Unconventional Source Rock Potential of the Goldwyer Formation, Canning Basin, Western Australia: Application of the Delta Log R Technique.
Geoscience Honours Degree, 2012
University of Adelaide
The Ordovician Goldwyer Formation in the Canning Basin is considered a favourable unconventional hydrocarbon target. This project concentrates on the use of petrophysical data for evaluating the source rock potentiality within the formation. Due to the advances in drilling methods, unconventional resources have become economically viable. The study of these resources can be done by a petrophysical means and with the integration of geochemistry. Unconventional source rock characterisation has been intensively studied since 2009 from the perspective of accessing unconventional hydrocarbons from the Barnett Shales. Resource evaluation mapping from an observation of the distribution of organic richness is a key component in exploration of unconventional resources.
To understand source rock characteristics and organic richness in the Goldwyer Formation through an observation of the values of Total Organic Carbon (TOC), the Delta Log R (DLOGR) technique was used for 12 wells spread across the Canning Basin intersecting the formation. The DLOGR technique can provide an interpolation of continuous (TOC) values over the source rock interval with limited geochemical data and also has the ability to extrapolate to wells without any geochemical sampling. It is derived by creating DLOGR separation through wireline logs and applying an empirical relationship with level of Maturity (LOM) and geochemistry to predict TOC (mentioned by Passey et al. (1990)). This method is especially useful to evaluate TOC distributions for wells with limited or no geochemical data. Prediction of TOC will help in resource evaluation and estimation.
The Goldwyer Formation consists of two shale members, an upper member and a lower member comprising two shales. These members are considered source rocks. The upper consists of alternating laminated carbonates and shale source rock in the form of G.prisca, which is considered a shale oil play located in the Barbwire Terrace. The lower shale member consists of interbedded shales, siltstones and claystones, which have been proven to be a shale gas play. Higher TOC values and thicker interval have been observed in the lower shale member spread in the Kidson Sub-Basin and Broom platform. The interval has shown a better quality TOC richness and is associated with a maximum flooding surface in the lower shale member.
The DLOGR technique was applied to the wells with the most available geochemical data sampling points. Overall, computing the correlation with the predicted TOC versus true TOC of the upper and lower members demonstrated a good fit to the true TOC values. Negative TOC values arising from this technique occurred in the upper shale member. These anomalous negative values were created by extreme inflections of the sonic log due to the cyclic nature of the carbonates and shales. Cross plot analysis has been associated with low gamma ray values (in the wells Aquila, Willara, McLarty, Munro, Pictor and Parda) and the negative TOC values. In general, the TOC quality in the wells analysed was significantly low and overall, the source generative potential was low.
The methodology of Bowman (2010) was used in conjunction with that of Passey et al. (1990). The method applies the same hypothesis as Passey et al (1990). The DTR separation showed a promising correlation with DLOGR separation in wells which have indicated hydrocarbon in the source rock interval of the formation.
This method, incorporating Passey et al. (1990) and Bowman’s (2010) methodologies for the development of unconventional resource assessment. The method, while successful most times a few areas and intervals may not always be applicable, it has led to some incorrect assumptions in interpretations.