1.2.1.2 Coal seam gas


Coal in the Cooper Basin is widely recognised as a major hydrocarbon-generating source for the Cooper–Eromanga petroleum system (e.g. Radke, 2009). However, coal seam gas is generally not targeted as a stand-alone resource; rather it is part of combined hydrocarbon targets, commonly occurring with tight gas and shale gas at the same locality.

In the Cooper subregion, there are no current or historic CSG production facilities. This section describes the general characteristics of coal seam gas reported in exploration drilling in the Cooper subregion. A prospective, CSG-only resource, subject to further appraisal, has been reported in the Weena Trough by Strike Energy Limited. This is discussed in more detail in Section 1.2.3 .

Gas peaks associated with coal seams of the Patchawarra, Epsilon and Toolachee formations have been recorded during drilling operations throughout the Cooper Basin. Such gas generally has low water content, relatively low carbon dioxide (less than 35%) and is high in methane (greater than 60%).

Gas from the Patchawarra coal seams intersected in exploration well Davenport-1/ST1 is primarily methane (51.2 mol %), carbon dioxide (25.8 mol %), nitrogen (16.8 mol %), ethane (4.8 mol %), and propane and heavier hydrocarbons (1.5 mol %). The Vm3 seam has an average gas content of 24.8 standard cubic centimetres per gram (scc/g) on a dry, ash-free basis, comprising 84% lost gas[2], 14% measurable gas[3] and 1.7% residual gas[4]. The Vu seam has an average gas content of 22.5 scc/g. This comprises 81% lost gas, 17% measurable gas and 1.7% residual gas (Beach Energy, 2012a). The desorbed gas composition from exploration well Davenport-1/ST1 exhibited the characteristics shown in Table 3 and Table 4 .

Table 3 Desorbed gas analyses for the Patchawarra Formation Vm3 coal seam from Davenport-1/ST1


Methane

Ethane

Propane

i-Butane

n-Butane

Carbon dioxide

Early

61.2%

2.7%

0.4%

0.1%

0.1%

35.7%

Mid

58.1%

4.6%

1.1%

0.2%

0.1%

36.0%

Late

60.8%

11.6%

3.0%

0.5%

0.1%

24.1%

Data: Beach Energy (2012a)

Nitrogen and oxygen were set to zero for this analysis

’Early‘ refers to gas released in the early stages of desorption testing, ’Mid‘ refers to gas released in the main part of the test, and ’Late‘ to the later stages of testing

Average analyses for sample taken from 1905.4 to 1923.6 m depth

Table 4 Desorbed gas analyses for the Patchawarra Formation Vm3 coal seam from Davenport-1/ST1


Methane

Ethane

Propane

i-Butane

n-Butane

Carbon dioxide

Early

64.2%

2.5%

0.5%

0.0%

0.0%

32.8%

Mid

58.6%

12.3%

2.2%

0.3%

0.1%

26.4%

Late

65.3%

11.8%

3.6%

0.5%

0.1%

18.7%

Data: Beach Energy (2012a)

Nitrogen and oxygen were set to zero for this analysis

’Early‘ refers to gas released in the early stages of desorption testing, ’Mid‘ refers to gas released in the main part of the test, and ’Late‘ to the later stages of testing

Average analyses for sample taken from 1975.75 to 2002.3 m depth

Gas from the 16.5 m thick Patchawarra Formation coal in exploration well Forge-1 had a gas content of 0.94 scc/g on a dry, ash-free basis; comprising 22% lost gas, 76% desorbed gas and 2% residual gas (Strike Energy Limited, 2010). The desorbed gas exhibited the characteristics shown in Table 5 . The favourable gas compositions from the Patchawarra coal have resulted in follow-up drilling, appraisal and production testing (for example Strike Energy Limited, 2014a).

Table 5 Desorbed gas analyses for Forge-1 Patchawarra Formation coal


Methane

Ethane

Propane

i-Butane

n-Butane

Carbon dioxide

Early A

64.3%

1.1%

0.3%

0.0%

0.0%

34.4%

Early B

61.4%

1.3%

0.4%

0.0%

0.0%

36.9%

Mid

57.1%

2.1%

0.8%

0.1%

0.1%

39.8%

Late

74.4%

1.8%

0.4%

0.1%

0.0%

23.3%

Data: Strike Energy Limited (2010)

Nitrogen and oxygen were set to zero for this analysis

‘Early’ refers to gas released in the early stages of desorption testing, ‘Mid’ refers to gas released in the main part of the test, and ‘Late’ to the later stages of testing

Average analyses for sample taken from 1313 to 1329.5 m depth

Coal from the Winton Formation intersected in exploration well Merninie-1 was sampled and analysed for gas composition. The dry, ash free gas content for the intersected coal averaged 0.86 scc/g (AGL Energy Limited, 2010). Average desorption analyses for these samples are presented in Table 6. This prospect was not progressed due in part to the gas composition characteristics (AGL Energy Limited, 2010).

Table 6 Desorbed gas analyses for Winton Formation coal from Merninie-1


Methane

Ethane

Propane

i-Butane

n-Butane

Nitrogen

Carbon dioxide

Early

38.3%

1.2%

0.0%

0.0%

0.0%

55.7%

4.9%

Mid

37.8%

0.9%

0.0%

0.0%

0.0%

66.0%

1.3%

Late

31.5%

0.9%

0.0%

0.0%

0.0%

66.3%

1.3%

Data: AGL Energy Limited (2010)

Oxygen was set to zero for this analysis

’Early‘ refers to gas released in the early stages of desorption testing, ’Mid‘ refers to gas released in the main part of the test, and ’Late‘ to the later stages of testing

Average analyses for sample taken from 452.2 m to 699.0 m depth

Last updated:
5 January 2018