The science and implementation of chemical amendment of coal seam water as an irrigation resourceDavid Macfarlane & Scott Dalzell

Irrigation Australia Conference – Gold Coast5 June 2014

GLNG CS Water Irrigation FootprintGAS FIELD AND PIPELINE

RSGPA

Irrigation Footprint-FairviewGAS FIELD AND PIPELINE

RSGPA

Irrigation Footprint - RomaGAS FIELD AND PIPELINE

RSGPA

CS Water as an Irrigation Resource

• CS water salts are predominantly NaCl and NaHCO3

• In Santos GLNG footprint this generally varies from 2000 to 12,000 microsiemens (µS)/cm in EC or about 1300 to 8000 mg/L salinity

• Fairview Project Area has EC median / range of 3670 µS/cm / 1900-11,000 µS/cm and SAR median / range of 143/ 75 to 268

• Roma Shallow Gas Project Areas has EC median / range of 3620 µS/cm / 2180-10,000 µS/cm and SAR median / range of 106 / 84-179.

3

Current & Potential Commercial CS Water Treatment Options

• Reverse Osmosis with micro-filtration &/or ion exchange front ends• Chemical amendment process 1: Associated Water Amendment

Facilities (AWAF) adding prescribed quantities of sulphuric acid and micronised gypsum

• Chemical amendment process 2: AWAF treatment of raw CS water + RO permeate blends

• Chemical amendment process 3: Land Amendment Irrigation (LAI) involving suitable quality CS water and suitable soils and soil surface addition of prescribed quantities of sodium bentonite sulphur prills and agricultural gypsum

• Chemical amendment process 4: Potential to blend IX filtrate or RO permeate with up to 8000 µS/cm CS water and utilise via LAI

3

Major soils and variability in an irrigation area

Treating CS water with an AWAF • Influent water ranges from 2000-3400 µS/cm EC with SAR up to 130• Up to 400 L/ML 98% sulphuric acid is applied to reduce bicarbonate

alkalinity from ~1000 mg/L to 200 mg/L & reduce pH from 8-9 to 5.3• Acidified water is stored for 1-2 days and then dosed with micronised

gypsum (<35 microns) to reduce irrigation water SAR and maintain SAR/EC balance for structurally/hydraulically stable soils

• Current AWAFs have output ECs of 3000 to 4000 µS/cm have safe target SARs of 18-30

AWAF chemistry:• Acid dosing: 2NaHCO3 + H2SO4 ==> Na2SO4 + 2H2O + 2CO2

• Every mole of sulphuric acid used generates 2 moles CO2 • SAR reduction using calcium only: SAR = [ Na ] / SQRT { ( [Ca]) /

2 } where concentrations are in milliequivalents per litre.

3

Commercial use of chemical amendment of CS water

Santos GLNG has built 3 AWAF facilities at the Fairview field:• AWAF1 – 10 ML/d capacity• AWAF2 – 2 ML/d capacity• AWAF3 – 4 ML/d capacityDesigned plant CS water amendment capacities:

Parameter Feed CS Water Amended CS waterpH 8.5-9.2 5.8-6.7

Alkalinity (mg CaCO3/L) 700-1100 120-280

SAR 100-150 20-30

EC (µS/cm) 2200-2900 2700-3400

Plan of AWAF 1 – 10 ML/d

Acid dosing

intake

degassing tanks

Filters & pumps

Ozonation unit

Sludge tank

2 x 5 ML storage tanks

Micronised gypsum silos & batching plant

Control room & irrigation pump station

AWAF Drip and Pivot Irrigation 3

Drip CWG planting Drip CWG at 36 months Planting leucaena twin rows

Drip CWG at 2 months Drip tube laying 1 m space Leucaena after 3 months

Drip CWG at 14 months Drip irrigated leucaena & Rhodes grass at 6 months

Leucaena after 5 months with inter-row grass

AWAF drip &pivot irrigation • 217 ha of AWAF pivot irrigation – pivots 10-50 ha

• Rhodes grass/leucaena pastures or fertilised Rhodes grass pastures

• Systems are designed to apply 6-10 ML/ha/yr over 5-6 years

• 72 ha drip irrigated Rhodes grass/leucaena drip lines 1 m apart, up to 4 ML/ha/yr over 5 yrs

