Coalbed natural gas (CBNG) from the Powder River Basin (PRB) in Wyoming and Montana is a significant component of the U.S. natural gas supply. Environmental concerns over the use of CBNG coproduced water are limiting the development of this important resource. The goal of the 10 tasks in this project is to assist in clearly defining the true environmental issues associated with this water and in developing cost-effective treatment or mitigation technologies that will allow production of the resource without harm to the environment.
University of Wyoming, Laramie, WY
The Summary of each of the tasks are briefly detailed below. The complete findings for each have been included in the final report.
The research was organized around nine separate, but interrelated, technical project tasks and one administrative task (Task 1). The nine technical project tasks were pursued by separate research teams at the University of Wyoming, but all nine tasks were coordinated to the extent possible in order to maximize information gained about CBNG co-produced waters. In addition to project management in Task 1, the key research tasks included: (2) estimating groundwater recharge rates in the PRB; (3) groundwater contamination of trace elements from CBNG disposal ponds; (4) use of environmental tracers in assessing water quality changes in ground and surface water systems; (5) development of a software toolbox to assess CBNG water treatment technologies; (6) potential value of CBNG water for enhanced oil recovery using low salinity waterflood; (7) evaluation of natural zeolites for low cost CBNG water treatment; (8) evaluation of aquatic toxicity testing methods required by regulatory agencies on some CBNG water discharges; (9) use of remote sensing to evaluate CBNG water discharges as habitat for West Nile Virus transmitting mosquitoes; and (10) a summary of lessons learned from historic CBNG management in Wyoming.
Many of the benefits and costs associated with CBNG development have been debated, but dealing with CBNG coproduced water quantity and quality has been the most difficult of all the issues. Resolving these issues is critical for continued development of CBNG resources in Wyoming and elsewhere—and for taking advantage of the potential benefits of large volumes of water in arid landscapes overall.
Beginning with a few producing wells in Wyoming’s PRB in 1987, CBNG well numbers increased to over 13,600 in 2004, with projected growth to 20,900 producing wells in the PRB by 2010. To produce gas from CBNG wells, it is first necessary to pump out some of the water from the gas-bearing coal seams, which are also groundwater aquifers. This reduces the pressure on the coal seam and allows the CBNG gas to be released from the coal and flow to the well for recovery. Large volumes of water of variable quality have been coproduced (in Wyoming, cumulative CBNG water production from 1987 through December 2004 was just over 380,000 acre-feet, or 2.9 billion barrels). Dealing with these volumes has been a major challenge.
To help address this challenge, investigators in this project are examining existing and potential water treatments, use, and disposal methods, impacts to groundwater, in-stream toxicity, West Nile virus concerns, and management lessons learned from development in Wyoming so far. The information gained can be applied to other areas undergoing, or about to undergo, CBNG development.
The project tasks and their respective status reports follow.
Task 1 (project management and outreach) - Five quarterly reports and one annual report have been submitted for the overall project. Researchers presented their first-year results at the American Society of Mining and Reclamation’s 24th Annual Conference in June, 2007 in Gillette, WY. Following the presentations, a reception was held for industry, government, non-governmental organizations and the public to meet with project investigators and discuss their work. Approximately 60 people attended the presentations. researchers from all tasks held three meetings to review progress, and completed task presentations on results to date at the American Society of Mining and Reclamation’s 24th Annual Conference in June, 2007 in Gillette, WY. Following the presentations, a reception was held for industry, government, non-governmental organizations and the public to meet with project investigators and discuss their work. Approximately 60 people attended the presentations.
Task 2 (estimation of recharge in Wyoming’s PRB with uncertainty bounds) - Monitoring continues at two sites in the PRB. Equipment includes an eddy covariance system, rain gages, meteorological weather station, ultrasonic snow depth sensors, data loggers, and soil moisture sensors. A sonic anemometer and solar radiometer have been added for winter data collection.
Monitoring data have been entered into a database of meteorological and precipitation information for the PRB. The Variable Infiltration Capacity (VIC) model was replaced by the Soil Water Assessment Tool (SWAT) as a more suitable and user-friendly land surface scheme for modeling efforts. Model input files including DEM, land use and land cover, soil, and vegetation have been completed. A sensitivity analysis of the SWAT concerning length of simulation and Hydrologic Response Unit definition has been completed.
