Fluid Flow History in Lower Triassic Bulgo Sandstone, Central Sydney Basin, Australia

The fluid flow history during diagenesis of the Lower Triassic Bulgo sandstone has been investigated through integrated analyses of petrography, stable isotope and fluid inclusion. Combined application of these techniques was intended to constrain the temperature, timing, chemistry and source of pore fluids during diagenetic cementation events in the Lower Triassic Bulgo sandstone. The diagenesis proceeded in two different flow regimes: early dynamic fluid flow regime and late slow static fluid flow regime. The former was characterized by a slight increase of δ(¹⁸O) of pore waters form estimated -15×10^-3 to -14×10^-3 with the temperature increasing from ~10 ℃ to ~75 ℃. During early diagenesis, early clays and pore filling carbonates precipitated from the pore waters. The late slow flow/static fluid regime was characterized by a rapid¹⁸Oenrichment process. δ(¹⁸O) of pore waters increased from -14×10^-3 to -5×10^-3 with the temperature increasing from 75 ℃ to 110 ℃. During the late diagenesis, kaolin (generation Ⅱ), quartz and illite crystallized. Oil migrated to the sandstones of the Bulgo sandstone during quartz cementation.