Bulk trapped fluid content data acquired from fluid inclusion analysis of more than 7,000 cutting samples from 26 wells onshore Canning Basin, Australia (Figure 1; Table 1), provide insight into the hydrocarbon potential of this largely unexplored basin. Although key unconventional targets are thought to reside within the Ordovician section, exploration risks include the thickness, distribution, and presence of producible reservoir; source distribution and maturity; and the ability to stimulate reservoirs. Samples examined in this study range in age from Cretaceous to Ordovician (Figure 2). The overall analysis of samples employed X-ray fluorescence (XRF) to determine inorganic elemental composition. Fluid inclusion petrography and microthermometry analyses were performed on intervals selected on the basis of initial bulk fluid inclusion analysis results. The resulting data allowed evaluation of the vertical and lateral distribution of hydrocarbons and nonhydrocarbon volatiles, oil gravity values, phase state, salinity, and burial temperature.
Homogenization temperatures above current reservoir temperatures are present in many of the petroleum and aqueous fluid inclusions, suggesting that fluids dropped through bubblepoint during uplift of 1000–1800 m and current reservoir fluids are likely dual-phase. Maturity values calculated from fluid inclusion data generally range from 0.6 to 1.3% vitrinite-equivalent. Regional variability in maturity within potential source intervals leads to variable fluid composition, with estimates that API oil gravity values (based on fluid inclusions) can range from 28 to 45°, although most measured values range from 37 to 44° API gravity.
Data indicate source rock potential in the Upper Ordovician Bongabinni Formation of the Carribuddy Group, Upper Ordovician Nita Formation, Middle Ordovician Goldwyer and Willara Formations, and the Lower Ordovician Nambeet Formation. Lateral and vertical distribution is not uniform within these units, and the prospectivity of the Ordovician Nita-to-Nambeet section is verified. Several formations within the Canning Basin exhibit potential for conventional exploration, including: Middle Jurassic Wallal Sandstone, Lower Permian Grant Group Sandstones, Devonian Tandalgoo Sandstone, Upper Ordovician Nita Formation, Middle Ordovician Willara Formation and Lower Ordovician Nambeet Formation. The study identified the presence of migrated and locally generated fluids, including a deep-sourced mature gas phase that appears to have invaded portions of the basin. The occurrence of shallow bacterial microseeps suggests associated deeper accumulations are present. It is anticipated that accumulations will be classified as combined conventional and unconventional reservoirs. The study identified multiple, individual targets, which vary geographically, indicating the need for a directed approach to optimize drilling and completion.