Goldwyer Formation Research Articles

High-resolution coupling of stratigraphic ‘sweet-spot’ lithofacies and petrophysical properties: A multiscale study of Ordovician Goldwyer Formation, Western Australia

The identification of stratigraphic ‘sweet-spot’ interval is significant in oil and gas formation evaluation. However, formation evaluation in macroscopic-scale merely provides low resolution and limited information, thus may lead to uncertainties in resource estimation. To accurately identify the ‘sweet-spot’ intervals amongst heterogeneous lithofacies, we conducted a very high-resolution and quantitative analysis from in-situ macroscopic scale to laboratory microscopic scale on the Goldwyer formation of Canning Basin, Western Australia. The comprehensive advanced well logging and slim-compact micro imager (SCMI) technologies were synthetically applied in couple with the laboratory nanoscaled experiments. The results unveiled an extraordinarily large lithofacies heterogeneity between different rock intervals, with distinguished features shown in Goldwyer I, II, and III members. The most favorable lithofacies is recognized as the laminated argillaceous thermally-matured organic matter (OM)-rich mudstone, which is widely developed in Goldwyer III as the major attributor to ‘sweet-spot’ intervals. Goldwyer III is exclusively characterized by thick mudstone intervals (94.4%), interbedded with thin calcareous mudstones (5.5%), corresponding to a depositional environment of low-energy distal section of the outer ramp settings. Microscopically, the most favorable lithofacies in ‘sweet-spot’ intervals develop numerous OM-/mineral nanopores for hydrocarbon storage. Illite-rich lithofacies develops abundant inter-particle pores from 2 to 17 nm that mainly contribute to pore volume for free gas storage capacity. OM-rich lithofacies with higher maturity have OM-pores with good connectivity, bearing large specific surface area that is beneficial for adsorbed gas capacity.

Integrated sedimentary and high-resolution mineralogical characterisation of Ordovician shale from Canning Basin, Western Australia: Implications for facies heterogeneity evaluation

An understanding of the nature of the facies heterogeneity is crucial for successful exploration and development of shale reservoirs. However, shale is a very fine-grained sedimentary rock and it is challenging to understand its heterogeneity through conventional techniques. This paper addresses this challenge for Ordovician Goldwyer Formation (Goldwyer-III shale) through a unique approach by integrating core data with high-resolution image logs (SCMI); petrographic information; Fourier transform infrared (FTIR); and hyperspectral drill core reflectance spectra acquired using a HyLogger3. The petrographic and FTIR data validates the usage of HyLogger3 as a tool to examine high-resolution vertical variations in the shale mineralogy. The results indicate that the Goldwyer-III shale is highly heterogeneous in terms of sedimentary features, organic richness and mineral composition. The studied shale is divided into four facies based on colour, sedimentary features, mineral composition and lithology. The facies include thinly laminated siliceous shale (TLSh), concretionary-banded calcareous shale (CSh), massive black shale (MBSh) and heterolithic shale (HSh). The total organic carbon varies from 0.35 to 4.5 wt% due to variation in facies as a result of fluctuation in oxic-anoxic conditions. The TLSh, MBSh and HSh facies have a higher TOC value (up to 4.5 wt %), T max (up to 450 °C), hydrogen index (up to 250 mgHC/g) and brittleness index (>0.4) comparatively. Whereas, the CSh facies has least TOC, Tmax, hydrogen index and brittleness index. Continuous high-resolution hyperspectral core log data, combined with petrography and conventional core logging, provides a much better understanding of heterogeneity in Goldwyer-III shale. This study offers a new workflow for rapid, continuous and accurate recognition of optimum facies for hydraulic fracturing. This approach can improve economic decisions when developing shale gas reservoirs. Based on TOC and mineralogical derived brittleness index cut-offs values, the high-quality brittle zones are recognised in TLSh and HSh facies deposited in medial (proximal to distal) depositional setting. • The marine shale is highly heterogeneous even at μm scale. • The integration of high resolution data provided a unique workflow for facies classification scheme in shale. • A continuous vertical facies heterogeneity is obtained. • HyLogger3 data with petrography and FTIR is validated for shale. • The influence of depositional setting on shale reservoir potential is discussed.

