Fitzroy Trough Research Articles

A speculative ridge within the Kidson Sub-basin – integrated interpretation from geophysical data

This paper presents an analysis of the basement geometry and its implications on the Kidson Sub-basin in the southern Canning Basin. Integration of seismic data primarily near the rim of the sub-basin with airborne electromagnetic data across its central portion reveals an east-northeast oriented ridge at Permian level, suggesting a possible elevated structure in the Ordovician and basement. The proposed ridge effectively separates the Kidson Sub-basin into two distinct parts, providing an explanation for facies and thickness variations observed in the Nambeet and Goldwyer formations, as well as the absence of the Willara Formation in the southeastern portion of the sub-basin. The presence of shallowing trends observed in seismic profiles along the southern flank of the ridge suggests the proximity of the basement high. The ridge is speculative and requires further work to verify its existence, potentially including passive and reflection seismic surveys across the structure. If confirmed, it might be a significant feature with far-reaching implications for the prospectivity of resources in the Kidson Sub-basin. The hydrocarbon sourced from the Nambeet, Goldwyer and Bongabinni formations in the NNW depocentre may have migrated via the extension of the Parallel Range Fault and be trapped in the footwall block over the ridge. Compared to the structures in the Fitzroy Trough, the traps within the Kidson Sub-basin are expected to maintain reasonable integrity and have good potential for petroleum accumulation and carbon sequestration in the thick Paleozoic succession.

Age and origin of the West Kimberley lamproites, Western Australia

New high precision 40Ar/39Ar ages are presented which more tightly constrain the eruption ages of the West Kimberley lamproites of northwestern Western Australia. The data show a southward progression in ages of the lamproites over a distance of ∼135 km, from ∼22.5 Ma in the northernmost lamproites of the Ellendale Field to ∼19 Ma in the Noonkanbah Field in the south, excluding the Walgidee Hill lamproite. The large (∼490 ha) zoned Walgidee Hills lamproite at the northern edge of the Noonkanbah Field is the youngest of the West Kimberley lamproites and represents a later pulse of lamproite magmatism at 17.4 Ma, >1 Ma after the main lamproite magmatism.The southward progression of lamproite ages extends across a wide swath from the Proterozoic King Leopold Orogen at the southern margin of the Kimberley Craton to the Phanerozoic Fitzroy Trough in the Canning Basin. The magmatism does not appear to be the result of the migration of a mantle plume, but more likely reflects small degrees of partial melting of old, thick, metasomatised lithosphere extending from the craton margin beneath the basin, with melting triggered by regional uplift and/or small-scale mantle convection at the craton margin. Emplacement of the lamproites likely exploited ancient trans-lithospheric structures associated with the Proterozoic orogen at the craton margin and structures associated with the formation of the Canning Basin in the Phanerozoic.

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.

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.

Building a 3D Geomechanical Model for the Fitzroy Trough

Building a 3D Geomechanical Model for the Fitzroy Trough

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.

Three-dimensional interpretation of tectono-sedimentary evolution and hydrocarbon prospectivity by the integration of airborne gravity gradiometer, regional gravity, magnetic, and two-dimensional seismic data in the Canning Basin, Western Australia

The Canning Basin is a largely unexposed and underexplored frontier basin, formed mostly in the Paleozoic. Geological knowledge of this basin is based predominantly on sparse regional “vintage” two-dimensional seismic and small three-dimensional (3-D) seismic surveys and less than 230 exploration wells. Following seismic interpretation, an integrated interpretation was completed on airborne gravity gradiometer (AGG), magnetic, seismic, well, and complementary data along the southwestern margin of the Fitzroy trough and Gregory subbasin. Seismic data were reinterpreted using AGG data to produce a better constrained geological model. A basement structure map, two intrasedimentary structure maps, and a formation distribution map were produced. The interpretation of seismic profiles, validated through 2.5-dimensional gravity gradiometer modeling, is essential to this workflow. Repeatedly reactivated west–northwest and northwest structural trends, inherited from Proterozoic orogenies, respectively delineate the Fitzroy trough and the Gregory subbasin with its northwestern structural extension into the Fitzroy trough, the Gregory subbasin trend. Subsidence occurred during two periods of extension. An asymmetric extensional system of the Fitzroy trough controlled Ordovician–Silurian deposition of the Carribuddy Group. Devonian–Carboniferous subsidence defines the Gregory subbasin trend. This Pillara extension reactivated structures in the east of the Fitzroy trough. Simultaneous activity of both extensional fault systems and growth faulting controlled the facies and thickness distribution of carbonates and clastics of the early Carboniferous Fairfield Group. The Meda and Fitzroy transpressional phases inverted faults of the Gregory subbasin trend and Fitzroy trough, producing prospects by structural interference. The improved understanding of tectono-stratigraphic relationships, including the 3-D distribution of carbonate reservoirs, benefited the planning of seismic surveys, prospect evaluation, drilling, and acreage relinquishment.