Data have been obtained and processed for the calibration of the SWAT model. SWAT calibration is in progress. Data from field collection campaign are being used to validate SWAT performance.
Preliminary results include importance of mountain-front infiltration, and the need to allow discharge from groundwater back to streams through fractures in mountain areas.
Task 3 (monitoring and modeling of groundwater contamination of trace elements from CBNG disposal ponds across Wyoming’s PRB) - CBNG product water is most often disposed of in large disposal ponds. Accumulation and leaching of trace elements in the disposal ponds is not clearly understood. Such information is necessary to predict contamination of shallow aquifers beneath these ponds.
The objectives of this study were to determine the chemistry of disposal pond water and leaching potential of trace elements from the disposal pond sediments into the groundwater system in Wyoming’s PRB.
The PRB consist of five sub-watersheds: Tongue River, Powder River, Little Powder River, Belle Fourche River, and Cheyenne River. Outfall, pond water, and sediment samples from these five rivers were collected in 2006 and 2007 according to standard operating procedures.
Water samples were then analyzed for major cations and anions, plus trace metals. Sediment samples were analyzed for eight trace metals of concern using toxicity characteristic leaching procedure. Geochemistry analyses were performed using MINTEQA2 to determine speciation, complexation, and mineral saturation processes. Statistical analyses were conducted to determine differences among sediments in watersheds and possible prediction models.
The two trace metals that were found to be leaching from pond sediments were barium (Ba) and Managnese (Mn). Barium did not differ among PRB watersheds in either year. Manganese did not differ among PRB watersheds in 2006 but did differ among watersheds in 2007.
Specific field measurements from disposal ponds, along with the pond trace metal concentrations, can be used to explain the concentration of trace metal in the sediment leachate that could potentially migrate downward into the shallow groundwater system.
The Ba concentrations in sediment leachates could be predicted from the concentration in the disposal pond water, temperature, pH, and year the samples were taken. The predictors for Mn concentrations in sediment leachates were Mn and alkalinity concentration in the disposal pond water. The regression model (r2 = 0.45) for barium sediment leachate (Y) was as follows: Y = 0.42102 – 0.02281 X pond Ba – 0.04891 X year + 0.0101 X temperature – 0.04266 X pH.
In contrast to the regression model that explained the concentration of Ba in sediment leachate, the regression model (r2 = 0.40) for leachable Mn had just two predictors: Y = 3.58918 + 1.04311 X pond Mn – 0.0489 + 0.000451 X alkalinity.
These findings are important both for determining if the shallow groundwater system is contaminated by trace metals from disposal ponds and for determining the toxicity of disposal pond sediments. Overall, these findings will be useful in the reclamation of CBNG disposal ponds.
Task 4 (environmental tracers applied to quantify impact of CBNG-related water production on surface and ground water and soil in Wyoming’s PRB):
Task 4a - The purpose of this part of the project is to sample the Powder River along its full length from Powder River, Wyoming to Terry, Montana at low flow (September) and high flow (May). In addition to standard water quality measurements on filtered water samples, we also obtained analyses of Li, B, As, Sr, Ba, Br, U, and isotopic ratios of Sr, O, and H. We collected suspended sediment and bedload for compositional and Nd and Sr isotopic analysis. Three sites are being sampled monthly. The purpose of the study is to understand weathering and transport processes in an arid river system, to obtain baseline data along stretches of the Powder River where there has not been natural gas or oil development, and to determine what parameters are most sensitive to input of CBNG co-produced water.
The State of Montana has set limits for EC (micros/cm) and SAR for water flowing across the state line into Montana. We observe great seasonal an geographic variability in these parameters at the headwaters of the Powder River where no anthropogenic influences are present. Especially during low flow samples from Sussex to Arvada exceeded Montana EC limits, although those collected in September, 2006 in Montana did meet the standard. SAR calculated from our samples is higher than that reported prior to CBNG development. Our SAR for river water was variable for the headwater tributaries and exceeded Montana standards for much of the length of the river. We note an increase in SAR in Montana near the confluence with the Yellowstone that exceeds the Montana standard in September, 2006.
