No abstract

Recent analyses of the potentially vast unconventional shale-gas resource in the Canning Basin, onshore Western Australia, estimate nearly 800 Tcf in the Goldwyer Formation alone. This and other Paleozoic marine shales share numerous characteristics with successful US shale-gas plays and commonly source conventional petroleum accumulations, although none has yet been produced directly. In order to further constrain volumetric estimates in the Canning Basin, we examined two formations that we identify as highly prospective, the Goldwyer and Laurel. Our assessment includes all data currently available for the basin and applies a combined volumetric modeling approach (USGS and PMRS). We compiled data regarding kerogen type, thermal maturity, hydrocarbon generation potential, rock mineralogy, and fluid analyses, in addition to data on porosity, permeability, and pressure and temperature variation, in every well that intersected these shales. Analysis showed maximum total organic content (TOC) of 6.4% (Goldwyer Formation), maximum vitrinite reflectance of nearly 2.0%, (Laurel Formation), and average Hydrogen Index of 0.13 gHC/gTOC (maximum of >1 in both formations). We then calculated total gas-in-place for the rock volumes corresponding to gas-prone sections of each shale (the Goldwyer III and Upper Laurel) by estimating total generation potential, original TOC, primary and secondary cracking of kerogen, and retained oil. Probabilistic analysis of the distribution of key parameters allowed estimation of total hydrocarbon in place, by applying a Monte Carlo simulation based on P90, P50, and P10. This resulted in the third independent estimate of Canning Basin shale-gas volumes and the first ever for the Goldwyer III and the Upper Laurel. Our work thus greatly improves confidence in estimates of the size of shale-gas accumulations in the basin, significantly increases the amount of data utilized in such estimations and provides the first reported volumes for previously unexamined shale layers.

The recent shale gas developments in the US have encouraged exploration for shale gas resource in WA. In the largely unexplored Carnarvon Basin, the Merlinleigh Sub-basin is predominately of Permian strata and has been shown to contain high-quality gas-prone source rocks from geochemical data. Three main potential shale layers, the Gneudna Formation, Wooramel Group and the Byro Group, were identified based on the shale ranking parameters. Geochemical data was collected and analysed for the type of kerogen, total organic content (TOC), generation potential and thermal maturity. These parameters enabled a gas-in-place resource estimation to be made for each of the formations. The TOC data from various wells were validated by using petrophysical logs and the ΔlogR method. In comparison with the geochemical data, both values produced a good match, validating both sets of data. The three layers were ranked according to their geochemical parameters and any petrophysical or geomechanical characteristics. It was identified that the Wooramel Group contains the best quality source rocks, followed by the Byro Group. The Gneudna Formation was found to have poor quality source rocks. The Monte Carlo method by Crystal Ball was selected to estimate the probabilistic resources of these three layers. According to the P50 estimations, the Byro Group, Wooramel Group and the Gneudna Formation contained resources of 51.6 tcf, 40.1 tcf and 1.4 tcf, respectively.

The recent developments of shale gas in the US have greatly encouraged exploration for the shale gas resource in Western Australia. The Merlinleigh Sub-basin of the Southern Carnarvon Basin in Western Australia has been found to contain high quality gas-prone source rocks from existing geochemical data. This paper demonstrates how log data can be used in the absence of geochemical data to increase the accuracy of resource assessments. An assessment of the Merlinleigh Sub-basin was used to calibrate and test the reliability and accuracy of the log method. A major parameter for resource estimation is the thickness of a source rock layer. This is usually determined by geochemical analysis and identifying high TOC intervals from cores. Undeveloped shale gas basins however, are limited in geochemical data whereas most of the drilled wells have wireline log data. Passey's (et al. 1990) ΔlogR method encompasses a multitude of algorithms that predicts TOC from well logs and precisely determines the thickness of a layer. The method is first calibrated with known TOC from cores before applying to wells without geochemical data. Prior studies identified three formation layers in the Merlinleigh Sub-basin; Byro Group, Wooramel Group and Gneudna Formation; potentially containing high quality source rocks. After applying Passey's delta log R method to determine thicknesses, each layer was ranked according to rock characterisation factors such as TOC, generation potential, vitrinite reflectance, porosity and permeability. The Monte Carlo method by Crystal Ball software was then selected to estimate the probabilistic resources of all layers. The production ability of each formation can also be estimated using standard open-hole log data for estimating the Ultimate Recovery in shale gas resources. In comparison, the TOC calculated from Passey's method produced results consistent with the known geochemical data, thereby validating both sets of data. The Wooramel Group was identified to contain the best quality source rocks, followed by the Byro Group, and lastly, the Gneudna Formation. According to P50 estimations from Crystal Ball, the Byro Group, Wooramel Group and Gneudna Formation contained resources of 51.6tcf, 40.7tcf and 1.4tcf respectively. The Ultimate Recovery for the above was found to be 4.69tcf, 3.71tcf and 0.13tcf respectively. Due to the low estimations for the Gneudna Formation, this paper will focus on the Byro and Wooramel Groups. This paper explores a unique way of using Passey's method for undeveloped resources having limited log data but no geochemical data. The log data was also used to estimate the Ultimate Recovery based on the production ability of each well. The exploration potential of the Carnarvon Basin in Western Australia for unconventional gas has been identified and is the first geochemical assessment for the Merlinleigh Sub-basin.

The recent shale gas developments in the US have encouraged exploration for shale gas resource in WA. In the largely unexplored Carnarvon Basin, the Merlinleigh Sub-basin is predominately of Permian strata and has been shown to contain high-quality gas-prone source rocks from geochemical data. Three main potential shale layers, the Gneudna Formation, Wooramel Group and the Byro Group, were identified based on the shale ranking parameters. Geochemical data was collected and analysed for the type of kerogen, total organic content (TOC), generation potential and thermal maturity. These parameters enabled a gas-in-place resource estimation to be made for each of the formations. The TOC data from various wells were validated by using petrophysical logs and the ΔlogR method. In comparison with the geochemical data, both values produced a good match, validating both sets of data. The three layers were ranked according to their geochemical parameters and any petrophysical or geomechanical characteristics. It was identified that the Wooramel Group contains the best quality source rocks, followed by the Byro Group. The Gneudna Formation was found to have poor quality source rocks. The Monte Carlo method by Crystal Ball was selected to estimate the probabilistic resources of these three layers. According to the P50 estimations, the Byro Group, Wooramel Group and the Gneudna Formation contained resources of 51.6 tcf, 40.1 tcf and 1.4 tcf, respectively.