Canning Basin Research Articles

Petrophysical analysis of the unconventional reservoirs of the Lennard Shelf and Fitzroy Trough in Canning Basin, Australia

A US operator with a commitment to future drilling, stimulation and testing of unconventional wells has initiated a new evaluation to better define and understand the hydrocarbon plays along the northern margin of the Canning Basin’s Lennard Shelf and Fitzroy Trough. The goal of the evaluation is to determine the commercial viability of the region. In this paper, an integrated petrophysical hybrid model that has been calibrated to core data is highlighted. From this model, multiple play types were identified, including an unconventional siltstone-shale play, a conventional basin-centred tight gas play and a fractured tight gas play with potential analogs to North American unconventional plays. Six primary lithofacies were identified through the integration of thin section analyses, core descriptions, logs and petrophysical models. The results were calibrated to high-resolution formation image data to better understand the thin-bedded nature of these plays. The lithofacies were also utilised for defining core poro/perm transforms. Furthermore, an integrated descriptive mud log algorithm was utilised to define the types of hydrocarbons, including wetness, balance and ratios as the hydrocarbons’ fingerprints. Significant gas influxes were noted at the intervals with highly permeable beds, at swarms of fractures and faults, as well as within the organic rich layers. In this study, a pressure top seal for the Laurel Formation was defined as well as the highlights of one well, which includes 11 zones and over 389m of net pay behind pipe. The significance of this work is that it highlights a path forward for unconventional development that, if economically viable, would provide increased energy independence for Australia.

Keys to successful negotiation of indigenous land use agreements and building consent for the development of natural resources, The Great Sandy Desert Project, a case study

Theia Energy Pty Ltd discovered a substantial hydrocarbon resource in the Canning Basin, NW in Western Australia, just 150-km SE of Broome. Since 2014, Theia Energy has built a robust working relationship with the traditional owners of the land that hold native title over their permits. This relationship has developed through negotiation meetings, on-country cultural heritage surveys and cultural awareness training. The relationship has culminated in the negotiation of indigenous land use agreements (ILUA) with the Karajarri People that manage the impacts of potential development of the resource including the impacts of hydraulic fracture stimulation, and provide significant economic development opportunities. The consistent exchange of information and views has developed mutual understanding and respect allowing for the effective and pragmatic treatment of risks to allow for the exploration, and if successful the development, of the onshore Canning Basin. The Great Sandy Desert Project has the potential to bring substantial benefits to regional communities and is significant for economic development of the West Kimberley, state revenue and national liquid fuel security. This study discusses important lessons learned in building trust with traditional owners and custodians of the land and how cultural values can be protected while providing social and economic opportunities for Indigenous Australians in a sustainable and culturally appropriate way. It reflects on the outcomes of the many scientific inquiries into hydraulic fracture stimulation and the perception of risks and impacts of traditional owners which must be addressed in a genuine, meaningful and effective way. It also sets out how traditional owners have, through the negotiation of the ILUA with Theia Energy and in the absence of clear policy from Government, chosen to establish their own system of regulation and economic participation in the project to address and manage risks and impacts from the development of resources on their country.

Barnicarndy Graben, southern Canning Basin: stratigraphy defined by the Barnicarndy 1 stratigraphic well

