Geochemical and isotopic characterization of water associated with Wyoming's coalbed natural gas development

Coalbed natural gas (CBNG) production is associated with the production of large volumes of produced water. Approximately 30,000 CBNG wells target the coal beds of Wyoming. Significant gas resources remain, but will require the continued production and management of large volumes of water.;In this study, we present the water quality and isotopic compositions of carbon, oxygen, and hydrogen for produced water from 245 CBNG wells from the Powder River Basin (PRB) of Wyoming and Montana, and from the Atlantic Rim of south-central Wyoming. Combining these data with previously published water quality and isotopic data of these CBNG producing areas creates a database that exceeds 550 entries. This extensive database allows us to distinguish variations in isotopic compositions and water quality that may occur by multiple processes.;In Chapter 1, we sort the approximately 30,000 producing, shut-in, permitted and abandoned CBNG wells in the PRB into producing coal zones. Focusing on the five largest CBNG producing coal zones, we calculate water: gas ratios, define "core producing areas," and identify potential areas of future development of these coal zones. In addition, we use water quality data for 503 new and previously published produced water samples from CBNG wells to map the spatial variability of total dissolved solids and sodium adsorption ratios within these core-producing areas and to identify potential beneficial uses.;In Chapter 2, we present the isotopic compositions of carbon, oxygen and hydrogen for produced water from 197 CBNG wells in the Powder River Basin of Wyoming and Montana. This extensive database allows us to distinguish variations in isotopic compositions that may occur by multiple processes. These include, dewatering of coal beds as part of the natural gas recovery process, incomplete hydraulic isolation of coal beds from adjacent strata and resulting mixing of ground waters from different aquifers, and variations associated with geochemical and biogenic processes that occur along ground water flow path.;In Chapter 3, we present the water quality and isotopic compositions from 48 Atlantic Rim CBNG natural gas wells. Using the PRB investigations as a foundation (Ch. 1 and 3), we focus on the geochemical and isotopic evolution of groundwater in coal bed reservoirs from recharge into the basin. We find that uninterrupted by faults or other structures continued methanogenesis within coal bed reservoirs can be identified by gradually increasing d 13CDIC,deltaD and HCO3. Methanogenesis does not affect delta18O of the coal bed reservoir, thus, delta 18O remains constant. Non-sealing faults are identified by lower delta 13CDIC, dD, delta18O and water quality variations.