The rapid move towards an LNG industry in Queensland has generated significant interest in developing coal seam gas (CSG) in the Surat region. With this increasing development comes the responsibility of managing the associated water byproduct of CSG extraction.
Compared to other industries, capital and operational expenditure on water treatment for CSG development is high and variable.
The major hindrances to associated water management are the uncertainties in quantity and quality of the water produced. Water production can range from 1,000-10,000 barrels of water per terajoule of gas produced, while the water quality can range from potable quality to water that is extremely saline.
Associated water production rates vary depending on well location and age. Water quality is dependent on the reservoir, which may produce waters that are high in salt and other constituents.
In the past, CSG operators have used deep well injection, evaporation and surface discharge as methods of associated water management. Recent changes in regulatory requirements and stakeholder expectations have prompted a change in how associated water is to be managed. Regulatory agencies are now seeing water as a resource and want to maintain environmental qualities.
Innovations
A number of innovative approaches can be considered when managing associated water.
Design and modelling
Associated water gathering systems and facilities should be designed to accommodate variability in water quantities and qualities. This includes examining the phasing of wells and gathering systems to manage varying salinity and peak production rates.
Using computer-based models for different scenarios to be simulated can be done quickly and at a low cost. The results of the simulations can then aid in generating estimates of capital and operational costs and the limitations of proposed installations.
Evolving regulatory drivers
Changing regulatory drivers have made associated water one of the most challenging issues when seeking environmental approvals. For example, evaporation dams may now be authorised where an applicant is able to prove that no other feasible alternatives are available.
Working closely with the regulatory bodies improves the quality of an associated water management plan and can assist the environmental approvals process.
Options for beneficial reuse/disposal
A number of options are available for beneficial use and disposal of associated water, including:
* Injection/re-injection
* Surface discharge agricultural use (irrigation)
* Municipal/indirect potable use
* Industrial use
* Evaporation.
Treatment technologies
A number of treatment technologies are available to achieve water quality suitable for beneficial use and disposal options, including blending and raw water treatment, desalination, and salt management.
Drilling and sampling
Information on water quantity and quality can be determined during the drilling stage. It is important that care is taken when sampling as the use of drilling muds can negatively impact water quality samples, providing elevated analyte concentrations. It is also important to establish a sampling protocol, to flush and filter samples taken during the drilling process, and to allow for contaminants and follow indicators.
Conclusion
Innovation and adaptability is the key to success. It is important to have an understanding of the associated water flow rates and qualities and to consider the entire water cycle from production to beneficial reuse. Working with regulators along the way will reduce potential roadblocks to CSG field development. Finally, remember to chase technologies to remain innovatively ahead of the game.
This article is a summary of Nick Hudson’s presentation at FutureGAS 2010. To read more about the event, turn to page 44.