Specific surface area: A reliable predictor of creep and stress relaxation in gas shales

In recent years, short-term creep parameters determined in the laboratory from cylindrical gas shale samples subjected to triaxial (in-situ) stress conditions have been used successfully to infer long-term deformation and stress relaxation at the reservoir scale across geologic time scales. Due to the viscoelastic formalism, both the laboratory creep response and field-scale stress relaxation can be modeled with power law functions of time involving the elastic compliance of the shale B, the time-dependence exponent n, and the amount of total strain ∊. Gas shales often exhibit a high specific surface area associated with their high content in clay minerals and/or total organic carbon (TOC). The low-pressure nitrogen adsorption technique can be used advantageously to estimate specific surface area (SN2); i.e., it is a relatively fast and cost-effective measurement conducted on powdered samples of shale material. A robust global empirical correlation between gas shale creep parameters and SN2 emerges from the analysis of laboratory data collected from multiple gas shale formations in Australia (the prospective Goldwyer Formation) and the United States (Barnett, Haynesville, and Eagle Ford formations), and spanning a broad range of clay content, organic matter, maturity, and porosity values. This data set also shows that the summed fractions of clay minerals, TOC, and porosity, the so-called weak phase fraction, correlates nearly as well with primary creep parameters. The weak phase fraction can also be estimated from faster and more cost-effective measurements or from well logs. To evaluate its predictive capacity, the key correlation between SN2 and creep parameters is used in a case study to predict the magnitude of present-day least principal stress Shmin across six depth intervals/lithologic layers in a prolific unconventional shale formation in the northeastern United States. Several Shmin measurements are available for verification, and our approach successfully captures the observed layered variation of stress with depth.

Shale lithofacies controls on porosity and pore structure: An example from Ordovician Goldwyer Formation, Canning Basin, Western Australia

The hydrocarbon storage and transport capacity of shale reservoirs are dependent on its complex pore systems. This study focuses on Ordovician Goldwyer Formation (Goldwyer shale) from Canning Basin, Western Australia. Multi-scale qualitative (X-ray diffraction, field emission scanning electron microscope, TESCAN integrated mineral analyser (TIMA) and thin-section analysis) and quantitative (Rock-Eval® pyrolysis, helium porosity on crushed samples, low-pressure gas adsorptions (N2 and CO2) and mercury injection capillary pressure (MICP)) approaches were applied on shale samples. The results indicate that the Goldwyer shale comprises five main lithofacies (namely organic-rich shale, argillaceous shale, siliceous shale, calcareous shale, and mixed shale) based on mineral composition and total organic carbon (TOC) content. The organic-rich and siliceous shales have highest porosity (>10%) followed by mixed shale and other lithofacies. Three types of pores, namely organic pores, interparticle, and intraparticle pores, are identified in Goldwyer shale. Most of the pores are narrow slit-like or bottle-necked shaped pores. The micropore and mesopore volumes and specific surface area (SSA) of all lithofacies are positively related to TOC except for the argillaceous shale. Conversely, the micro and mesopore parameters (SSA and pore volumes) exhibited inverse relations with total clay content for all lithofacies except argillaceous shale. This indicates that the total clay and TOC content is the main controlling factors for pore structure of Goldwyer shale. The whole pore aperture exposed that mesopores are more abundant in Goldwyer shale; however, few micro and macropores are also found in different lithofacies. The organic-rich, siliceous and mixed shales could be deemed as the most essential lithofacies types for fluid flow via pore systems due to high porosity and feasible pore structures.

Implications of thin laminations on pore structure of marine shale reservoir: Goldwyer Formation case study from Western Australia

The pore structure of a shale reservoir is a major control on hydrocarbon potential, yet shale pore systems are complex and affected by various factors. This paper focuses on the differences in pore structure between thinly laminated and massive black shale (MBSh) beds in the Ordovician Goldwyer-III shale, Canning Basin, Western Australia. A multiscale approach included image logs, core descriptions, thin sections, scanning electron microscope and X-ray diffraction analysis with low-pressure nitrogen and carbon dioxide gas adsorption tests. The results indicate that the Goldwyer shale comprises laminated beds of quartz silt and shale with thin beds of organic-rich clay, plus minor interbedded carbonate bands or concretions. The pore types are subjected to rock type, and the thinly laminated shale (LSh) is enriched in intergranular and intragranular pores. In contrast, the MBSh mainly comprises organic matter pores. The LSh is slightly enriched in mesopores but has negligible micropores. The mesopores are wedge-shaped and associated with an inorganic matrix of clay and pyrite. In comparison, the MBSh contains both mesopores and micropores. These pores are slit-like and related to organic matter and clay. The clay content and total organic carbon fluctuations control the development of mesopores and micropores in both the laminated and MBSh beds in the Goldwyer-III shale. The MBSh layers are suggested as the most important rock types for fluid flow via pore systems due to higher total pore volume, specific surface area and gas adsorption capacity.

