Supersequences Of Discussion And Interpretance Of Hydrocarbons
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6.0 Discussion and Interpretation
6.1 Source Rock
The major source units modelled for both transects include the blue whale supersequence, the upper white point supersequence and the tiger supersequences, these three units are considered to have the highest potential of having sourced hydrocarbons that we preserved in traps.
Fluviodeltaic sandstones of the Potoroo Formation have excellent reservoir potential (net to gross ratio of more than 70% and porosities over 35% in Potoroo 1, and well over 20% in Gnarlyknots 1A even below 3000 m), but they may lack an adequate regional seal. However, thick and laterally extensive claystone units within the Hammerhead Supersequence are likely to be present and provide…show more content… Other principal reservoir candidates are deltaic sandstones of the Ceduna and Platypus formations, where porosities of up to 30% have been encountered. Locally, marine sandstones of the Tiger Supersequence (Wigunda and Potoroo formations) also have excellent reservoir quality. Away from regional highs, prodelta mudstone of the Wigunda Formation provides an effective seal for these highly porous intervals.
Of secondary interest are fluviolacustrine lithologies intersected within the Loongana and lower Borda formations. Although of highly variable reservoir quality, these intervals have poor to moderate overall porosity, mainly due to the high depth of burial. Shales of the Madura and Toondi formations and intraformational shale of the Loongana Formation can provide adequate seal for these potential reservoirs. Major cap rocks exist in the Borda and Neptune formations.
Excellent quality reservoir rocks have been encountered in the overlying Eucla Basin, within the marine Wobbegong Supersequence (Pidinga Formation and Hampton Sandstone).
6.4 Timing of Maturation and Migration
Present-day maturity levels, based on the constraints described above, are shown in Figure 16. On the northern transect (Fig.
16a), the oil window is typically reached at depths between 2.0 and 2.5 km below sea surface. Thus, along this transect, the lower
Tiger Supersequence is mature for oil generation in the central part of the