Management of Saline-Sodic Waters from Coalbed Natural Gas Production.
George F. Vance, Univ of Wyoming, Dept of Renewable Resources, 1000 E University Ave, Laramie, WY 82071-3354
Coalbed natural gas (CBNG) is recovered from coal seams when water is removed to reduce hydrostatic pressure that, in turn, allows desorption of methane (i.e., natural gas). There are more than 25,000 CBNG gas wells permitted or drilled in the Powder River Basin (PRB) of Wyoming and Montana, with estimates ranging from 50,000 to 100,000 new wells to be drilled in the future. Each well has the capacity to discharge from >1 to more than 100 litter of water per minute over an average 8 year lifespan. These CBNG co-produced waters are dominated by sodium bicarbonate chemistry. Concerns associated with CBNG co-produced waters are related to its salinity (total salts) and sodicity (sodium (Na), specifically sodium adsorption ratio (SAR)) and the affect these characteristics have on soils, vegetation, wildlife and livestock. Some CBNG waters are currently being used for land application on rangelands and for production agriculture; however, direct land application of saline-sodic high bicarbonate CBNG waters can potentially cause permanent damage to native soils and vegetation. CBNG producers have developed water management programs that include sulfur burners to eliminate bicarbonate and soil treatments (sulfur and gypsum) designed to address problems that might occur due to pH changes, calcium carbonate formation, clay dispersion and toxicity. Vegetation management concerns include changes in the relative composition and dominance of vegetation communities from differential tolerances of individual species to altered conditions. In order to avoid permanent damage to fragile agricultural and rangeland ecosystems, it is necessary to reduce the Na concentrations in the CBNG water so they can be used safely for irrigation (i.e., crop production) or discharged to natural drainages (i.e., recreation and wildlife).