Laurel Gas Play, Canning Basin - Recent Stratigraphic Learnings

Well, core and seismic data from the Lennard Shelf and Fitzroy Trough were integrated to produce a predictive sequence stratigraphic framework of the Laurel Formation consisting of Lower, Middle and Upper depositional sequences. Significant encouragement for potentially commercial flow rates was achieved by the hydraulic stimulation of the Middle Laurel in the Eastern Gas Province (Valhalla North 1 and Asgard 1 wells) in late 2015 and in the Western Gas Province (Yulleroo) in 2010. The Laurel tight gas play extends over a 20,000km2 area developed within a 2000m thick succession of marine clastics and carbonates. Condensate rich wet gas associated with overpressure is encountered regionally within low porosity and permeability sands at depths below 2000m. This was correlated across the basin from Yulleroo to the Meda Embayment and Northern Gas Province where a number of prospective plays were identified. Upper Laurel shallow marine sandstones commonly possess good oil and gas shows and have potential for tight gas where overpressured. A prominent Middle Laurel lowstand prograding shelf slope wedge supported by the presence of conglomerates in updip wells suggest better clastic sediment supply and the potential for the development of conventional lowstand topset sandstone reservoirs in the Northern Province. The Middle Laurel interval in the Northern Gas Province likely consists of a similar and potentially better tight gas reservoir than the interval stimulated in the Eastern Gas Province. Further drilling is required to confirm this and also to prove the viability of the tight gas play in the Northern Gas Province

New Insights into a major Early-Middle Triassic Rift Episode in the NW Shelf of Australia

The offshore Roebuck Basin is an amazingly complex and unexpected piece of North West Shelf geology. Large scale seismic geometries within the Triassic section is interpreted to define a complex of lava deltas associated within even a bigger scale rift complex. The location of the magmatic outpouring can be associated with a failed triple junction. Gravity and magnetic modelling supports this model and the apparent thickness of the volcanic complex is up to 10km.The impact of this rifting is felt regionally along the three arms of the proposed triple junction. The northern arm is easily identified and extends up to the proto-Barcoo and proto-Caswell sub-Basins. The eastern arm propagates with strike-slip motion through the Fitzroy Trough creating numerous transpressional and transextensional features in the Palaeozoic and Early Triassic stratigraphy -previously known as the Fitzroy Movement. The western arm is only recognised to the north of Wombat Plateau. In this area, the Early Triassic thins dramatically and sets up the uplifted outboard edge of a broad epicentre extending across the present-day Northern Carnarvon Basin. The sequences described above across all three arms are overlain by a major unconformity that is interpreted to be a product of these rifting/uplift events.This paper highlights that a regional approach, incorporating data from multiple sources, geographical areas and formations, assists with the broader understanding of tectonic history of the North West Shelf during the Early Triassic to Middle Triassic.

Sequence stratigraphy influenced by tectonics and implications for reservoir development, latest Devonian–Early Carboniferous ramp, Canning Basin, Australia

