Geologic Framework of the Laurel Formation, Canning Basin

Abstract

Abstract The main geological and geochemical characteristics of the Tournaisian Laurel Formation across the Fitzroy Trough and Lennard Shelf in the northern regions of the Canning Basin are described in this article. From there it continues to the Laurel Formation, referred to as the total shale section, which are the shale facies thatwere assessed in this study. The Lower Carboniferous Laurel Shale is believed to be the source rock of the oil and gas reservoirs in the Lennard Shelf and Fitzroy Trough. Although the coring process is highly expensive, the core-based measurements are still considered superior and more reliable in their petrophysical characterisation of shale gas resources. Wireline logging was also studied to characterise the rich organic shale facies in terms of both TOC estimation and lithological identification. A combination of wireline logging and conventional core data was extensively focused on to elaborate the petrophysical and geological study; in particular, the vertical heterogeneity of the shale rock is very high, and drilled wells in the Fitzroy Trough are limed. About 15 cored wells were logged and more than 40 un-cored wells were calibrated to cover the largest possible area for the study. A quantitative X-ray diffraction analysis and Scanning Electronic Microscope study were conducted for five shale samples collected from different intervals in the Laurel Formation. Detailed mineral composition and texture analyses have shown four main lithofacies within the Laurel Shale (excluding the carbonate section). In most of the Fitzroy Trough, the sedimentary strata are thick and deep, and south-east in the Lennard Shelf, the total shale section is more than 400m thick, identified as mature to over-mature in the Fitzroy Trough, and immature to marginally mature in the Lennard Shelf. Measurement and estimations of total organic content (TOC) proved to contain rich organic shale in both areas. The Laurel Shale section yielded up to 5.0 wt% TOC in both the Fitzroy Trough and the Lennard Shelf. In this paper, electrofacies analysis, petrophysical study, rock typing approaches, and vertical and lateral facies distribution have been studied for the Laurel Formation in the onshore Canning Basin.