High-resolution coupling of stratigraphic ‘sweet-spot’ lithofacies and petrophysical properties: A multiscale study of Ordovician Goldwyer Formation, Western Australia

The identification of stratigraphic 'sweet-spot' interval is significant in oil and gas formation evaluation. However, formation evaluation in macroscopic-scale merely provides low resolution and limited information, thus may lead to uncertainties in resource estimation. To accurately identify the 'sweet-spot' intervals amongst heterogeneous lithofacies, we conducted a very high-resolution and quantitative analysis from in-situ macroscopic scale to laboratory microscopic scale on the Goldwyer formation of Canning Basin, Western Australia. The comprehensive advanced well logging and slim-compact micro imager (SCMI) technologies were synthetically applied in couple with the laboratory nanoscaled experiments. The results unveiled an extraordinarily large lithofacies heterogeneity between different rock intervals, with distinguished features shown in Goldwyer I, II, and III members. The most favorable lithofacies is recognized as the laminated argillaceous thermally-matured organic matter (OM)-rich mudstone, which is widely developed in Goldwyer III as the major attributor to 'sweet-spot' intervals. Goldwyer III is exclusively characterized by thick mudstone intervals (94.4%), interbedded with thin calcareous mudstones (5.5%), corresponding to a depositional environment of low-energy distal section of the outer ramp settings. Microscopically, the most favorable lithofacies in 'sweet-spot' intervals develop numerous OM-/mineral nanopores for hydrocarbon storage. Illite-rich lithofacies develops abundant inter-particle pores from 2 to 17 nm that mainly contribute to pore volume for free gas storage capacity. OM-rich lithofacies with higher maturity have OM-pores with good connectivity, bearing large specific surface area that is beneficial for adsorbed gas capacity. & COPY; 2022 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).