The Cl/Br ratio of water samples is high, as is typical of arid watersheds with alkaline soils. Beaver Creek, which is dominated by CBNG produced water, has a much lower Cl/Br than the Powder River.
The Sr isotopic ratio of Powder River water decreases downstream, reflecting dilution of radiogenic Sr from Wyoming’s Precambrian rocks exposed in Laramide uplifts by Sr from younger, less radiogenic rocks. The Sr isotopic ratio of suspended sediment parallels that of the water but is displaced to higher ratios because unradiogenic Sr from carbonate is concentrated in the dissolved load. Oxygen and hydrogen isotopic compositions of Powder River water are generally more negative than North Platte river water, consistent with a source at higher elevation and/or dominated by cold-weather precipitation. Powder River samples are typically less negative than CBNG co-produced water, which may have been recharged during colder climatic conditions. Both sets of samples have been variably affected by evaporation at some stage of their history.
Our preliminary conclusions are: 1) the natural variability of EC for Powder River upstream of CBNG development is in excess of Montana’s standards, 2) the natural SAR upstream of CBNG exceeds Montana limits, 3) SAR increases along the stretch of the Powder River where CBNG production is concentrated, 4) Stable O, H isotopic data shows colder precipitation for Powder River than North Platte, and 5) Sr isotope data represents a mass balance of various natural and anthropogenic inputs of Sr to the river.
Task 5 (toolbox to evaluate treatment technologies for CBNG coproduced water):
The toolbox and User’s Manual will be available to the public via the internet by May, 2008.
Task 6 (application of CBNG water to improved oil recovery by low salinity waterflooding in Wyoming) - There are two subtasks for Task 6 – CBNG water data survey and laboratory tests to evaluate the possibility of application of CBNG water to improved oil recovery by low salinity waterflooding in Wyoming.
The survey for CBNG production water and Wyoming oil reservoirs has been conducted. Necessary data have been collected for the evaluation of the potential of low salinity CBNG water injection to specific oil fields for improved recovery. Up to now the database includes the distribution of CBNG wells, CBNG water disposal outfalls and oil wells in the Powder River Basin (PRB). Water production history and the water composition and salinity from each outfall have also been collected. Other important parameters including the lithology of the production reservoirs, formation water salinity, water injection history, and reservoir production history have also been collected. Those data have been collected in spread sheets. Data sources were from the US Geological Survey, Wyoming Oil and Gas Conservation Commission, Wyoming Department of Environmental Quality, and the oil and gas producers. The database can be used to evaluate the compatibility, feasibility and cost of using CBM water from a specific outfall for a specific oil field to improve the oil recovery.
Tasks on laboratory study include mineralogy studies and core flood tests by using reservoir rock and crude oil. Two major Wyoming production formations on and around the Powder River Basin, Tensleep and Minnelusa formations, have been selected for the study. Mineral constituents and distribution studies on Tensleep and Minnelusa rocks have been studied by using thin sections and scanning electron microscope methods. The study indicated that Tensleep and Minnelusa rock are in good sorting and are typically composed of quartz, feldspar, dolomite and anhydrite cements. The sands contain interstitial dolomite crystals in the range of about 5 to 10 microns in diameter. Core flood tests have been performed by using Tensleep/Minnelusa rock, formation brine, CBNG production water and the crude oil. The cores were first flooded with high salinity Minnelusa formation brine of 38,651 ppm to establish residual oil saturation. Coalbed methane production water of 1,316 ppm was then injected. Tertiary recovery by injection of low salinity coalbed methane brine ranged from 3 to 9.5% with an average recovery of 7%. Those results indicated that CBM water from the Powder River Basin might be used to improve oil recovery for Tensleep/Minnelusa sandstone reservoirs. The effect of the unique mineralogy of the Tensleep rock has also been studied. One core was pre-flushed with copious pore volumes of hydrochloric acid to remove the dolomite mineral from the core. Waterflood test was repeated. Results showed that after the removal of the dolomite crystals including growths on the surfaces of quartz grains, the oil recoveries given by waterflooding no longer showed dependence on brine composition. This result along with the results obtained previously will be presented at the 16th SPE Improved Oil Recovery Symposium to be held in Tulsa, Oklahoma in April 2008. The title of the paper is: Application of coalbed methane water to oil recovery by low-salinity waterflooding.
