Coal Bed Methane Hazards in New South Wales by C. M. Atkinson, January 2005, for Tony Davis & Associates, Australian Gas Alliance, New South Wales
· The development of a significant gas field in the district based on Coal Bed Methane will severely impact on the security of supply of this water, by radically altering the groundwater levels, and purity.
· Both local and overseas experience shows that fundamental changes in underground pressures can result in serious escapes of methane gas into the environment. Elsewhere this has taken the form of soil poisoning and vegetation destruction, methane venting into nearby wells, surface gas escapes and collection in surface hollows with the resultant danger to human life.
· Additional, poorly researched factors include the danger of organic coal chemicals leaching out during gas production. Research suggests these organic chemicals have carcinogenic and genetic effects. The possibility of significant surface subsidence over a prolonged period cannot be ruled out without further research.
· Based on these conclusions, there should be no further drilling in the area until a full and independent hydrology study has been carried out. Consideration should also be given to classifying coal bed methane sites as industrial chemical sites controlled by the relevant regulations.
Based on field research, Jones’ (2005) findings included the following comments:
“Groundwater modelling has shown that overhead groundwater leakage will occur in the study area during Sydney Gas Ltd dewatering operations and closure.”
“Dewatering of coal seams will allow for groundwater migration towards coal seam voids. This has a significant potential to effectively dewater sections of the study area.”
“Riparian vegetation and wetlands are at risk by a lowering of the groundwater levels and methane migration into the overlying aquifers during gas production.”
On 19 March 2004 Sydney Gas Ltd began drilling two production test wells alongside the earlier cored drillholes. Drill hole JB1A was designed to test the coal bed methane potential of the Great Northern seam at a depth of approximately 410m –417m below surface. Borehole JB2A, drilled alongside hole JB2, was drilled to test production data from 21m of coal in three coal seams: Great Northern seam at 429m-436m, the Montrose/Wave Hill (530-541m), the Borehole seam at 555m-558m. Target coal seams in each borehole were fractured (“fracced”) to improve the permeability, and then pumping tests were carried out. Removing the water from the coal seams around the borehole reduces the underground pressure and allows any gas present to be desorbed from the coal and be pumped to the surface.
Jones (2005) also correctly points out that long experience in the USA, and more recent experience in New South Wales shows that once the head of water is removed, the coal gas, mainly methane, is mobile and can migrate by uncontrolled pathways to the surface, or to nearby openings such as water wells. In surface methane seepages through soil, the methane displaces the soil oxygen, the soil becomes anoxic leading to total death of the vegetation. This vegetation destruction has been well publicised in the Cataract River area south of Sydney, where methane has spread up through cracks induced by coal mining subsidence.
In September 2004, within a fortnight of the beginning of gas testing, a coal bed methane well north of Newcastle, NSW, was shut down as several boreholes up to 300m away began to blow off methane gas. This was the first reported case of a serious migration of methane gas from coal bed methane operations in New South Wales.
Molopo Australia Limited has a 25% interest with the operating company AJ Lucas Coal technologies Pty. Ltd, in the Stratford gas prospect near Gloucester, approximately 100 kilometres north of Newcastle. Drill hole LMG-03 was one of two test production drill holes completed by the partners and four coal zones with an aggregate thickness of 16 metres (some announcements quote 23 metres) of coal had been fracture stimulated with sand and water. A 6-12 months testing period began in late August 2004. However, Molopo announced on 7th September that all tests had been halted after methane had erupted from a number of old boreholes in the area. At the time a strong gas flow of 280,000 cubic feet/day had been recorded even though the water level was still about 300 metres above the coal seams. Two and a half months later Molopo Australia Limited announced that test pumping of LMG-03 had resumed. Three boreholes from an earlier coal exploration had started producing methane, and these along with eight other boreholes had now been sealed with concrete, the company explained. The project manager explained in November that this accidental methane eruption had shown how good the lateral connections were in the reservoir.
In this case there were apparently no serious injuries and the methane gas migrated into nearby boreholes rather than houses, essential water supplies or livestock areas. This example shows that even with only a partial withdrawal of the hydrostatic pressure, methane will migrate quickly and in unpredictable directions. If the drill site conditions laid down by the State Government are similar at Stratford to those elsewhere, the most visible safety precautions would have been a wire fence and a locked gate.
Hazards of coal bed methane exploration in the Bohena area of the Pilliga East State Forest near Narrabri include the bulldozing of the critical habitat of rare fauna, the collapse of the dam wall after a thunderstorm and most critically, the locally catastrophic underground seepage of caustic groundwater into the surrounding forest. … A barbed wire fence now encloses an area of about 80 metres by 90 metres containing the boreholes Bohena 2 and 2D, and the holding dam. This dam was built to contain the ground water pumped from underground. Portions of the settling dam wall collapsed and a very saline/sodic fluid poured in to the forest at the southern edge of the site. This collapse probably followed a heavy storm in November 2000.
The collapse of the retaining dam wall was a separate event from the extensive leakage from the dam (excavated in sandy soil) which resulted in the spread of sodic/saline liquid through the subsoil and shallow aquifers. Slight depressions in the forest floor were filled with a black treacle-like liquid. Water in the retaining dam and the black sludge were sampled by the NSW Environmental Protection Agency in April 2001. Limited analyses showed the black sludge contained high levels of tannin. The sodium level in dam water samples was 3,700 mg/litre.
The repaired dam wall remained intact but the area of dying vegetation continued to expand at this site. In addition, trees began to die at two other sites (No.4 and No.3) up to a kilometre away where the saline water from No.2 site had been diverted to through a polythene pipe. By November 2001 the pollution front at No.2 site could be traced eastwards over distance of 250m and a maximum width of 100 metres. … The limited chemical analyses, the persistence of black tannin rich fluids emerging from the sub-soil and the death of normally resistant Casuarinas, all point to a chronic case of sodic soil poisoning, worse than cases described from methane gas fields in the Powder River Basin USA [Emphasis added]