Coal seam gas (CSG) produced water passes through multiple systems and processes as it moves from well to beneficial use. While this can be represented quite simply at a high level – there are multiple interfaces, systems and processes at each of the steps:
- Gathering system – wells, trunk lines and field storages
- Water treatment facilities and associated storages
- Treated water and brine management end use
Figure 1: Conceptual CSG water strategy
Understanding and managing the inter- and intra-system interfaces – and selecting the right solution – is crucial to achieving a successful outcome for capital and operating costs, water quality, beneficial use of treated water and brine, and overall asset integrity.
There are other factors that also have a strong influence – social considerations, community preferences, stakeholder organisations and political drivers – however, this article will focus on the technical considerations.
Optimising the gathering system – wells and trunk lines
It’s acknowledged that gas gathering system architecture is linked to water. For example, common pipe corridors and the co-location of field compression stations with water transfer stations and water treatment facilities.
In its simplest form, the gathering system collects and transports water from multiple well sites to the location of the water treatment facility. The scale of gathering systems varies considerably and is dictated by a number of factors, though many existing networks range from a few mega litres per day to over 100 mega litres per day of gathered water.
For scale, a gathering system feeding a 50-plus mega litre per day water treatment facility network consists of 1000 to 1500 km of DN100/150 pipe feeding to multiple small in-field storages and 200 to 300 km of interlinking DN300/950 trunk mains feeding regional storages.
Land use, land owner boundaries, natural impediments such as rivers and topography, pipe material, pressure ratings, and procurement and installations are all factors to consider when determining the type of network configurations. Though typical configurations include:
- Point of production to local use: if water quality is suitable, gathering and transportation to point of use can be simple and may provide the opportunity to use the consumer’s storages
- Branch and trunk: a system of gathering mains feeding into trunk mains and field based storages prior to transfer to water treatment facilities
- Drainage zones: a region for collecting water to a common raw water transfer station
Relying on a standalone raw water interconnection trunk line can be costly. Analysis of gathering system interconnectivity between raw water transfer stations and trunk lines shows significant advantages when operated bi-directionally.
This interconnection of the storages and water treatment facilities comes at a relatively modest additional cost but provides flexibility to manage storages, water treatment facilities, changing raw water production rates and - to some extent - quality. By giving the flexibility to move water around a network, it also gives the opportunity to maximise third party agreements such as water end use agreements.
Water treatment facilities and water storages – protecting the core
What’s in the water? Water blending, pipeline corrosion management and well/drilling products
Water quantity and quality reaching the water treatment facilities will change over time. This can be as a result of hydro-geological influences and design and operation, including:
- Aging of existing wells
- Drilling of new wells
- Fracking well drilling mud
- Corrosion inhibitors
All CSG producers recognise these factors however; it is very evident in our experience that irregular discharges can enter the system. A high-level of control and monitoring is required to ensure the water treatment facility and its product streams are not compromised.
Reliability and maintenance – bigger water treatment facilities and water storages versus spares strategy and reliability management
The water treatment facility has to be reliable enough to achieve product specification over the life of its gathering field, and to ensure it does not impact gas production. Availability and treated water recovery criteria imposed on the plants tend to be high with 98% and 97% being common. While the availability of technologies is broad, the selection utilised must be relatively narrow to meet “gas-on” schedules, provide a reliable and robust plant and meet the recovery criteria.
In addition, operating plants are consistently providing real-time data on reliability and maintenance burdens. This data can form the basis of a root and branch assessment of performance, covering:
- Reliability, Availability and Maintainability (RAM) studies: data on performance and component lifecycle
- Plant redundancy arising from reduced plant throughput: opportunities for alternative spares and maintenance strategy
- Conjunctive use strategy of facilities: both within and between the CSG producers
Our studies have shown that there is a significant cost benefit in providing additional raw water storage capacity for a reduction in peak raw water flow for smaller water treatment facilities. This gives a corresponding reduction in the peak capacity requirement of the water treatment facility size and as a result, installed treatment capacity, spares inventories and maintenance requirements.
The reduction in size depends to an extent on the configuration of the gathering system and field ramp up; a peak capacity reduction of up to 20% is possible. We found the opposite for the larger water treatment facilities, where it was economic to add additional capacity.
Manage inter plant streams – recovery costs less than waste management
Water treatment facilities are often located in remote locations, making transport costs to move materials to or from the site higher than metropolitan areas. A material efficiency/waste management hierarchy (avoid, reduce, reuse, recycle, disposal) is essential to determine the costs of off-site versus on-site recovery/treatment. Some of the wastes arising on-site and their recovery methods include:
Figure 2: Type of wastes and recovery methods
There will always be a residual waste volume on the site. The best way to manage this will be case specific; examples include long-term storage on site and tankering from site to a regulated waste facility.