• Standard baseline application of 3 t/ha gypsum prior to irrigation

• Pastures fertilised with N, P, & S

• Expected levels of production are: >4 LSU/ha (1 LSU = 400 kg steer) producing >1000 kg beef/ha/yr

• 1075 ha Chinchilla White Gum on Springwater and 200 ha CWG on Fairview with surface and sub-surface, 4 m tree row spacing and expected marketable sawlog yield yr 25 of 250 m3/ha

AWAF 1 Applied Research 2009-2011• Investigation of United States experience of chemical amendment • Required acid dosing for specific bicarbonate levels in treated water • Target soil solution Na, Ca, bicarbonate requirements following irrigation for

sustainable soil condition• Pre- and post-treatment bicarbonate dynamics in CS water • Periodic land amendment gypsum requirements to protect against high

rainfall• Engineering integrity limits of sulphuric acid dosing• Gypsum solubility and CS water pH relationships and optimum dosing rates• Gypsum vs gypsum + Mg SO4 for SAR control in hypermagnesic soils• Managing the hydroscopicity of micronised gypsum• Periodic acid flushing to avoid calcium salts in drip lines and emitters• Variability in emitter output• TDS conversions for CS water for salinity loading calculations

 

3

LAI – US Experience• LAI implemented in >95 irrigation projects since 1999• Typical Powder River Basic CS water quality:

• Salinity 2500-3600 µS/cm;• SAR 40-80;

• GPS precision spreading of gypsum and sulphur required• overlapping S drops soil pH to 3 → strips poor lucerne

growth• Apply 2-5 ML/ha in summer over 7-9 yr period• For average 3 m deep clay loam soil under LAI

• SAR ranged from 6-18 and averaged 10-12;• EC ranged from 4-5 dS/m

• Lower costs/ML treated than for RO or Ion Exchange (e.g. Higgins Loop) water treatment systems

Land Amendment Irrigation - US

Gypsum and sulphur applied twice in 7 mth growing season with gps tractors.

8 yr old LAI lucerne - hydraulic conductivities tested at 3 depths/6 months.

8 yr old lucerne on LAI clay loams in better condition than adjacent river water pivots.

LAI occurs on clay loams & light clays on slopes up to 6-8%

Requirements for commercial LAI• Soil hydraulic conductivity >40 mm/day • Soil depth >1.5 m and starting profile salinity <1 dS/m• CSG water applied EC <4000 µS/cm• Target crops have high yield/water use salinity thresholds• If reach trigger values (≤ 75% threshold) reached provide salinity

flushing irrigations – do not restrict water use of the crop pump• Peripheral non-irrigated buffers of deep rooted perennial species

up to 100 m width required• No major aquifer within 35 m below root zone and separated by

stratigraphies of 15-20% porosity• Minimum area of 50 ha / block, up to 4 x 50 ha blocks within 2 km

of each other sufficient to attract a reliable land amendment contractor

Red Kandosol Yellow Kandosol Tenosol Deep A Chromosol

Reduced potential LAI soilsDermosol Vertosol

Shallow A horizon Chromosol

Good potential LAI soils

Managing CS water with Pivot LAI1. Regularly apply small amounts of S-bentonite on poorly buffered

soils to prevent fluctuations in soil pH2. Induce leaching (~10-15% leaching fraction) to maintain soil root-

zone salinity within acceptable limits3. Leaching irrigation applied during winter when crop ET demand is

low likely to most effective4. Field observations of soil hydraulic conductivity backup routine

soil chemistry monitoring5. Continuous/periodic environmental monitoring adaptive

management prevents adverse impacts on soil/water resources

LAI can be implemented on long-term, large-scale centralised, or medium term decentralised or short-term local appraisal irrigation projects where water quality is suitable.

