002. The TDS has decreased since then, and the most recent measurement (November 22, 2006) was 3,434 mg/L. Continued decrease in the salt load in the shallow aquifer at this location is expected.
Partnership projects already exist with BLM and USFS. The regional monitoring program will ensure a sound scientific effort to monitor ground-water changes in CBNG production areas. The project will benefit all parties, including resource developers, regulators, land-management agencies, and the general public by providing critical information on baseline conditions and changes that occur during and after CBNG production. These data will facilitate decisions regarding permitting of leases, development of resources, and techniques for development. All data will be incorporated into the Ground-Water Information Center database, which is freely accessible to anyone.
A regional ground-water monitoring program has developed through long term partnerships among BLM, USFS, MBMG, and the U.S. Environmental Protection Agency (EPA). Monitoring associated with coal activities has been conducted by MBMG in this area since the mid-1970s. Monitoring plans are in place that are designed to document baseline ground-water conditions, changes due to gas and water production, and recovery of aquifers following development in the Powder River Basin (PRB) in Montana. In order to provide scientific data and interpretations for decision makers, the required monitoring data include water levels in wells, spring flow rates, and qualities and quantities of production waters and shallow ground water.
CBNG production continues in CX field in Montana and in Wyoming near the state line. Water production has begun in the Coal Creek field. The regional ground-water monitoring network documents baseline conditions outside production areas, changes to the ground-water systems within the area of influence, and the aerial limits of drawdown within the monitored aquifers. Outside the area of influence of CBNG production, ground-water conditions reflect normal response to precipitation and the long-term response to coal mining.
Water discharge rates from individual CBNG wells in CX field have been lower than predicted, averaging 3.1 gpm during 2005 from 516 wells. The highest water production rate, averaged over a 1-month period, was 30.1 gpm from one well, and some wells are producing methane without pumping water. Within CX field, ground-water levels have been drawn down by over 150 feet in the producing coalbeds. The actual amount of drawdown in some wells cannot be measured due to methane release from monitoring wells. After 6 years of CBNG production, drawdown of up to 20 feet has been measured in the coal seams at a distance of roughly 1 mile and a maximum distance of 1.5 miles outside the production areas. These distances are similar to, but somewhat less than, that predicted in the Montana CBNG environmental impact statement. Water levels in several wells near Ash Creek mine have raised in response to decreased water production by the gas company in that area. At Coal Creek field, 6 feet of drawdown during a period of 9 months has been measured at a distance of 2.5 miles from the nearest producing well.
Current Status (July 2007)
Project terminated due to budget shortfall.
Project Start: November 30, 2005
Project End: November 30, 2008
Anticipated DOE Contribution: $253,000
Performer Contribution: $69,000 (27 percent of total)
Other Government Organizations Involved: BLM, USFS, EPA, and MBMG.
NETL – John Ford (firstname.lastname@example.org or 918-699-2061)
BLM – Andrew L. Bobst (email@example.com or 406-233-2804)