Abstract The interpretation of geologic observations utilizing sequence stratigraphic approach provides a better understanding of controlling mechanisms, i.e. tectonics, eustasy and sediment supply. However, assessing the role of each individual mechanism may be complicated because of the interplay between accommodation, influenced by tectonics and eustasy, and sediment supply. In this study, the sequence stratigraphic framework of the mixed carbonate–siliciclastic Fairfield Group was re-evaluated in association with the extensional tectonic activity to understand the effect of tectonics in controlling depositional facies and sequences. The main phase of extensional tectonic activity in the mid-Devonian led to normal faulting and fault block rotation and tilting, and created the Fitzroy Trough depocentre in the northern margin of the Canning Basin. During the Fairfield Group deposition in the latest Devonian–Early Carboniferous, the Fitzroy Trough underwent at least two pulses of extension. The subsurface data reveal that the extensional pulses resulted in the development of accommodation, suggested by the formation of depositional facies associations and systems tracts that are indicative of an increased accommodation and rapid sedimentation, i.e. transgressive systems tracts. The fault-related antecedent topography also exerted an important control on accommodation and led to an increased thickness of strata in the hanging wall of major normal faults in the Fitzroy Trough. The review of the distribution of known conventional and unconventional reservoirs in the Fairfield Group using the tectonically-influenced sequence stratigraphic framework shows that tectonic setting significantly controlled the distribution of the reservoirs. The conventional reservoirs developed in porous, permeable inner-ramp carbonates of the highstand systems tracts (HST). These are developed on shallow-water, platform tops that were formed on the tilted fault blocks in an extensional setting. The unconventional reservoir was encountered in tight (low porosity, low permeability) mid-outer ramp siliciclastic of transgressive (TST) and lowstand systems tracts (LST) of siliciclastic-dominated sequences that were deposited during extensional pulses in the basin.

Extent and persistence of photic zone euxinia in Middle–Late Devonian seas – Insights from the Canning Basin and implications for petroleum source rock formation

Abstract Late Devonian mass extinctions attributed to extensive anoxia and/or euxinia of the oceans are associated with widespread deposition of organic-rich shales. Also in the epeiric waters of the Canning Basin (Western Australia), photic zone euxinia (PZE) prevailed during the Givetian–Frasnian, with geochemical evidence for PZE on the northern (Lennard Shelf)–, and southern (Barbwire Terrace) margins of the Fitzroy Trough. On the Lennard Shelf, shales record episodic pulses of PZE associated with high algal activity due to enhanced nutrient supply, whereas a restricted marine setting on the Barbwire Terrace is thought to be the main driver for the development of persistent PZE and associated bacterial predominance. Structural evidence indicates that the Fitzroy Trough was a confined basin during the Late Devonian with the possibility of limited ocean circulation. Widespread PZE is expected to have developed in the poorly mixed water column, if the basin received sufficient nutrient supply for enhanced primary production. Notwithstanding the presence of anoxia during deposition of potential source rocks, only two small Devonian-sourced oil fields and numerous oil shows have been found in the Canning Basin. Biomarker assemblages show that the oils produced from the Lennard Shelf fields (i.e. Blina-1, Blina-4 and Janpam North-1) have substantially different molecular compositions to the minor oil recovered from Mirbelia-1 on the Barbwire Terrace. A correlation was established between the Lennard Shelf oils and rock extracts from the Gogo Formation at Blina-1 and McWhae Ridge-1 based on their hopane, sterane and carotenoids abundances. A definitive source correlation was not obtained for the Mirbelia-1 oil, but it did show some genetic affinity to the Givetian–Frasnian extracts from the Barbwire Terrace, suggesting that local source rocks are developed in the region.

The petroleum prospectivity of the Oobagooma Sub-basin and adjacent Leveque Platform, North West Shelf, Australia

The Oobagooma Sub-basin of the Roebuck Basin includes the offshore extension of the onshore Fitzroy Trough of the Canning Basin. Together with the Leveque Platform, it covers an area of approximately 50,000 km2, yet only 14 exploration wells have been drilled in the area to date, five of which were drilled in the past 30 years. The sub-basin contains sediments ranging in age from Ordovician to Recent. This study examines the petroleum prospectivity of a region that is one of the least explored on Australia’s North West Shelf. Recent exploration drilling has revived interest in the area, with the 2014 Phoenix South–1 oil discovery in the offshore Bedout Sub-basin and the 2015 Ungani Far West–1 oil discovery in the onshore Fitzroy Trough. The two most significant source rock sequences relevant to the Oobagooma Sub-basin are the Carboniferous Laurel Formation and the Jurassic section. The former interval is part of a proven petroleum system onshore and is the source of the gas discovered at Yulleroo and oil at Ungani and Ungani Far West. A thick Jurassic trough to the north of the Oobagooma Sub-basin is believed to be the source of the oil and gas in Arquebus–1A and gas in Psepotus–1. Hydrocarbon charge modelling indicates significant expulsion occurred during both the Cretaceous and Tertiary from both source intervals. Trap timing is generally favourable given that inversion structures formed in several episodes during the Late Jurassic to Late Tertiary. The Early Triassic, now proven to be oil prone in the Phoenix South area (Molyneux et al, 2015), provides an additional (albeit less likely) source for the Oobagooma Sub-basin. These rocks are thin to absent within the Oobagooma Sub-basin, so long-distance migration would be required from deep troughs to the west.

