PRODUCED WATER VARIABILITY AND WATER MANAGEMENT STRATEGIES IN THE COALBED METHANE PLAY OF THE BLACK WARRIOR BASIN, ALABAMA

Large volumes of formation water are produced in conjunction with coalbed methane (CBM) gas. The Black Warrior basin of Alabama is a mature CBM play with a range of water management issues. The long production history of the area provides an excellent opportunity to study the hydrology and water chemistry of the basin and their effects on CBM production.

The volume of water produced and the timing of that production and water chemistry both vary across the CBM play and affect water management. In areas where water production is relatively low, the water can be handled easily and water handling has little impact on development and production of gas; where water production is high, gas production may be limited by the ability to treat and dispose of co-produced water. Development in an area may also be delayed by high water production in newer wells. Since water production typically peaks within the first few years of production, managing the timing of peak production is one possible method to avoid early high water production limiting development.

Water treatment in the Black Warrior Basin relies primarily on aeration and settling ponds to remove silt, clay, iron, and manganese compounds, with reverse osmosis being used in some high yield, high TDS areas. The fresher water in the eastern CBM fields can be treated and disposed of fairly easily. More saline water requires more involved treatment before disposal and may limit the ability of producers to pump wells to capacity and limits development along southern and western edges of the CBM play. Other treatment options exist, such as artificial wetlands, which may prove more efficient and adaptable, particularly for very saline waters.

All co-produced water is disposed of in-stream at this time. Salt-water disposal (SWD) wells have supplemented in-stream disposal in the past but injectivity fell off quickly in those wells, making SWD wells problematic and an unlikely alternative using current technology. However, there is also the potential for beneficial use of some of the produced water - fresh water might be appropriate for agricultural, industrial, or even municipal use; more saline waters could be used in hydraulic fracturing or aquaculture. Reuse of water, rather than disposal, can reduce stress on aquifers and municipal water supplies and turn a burden into a benefit.