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.

Geomechanical appraisal and prospectivity analysis of the Goldwyer shale accounting for stress variation and formation anisotropy

Profitable exploitation of unconventional shale gas reservoirs relies on the success of hydraulic fracturing stimulation. This is more likely in brittle rock formations because natural and hydraulic fractures remain open after stimulation, allowing for more hydrocarbon production. Identification of the most favourable depth intervals relies on the robust analysis of available well-logs, and on laboratory-derived mechanical and elastic data obtained under controlled stresses replicating the actual conditions at depth. Beyond their use for predictive geomechanical modelling such laboratory data can act as calibration points for existing well-logs. Well-logs can also be used to guide the selection of the rock samples to be characterised and tested in the laboratory, ensuring that they are representative of the rock formation. Here we apply the above principles and demonstrate how this improves the geomechanical appraisal of the Goldwyer formation and assesses its prospectivity. This workflow integrates Rock-eval geochemical analyses, elastic properties, anisotropy, in-situ stress state and pore pressure, mechanical brittleness and fracturing indices derived from petrophysical and sonic logs in the Theia-1 and Pictor East-1 wells. We estimated an average total organic carbon of 2 w. t.% (maximum 5 w. t.%), a moderate to high dynamic Young's modulus (14–52 GPa), a low Poisson's ratio (0.24–0.27), and an average elasticity-based brittleness index B1 of 41% in the deeper G-III unit. This unit also exhibits a low differential horizontal stress ratio and a high fracture index. Such attributes suggest a good prospectivity of the G-III unit, not only in terms of potential resources but as importantly in terms of fracability.

Impact of the stress state and the natural network of fractures/faults on the efficiency of hydraulic fracturing operations in the Goldwyer Shale Formation

Cost-effective hydrocarbon production from low-permeability unconventional reservoirs requires multi-stage hydraulic fracturing (HF) operations. Each HF stage aims to generate the most spatially extended fracture network, giving access to the largest volume of reservoir possible (stimulated volume) and allowing hydrocarbons to flow towards the wellbore. The size of the stimulated volume, and therefore, the efficiency of any given HF stage, is governed by the rock’s deformational behaviour and presence of pre-existing natural fractures/faults. Naturally elevated pore pressures at depth not only help to reduce the injection energy required to generate hydraulic fractures but can also induce slip along pre-existing fractures/faults, and therefore, enhance production rates. Here we analyse borehole image, density, resistivity and sonic logs available from a vertical exploration well in the Goldwyer Shale Formation (Canning Basin) to (i) characterise the pre-existing network of natural fractures; and (ii) estimate the in-situ pore pressure and stress state at depth. The aim of such an analysis is to evaluate the possibility of fracture/fault reactivation (slip) during and following HF operations. Based on this analysis, we found that an increase in the formation's pore pressure by only a few MPa (typically ~5–10 MPa) could lead to slip along pre-existing fractures/faults, provided they are favourably oriented with respect to the prevalent stress field for future production. We also found that slip along the horizontal or sub-horizontal bedding of the Goldwyer Formation is unlikely in view of the prevalent strike-slip faulting regime, unless an extremely large overpressure exists within the reservoir.

