The recently drilled deep stratigraphic drill hole NDI Carrara 1 penetrates the carbonate formations of the Cambrian Georgina Basin as well as the underlying Proterozoic successions of the Carrara Sub-basin. The Proterozoic section consists predominantly of tight shales, siltstones, and calcareous clastic rocks. This study aims to assess the petrophysical properties of the Proterozoic shales using conventional wireline logs.
Gamma ray and neutron-density crossplots were used to calculate shale volume fraction, and neutron-density crossplots were applied to compute the total and effective porosity of non-shale rocks. Total organic carbon (TOC) content was interpreted using artificial neural networks, and was used to derive the volume of organic matter was converted from TOC content. Bulk density logs were corrected by removing the kerogen effect in the organic-rich shales. Matrix and kerogen densities were obtained by correlating the reciprocal of grain density with TOC content. Total shale porosity was calculated from kerogen-corrected density porosity and organic porosity. Effective porosity was estimated by removing the shaliness effect. Water saturation was derived using the Simandoux equation.
The Proterozoic Lawn Hill Formation in NDI Carrara 1 exhibits petrophysical properties that indicate a favourable potential for shale gas resources. Herein, we define three informal intervals within the intersected Lawn Hill Formation; the upper Lawn Hill, the Lawn Hill shale, and the lower Lawn Hill. The net shale thickness of the upper Lawn Hill and Lawn Hill shale intervals are 165 m and 149 m, respectively. The increased TOC content and organic porosity of the upper Lawn Hill and Lawn Hill shale implies higher adsorbed gas content potential. The Lawn Hill shale has the highest gas saturation (average of 31.1%) and the highest potential for free gas content, corresponding to the highest methane responses in logged mud gas profiles.
This extended Abstract was submitted to/presented at the Australasian Exploration Geoscience Conference (AEGC) 2023, Brisbane (https://2023.aegc.com.au/)