More tests may be performed to determine the effect of CBM water on oil recovery for other candidate reservoirs. Factors that also impact the viability of using CBM water to improve oil recovery including the relative locations of CBM wells and target reservoirs, the compatibility of the rock and fluid properties, and transportation costs will be analyzed.
Task 7 (enhancing the beneficial use of CBNG waters) - Originally, a field-scale reactor was proposed for treating CBM water. However, after further consideration it was decided that a low-tech approach would be a better option and zeolite-lined evaporation ponds were chosen as the best available treatment option. An appropriate site for the field test has been identified. The field test will be at an active CBM site located adjacent to the University of Wyoming’s Sheridan Research and Extension Center. The property is owned and operated by Marathon Oil.
A draft work plan for field testing the infiltration ponds has been developed. Soil and water samples have been collected from the site. The water samples were found to have a SAR value of 29.4 mmol1/2 L-1/2. This is significantly higher than the acceptable limit of 10 mmol1/2 L-1/2 but well within the range of values (5-70 mmol1/2L-1/2) for PRB CBM water. The electrical conductivity (EC = 2.02 dS m-1) and pH (7.93) also lie within the range of values (0.4-4.9 dS m-1 and 6.8-8.0).
A companion bench-scale column study, which incorporates soil collected from the field-test site and a surrogate CBM water, is currently underway. Preliminary results from the column study indicate hydraulic conductivity values between 2.2 x 10-4 cm s-1 and 4.0 x 10-4 cm s-1. The average of these values corresponds to 95.6 m yr-1of hydraulic conductivity, which is well within the range for the type of soil we are studying (77.3 m yr-1 for clay loam and 199 m yr-1 for sandy clay loam).
Results from the study will be used to aid in the final design and construction of infiltration ponds.
Task 8 (longitudinal changes in toxicity of CBNG produced water along Beaver Creek in Wyoming’s PRB) - In-stream toxicity studies using caged fathead minnows (Pimephales promelas) larvae, concurrent laboratory toxicity tests and water quality analyses were conducted July 30, 2006 to August 3, 2006; October 15 to October 19, 2006; and January 23 to January 27, 2007 to evaluate longitudinal changes in potential toxicity of coalbed natural gas (CBNG) produced water along Beaver Creek in the Powder River Basin, Wyoming. Two additional studies evaluating ammonia transformations during transport and storage were performed in October 2006 and March 2007. All tests were conducted in or with coalbed natural gas product water and its receiving water in this effluent-dominated ephemeral drainage
The study highlighted the fate and effect of ammonia in these waters because ammonia is perceived to be a major potential toxicant in some CBNG produced waters. However, because Na+ HCO3- concentrations are also often elevated relative to most surface waters, the combined effects of ammonia and NaHCO3 (and all other constituents in this CBNG produced water) were addressed in the in-stream and laboratory toxicity tests. Chemical analyses were used to characterize the effluent and receiving water and to compare the ammonia concentrations to the U.S. Environmental Protection Agency’s aquatic life criteria for ammonia (USEPA 1999). In the laboratory, two whole effluent toxicity (WET) test method environments were compared, using ambient-pH and CO2 pH-controlled chambers. Complementary studies sampled fish, amphibian, and reptile populations along Beaver Creek before the summer 2006 field bout. Finally, collection, transport and storage methods for CBNG produced water were evaluated to determine if ammonification occurred during transport of the CBNG produced water and /or stream water from the Powder River Basin to the laboratory.
Results were similar for all three seasonal periods. No acute toxicity was attributed to the CBNG produced water at any of the study sites. Although ammonia and NaHCO3 concentrations were elevated relative to many surface waters, 96-h survival of the fish did not decrease significantly in any of the CBNG produced waters and receiving waters tested in the laboratory; and all occurrences of significantly decreased survival of caged fish in the field were attributed to either (1) damage of the cages by muskrats or (2) low overnight temperatures during the fall and winter filed bouts (Johnson 2007). Additionally, amphibians and fish were observed in or along Beaver Creek from the CBNG discharge point to the confluence with the Powder River (Figure 4).