New Geological Insights from the Barbwire Terrace using Falcon5 Data, Canning Basin

The Barbwire Terrace in the Canning Basin has always presented explorers with an enigma. It has long held interest for hydrocarbon explorers and also mineral explorers looking for 'Mississippi Valley Type' sulphide mineralisation, being on the opposite side of the Fitzroy Trough to the Lennard Shelf (host to multiple oil fields and MVT's in the Cadjebut/Kapok area) (Copp, 2008). Seismic interpretation on the Barbwire Terrace has been difficult, not only due to the paucity of modern reflection seismic data, but also due to the difficulty in imaging through the carbonate/dolomites of the Pillara and Nullara sections. The Airborne Gravity Gradiometry (AGG) survey was designed to capture a large comprehensive grid of geophysical information about the southern margin of the Fitzroy Trough. The survey is instrumental in providing a greater understanding of an area of the Canning Basin that is poorly understood, yet has had many hydrocarbon shows and indications. While CGG undertook a more traditional workflow of interpreting the AGG, aeromagnetics and seismic data, a parallel approach, using Geoproxima processing technology (differential geometric analysis for digital data) provided additional insights on features and objects not readily recognisable using traditional colour bar stretches and sun illumination.

Tectonic and climatic controls on the deposition of the Permo-Carboniferous Grant Group and Reeves Formation in the Fitzroy Trough, Canning Basin, Western Australia

Interpretation of seismic and well data from the Fitzroy Trough, Barbwire Terrace and Lennard Shelf provides constraint for the tectonic and climatic control on the deposition and architecture of the Permo-Carboniferous Reeves Formation and Grant Group in the Fitzroy Trough.An angular unconformity is recognised at the base of the Reeves Formation, recording the middle Carboniferous Meda Transpressional Movement. This separates two major extensional phases that affected the basin: the Devonian–Early Carboniferous Pillara Extension and the Late Carboniferous Point Moody Extension. The Reeves Formation is interpreted to have been deposited during the Late Carboniferous Point Moody Extension phase, and as such is a syn-rift sequence. Its distribution is restricted to the Fitzroy Trough, with a thickness in-excess of 1875 m deposited in the half-graben, clearly observed to thicken toward the actively moving Fenton Fault. Compressional anticlines underlying the Reeves Formation, and located at left-lateral bends in the Fenton Fault, indicate associated dextral strike-slip movement.Extensional faulting ceased prior to deposition of the overlying Grant Group. Thickening of the Grant Group into the Fitzroy Trough is interpreted to be the result of thermal sag following the main extensional event, and associated compaction of the underlying thick syn-rift sequence and minor displacement along the Fenton Fault.The well-established subdivision of the Grant Group into the Betty, Winifred and Carolyn formations is interpreted to correlate directly with the subdivision of the group proposed by Redfern (1990) on the Barbwire Terrace into Hoya, Calytrix and Clianthus formations. Evidence for climatic control on the depositional style and architecture includes the prominent glacially eroded Base Grant Group unconformity and prominent erosional surfaces associated with facies (diamictites, varved mudrocks) that all suggest a glacial depositional environment. Deglaciation and relative rise in base level gave rise the mudstone dominated middle unit. The absence of glacial signature within the uppermost Clianthus Formation on the Barbwire Terrace (laterally equivalent to the Carolyn Formation on the Lennard Shelf) is attributed to restriction of the remnant ice sheet or glaciers to the margins of the basin, at the final stage of glaciation of the basin.

The late Carboniferous basal Grant Group unconformity, Canning Basin, Australia: a complex surface recording glacial tectonic and halotectonic processes