Funded by Geoscience Australia’s Exploring for the Future initiative and operated by the Geological Survey of Western Australia, the Waukarlycarly 1 deep stratigraphic drillhole was designed to investigate the geology of the little-known Waukarlycarly Embayment and assess the petroleum, mineral, groundwater and CO2 storage potential of the area. Based on consultation with the Western Desert Lands Aboriginal Corporation on the cultural significance of the name, Waukarlycarly, it has been agreed to change the name of the well to Barnicarndy 1 and the tectonic subdivision to the Barnicarndy Graben. This and all future publications will now refer to the Barnicarndy 1 stratigraphic drillhole (previously Waukarlycarly 1) and the Barnicarndy Graben (previously Waukarlycarly Embayment). Drilling commenced on 1 September 2019 and reached a total depth (TD) of 2680.53m on 30 November 2019, recovering more than 2km of continuous core. The cored interval extended from 580m to TD in Neoproterozoic Yeneena Basin dolostone, which was unconformably overlain by a thick, lower Canning Basin Ordovician stratigraphy, including richly fossiliferous marine mudstones with common volcanic ash beds. A major unconformity is located at the top of the Ordovician section where it is overlain by sandstones and muddy diamictites of the Carboniferous–Permian Grant Group, followed by a Cenozoic succession near surface. Ditch cuttings were collected from surface to 580m at 3m intervals. The pre-Grant Group Paleozoic succession is unique within the Canning Basin, indicating that the Barnicarndy Graben’s depositional history is markedly different when compared with adjacent structural subdivisions, such as the Munro Arch and Kidson Sub-basin. Detrital zircon geochronology, biostratigraphy and borehole imaging interpretation assisted in the definition of two new geological units within the Ordovician stratigraphy of Barnicarndy 1: the Yapukarninjarra and Barnicarndy formations. Preliminary routine core analysis data indicates the potential for CO2 storage within the Barnicarndy Formation beneath a Grant Group seal. The well also provides new insights into the structural interpretation of the Barnicarndy Graben.

Petrophysical and geochemical interpretations of well logs from the pre-Carboniferous succession in Barnicarndy 1, Canning Basin, Western Australia

Barnicarndy 1 is a stratigraphic well drilled in the southern part of the Canning Basin’s Barnicarndy Graben under Geoscience Australia’s Exploring for the Future program in collaboration with the Geological Survey of Western Australia to provide stratigraphic data for this poorly understood tectonic component. The well intersects a thin Cenozoic section, Permian–Carboniferous fluvial clastics and glacial diamictites and a thick pre-Carboniferous succession (855–2585mRT) unconformably overlying Neoproterozoic metasedimentary rocks. Three informal siliciclastic intervals were defined based on core lithology, well logs, chemical and mineral compositions: the Upper Sandstone (855–1348.1mRT), Middle Interval (1348.1–2443.4mRT) and Lower Sandstone (2443.4–2585mRT). The Middle Interval was further divided into six internal zones. Both conventional methods and artificial neural network technology were applied to well logs to interpret petrophysical and elastic properties, total organic carbon (TOC) content, pyrolysis products from the cracking of organic matter (S2) and mineral compositions. Average sandstone porosity and reservoir permeability are 17.9% and 464.5mD in the Upper Sandstone and 6.75% and 10mD in the Lower Sandstone. The Middle Interval claystone has an average porosity and permeability of 4.17% and 0.006mD, and average TOC content and S2 value of 0.17wt% and 0.047mgHC/g rock, with maximum values of 0.66wt% and 0.46mgHC/g rock, respectively. Correlations of mineral compositions and petrophysical, geomechanical and organic geochemical properties of the Middle Interval have been conducted and demonstrate that these sediments are organically lean and lie within the oil and gas window.

Australian exploration review 2020

Australian exploration battled on through the challenging headwinds of 2020 and surprisingly, 2020 saw an increase in exploration drilling on 2019 activity. Twenty-five exploration wells were drilled in 2020 versus 20 exploration wells drilled in 2019. Eight discoveries were made during the year, with the most significant being the Enterprise discovery in the Otway Basin. 2020 also saw a return to exploration drilling in the Beetaloo Sub-basin unconventional plays. Appraisal drilling was dominated by Cooper-Eromanga Basin and coal seam gas activity. There were no offshore appraisal wells in 2020. The exploration farm-in deals of note were Santos taking additional equity from Armour in their South Nicholson Basin unconventional project and Origin taking additional equity from Falcon in their Beetaloo Sub-basin unconventional project. Origin also farmed into the Canning Basin position of Buru Energy and Rey Resources. Australia is set for an exciting year of exploration ahead with a return to exploration drilling in the Bedout Sub-basin, further exploration drilling in the North Perth Basin and a continuation of drilling and testing of the unconventional plays in the Beetaloo Sub-basin.

