To develop unconventional high temperature nanofiltration membrane technology for removing salinity and mineral content from produced water resulting in greater utilization of domestic fuel reserves.
Eltron Research Inc., Boulder, CO
Energy reserves of oil and natural gas in the Unites States and North America have seen significant increases in exploitation over the past 20 years, especially those from unconventional origins such as heavy crudes, tar sands, gas shale, coal seams and tight sands. Vast quantities of water are used and co-produced during the extraction of these resources. The largest growing source of produced water originates from the development of unconventional gas resources, particularly those from coal bed methane (CBM) and gas shale. The quantity of water produced over the life of a well ranges from 1 to 3 bbl/mcf of gas, posing several challenges to onshore produced water management and treatment. Current produced water treatment employed for CBM production in the Powder River Basin have resulted in combined treatment costs in the range $0.35 to $0.73 per barrel of treated water. This economically limits recovery of gas to about 83% of full potential (at 500 mg/L total dissolved solids limit and $5.70/Mcf) relative to untreated surface discharge. To ensure continued development of unconventional energy reserves, a more comprehensive suite of cost-effective and cost-saving produced water management and treatment options is required.
Reclamation of produced water for beneficial uses is a potential benefit that currently attracts a large amount of attention and involvement by public and private interests, especially in regions where the growth in demand for freshwater resources is approaching or exceeding sustainable supplies. This is particularly the case across the much of the western U.S. where ranching, agriculture, industry, power generation and municipalities are all heavily competing for access to freshwater resources. This large region is also home to the majority of basins with the fastest growth rates for development of oil and gas resources, including CBM. For example, of the estimated 61 Tcf CBM in the Powder River Basin, approximately 23.3 Tcf is economically recoverable. At a typical water-to-gas production ratio of about 2 bbl/Mcf, this represents more than 40 trillion bbl of produced water to manage. As many as 50,000 wells could be producing CBM by the end of the next decade. Therefore, maintaining economic viability of CBM production in the Powder River Basin and elsewhere, while meeting environmental standards, is of great importance to domestic energy and supplemental water resources.
Tar sands (also known as oil sands and bitumen) are estimated to contain more than half the world’s petroleum reserves. U.S. tar sand resources are estimated at 60-80 B bbl oil, with the richest reserves found in Utah and California. However, their development is not yet viable due to water and environmental constraints. With the exception of the large strip mining operations in Alberta, Canada, this resource must be produced by in situ extraction methods. Steam assisted gravity drainage (SAGD) is a preferred method for recovering this resource, with 60% recovery achievable. However, the economics for oil production from tar sands are significantly affected by steam generation, access to fresh water and produced water treatment. More than 3 bbl water/bbl oil are necessary for tar sand production. Cost-effective recycle of the produced water for boiler water feed will reduce the makeup volume, but also having the ability to recycle the water at high temperature (assisted by the proposed membrane technology) would reduce the energy (natural gas) required to re-heat the water for steam. These resource and energy saving benefits will help make tar sand production more economically and environmentally feasible.
Geothermal and enhanced geothermal energy resources for power generation are potentially significant pieces of the United States’ independent energy portfolio. Enhanced geothermal systems (EGS) are projected to have the potential to produce more than 100,000 MW of electricity in the U.S. over the next 50 years. One of the significant limitations to development and exploitation of geothermal resources is the lack of freshwater in geothermally productive regions to support cooling tower makeup and other operational needs. Another complication is managing geothermal brines to minimize impacts on operations and the environment. Development of technologies such as that proposed will help to create viable treatment strategies for geothermal brine for cooling tower water makeup and brine management, which would help enable future development of geothermal energy resources.
This project focuses on developing a cost-effective, highly robust unconventional nanofiltration (NF) technology to treat produced water for beneficial uses or discharge to surface and ground waters. Beneficial uses can include water for irrigation, livestock, mining, impoundment for later use, municipal and industrial use as well as on-site recycling for cooling tower makeup or reuse in the resource extraction process. The proposed durable NF filter technology will operate at produced water temperatures, reduce salinity, hardness and metals, handle fine, suspended particles, and will tolerate system upsets and uncontrolled shut downs. The primary benefits of the technology are simplification or removal of upstream pre-treatment, treatment of water at production temperatures, greater water throughput, lower driving pressures (less energy), and reduction in brine volume relative to reverse osmosis(RO) filtration.
The overall goal of the Phase I program is to verify and demonstrate the feasibility of producing high temperature NF membranes that are chemically and mechanically robust for produced water treatment and other higher temperature applications in energy production. Two of Eltron’s best NF polymer formulations will be deposited onto microporous alumina tubes. The composite membranes will be characterized for structure, thermal properties, water permeability and rejection performance of salts and organic contaminants, and suspended particles. Filter performance characteristics will be evaluated as a function of temperature, pressure, and feed stream makeup. Estimates of potential water recovery rates and waste brine volume will be made based on preliminary performance data. A prototype membrane cartridge will be designed in anticipation of its fabrication and testing during the Phase II program.
Solvent systems and processing parameter ranges involved with membrane fabrication were determined. The fabrication process is now reproducible, reliable and will allow for deposition of membranes inside ceramic monolith UF substrates. Optimization cycles were completed to improve filter performance and samples were sent to the Colorado School of Mines for testing. Initial testing has demonstrated 60-70% salt rejection (2000 mg/L MgSO4) around 0.55 gfd/psi water flux.
Over one hundred polymer formulations were included in trials with a consistent salt rejection of >90% demonstrated by the most promising formulation. More testing involving the repeatability of membrane salt rejection will be included in the proposal for Phase II funding. Membranes have been sent to AQWATEC at the Colorado School of mine for testing with produced water. Results from the water treatment testing of membranes with coal bed methane water from the Powder River Basin in Wyoming will be complied for the final report and Phase II proposal. The design of a membrane filter cartridge includes economic and environmental analyses based on various levels of salt rejection.
Phase 1 of this project ended April 19, 2010. Research will continue under Phase 2, which began in August, 2010.