DEVELOPING PRODUCED WATER MANAGEMENT STRATEGIES FOR COALBED METHANE OPERATIONS IN THE BLACK WARRIOR BASIN

Management of produced water is arguably the most important issue coalbed methane producers face today. In the Black Warrior basin, produced water has been disposed safely in streams for decades, yet this practice is the subject of increasing environmental scrutiny. Much of this water may have beneficial uses within the coalbed methane industry, and opportunities for beneficial use may also exist in agriculture and in municipalities with water supply problems.

This study considers produced water management strategies in the context of an integrated hydrogeologic framework that controls reservoir performance and the quantity and quality of co-produced formation water. Basin hydrology is controlled in large part by meteoric recharge along a major fold limb along the southeastern margin of the Black Warrior basin, which brings reservoir coal seams to the surface. Fresh-water plumes (500-10,000 mg/L TDS) with sodium bicarbonate water extend far into the interior of the basin and influence reservoir pressure and water yield. Water within the fresh-water plumes provides the best opportunities for beneficial use, particularly where TDS content approaches that of potable water.

Basinward of the recharge area, total dissolved solids content increases, and sodium chloride water with TDS content of 10,000 to 60,000 mg/L is produced. Geochemical analysis indicates that distinct relationships exist among water composition, gas composition, gas content, the isotopic character of vein fills, and the thermal maturity of coal. Opportunities for beneficial use of saline water appear limited, and production operations can be optimized to improve reservoir economics and to minimize environmental impact. Indeed, careful selection of coal seams with high gas saturation can ensure economic gas production while limiting the volume of high salinity fluid that needs to be disposed.