Velocity anomalies and out-of-plane reflections in Barnicarndy 1, Canning Basin

Barnicarndy 1 was drilled as a stratigraphic well and penetrated 2585m of clastic sedimentary rocks overlying an angular unconformity composed of Proterozoic dolomite basement near SSE end of the eponymous graben (previously known as the Waukarlycarly Embayment) of the Canning Basin. The post-drilling data exhibited several types of anomalies and inconsistencies, including ultra-slow velocity of the vertical seismic profile (VSP) within the top 210m, substantially high velocity from 210 to 1390m, poor synthetic–seismic correlation, and discrepancies between the prognosis and actual depths. The VSP shows that the uppermost sedimentary section has an average velocity of less than 1000m/s, which is unrealistically slow and probably caused by a systematic time delay in the data acquisition. Such a delaying effect was removed when calculating the VSP interval velocity, which had reasonable consistencies with sonic velocity and lithological packages. The consistencies verify that the sections from 210 to 1390m have high velocities that are beyond the range of offset wells at equivalent depths and do not follow an expected trend along most of the well trajectory. Quantitative analyses of multiple synthetic correlations suggest that the depth discrepancies in the prognosis are not related to pre-drilling seismic interpretation, as the two-way time picks for major boundaries mostly match what has been penetrated in Barnicarndy 1. Two thirds of the depth error for basement prognosis comes from the unexpected high velocity in the shallow formations. The velocity anomalies indicate that the Barnicarndy Graben possibly has a complex history of tectonic movement, and thick sections could have been eroded during the Late Triassic. The remaining discrepancy in depth prognosis for the basement is related to the out-of-plane seismic reflection near the SSE end of the graben. The steeply dipping basement causes out-of-plane issues for 2D seismic data, and the Kidson seismic survey images the shallower basement reflected from further south, rather than what is vertically below the survey route.

Varying least principal stress along lithofacies in gas shale reservoirs: effects of frictional strength and viscoelastic stress relaxation

Compositional variation of rock properties in unconventional shale reservoirs impacts not only hydraulic fracturing stimulation but also the variability of induced shear slip on pre-existing fracture networks. Lithological layering is also responsible for varying stress states in various unconventional reservoirs subjected to normal, strike-slip, reverse or hybrid faulting regime (a combination of any two of them). Three possible mechanisms are considered to evaluate the layer-based stress profile in the sub-surface, that is viscoelastic stress relaxation, elevated pore pressure and variation in rock frictional strength. We conducted multistage triaxial deformation tests with varying strain rates (5×10−7 to 10−5s−1) on shale sample originating from three lithological units of the Goldwyer shale formation, that is G-I, G-II and G-III in the Broome platform of onshore Canning basin. Additionally, pore pressure was estimated from wireline logs, and tectonic stress accumulation was modelled using time-dependent deformation (creep) data. The above analysis suggests that varying frictional strength alone could not explain the variation of the least principal stress; however, the inclusion of stress relaxation also contributes, whereas elevated pore pressure has no effect. Using this approach, we could also relate the changes in minimum principal stress (Shmin) from one lithofacies to the other and anticipate how this will impact the optimum design of landing zone during horizontal drilling and completion in unconventional field development.

