characteristics Coal seam Lowering of special purpose packers 5 days Very low permeability on slim rods into the wellbores with testing packers isolating specific target coal seams for small-scale downhole water production and injection tests to determine permeability. Cementing Full cementation of casing from shoe Up to 2 Very low production to surface. days casing HF fluid injection phase or pressurisation phase Well Well stimulation through a Up to 1 Accidental leaks of ‘fracture perforation treatment’ opens up the paths in coal week chemicals during transport and seams so they are wide enough to (depending and hydraulic fracturing hydraulic allow gas flow. Fracture treatment on the mixing and injection fracturing involves pumping water, sand and number of Loss of hydraulic fracturing additives into the selected zones at stages to fluid in the coal seam high rates. be formation performed) Leaks into overlying 1–3 days to aquifer during hydraulic complete fracturing hydraulic Leaks from storage ponds fracturing containing flowback water Depressurisation phase Production Production of gas from coal for 12-15 from storage ponds testing evaluation and appraisal. months containing produced water Production CSG wells pump water and gas from Up to Leaks from storage ponds phase the coal seams. Water and gas are several containing produced water separated on the surface, water is decades for Leaks from pipelines pumped to storage ponds awaiting a well Dust control with produced treatment and / or reuse. (20–30 y) water Flooding from storage ponds Post-operational or return to equilibrium Site that are unsuitable for production Days to Improperly plugged wells rehabilitation or have ceased producing gas will be weeks could provide pathways for plugged with cement. contaminated groundwater. Storage ponds are to be cleaned out, Storage remain on site and the liners removed and disposed with residual contamination of in a licensed facility. accumulated at its base, followed by leakage through the liner. Monitoring Long-term stewardship, monitoring Up to Very low groundwater level and quality. several decades
characteristics Coal seam permeability testing Lowering of special purpose packers on slim rods into the wellbores with packers isolating specific target coal seams for small-scale downhole water production and injection tests to determine permeability. 5 days Very low Cementing production casing Full cementation of casing from shoe to surface. Up to 2 days Very low HF fluid injection phase or pressurisation phase Well perforation and hydraulic fracturing Well stimulation through a ‘fracture treatment’ opens up the paths in coal seams so they are wide enough to allow gas flow. Fracture treatment involves pumping water, sand and additives into the selected zones at high rates. Up to 1 week (depending on the number of stages to be performed) 1–3 days to complete hydraulic fracturing Accidental leaks of chemicals during transport and hydraulic fracturing mixing and injection Loss of hydraulic fracturing fluid in the coal seam formation Leaks into overlying aquifer during hydraulic fracturing Leaks from storage ponds containing flowback water Depressurisation phase Production testing Production of gas from coal for evaluation and appraisal. 12-15 months from storage ponds containing produced water Production phase CSG wells pump water and gas from the coal seams. Water and gas are separated on the surface, water is pumped to storage ponds awaiting treatment and / or reuse. Up to several decades for a well (20–30 y) Leaks from storage ponds containing produced water Leaks from pipelines Dust control with produced water Flooding from storage ponds Post-operational or return to equilibrium Site rehabilitation that are unsuitable for production or have ceased producing gas will be plugged with cement. Storage ponds are to be cleaned out, and the liners removed and disposed of in a licensed facility. Days to weeks Improperly plugged wells could provide pathways for contaminated groundwater. Storage remain on site with residual contamination accumulated at its base, followed by leakage through the liner. Monitoring Long-term stewardship, monitoring groundwater level and quality. Up to several decades Very low
technical-report-number-06-lit-rev-identification-potential-pathways.docx