Shale Gas Volumetrics of Unconventional Resource Plays in the Canning Basin, Western Australia

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.

Ensemble Learning for Predicting TOC from Well-Logs of the Unconventional Goldwyer Shale

“…The formation's complexity is responsive to poor correlation coefficients from traditional TOC techniques (Schmoker and Passey) with an R 2 value of 0.43 and 0.44 [27]. Moreover, the MLR method, which builds TOC log with linear regression algorithm from wire-line logs can reach an average correlation of 0.77 on the studied wells, but it is difficult to generalize because of the difference in log response and proven non-linearity across the Goldwyer formation from previous work in the Canning Basin [28,31]. Due to the non-unique relationship of wire-line logs and core TOC (laterally as well as spatially) in shale gas reservoirs, data-driven techniques are more reliable to improve prediction not only in a well, but also across the reservoir interval.…”

“…The location of the studied basin and its general stratigraphy column are shown in Figure 1. Most prospective sub-divisions are Broome platforms [31] and the maximum organic richness observed in Theia-1 well (DMIRS unpublished report, 2019), which lies inside this platform (Figure 1a). Ten wells are chosen (see Table 1 about the well information) where core TOC is available within the formation.…”

“…The Goldwyer formation of the Canning Basin is highly complex in nature, which can be inferred from the large variety of core TOC value ranges from 0.16 wt % to 4.47 wt % with standard deviation of 1 wt % (Table 3) and also from previous research publication on maturity index, lithology, and core description of the drilled wells [5,31,59]. Figure 17 displayed the core plugs extracted from a well in the Goldwyer formation where it is very clear that the depositional environment is changing rapidly from shallow to deeper section.…”

“…Our study area is located inside the Canning Basin, which is a massive, intra-cratonic Paleozoic sedimentary basin with limited exploration activity because it is relatively less well drilled than the prospective Ordovician Goldwyer shale formation [5,28,30]. The organic richness of Goldwyer shale is highly variable across the basin [28,31]. There is no guarantee that any of the above single ML methods are suitable for building the optimum TOC profile across the basin.…”