Porosity and Water Saturation Estimation for Shale Reservoirs: An Example from Goldwyer Formation Shale, Canning Basin, Western Australia

Porosity and water saturation are the most critical and fundamental parameters for accurate estimation of gas content in the shale reservoirs. However, their determination is very challenging due to the direct influence of kerogen and clay content on the logging tools. The porosity and water saturation over or underestimate the reserves if the corrections for kerogen and clay content are not applied. Moreover, it is very difficult to determine the formation water resistivity (Rw) and Archie parameters for shale reservoirs. In this study, the current equations for porosity and water saturation are modified based on kerogen and clay content calibrations. The porosity in shale is composed of kerogen and matrix porosities. The kerogen response for the density porosity log is calibrated based on core-based derived kerogen volume. The kerogen porosity is computed by a mass-balance relation between the original total organic carbon (TOCo) and kerogen maturity derived by the percentage of convertible organic carbon (Cc) and the transformation ratio (TR). Whereas, the water saturation is determined by applying kerogen and shale volume corrections on the Rt. The modified Archie equation is derived to compute the water saturation of the shale reservoir. This equation is independent of Rw and Archie parameters. The introduced porosity and water saturation equations are successfully applied for the Ordovician Goldwyer formation shale from Canning Basin, Western Australia. The results indicate that based on the proposed equations, the total porosity ranges from 5% to 10% and the water saturation ranges from 35% to 80%. Whereas, the porosity and water saturation were overestimated by the conventional equations. The results were well-correlated with the core-based porosity and water saturation. Moreover, it is also revealed that the porosity and water saturation of Goldwyer Formation shale are subjected to the specific rock type with heterogeneity in total organic carbon total clay contents. The introduced porosity and water saturation can be helpful for accurate reserve estimations for shale reservoirs.

Kinetics of hydrocarbon generation from the marine Ordovician Goldwyer Formation, Canning Basin, Western Australia

Pyrolysis and bulk kinetic studies were used to investigate the hydrocarbon generation potential and source rock organofacies variability of marine organic-rich rocks from the Middle Ordovician (Darriwilian) Goldwyer Formation in the Canning Basin, Western Australia. Rock-Eval pyrolysis results for the analysed immature to mid-mature calcareous mudstones imply that the upper Goldwyer Sequence I contains oil-prone type I kerogen, while the lower Goldwyer Sequence III contains type II/III oil- and gas-prone kerogen. This is supported by pyrolysis gas chromatography (Py-GC) results that show the presence of homogenous organofacies in the Goldwyer Sequence I having aliphatic molecular signatures, possibly due to selective preservation of lipids derived from Gloeocapsomorpha prisca (G. prisca). The heterogeneous organofacies of the Goldwyer Sequence III contain aromatic moieties in similar abundance to the aliphatic compounds. The calcareous claystones of the Goldwyer Sequence I have the capacity to generate low wax paraffinic oil, whereas the Goldwyer Sequence III has potential for paraffinic-naphthenic-aromatic (P-N-A) low wax oils, gas, and condensate.The temperature for hydrocarbon generation for the type I kerogen, assuming a constant geological heating rate of 3 °C/my, is estimated to occur over a narrow interval between 145 °C and 170 °C for the Goldwyer Sequence I samples. Generation from the type II/III kerogen occurs from 100 °C to 160 °C in the Goldwyer Sequence III samples which are significantly less thermally stable than the Goldwyer Sequence I samples. The kinetic results for both sequences were used in standard thermal and burial history plots to evaluate their transformation ratio and hydrocarbon generative potential. This provided basin-specific kinetic inputs for burial history modelling and better constraint on kerogen transformation and hydrocarbon generation on the Broome Platform.