Biogeochemically, the temperature- and pH-sensitive ammonia toxicity was mitigated as the produced water interacted with the sediment and the stream community, and as calcite (CaCO3) formation buffered the pH of the effluent. Calcium and Ba2+ concentrations decreased longitudinally from the outfall as SO42- concentration increased, probably due to dissociation of gypsum (CaSO4) in the stream sediment followed by precipitation of CaCO3 and barite (BaSO4) from the water column. Therefore, interaction of CBNG water with the stream bed helped minimize aquatic toxicity. Some of the ammonia was also probably assimilated by plants and microbes, decreasing the potential for ammonia toxicity and increasing the primary production of the ecosystem.
This research concluded that potential acute toxic effects of ammonia and NaHCO3, although present in significant concentrations in CBNG effluent, appear to be mitigated by the biogeochemical interactions between of the effluent and the in-stream environment. Survival in the in-stream and laboratory toxicity tests, observations of aquatic life, and non-exceedance of USEPA (1999) acute ammonia criterion indicate no overt adverse effects of CBNG produced water in this study reach of Beaver Creek. However, because only acute toxicity (i.e., survival) was investigated, further toxicity tests using younger-age fish would be needed to determine potential chronic toxicity effects.
Current Wyoming water quality standards require WET tests on some produced waters from deep coal seams in the Powder River Basin. In this study, the ambient-pH and CO2 pH-controlled WET tests had similar acceptable survival at 96 h; however, at 144 h (i.e., 96 h after renewal of the exposure water), the fish in the ambient-pH treatments had increased mortality probably due to the upward pH drift and increased un-ionized ammonia concentrations. Based on these results, the CO2 pH-controlled test method is more appropriate for this type of CBNG produced water because it maintains the pH in laboratory toxicity tests closer to in-stream conditions than the ambient-pH test method.
Total ammonia concentrations increased by approximately 1.5 mg N/L in less than 24 hours when unpreserved CBNG effluent and stream-water samples were transported from the Powder River Basin to several different laboratories. Nitrogen budgets indicated that sufficient organic nitrogen was present to account for the apparent ammonification. This relatively rapid production of additional ammonia might differ in other CBNG produced waters, depending on the amount of labile organic nitrogen in the water; however, the important point is that ammonification could bias WET tests with CBNG-related waters by increasing ammonia concentrations by the time the waters arrive at the laboratory. Even static-renewal WET tests started immediately after a CBNG produced water or its receiving water is collected might have an elevated total ammonia concentration before the end of the first 24 h of exposure, much less before the end of the customary 48-h exposure-water renewal period. Because WET tests should not be conducted using acid-preserved effluents, regulatory and management agencies should consider possible ammonification when selecting appropriate tests to measure toxicity in CBNG produced waters and when interpreting results of the tests.
Task 9 (enhanced risk assessment of West Nile virus resulting from CBNG production waters - The goal of this research is to identify and carry out improved methods for quantifying Culex tarsalis mosquito larval habitat in the area affected by co-produced waters during CBNG extraction processes.
Research has focused on integrating intensive field sampling of mosquito larvae habitat with remote sensing analyses. A field campaign was carried out in the Powder River Basin, Wyoming in late summer, 2006. This field effort was timed to be coincidental with the period of highest risk of exposure to West Nile Virus in the region. Mosquito larvae were identified in the lab down to the genus and species with the results mapped in a geographic information system.
The vast majority of the water bodies sampled were positive for C. tarsalis, the mosquito vector most responsible for transmission of West Nile Virus in Wyoming.
Remote sensing data were collected that aligned temporally with the field sampling data at a range of spatial scales.
Over the past 6 months research on this task has focused on lowering the detection limit for small water bodies in order to discriminate habitat at the finest detail possible. Mosquito habitat requires the presence of standing water bodies, and research has been focused on this aspect of detection, which will then allow us to merge the results with prior GIS analyses to identify small habitats that are critical for risk assessment.
