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Innovative Commercial and Technical Solutions for CSG Produced Water Treatment Project

Santos are developing the Narrabri Gas Project (NGP) in the Australian State of New South Wales (NSW), about 600 km from Sydney. The NGP has the potential to supply up to 50 per cent of NSW’s natural gas demands by domestic and industrial users. The NSW State Government has recently implemented a range of new policy and legislation, making the NSW CSG industry one of the most highly regulated in the world.

The exploration and appraisal activities conducted to date have resulted in the extraction of PFW that is stored in two state-of-the-art storage ponds at Leewood. The ponds have a storage capacity of approximately 300 ML each, and are double-lined, with leak detection systems and remote monitoring capabilities. Each pond is divided in halve so that there are effectively four ponds - called Cell 1 to 4. Two cells are expected to be full of PFW, while Cell 1 is largely full of legacy brine. The remaining cell will be used to store the highly concentrated

brine produced by the WBTP, as the other ponds are treated and emptied providing further storage for ongoing field activities. The water qualities are shown in Table 1.

Osmoflo has been contracted to safely provide four primary services under the agreement:

• Provide irrigation quality “treated water” at 1 ML/day from the facility;

• Process of all of the ”legacy brine” within 15 months;

• Meet a final brine concentration target of greater than 90,000 mg/L TDS; and

• Remove so l ids (a lga l , e tc) f rom the process

• The plant design must take into account leakage/spillage mitigation measures and low audible and visual impact on the site.

PROJECT SOLUTION

Full Performance Risk ContractThe tailored commercial structure is a first

of its kind for the CSG industry. It has been centered around a fit-for-purpose WBTP, where the design, construction and operation must comply with all applicable Australian Standards, good water industry practice and any related project approvals from the Government. The payment structure has two pr inciple components:• Operating Lease for the Facility (off-

balance sheet as Osmoflo retains ownership and risk over the term). This payment has ‘fixed’ charges under the operational lease and for the O&M services, and a ‘variable’ charge based on actual throughput.

• Lump-sum component for the Associated WTP Infrastructure – which is mainly the fixed or buried infrastructure. Osmoflo constructs and owns the Associated WTP Infrastructure until Practical Completion date and then transfers ownership to Santos on payment of the lump-sum fee.

The coal seam gas (CSG) exploration and appraisal activities by Santos in Narrabri, New South Wales (NSW), Australia results in produced formation water (PFW) that is stored in specially constructed double lined ponds. Santos is seeking to treat this water for beneficial reuse in irrigation, dust suppression, construction and drilling, and emergency firefighting purposes. Santos have outsourced this requirement to Osmoflo under a hybridized build, own and operate model, which includes the design and delivery of a water and brine treatment plant (WBTP), and specialist operation and maintenance services for 3 yrs initially, with a possible extension to 5 yrs. The WBTP is containerized to allow demobilization and future possible re-deployment, and to find an appropriate balance between the often competing drivers of the projects technical objectives, and the commercial requirements of delayed and minimized capital expenditure.

The PFW and legacy brine has a wide salinity range of 18,000 to 51,000 mg/L and algae counts up to 8.8 million cells/mL These need to be desalinated to produce irrigation quality treated water of salinity 90,000 mg/L in order to minimize the brine volumes

CASE STUDY

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WATER AND BRINE TREATMENT PLANT

Pond Transfer and FeedwaterEach pond will have a containerized

pump station to transfer the water from

the pond to the WBTP. The container will

be bunded internally so that any leakage or spillage from flanged connections and pumps will discharge back into the pond. The container also consists of the pond return pipework to allow discharge of washwater or final brine (via manual valve selection) to each cell from the WBTP.

Parameter Units Produced Water

Legacy Brine

pH - 7.5 - 8.75 9.59

Electrical Conductivity uS/cm 20,220 51800

Chloride mg/L 2,300 5310

Alkalinity (HCO3)# mg/L CaCO3 12,600 7350

Alkalinity (CO3)# mg/L CaCO3 830 21800

Alkalinity (Total) mg/L CaCO3 12,700 29200

Sodium (Total) mg/L 6,800 25600

Barium (Ba) mg/L 15.4 11.6

Barium (Filtered) mg/L 12.6 9.73

Calcium (Total) mg/L 14.6 22

Calcium (Filtered) mg/L 10 20

Strontium (Total) mg/L 4.6 3.1

Strontium (Filtered) mg/L 3.7 2.53

Fluoride mg/L 6.5 27.1

Silica mg/L 25 91.2

Sulphate mg/L 17.8

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bund. The bund surface will have a rubble finish. The chemical storage and loading area on the southern side of the bund will be sealed with 40 mm asphalt surfacing with heavy duty binder. Gradient within the bund is towards closed sumps so that any overland flow, including rain water, can be tested and confirmed to be harmless before release.