1D petrophysical characterization of reservoirs in the Canning Basin, Australia

La caracterización petrofísica de yacimientos desempeña un rol importante en la industria petrolera, siendo primordial en el gerenciamiento integral y la optimización de procesos de recuperación. El siguiente trabajo planteó el modelado petrofísico y de facies para las unidades formacionales del Grupo Grant y el yacimiento Anderson dentro del Bloque-Bunda-3D-2009 de la cuenca Canning en Australia. Esta propuesta fue dividida en dos etapas. La etapa conceptual se basó en el estudio de la migración y acumulación de hidrocarburos en el área, y la creación de un inventario desde la información registrada en el Sistema de Gestión de Información Geotérmica y de Petróleo de Australia Occidental (WAPIMS). La segunda etapa se desarrolló considerando que la cantidad y distribución de lutitas presentes en las areniscas, tienen un gran impacto en la productividad de los yacimientos de hidrocarburos. Así, el primer paso fue calcular el volumen de lutitas a través del índice lineal de rayos gamma. Posteriormente, se modelaron las facies mediante el uso de redes neuronales y los resultados fueron comparados con las descripciones litológicas reportadas de los núcleos de diámetro completo de perforación. La porosidad efectiva fue modelada mediante el registro de densidad volumétrica de la roca y el tipo de distribución de arcilla; la saturación de agua mediante la correlación de Poupon-Leveaux y el modelo de permeabilidad horizontal fue generado con los datos de análisis convencionales de núcleos de diámetro completo de perforación. Se resalta que la presencia de pirita afectó la respuesta de los registros de densidad volumétrica, porosidad neutrón y de resistividad para algunos pozos del área. Igualmente, el hidrodinamismo actuante y la presencia de agua meteórica en los acuíferos incidió en la respuesta del registro eléctrico resistivo, resultando complejo la identificación de contactos agua - hidrocarburo

The Late Devonian ammonoid subfamily Paratornoceratinae

Ammonoids of the subfamily Paratornoceratinae are characterised by disc-shaped adult conchs; furthermore they display a wide range of ontogenetic pathways leading to a similar adult conch morphology. The subfamily Paratornoceratinae occurs in the late early Famennian shelf sediments of various regions from the Anti-Atlas of Morocco to the Canning Basin of Western Australia; where endemic species of the genera Paratornoceras and Acrimeroceras appear in stratigraphic succession. We revise the species Paratornoceras lentiforme (Sandberger, 1857) and describe the new species Paratornoceras thuringense Korn, Bartzsch & Weyer n. sp., P. harounense Korn & Ebbighausen n. sp., P. ayense Korn & Buchwald n. sp., P. peterseni Korn & Buchwald n. sp., Acri meroceras hoppeckense Korn & Buchwald n. sp., A. ropicense Korn, Bartzsch & Weyer n. sp. and A. saalense Korn, Bartzsch & Weyer n. sp.

Interplay of eustatic, tectonic and autogenic controls on a Late Devonian carbonate platform, northern Canning Basin, Australia

AbstractFrasnian reef complexes along the northern margin of the Canning Basin in northwestern Australia evolved during rifting of the Fitzroy Trough. Geological investigations of the Frasnian Hull platform, which developed on an active tilted fault‐block, reveal significant lateral and vertical facies variations superimposed on prominent metre‐scale cyclicity. This study uses numerical analyses of facies and magnetic susceptibility data from three measured sections along the Hull platform to test whether a tectonic signal can be distinguished from eustatic and other signals.Geostatistical analysis of facies variations reveals an exponential distribution of thin (<3 m) facies, characteristic of stochastic depositional processes. Thick subtidal facies predominate in the Guppy Hills (GH) and southeastern Hull Range (SHR) sections near the hangingwall margin, and thick shallow‐subtidal to intertidal facies dominate the Horse Springs drillcore (HD 14) section near the footwall margin. Power and wavelet spectral analyses indicate a strong periodic component; Average Spectral Misfit and spectral optimisation methods confirm the presence of Milankovitch eccentricity signals and suggest the presence of obliquity and precession signals. However, the results also expose strong temporal and spatial variation providing evidence for tectonic control. Spectral analyses show strongest periodicity is recorded in short intervals that are not correlated across the platform and provide evidence of variations in sedimentation rate and hiatuses. Time series for the neighbouring GH and SHR sections show no overall statistical correlation, and Markov analysis indicates weakly ordered vertical facies transitions that do not correlate across the platform. Subtidal to intertidal facies data from HD 14 core suggest that at least 35% of the section is absent, almost obscuring the Milankovitch signal. The results indicate a complex set of controls on deposition on the Hull platform with local tectonic effects having produced spatio‐temporal moderation of the underlying eustatic signals and autogenic processes adding a localised stochastic response.

