New technology is needed to economically render coal bed methane (CBM) product water suitable for:

irrigation of sensitive crops, application to vulnerable soils, unrestricted beneficial discharge to surface waters, and use of an otherwise wasted resource - groundwater.

     Drake Engineering Incorporated (DEI), a Montana-based private research and development firm subcontracted to Montana State University, is currently pilot testing an innovative process to economically and reliably treat CBM product water to achieve virtually any specified treated water quality. DEI's proprietary CBM Water Treatment System (CBM-WTS) is engineered and designed to meet a set of challenging performance requirements dictated by the unique needs of both the producers and potential consumers of treated CBM product water. This project was developed collaboratively with Montana State University with support from the Department of Energy National Petroleum Technology Office in Tulsa, Oklahoma.

• Feed Specification - CBM-WTS can treat CBM product waters exhibiting the full range of chemical compositions found in the Powder River Basin of the Montana and Wyoming CBM plays.
• Chemical Removal - CBM-WTS was designed to target removal of sodium ions. The treatment objective during development has been to reduce product water alkalinity, salinity (specific conductance), and sodium adsorption ratio (SAR), as needed, to render the water suitable for any specified agricultural, aquacultural, or industrial beneficial use. Chemcial removal efficiency is field adjustable using a single controller set point.
• Throughput - CBM-WTS modules are designed for application at any target throughput ranging from 50 gallons per minute to over 1,000 gallons per minute. CBM-WTS modules are designed to provide automatic turndown of up to 50% based on design throughput and feed water composition. Design basis module throughput is 200 gallons per minute. A module of this size could serve approximately 10 new CBM wells or perhaps as many as 20 equilibrium production wells.
• Secondary Waste - The only process waste is salt concentrate for which secondary markets have been identified. The generation rate of liquid waste concentrate depends on input water salinity but is generally less than two percent of the treated water throughput. The low volume of salt concentrate is amenable to simple evaporative crystallization or calcining to produce a benign, dry, merchantable, solid product having negligible (0.05%) volume when compared to the volume of water treated.

• Size - A CBM-WTS module capable of processing 1,000 gallons per minute occupies a footprint of less than 50 square feet and has an empty weight less than 1,000 pounds.
• Utilities - Electrical power requirements for process equipment, instrumentation, controls and telemetry total less than 700 watts. CBM-WTS modules may be powered from the grid or may be easily adapted for solar power or parasitic hydroelectric generation.
• Reliability and Availability - CBM-WTS modules use only low-torque, low-speed rotating equipment and have no critical wear surfaces. All processing operations are performed at ambient temperature and discharge water pressure. All materials are suitable for the intended service and are selected and sized with appropriate wear and corrosion allowances to provide a 20-year service lifetime.
• Maintainability - CBM-WTS modules are designed for unattended operation. Two control sensors (EC and pH) require periodic (monthly or quarterly) maintenance or replacement. Likewise, only two process reagents require periodic replenishment.

     Estimated treatment costs depend on the size of the CBM-WTS and the site-specific treatment specifications. Target unit treatment costs are less than five cents per barrel (42 gallons) for a large (1,000 gpm) system, designed to remove 50% of sodium and bicarbonate from typical CBM product water. Treatment costs include capital recovery, reagent costs, and maintenance labor.

Test Run Objective: Treat feed water that closely approximates surrogate Powder River Basin coal bed methane product water.

1. Functional and chemical performance of CBM-WTS were verified.
2. Pilot plant successfully treated feed water exhibiting 50 meq/l NaHCO₃.
3. Sodium concentration in feed water was reduced by 70%.
4. Feed water SAR was reduced from 33.8 to 10.5, about 68%.
5. Feed water pH was reduced from 8.1 to 6.1 and rebounded to above 7 after equilibration with atmosphere.
6. Run Data Summary: analytical data for: 1) target surrogate water, 2) raw makeup water, 3) surrogate feed water and 4) mid-run CBM-WTS product water.

Geochemical Constraints on Selection of CBM Product Water Management Strategies

Presented by Ron Drake (Drake Engineering Incorporated, Helena, Montana) at the 2004 Montana Soil and Water Conservation Society Annual Meeting in Billings, Montana.