The first phase of research related to identifying water bodies focused on sharpening Landsat satellite images in order to reduce detection limits of small water bodies. Pan-sharpened Landsat imagery was used to map waterbodies of a wide variety of sizes in the PRB in northcentral Wyoming, USA. Although Landsat and similar medium resolution datasets do not have detailed spatial information at fine resolutions required to map small waterbodies, they do contain rich spectral information. Panchromatic data collected by satellites have an appropriate spatial resolution, but lack detailed spectral information. Thus, image fusion techniques were used to create a pan-sharpened image by merging multispectral (30-m resolution) and panchromatic (15-m) bands from Landsat 7 imagery. Both the original and the pan-sharpened images were used to map waterbodies and estimate their area, being compared to photo-interpretation results. The accuracy of mapping waterbodies with pan-sharpened imagery was significantly higher than the original Landsat data for waterbodies ranging in size from 901 to 8100 m2. Large reservoirs (>8100 m2) were very accurately mapped, both images producing identical results (96%). Neither image was able to suitably detect very small waterbodies (<900 m2). Detailed analysis within 901–3600 m2 size category revealed that the benefits of pan-sharpened imagery were most pronounced (25% higher accuracy) for mapping waterbodies ranging in size from 1801 to 2700 m2.
The second phase of this research focus involved acquiring and testing high resolution imagery and determining its value relative to Landsat. The ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite platform acquires remotely sensed data in relatively higher spatial resolution compared to the more commonly used Landsat platform, but collects these data in fewer spectral regions. In this study we evaluated the benefit of higher spatial, but lower spectral resolution ASTER data for mapping retention ponds and distinguish them based on water clarity (clear or turbid). We compared these results to the higher spectral, but lower spatial resolution Landsat data to quantify the value of higher spatial resolution data. Smaller water bodies (900 - 3600 sq. m.) showed significant improvement in detection using ASTER.
While results for intermediate sized ponds (3600 - 8100 sq. m.) were high for Landsat, we achieved 100% accuracy with ASTER. Both platforms achieved 100% accuracy for large ponds (> 8100 sq. m.). Methods and results from this study may prove useful for research involving ecological or hydrologic change as well as for land management agencies tasked with inventory and monitoring.
Task 10 (integrating CBNG science and management: lessons learned and ways forward) - A timeline was created illustrating the major decisions from 1900 to the present that have affected CBNG development in the Powder River Basin. The Task 10 team is now making this timeline interactive and will post it on the Wyoming Energy Resource Information Clearinghouse (WERIC). WERIC is a joint project of University of Wyoming's William D. Ruckelshaus Institute and the Helga Otto Haub School of Environment and Natural Resources, the University of Wyoming's Wyoming Geographic Information Sciences Center, the Bureau of Land Management and the United States Department of Energy Office of Science. This interactive timeline will better allow individuals to visually understand the many steps that have played a role in the CBNG development process, and, in addition, what decisions, if made differently, might have changed and/or impacted the Powder River Basin.
Temporal and spatial trends in gas and co-produced water outputs associated with Coalbed Natural Gas (CBNG) development were analyzed within the Powder River Basin (PRB), Wyoming. This area has undergone rapid development for natural gas, with the permitting of over 40,000 wells, the majority of which will produce water that will be managed through surface disposal. Total gas and water output were summarized by 12 digit Hydrologic Unit Codes within the basin using a customized Geographic Information Systems (GIS) software program. Each unit was summarized by year from before large-scale development began (1996) through 2006 for all land ownership designations using freely available data provided by the Wyoming Oil and Gas Conservation Commission. This research is part of a broader effort aimed at identifying and interpreting key policies and time points that influenced the pace and pattern of development in the PRB. Spatial and temporal analyses of these data were correlated to a timeline of regulatory, policy, and economic stimulus to identify potential causal mechanisms that influenced CBNG development.
Some of the most important conclusions drawn from the research in this project include the following (see individual task reports for additional key research conclusions):
All project activities have been completed. The final report is available below under "Additional Information".
Funding was provided by a Congressional mandate for research to be conducted through the University of Wyoming at Laramie, WY.
$490,126 (25% of total)
Final Report [PDF-3.88MB]