Ordovician conodont biostratigraphy of the Willara Formation in the Canning Basin, Western Australia

The conodont fauna from the Willara Formation, a carbonate-dominated stratigraphic unit widely distributed in the subsurface Canning Basin of Western Australia, is represented by 41 species, including a new species, Erraticodon neopatu Zhen n. sp. The Jumudontus gananda and Histiodella altifrons biozones are recognized in the lower and upper parts, respectively, of the Willara Formation. Deposited primarily in shallow nearshore settings, the Willara Formation is characterized by the occurrence of predominantly long-range coniform species of Triangulodus, Scalpellodus, Drepanoistodus, Drepanodus, and Kirkupodus. Several widely distributed age-diagnostic species, including Histiodella altifrons, Histiodella holodentata, Histiodella serrata, and Jumudontus gananda, serve as keys for biostratigraphic analysis and correlation. Our study also shows that the basal and top boundaries of the Willara Formation are diachronous across the basin, extending from the middle Floian (Oepikodus communis Biozone) to middle Darriwilian (Histiodella holodentata-Eoplacognathus pseudoplanus Biozone). This contribution provides crucial new biostratigraphic data for precise correlation of the Willara Formation with its time equivalents regionally and internationally.

Revision of the Darriwilian (Middle Ordovician) conodonts documented by Watson (1988) from subsurface Canning Basin, Western Australia

The conodonts documented by Watson form one of the best-known middle Darriwilian faunas from Australia. The present contribution is based on the re-examination of this material. Thirty-one conodont species from the subsurface Goldwyer and Nita formations of the Santalum 1 A drill core section of the Canning Basin, Western Australia are documented and described, including two new species, Belodina watsoni sp. nov. and Scalpellodus percivali sp. nov. The revised fauna is characterized by diagnostic species, namely Histiodella holodentata, Histiodella triangularis, and Eoplacognathus pseudoplanus. It provides compelling evidence to correlate this stratigraphic interval represented by the upper part of the Goldwyer and overlying Nita formations in the Santalum 1 A drill core section to the Histiodella holodentata or Eoplacognathus pseudoplanus biozones of middle Darriwilian age. However, in the Canning Basin, the faunal change signaled by the disappearance of H. holodentata and appearance of E. pseudoplanus reflects shifting of depositional settings from intermediate to outer shelf environments to shallower inner shelf conditions, coinciding with a regional regression event. New taxonomic data also enable more precise regional correlation of middle Darriwilian rocks across the Canning Basin and the Amadeus and Georgina basins in northern-central Australia.Y.Y. Zhen [yong-yi.zhen@planning.nsw.gov.au], Geological Survey of New South Wales, Division of Mining, Exploration and Geoscience, Department of Regional New South Wales, W.B. Clarke Geoscience Centre, 947–953 Londonderry Road, Londonderry NSW, 2753, Australia.

The Paleozoic prospectivity of the Browse Basin, Australia

Most of the discovered hydrocarbons in the Browse Basin occurred within the Mesozoic intervals, while deeper Paleozoic sequences have been seldom explored. Lack of Paleozoic exploration in the Browse Basin has been attributed to the lack of well penetrations, poor understanding of the petroleum systems and paucity of seismic data. The onshore Canning Basin with several commercial fields and discoveries is the most appropriate analogue for understanding the Paleozoic sequences in the region. With the integration of geophysical data (i.e. gravity, magnetic and seismic), well data and geology, the Paleozoic prospectivity of the Browse Basin can be further enlightened. Modern long offset (8 m) Vampire 2D seismic data were acquired by Searcher to address some of the complex challenges in the Browse Basin. Reservoir quality of the Brewster Formation, volcanic discrimination within the Plover Formation and identification of deeper Triassic and Paleozoic plays are some examples of these challenges in the Browse Basin. Recently Searcher reprocessed this regionally important Vampire 2D seismic dataset that ties to 60 wells. The broadband pre-stack depth migration reprocessed data were inverted to extract three petro-elastic properties of acoustic impedance, Vp/Vs and density by three-term amplitude versus offset inversion algorithm to improve imaging of deeper plays and delineate reservoir properties. This paper discusses how several potential Paleozoic reservoir-seal pairs can be identified in the Browse Basin by utilising the integration of Vampire 2D seismic data, quantitative interpretation products, regional geology and knowledge of the Canning Basin’s fields and discoveries. Previously there was little exploration of Paleozoic plays because they could not be imaged on seismic data. The potential Paleozoic reservoirs identified in this study include Permo-Carboniferous subcrop, Carboniferous-Devonian anticline and Carboniferous-Devonian rollover plays.

