Toolachee Formation

The Gidgealpa Field currently produces gas from the Early Permian Patchawarra Formation and Tirrawarra Sandstone, the Late Permian Toolachee Formation, and oil from the Jurassic Namur, Birk-head, Hutton and Poolowanna Formations (Fig. 2). The abundant dispersed organic matter in the intraformational shales and siltstones, and possibly... 

Fig. 19. Seismic traverse along line B-B (see Fig. 21) illustrating the major seismic horizons and the high-amplitude zone caused by major calcite cementation in the Lower Namur Sandstone, Gidgealpa Field. Note the lateral variation in seismic character of the high-amplitude zone caused by variable carbonate cementation. Horizons C, top Cadna-Owie Formation P, top Permian (Toolachee Formation).

Seismic mapping shows that carbonate cement distribution broadly follows the structural trend of the GMI anticline, in a SSW-NNE direction (Figs lA and 21). The carbonate cements extend over an area up to 7.5 km wide and at least 20 km long, covering an area of 150 km. Comparison of the carbonate cement isopach map with a depth structure contour map for the top Toolachee Formation (McIntyre et al., 1989) demonstrates that the cements concentrate near the crest of the Gidgealpa Field in the Lower Namur Sandstone. The high amplitudes produced by the carbonate cementation decrease downflank, and phase out completely in more off-structure regions of the fi eld. 

Martin, K.R. Hamilton, N.J. (1981) Diagenesis and reservoir quality, Toolachee Formation, Cooper Basin. Aust. Petrol. Explor. /lii. J., 21, 143-154. 

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