Tested Kandosols and Red Vertosols - dominant soils

Would LAI leave soils in the same or better condition than AWAF system ?

Tested 36 ML/ha of AWAF CS water of 3000-3200 µS/cm…….

Key findings: LAI surface applied gypsum and S left soils in better SAR condition than AWAF

Whole profile salinity of LAI was 5% higher than for AWAF systems

Profile sodicity of LAI and AWAF soils similar

S bacteria may take time to increase in soils – S may need to be applied 3 times in first year then twice / yr thereafter

Root zone impacts AWAF vs LAI

Large intact soil cores at UQ

Parameter Kandosol- HIGH POTENTIAL

Dermosol – REDUCED

POTENTIALWater infiltration – unsaturated flow @ 9

ML/ha 40 mm/hr 15 mm/hr

Deep drainage (mm) 84 1∆ Root Zone SAR 117.6 18.724.3

∆ Root Zone EC fc (dS/m) 0.32.83 9.215.6∆ Root Zone pH 6.76.4 8.747.85

∆ Root Zone Ca (mM) 0.160.5 1.112.7∆ Root Zone Mg (mM) 0.532.54 10.3728.9∆ Root Zone S (mM) 0.184.25 1.266.51∆ Root Zone Al (mM) 0.010.03 0.020.01

∆ Root Zone EC/100 mm rain leaching (dS/m) -0.05 +0.4

∆ Root Zone SAR/100 mm leaching rainfall -3.5 -2.3

Estimated ML/ha to 7 dS/m ECse threshold 35 ML/ha 15-20 ML/ha

Soil impacts of LAI - after 9ML/ha LAI & 400 mm rainfall

Comparing AWAF, AWAF + extra gypsum, LAI and local bore water irrigation systems

Current comparative field trial

AWAF 1 water – 2800 µS/cm, SAR 21

AWAF 1 water + gypsum @ 514 kg gypsum/ML/ha

Dam water – 300 µS/cm, SAR <1

Raw CSG water 2900 µS/cm and SAR 123 + 514 kg gypsum/ML/ha & 210 kg S/ML/ha

Irrigation started May 2013 – finished January 2014 with 7 ML/ha applied

No differences in yield observed between treatments under irrigation.

No significant differences in infiltration with 7 ML/ha – local farmers agree no difference in surface soil conditionRecent analyses suggest 50-200 ha commercial non-central / remote field area gathering system – storages - LAI treatment has total cost of approximately 50% cost of contracted relocatable Reverse Osmosis treatment and waste management and that LAI can reduce short term appraisal water CS water management to ≤ 40% trucking cost to suitable storage.

IR6(3) comparative trial key data

Using broad scale soil association/land resource maps to focus LAI soils reconnaissance

Environmental impacts-AWAF vs LAI vs ROP systemsParameter LAI pivot

Rhodes/leucaenaAWAF trees – drip AWAF Rhodes/

leucaena - dripROP pivot Rhodes/leucaena

1. Energy usage low moderate moderate high

2. Waste management status at project end

All salt within top 6mbgl All salt within top 6mbgl All salt within top 6mbgl CS salt within 3 mbgl + RO brine deep injected