Treated water end use and brine management – a product people want
Know your end user – getting it right early is a win for everyone
Multiple options exist for beneficial end use such as transport to local water ways, irrigation, re-injection of untreated/treated water/brine into a suitable aquifer and water substitution.
Figure 3: Spectrum of CSG water beneficial use
There is no single preferred option. Understanding the end use, the end user and their risk profiles, seasonality and availability are critical to developing a robust and practical solution.
Early engagement and identifying flexible solutions will help avoid cost and potential delays in delivery.
Guidelines, regulation and best practice – a volatile mix?
Regulations for CSG produced water are in place at the Federal and State Government level. In Queensland, CSG water is regulated under numerous pieces of legislation, including:
- The Petroleum and Gas (Production and Safety) Act 2004
- The Petroleum Act 1923
- The Environmental Protection Act 1994
- The Water Act 2000
The response of government, regulators and industry has been to put in place and operate under a series of guidelines and policies to provide consistency and a degree of certainty. For example the Department of Environment and Heritage Protection (DEHP) specifically developed the Coal Seam Gas Water Management Policy, 2012 to define the meaning of beneficial use in the CSG context.
Brine – commodity versus waste management. An understanding of the product, market and risks is vital
All CSG producers are exploring the commercial opportunities for the beneficial use of salt. Multiple brine disposal alternatives are currently being investigated and/or trialled. These include selective salt recovery, regulated waste disposal of mixed salts, brine injection and ocean disposal. Combined solutions are also viable, for example in the Bowen Basin injection/evaporation may be economic due to the lower salinity and water quantities than the Surat. Also under consideration is collaboration amongst the CSG companies on a 'joint industry' salt recovery solution.
A review undertaken of the markets for sale of salt, soda ash and other products from crystallisation shows world markets are extensive and would readily absorb expected Australian production volumes. The Australian domestic market for salt is approximately 0.9 million tpy per year. A further 10 million tpy of salt are produced for export with the global demand at around 280 million tpy. Similarly, the Australian market for soda ash is about 0.4 million tpy with a global production of 48 million tpy.
The risk associated with salt recovery must not be underestimated and many factors must considered such as the commoditised nature of salts and their susceptible to fluctuations in the market price and the value of the Australian dollar, the product value being generally less than the distribution costs to market, and the proprietary technology involved in salt recovery leading to build-own-operate contractors not accepting price and distributions cost risks.
Do we fully understand the system interfaces for beneficial use?
The short answer is we’ve learnt a lot - but still have a long way to go. The recent and ongoing start-ups and growing experience with operation and maintenance of CSG assets, together with the vast wealth of lessons learned must be used to generate and apply more optimal solutions to the future expansion of the CSG industry.
With each of the major companies in Queensland is investing around AUD $1Bn in the collection, transport, treatment and beneficial reuse of water there remains a host of savings to be made in modularisation, system optimisation and asset management amongst many others.
With other companies entering the market conjunctive use of assets within and between companies must also be considered. The upstream assets put in place to date are capable of transporting and treating the projected peak water demands expected in the first five years. Peak demands will drop off over time as a result of optimised well management, movement to less wet wells and general maturity of the fields.
The opportunity to share assets and develop beneficial collective use schemes is a significant driver for efficiency.
Ly et al, Desalination and the Challenge for the CSG Industry – Develop a Holistic CSG Brine Management Solution,
Brannock et al, brine management of coal seam gas water: pure salt recovery & other methods, OzWater 2011
DEHP, Coal Seam Gas Water Management Policy 2012
CSIRO, Coal seam gas - produced water and site management, April 2012
Santos, Coal Seam Gas Water, www.santos.com/coal-seam-gas/coal-seam-gas-water.aspx (Jun 2013)
QGC, QGC reaches water treatment milestone, www.qgc.com.au/news-media/NewsDetails?Id=4825, (Oct 2013)
APLNG, Sustainable Water Practices, www.aplng.com.au/home/sustainable-water-practices (Jan 2014)
This article was co-authored by a number of our water experts at Advisian:
- Steven Page - Water Specialist Services Service Line Lead, APAC
- Lyvonne Ly - Senior Process Engineer, Water/Wastewater
- Ryan Edge - Senior Process Engineer, Water/Wastewater
- Scott Campbell - Portfolio Manager, Water/Wastewater
- Dominic Dowling - Principal Environment & Sustainability