The angular unconformity at the base of the Grant Group forms a distinctive surface evident both at outcrop and in the subsurface on seismic and well logs. Detailed analysis of a 2D seismic dataset, integrated with available well data, suggests a complex suite of processes controlling the formation, deformation and resultant morphology of this surface. They can be subdivided into three categories depending on whether the mechanisms pre-dated, were coeval with, or post-dated deposition of the Grant Group. Pre-Grant faulting during the Devonian–Lower Carboniferous Pillara Extension resulted in development of significant paleotopography that influenced the morphology of the Base Grant Group unconformity. The pre-Grant interval contained thick salt, which was locally removed in the Silurian, with the development of isolated bodies of thickened Worral Formation. Later after deposition of the Grant group, the remainder of the Mallowa salt underwent dissolution/withdrawal, resulting in collapse of the flanks of earlier Worral pods of sediments, forming a ‘sombreros’ structure and folding the Base Grant Group unconformity. The main syn-Grant processes include regional glacial erosion, and extensive development of paleo-tunnel valleys that formed beneath and at the margin of the Permian–Carboniferous ice sheet as it advanced into the Fitzroy Trough. This created significant relief on the Base Grant Group unconformity, with tunnel valleys characterised by steep-sided, often U-shaped valleys up to 525 m deep and 12 km wide. Post Grant deposition, the unconformity surface was subsequently modified during the Triassic–Jurassic Fitzroy Movement, resulting in fault reactivation and development of a series of en-echelon anticlines associated with a regional wrench system.

Estimating the amount of uplift during Canning Basin tectonic events using well logs

SUMMARY The on-shore Canning Basin, located in northern Western Australia, has a long and complex depositional and tectonic history spanning almost the entire Phanerozoic. The succession includes several regional unconformities and estimating the amount of uplift with which they are associated can provide important constraints on the geohistory of the basin. Estimation of uplift based on analysis of sonic slownessand density-depth data is a well-established method but has mostly been applied to Mesozoic basins which have experienced relatively little deformation. Application of the method to the Canning Basin requires careful definition of the ‘reference curves’, with particular attention paid to the geological context of the reference well locations, and the use of a combination of density and slowness data. Initial results, from the Permian Noonkanbah Formation have produced results which are consistent with the known history of the Canning Basin. The map apparent uplift suggests only a few hundred meters of uplift has occurred and the dominant trend is parallel to the Fitzroy Trough, the main fault controlled depo-centre in the northeast of the basin.

Geological evolution of the Kimberley region of Western Australia

The history of the Kimberley region in the far north of Western Australia began in the Paleoproterozoic with rifting along the North Australian Craton margin at 1910-1880 Ma, followed by plate collision as part of a series of 1870-1790 Ma events that formed the Diamantina Craton within the supercontinent Nuna. Collision involved the accretion of an intra-oceanic arc to a continent that included the Kimberley Craton before final collision and suturing with the North Australian Craton. The c. 1835 Ma Speewah Basin formed as a retro-arc foreland basin to the W. The post-orogenic, c. 1800 Ma shallow-marine to fluvial Kimberley Basin and its equivalents had a provenance to the N and extended across both the Lamboo and Hooper provinces. Subsequent late Paleoproterozoic and Mesoproterozoic basins formed broadly similar depositional settings during break-up and reassembly into the supercontinent Rodinia. The intracratonic Yampi Orogeny generated large-scale folding and thrusting and sinistral strike-slip faulting between 1400-1000 Ma. The Neoproterozoic Centralian Superbasin formed as a broad intracratonic sag basin throughout central Australia between c. 830 Ma and the earliest Cambrian, including a series of basins across the Kimberley. Glacigene rocks are present with the most widespread being equivalent to the c. 610 Ma Elatina (Marinoan) glaciation. Folding, thrusting and strike-slip faulting during the c. 560 Ma King Leopold Orogeny caused a widespread unconformity at the base of the Ord and Bonaparte basins marked by the c. 508 Ma Kalkarindji Continental Flood Basalt Province. In the Early Ordovician, thermal subsidence initiated the Canning Basin. Paleozoic sedimentary rocks, including Devonian reef complexes, were deposited on the Lennard Shelf and in the Fitzroy Trough. In the Halls Creek Orogen, Devonian sedimentary rocks were deposited in subbasins of the Ord Basin during the c. 450-300 Ma Alice Springs Orogeny. A widespread glacigene succession followed in the Canning Basin, but by the early Triassic deposition was restricted and the remainder of the Mesozoic succession forms a veneer over much of the basin.