Water storage tanks within the bund will be heavy duty polyethylene tanks with multiple modes of tank level detection to minimize the risk of overflow. These include tank level transmitter with high level shutdown interlock, high level switch in the tank and a high level switch in a sealed (from rain) drum where the tank overflow is directed into.

The majority of equipment is containerized, which will minimize on site construction. All containers will have drip drains where all drain and sample lines are directed into. The drip drains will be piped to sumps to prevent uncontrolled spillage into the bund.

Other major infrastructure outside of the bund includes generators and a treated water storage tank that is a 5,000 kL bolted modular panel tank with plastic liner. Power generation is an important part of WBTP as power is a major part of the operating costs. It has been designed with three generators. The 1400 kW generator is a containerized reciprocating gas engine that supplies all the necessary

power with spare capacity. It uses fuel gas from Santos’ CSG operations to significantly reduce the operating costs of the WBTP. The 656 kW and 240 kW diesel generators are backup generators.

Water TreatmentOsmoflo’s extensive experience of membrane filtration and RO treatment of CSG produced water was a key to ensuring robust and flexible treatment design with high level of automation. The high algae counts in the pond water ensure the need for a robust pretreatment process and could be compared to the issues of dealing with algal blooms in seawater RO desalination. Laboratory analyses showed that the algae are of small particle size mostly

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increases the calcium in the blended permeate and ensures the sodium adsorption ratio (SAR) or sodicity is 90,000 mg/L for the final brine TDS. One of Osmoflo’s key strength in securing this contract was the use of the in-house developed and patented Brine Squeezer process to reduce the RO brine reject volumes cost effectively. It has been demonstrated in two applications to increase the overall plant recovery 92-95 per cent from 70-75 per cent resulting in only 5-8 per cent brine to dispose of. The Brine Squeezer (OBS) process

incorporates many existing and available

equipment and learned techniques to

manage and mitigate fouling and scaling

of increasingly concentrated brine

streams - with some innovative features

and techniques including:

• Use of unique combination of membrane properties

• Use of sacrificial coating (when required) to manage fouling and scaling

• Use of innovative cleaning strategies to effectively clean foulants/scales.

Other simple features to manage fouling

and scaling include operation at high

crossflows, low fluxes and higher ionic

strength.

The OBS is expected to produce a brine

concentrate 100,000-120,000 mg/L and

in blending with the small amount of

PFW or legacy brine remaining in the

ponds the final brine TDS of >90,000

mg/L is able to be achieved. The higher

final brine TDS allows for more cost-

effective further concentration and salt

recovery as part of the CSG industry’s

vision for beneficial reuse of salts and

solids disposal offsite.

The OBS system has the highest level of

automation, intelligently adjusts operating

parameters for the higher fouling and

scaling conditions and automatically

cleans the membrane. Frequent CIPs are

expected and the membranes are used as

a semi-consumable as they are operating

outside the normal boundary of RO. The

innovative hot water CIP technique on

the OBS will easily remove biofouling,

organic fouling and some of the scaling.

The unique sacrificial coating will only

be used to enhance scale removal and

reduce CIP chemicals.

Solids DewateringDAF and centrifuge were selected for solids dewatering due to proven tracking records in algae laden water and flexibility in handling variations in flows and solids concentration. The jar testing correlated that the use of fi ltered feedwater (same ionic species as the PFW or legacy brine) for backwashing the MF (which forms the majority of the solids to be dewatered) will cost >$200,000 per month in chemicals in the dewatering process. This was costly and a more cost-effective design of using the permeate from the OBS for MF backwashing was developed. The significant lower TDS and alkalinity of the OBS permeate are expected to significant reduce the chemical consumption from extensive field experience.

The DAF design incorporates a conservative detention time of approximately 30 mins for coagulation to ensure adequate reaction time since experience indicated algae are one of the more difficult types of solids to coagulate. The hydraulic loading of the whole DAF has been sized conservatively so that there is a 40 per cent contingency over the normal feed flow.

The centrifuge has also been sized conservatively to treat the DAF sludge under 16 hours and incorporates an automatic greasing which will reduce maintenance frequency and effort. It is designed to produce a sludge cake of 18-20 per cent dry solids that is suitable for disposal off site via trucking.

Figure 2: Schematic of the Brine Squeezer Process

Author’s Details

Hiep LeTechnical Services Manager

OsmofloE-mail: hiep.le@osmoflo.com

www.osmoflo.com