Middle Ordovician (Darriwilian) conodonts from the Goldwyer Formation of the Canning Basin, Western Australia

Zhen, Y.Y., Normore, L.S., Dent, L.M. & Percival, I.G., 11 July 2019. Middle Ordovician (Darriwilian) conodonts from the Goldwyer Formation of the Canning Basin, Western Australia. Alcheringa 44, 25–55. ISSN 0311-5518Middle Ordovician conodonts attributed to 46 species were recovered from a stratigraphic interval spanning the Willara, Goldwyer and Nita formations in core sections from the Sally May-2 and Theia-1 petroleum exploration wells in the Canning Basin, Western Australia. The Histiodella serrata, Histiodella holodentata and Eoplacognathus pseudoplanus biozones are recognized in the lower and middle part of the Goldwyer Formation, indicative of an early–middle Darriwilian age. This revised conodont biostratigraphy enables more precise correlation with North America and North and South China. Several biogeographically distinctive conodont species, most likely of North Chinese origin, are recorded from the Goldwyer Formation. Their presence signals a strong palaeobiogeographic connection between the Sino-Korean Craton and the Canning Basin on the western margin of eastern Gondwana during the late Middle Ordovician.Y.Y. Zhen* [yong-yi.zhen@planning.nsw.gov.au], W.B. Clarke Geoscience Centre, Geological Survey of New South Wales, 947–953 Londonderry Road, Londonderry NSW 2753, Australia; L.S. Normore [leon.normore@dmirs.wa.gov.au]; L.M. Dent [louisa.dent@dmirs.wa.gov.au], Department of Mines, Industry Regulation and Safety, Mineral House, Geological Survey of Western Australia, 100 Plain Street, East Perth, WA 6004, Australia; I.G. Percival [ian.percival@planning.nsw.gov.au], W.B. Clarke Geoscience Centre, Geological Survey of New South Wales, 947–953 Londonderry Road, Londonderry NSW 2753, Australia;

Petroleum geochemistry, burial history and shale gas potential of the Goldwyer Formation - Canning Basin, Western Australia

Several organic-rich shale horizons in the Canning Basin, Western Australia, acted as source rocks for conventional oil and gas fields. The aim of this study is to investigate one of its units, the Goldwyer Formation (Ordovician in age, as the Utica Shale in USA) as a potential shale gas play. Geochemical analysis such as Rock-Eval pyrolysis and total organic carbon (TOC) estimation, as well as thermal and burial history modelling were used. The organic matter is mixed type II/III kerogen and the total organic carbon (TOC) values range between 0.16 and 4.8 wt%. Tmax values between 335°C and 471°C and vitrinite reflectance values between 0.71 and 1.3 Ro% point to the main oil to wet and dry thermogenic gas zones, with a trend of increasing maturity in the west-central part of the basin. The results of this study show that the Goldwyer shale may be considered as potential shale-gas play. [Received: September 3, 2016; Accepted: March 2, 2017]

Exploration of an unconventional petroleum resource through extensive core analysis and basin geology interpretation utilising play element methodology: the Lower Goldwyer Formation, onshore Canning Basin, Western Australia

Theia Energy Pty Ltd1 (Theia Energy) discovered a potential unconventional hydrocarbon resource in the Ordovician Lower Goldwyer (GIII) Formation shale located on the Broome Platform of the onshore Canning Basin. The collation, processing, analysis and interpretation of all available regional data culminated in a successful exploration well, Theia-1 (drilled in 2015), which, based upon petrophysical and core analyses, intersected a 70 m gross oil column at 1500–1570 m depth. Theia-1 recovered essential core and wireline log data required to analyse and assess the play elements and reservoir properties necessary for a viable shale oil and gas development. Utilisation of an ‘Unconventional Play Element’ methodology has proven the unconventional hydrocarbon potential of the GIII Formation, and preliminary modelling indicates that economic stimulated flow rates may be achieved. Further operations (a test well with multi-stage hydraulic fracture stimulation) are scheduled in the coming permit year to further quantify the presence of extractable organic matter in the GIII Formation, assess hydrocarbon flow rates, determine fluid composition and appraise commercial viability. This paper will discuss Theia Energy’s exploration campaign in the onshore Canning Basin starting with the regional evaluation, which encompassed all available geoscience data (offset wells, pre-existing seismic and potential analogue fields) and modern specialised shale analysis (sequence stratigraphy, paleogeography, geochemistry, unconventional petrophysics and petroleum systems modelling), to develop a robust regional geological model for the GIII Formation. Pre-drill analysis reduced exploration risk and successfully identified the key geological play elements essential for the successful Theia-1 exploration evaluation program.