Fault-seal potential of the Palaeozoic in the northwest Canning Basin

As part of a Geological Survey of Western Australia organised review of the Canning Basin involving UWA and CSIRO, the fault-seal potential for the northwest Canning Basin has been analysed. This study has two foci: firstly identifying potential for fault-bound hydrocarbon reservoirs in the Early Permian (Poole Sandstone and Upper Grant Group). Secondly, James Price Point, 55 km north of Broome, is the chosen location for an LNG facility to service the northern North West Shelf gas fields. As such, the study aims to highlight potential CO2 sequestration reservoir sequences occurring inside 200 km of James Price Point, the economically feasible distance for CO2 delivery to an injection site. Historically, hydrocarbon exploration drilling in the Fitzroy Trough targeted anticlinal structures, which proved unsuccessful due to localised, but significant, erosion of the Permian sequence including the Noonkanbah Formation top-seal on anticlinal crests. Given there is potential for untested, fault-bound traps to exist, which might provide an alternative to the anticlinal traps, it will be useful to identify the distribution of shale-rich, top-seal and fault-seal prone sequences, and where these occur at suitable reservoir depths. The study shows the Early Permian sequences on the flanking terraces of the Fitzroy Trough commonly have suitable top-seal and fault-seal prone sediments. In wells analysed in the Fitzroy Trough itself, the Early Permian sequence is poorly represented, but Permo-Carboniferous sediments observed indicate some sealing potential might exist there. Moving south onto the Broome Platform and into the Wiluna Sub-basin, the Early Permian sequences still display some sealing potential, but Ordovician units might provide more suitable targets for sequestration in these areas.

New heat flow data aids exploration in the Canning Basin, Western Australia

The Geological Survey of Western Australia (GSWA) is providing new heat flow data and continuing studies in subsurface temperatures to understand the origin, migration and accumulation of geofluids in petroleum and geothermal systems of the Canning Basin. The study includes an investigation of subsurface temperatures from 274 wells, thermal conductivity measurement of 50 core samples from 22 wells, and single-dimensional (1D) heat-flow modelling of 101 wells. Thermal conductivity measurement of Canning Basin formations range from 1.06–5.83 W/mºC and modelled surface heat-flow ranges from 20–160 mW/m². The lowest measured thermal conductivity is in the Ordovician Goldwyer Formation at 1.06± 0.28 W/mºC, and the highest values are in the Upper Carboniferous Reeves Formation at 5.83 ± 0.22 W/mºC. Generally, estimated heat-flow values are lower where thick sedimentary deposits are present such as the Fitzroy Trough, Lennard Shelf, and Kidson Sub-basin, with values less than 65 mW/m². The heat flow values increase to over 80 mW/m² on the Broome Platform and Jurgurra, Mowla and Barbwire terraces. Lower heat-flow values have been modelled in West Blackstone–1 (47 mW/m²), Curringa–1 (52 mW/m²), Kennedia–1, Napier–2 and Pearl–1 (55–52 mW/m²). Higher heat-flow values have been modelled in Goodenia–1, Lovells Pocket–1, Kanak–1, Cudalgarra North–1, and Cudalgarra–1, where heat-flow values are over 100 mW/m². These new thermal conductivities, corrected temperatures, and heat-flow values support improved modelling of the Canning Basin petroleum and geothermal systems.

Constraints on the current rate of deformation and surface uplift of the Australian continent from a new seismic database and low-T thermochronological data

Estimates of the current rate of deformation and surface uplift for the Australian continent are derived by integration of a new seismic database and show that parts of the continent are currently experiencing deformation at a rate of 1– 5 × 10−16/s and uplifting at a rate of 10–50 m/Ma. In the east, these regions coincide with the regions of maximum topography, suggesting that, if this uplift rate is long-term, up to 50% of the present-day topographic relief in the southeastern Highlands and Flinders Ranges has formed in the last 10 Ma, i.e. the time we estimate for the onset of the present-day stress field experienced by the Indo-Australian Plate. These estimates are supported by fission-track data from the Snowy Mountains, which indicate that a non-negligible proportion of the present-day relief is the remnant of a much older topography formed during the various accretion or breakup events along the eastern margin of the continent in Late Paleozoic to Early Mesozoic time and that younger relief growth (i.e. younger than 100 Ma) must be limited to less than a kilometer in amplitude. By contrast, in the western part of the continent no such correlation exists between present-day topography and uplift predicted by integrating seismic strain rate over 10 Ma. This suggests that the apparently high level of seismic activity observed in the southwestern part of the Yilgarn Craton and along Proterozoic mobile belts, such as the Albany–Fraser Province of southeastern Western Australia and the Fitzroy Trough of northern Western Australia, is transient or that, contrary to what is happening in the east, erosional processes are able to remove surface relief created at the relatively slow rate of 10 m/Ma, potentially because there existed no finite amplitude topography prior to the onset of the present-day compressional stress field.