3. Soil structure / SAR/EC balance

Stable all rainfall events Stable & needing extra gypsum -high rainfall yrs

Stable & needing extra gypsum -high rainfall yrs

Stable & needing extra gypsum -high rainfall yrs

5. Soil hyd.cond 80-100% baseline > 80% baseline 80-100% baseline > 80% baseline

6. Surface water Nil impact expected Nil impact over 5 yrs Nil impact expected Nil impact over 5 yrs

7. Ground water Nil impact Nil impact Nil impact Nil impact

8. Weed flora/ecological diversity

Nil weed impact under Leucaena Code, nil impact native veg

Nil weed impact, nil impact native veg, wildlife corrodors

Nil weed impact under Leucaena Code, nil impact native veg

Nil weed impact under Leucaena Code, nil impact native veg

9. Productivity – irrigation vs dryland

X 20-25 beef production if median rain + 5-6 ML/ha/yr

20% increase merchantable volume

X 20-25 beef production if median rain + 5-6 ML/ha/yr

X25-30 beef production if median rain + 8 ML/ha/yr

10.Productivity - post-irrigation

Post-irrigation vs baseline Rhodes similar, if +leucaena x3

Post-irrigation vs baseline CWG similar

Post-irrigation Leucaena/Rhodes vs baseline Rhodes x3

Post-irrigation Leucaena/Rhodes vs baseline Rhodes x3

Management of environmental risks of chemical amendmentEnvironmental risks/ mitigation:1. Fail to maintain sustainable soil chemical conditions / real time soil monitoring

and periodic soil & analysis, use proven salinity / sodicity /water balance modelling, treat water or amend soils for stoichiometrically correct levels of calcium and sulphuric acid entering system for bicarbonate and SAR management

2. Increase soil salinity / regular monitoring, develop soils with low-moderate starting salinity, adequate hydraulic conductivity, manage irrigation practice & crop selection for target water / salt leaching fractions beyond root-zone

3. Movement of CS water salinity beyond the irrigation environment impacting surface water or groundwater / regular monitoring, irrigation application & buffer management controls, sub-root zone unsaturated zone being >35 m deep of 15-20% porosity, conservative 2-D seepage modelling, adaptive irrigation management

Total costs - centralised CS water managementAssumptions: 10 ML/d, 10 yrs operation with CAPEX written off, gathering system cost $31 M, standard irrigation and monitoring CAPEX & OPEX /haParameter LAI + Forages AWAF + CWG AWAF +

ForagesROP + brine injection + forages

Gathering, Storage Treatment and monitoring CAPEX

54 73 67 100

Treatment+irrigation+monitoring OPEX

28 27 21 100

TOTAL COST index 48 62 50 100%

TOTAL COST INDEX less gathering system

37 57 42 100%

Comparative process risks of LAI vs AWAF as chemical amendment water treatment systems

Process Risk

Current AWAF design LAI

Sulphuric acid/ S-bentonite

Sulphuric acid from Townsville every 20 days – higher truck movements >safety risk

S-bentonite trucked 2-3 times per year from Brisbane – < truck movement safety risk & low cost onsite storage

98% sulphuric acid (33% S @ $300/t delivered) high hazard product – human safety and engineering risk to stainless steel and PVC components

Dry storage of S-bentonite (90% S @ $600/t delivered) which is a low hazard product – endloader bucket must not create sparks possible ignition

Gypsum Micronised gypsum @ $400/t has flowability/hydroscopic challenges and requires steep coned silos, fluidised air supply for regular flow &uniform dosing

3-6 months field requirement for agricultural gypsum @ $180/t is easily spread with S-bentonite. Generally use 1-1.2 tonnes gypsum/ML

Reliability of input supply

Low supply chain risk with multiple local suppliers. If wet weather stops acid delivery it also stops irrigation.

If Brisbane S-bentonite supply lost, costs and delivery lead times from Geelong or overseas would increase.

Santos GLNG business benefits

Chemical amendment of CS water delivers the following benefits:1. Flexibility in CS water management planning2. Reduced water treatment costs3. Shorter lead time to beneficial CS water use accelerates field

development4. Least cost centralised and decentralised water treatment options for

commercial and appraisal irrigation projects for suitable water quality5. LAI offers enhanced process safety and reliability over AWAF and ROP

+ brine injection systems based on 5.7 years Fairview experience6. Superior environmental outcomes - best practice LAI vs best practice

AWAF and ROP irrigation system management will consistently reduce the risk of soil structural degradation by maintaining superior soil EC/SAR balance in surface soil