Carbonate reservoir development in the Canning Basin, Western Australia

We present a multidisciplinary study investigating depositional and diagenetic impacts on pore system variability in carbonate systems from the Canning Basin. With some of Australia’s only known co...

All that wobbles isn’t necessarily azimuthal anisotropy

SummaryOnshore 3D seismic data is often acquired with rich azimuth coverage by utilising orthogonal shooting (or cross-spread) layouts. This means that azimuthal anisotropy, if present, can be readily observed and its effects on the data can be quantified and accounted for as part of the processing and imaging flow.In this example from the Canning Basin, the data appeared initially to be exhibiting the effects of azimuthal anisotropy. However, with careful handling and honouring of the azimuths of the acquired data during the PreSDM velocity model building, it was possible to correct for most of the variation simply with a laterally variable velocity model, without the need to invoke the presence of azimuthal anisotropy.

New insights into the offshore Canning Basin using a seamless onshore/offshore stratigraphic model

The Canning Basin in Western Australia is classified as a frontier basin. Of the 345 wells drilled onshore, only eight have intercepted small commercial hydrocarbon deposits. The offshore Canning B...

Litho-structural controls on mineralisation at the Pillara carbonatehosted Zn-Pb Deposit, Lennard Shelf District, Western Australia

The Pillara Zn-Pb deposit is located on the northeast margin of the Canning Basin, Western Australia where it is hosted by a series north-northeast-trending, en echelon, conjugate normal faults tha...

Geochemical characteristics of early Carboniferous petroleum systems in Western Australia

Abstract A geochemical study was conducted to establish oil-oil correlations and evaluate potential source rocks within the latest Devonian–earliest Carboniferous succession of the onshore Canning Basin, Western Australia. Aromatic hydrocarbons, together with the routinely used saturated biomarker ratios and stable carbon isotopes, demonstrate that the recently discovered Ungani oilfield located on the southern margin of the Fitzroy Trough are similar, but not identical, to the early Carboniferous Larapintine 4 (L4) oil family present to the north of the Fitzroy Trough on the Lennard Shelf. The L4 oil family has been correlated to a lower Carboniferous (Tournaisian) source rock core sample from the Laurel Formation at Blackstone-1 although its bulk geochemical properties signify that it could generate substantially more gas than liquid hydrocarbons. The Ungani oils can be distinguished from the L4 oils by their higher concentrations of paleorenieratane and isorenieratane, coupled with more depleted δ13C values for n-alkanes, pristane and phytane compared with other components. Hopane isomerisation ratios show distinct grouping of the two oil families that reflect both source and maturity variations. The oil from Wattle-1 ST1 on the Lennard Shelf has an unusual composition, exhibiting some molecular and isotopic features similar to both the L4 and Ungani oils. Source rocks for the Ungani and Wattle-1 ST1 oils are unknown since their geochemical signature does not match that of the Tournaisian Laurel Formation or the Middle−Upper (Givetian–Frasnian) Devonian Gogo Formation which sourced the Devonian-reservoired Larapintine 3 oils at Blina and Janpam North-1. It is postulated that such potential oil-prone source rocks could occur within the Famennian–Tournaisian succession.