Geochemical processes controlling trace elemental mobility in coalbed natural gas (CBNG) disposal ponds in the Powder River Basin, WYInternational Journal of Coal Geology


K.J. Reddy, C. Helmericks, A. Whitman, D. Legg
Economic Geology / Geology / Fuel Technology / Stratigraphy


em o

Received 23 April 2013


Energy demand

Natural gas

Produced water

Geochemical process

Sediment sample ed tives of this research were to 1) examine the chemistry of CBNG produced water in isposal ponds and 2) determine possible leaching of trace elements from the disposy 2035 (RIENR, 2005). nne River (CHR), Belle owder River (PR), and 1.7 trillion cubic feet

International Journal of Coal Geology 126 (2014) 120–127

Contents lists available at ScienceDirect

International Journa l seThe US Geological Survey conservatively estimatesmore than 700 tcf (trillion cubic feet) of CBNG deposits in the US (Rice, 1997). The CBNG extraction is significant in many central and western states in the US, (TCF) of recoverable methane (DeBruin et al., 2004).

The CBNG is formed over eons in deep confined coal seams through biogeochemical processes. The CBNG is extracted through drilling intoeconomies and population growth. Although demand for natural gas has been historically volatile, current global requirements for clean energy suggest that demand for natural gas will continue well into the future. 139,000 wells will be brought into production b

The PRB consists of five sub-watersheds: Cheye

Fourche River (BFR), Little Powder River (LPR), P

Tongue River (TR), and holds approximately 3Though CBNG deposits are not as extensive as other fossil fuels, their importance is growing as a source of energy. A review of global energy supplies over a period of 27 years indicates a steady increase (N30%) in use of natural gas (including, CBNG) driven by expansion of global

River Basin (PRB), Wind River Basin (WRB), and greater Green River

Basin (GRB). Among these, the PRB has experienced extensive CBNG development. For example, in the PRB during the month of August, 2008, there were 18,256 CBNG wells in production, and it is estimated thatas well as in other countries including Cana

New Zealand. The CBNG development in th

Wyoming,Montana, Colorado, Utah, andNewM ⁎ Corresponding author.

E-mail addresses:, kjreddy@physics.h 0166-5162/$ – see front matter. Published by Elsevier B.V natural gas (CBNG). to supplement the nations' energy demands (Bank and Kruuskraa, 2006). Wyoming has approximately one-third of the recoverable CBNG reserves in the US. Wyoming's CBNG reserves are found in the PowderMethane is a main constituent of coalb1. Introductionwere collected from the Powder River Basin (PRB), WY during the summermonths of 2006 to 2009. Water sampleswere analyzed for pH,major cations, anions, and trace elements. Geochemical analysis was performed using

MINTEQA2model to determine speciation, complexation, andmineral precipitation and dissolution processes to determine the mobility of trace elements in CBNG disposal ponds. Two types of SAR calculations were made: 1) practical SAR (SARp) was calculated based on Na+, Ca2+, and Mg2+ concentrations and 2) true SAR (SARt) was calculated based onMINTEQA2 calculated activity ofNa+, Ca2+, andMg2+. Sediment sampleswere analyzed for trace elements using toxicity characteristic leaching procedure (TCLP) to predict potential mobility of trace elements into the shallow aquifer. Research results suggest the pH of the CBNG producedwater outfalls increases substantially in corresponding disposal ponds due to degassing of CO2 (carbon dioxide) from the disposal ponds.

Observed high SAR values in CBNG disposal ponds compared to outfalls were attributed to increase in Na+ and decrease in Ca2+ concentrations. The decrease in Ca2+ concentration is attributed to the precipitation of calcite.

Trace element concentrations such asAs (arsenic), Cr (chromium), andCu (copper) appear to increase in disposal ponds. Barium (Ba) andMn (manganese) concentrations in the disposal ponds decreased substantially by precipitating as carbonate minerals into the sediments. Results of this study suggest that veryminimum or no leaching of trace elements could occur fromdisposal pond sediments. However, further research is required to understand the role of SAR and sediment mineralogy in leaching of trace elements from CBNG disposal pond in the PRB,WY.

Published by Elsevier B.V.Accepted 2 January 2014

Available online 11 January 2014 al pond sediments into shallow aquifers. The CBNG outfall water, disposal pond water, and sediment samplesReceived in revised form 17 December 2013 lying shallow aquifers. Objec outfalls and corresponding dGeochemical processes controlling trace el natural gas (CBNG) disposal ponds in the P

K.J. Reddy ⁎, C. Helmericks, A. Whitman, D. Legg

Department of Ecosystem Science and Management, University of Wyoming, Laramie, WY, USA a b s t r a c ta r t i c l e i n f o

Article history: A concernwith CBNG produc j ourna l homepage: www.eda, Australia, China, and e western US, including exico, is growing rapidly (K.J. Reddy). .ental mobility in coalbed wder River Basin, WY water disposal ponds is the potential migration of trace elements into the underl of Coal Geology v ie r .com/ locate / i j coa lgeothe coal seam, followed by pumping of the groundwater (produced water) to the surface. Methane is separated from the produced water at the wellhead. Each well produces large quantities of water. The

Wyoming State Geological Survey has projected that approximately 7.01 billion m3 ofwaterwill be discharged from the CBNGdevelopment in the PRB (DeBruin, 2004). To dispose the produced water, 2–10 CBNG 121K.J. Reddy et al. / International Journal of Coal Geology 126 (2014) 120–127wells are combined in amanifold systemand then discharged to a single outfall that flows into disposal ponds. Other produced water management practices include discharging into stream channels, spraying into the atmosphere, and reinjecting into the aquifer (Wheaton and

Donato, 2004). However, discharging produced water into disposal ponds is a common practice in the PRB (Reddy, 2010). Brinck et al. (2008) reviewed the published research of CBNG produced water in the PRB and described the geochemical evolution of produced water in the ponds and its potential effects on soils, plants, groundwater and implications for irrigation. In a recent study, Bern et al. (2013) examined shallow groundwater and soil chemistry response to subsurface drip irrigation (SDI) using coalbed methane produced water. Results from these studies indicate that one way of deriving beneficial uses for CBM produced water is through SDI process.