Petroleum geochemistry, burial history and shale gas potential of the Goldwyer Formation - Canning Basin, Western Australia

Several organic-rich shale horizons in the Canning Basin, Western Australia, acted as source rocks for conventional oil and gas fields. The aim of this study is to investigate one of its units, the Goldwyer Formation (Ordovician in age, as the Utica Shale in USA) as a potential shale gas play. Geochemical analysis such as Rock-Eval pyrolysis and total organic carbon (TOC) estimation, as well as thermal and burial history modelling were used. The organic matter is mixed type II/III kerogen and the total organic carbon (TOC) values range between 0.16 and 4.8 wt%. Tmax values between 335°C and 471°C and vitrinite reflectance values between 0.71 and 1.3 Ro% point to the main oil to wet and dry thermogenic gas zones, with a trend of increasing maturity in the west-central part of the basin. The results of this study show that the Goldwyer shale may be considered as potential shale-gas play. [Received: September 3, 2016; Accepted: March 2, 2017]

Improved Imaging of the Subsurface Geology in the Mowla Terrace, Canning Basin using Gravity Gradiometry Data

A study was undertaken to test whether it is possible to map basement configuration and sedimentary horizons from the gravity gradiometry (AGG) data. This was within the EP431 Buru Energy permit on the Mowla Terrace in the onshore Canning Basin.By applying the Horizon Mapping method, using Energy Spectral Analysis Multi-Window-Test as described in the Methodology section (ESA-MWT), to AGG data, we conducted a test study on a narrow 8km long swath along 2D seismic traverse HCG-300, and at three wells: Pictor -1, Pictor-2 and Pictor East-1, with three additional wells located nearby.ESA-MWT was applied to gridded Bouguer and tensor gravity data. The ESA-MWT procedure was conducted at stations 1km apart. At each station, multiple spectra were computed over incrementally increasing windows. For each spectrum, the depth was interpreted and plotted versus window size, and from these graphs, multiple Depth-Plateaus were detected at each station. These Depth-Plateaus correspond to density contrasts within the sediments and the underlying basement. These were then laterally merged with those from adjacent stations to form density interfaces. The results were validated with seismic and the litho-stratigraphy from well data which showed a good correlation with the tops of several sedimentary formations and intra-formational lithological boundaries. Ten density interfaces were mapped: Top Precambrian Basement, Top Nambeet Formation, Intra-Willara Interface, Top Acacia Sandstone, Top Willara Formation, Intra-Goldwyer Interface, Top Goldwyer Formation, Top Nita Formation, Intra-Tandalgoo Group Interface and Intra-Tandalgoo Group Interface.The geological model built along the Test Profile from interpretation of the AGG data shows good correlation with the wells and seismic data.

Sweet-spot mapping through formation evaluation and property modelling using data from the Goldwyer Formation of the Barbwire Terrace, Canning Basin

Abstract The Goldwyer Formation of the Canning Basin has been regarded as a highly prospective shale play. This study assesses the potential prospectivity of this source rock as an unconventional hydrocarbon resource. Considering the sparsity of wells penetrating the Middle Ordovician Goldwyer across the vast under-explored area of the Canning Basin, a basin-wide study of the source rock is not warranted. Goldwyer assessment of the Barbwire Terrace, a subdivision of the Canning Basin, is carried out instead. This assessment includes the estimation of key shale play properties, such as, total organic carbon, total porosity, water saturation, and brittleness index. Each property was estimated from available well data by testing multiple estimation methods. TOC values were derived from multiple regressions of different well data. A simplified Archie's equation was used to estimate water saturation. Density porosity method was primarily used for total porosity estimations. Sonic data along with density were utilized to estimate brittleness index. Each property was then modelled across the Goldwyer Formation within the terrace. This provided geostatistical estimates on the propagation of such properties. In order to generate sweet spot maps for the Barbwire Terrace, averaged maps of different properties were combined in a weighted manner. This approach attempts to simplify the complexity of unconventional resource assessment, which therefore has provided a single product evaluating the prospectivity of the Goldwyer as a hydrocarbon resource. Results have shown that TOC and porosity are mostly the deciding factors for the prospectivity of this source rock, given that their values can be too small where the Goldwyer is deemed non-prospective. Nonetheless, sweet-spot maps show that most prospective zone is the Upper Goldwyer (Goldwyer I), followed by the upper parts of the Lower Goldwyer (Goldwyer III). More specifically, southern flanks of north-western and middle regions of the Barbwire Terrace tend to be more prospective. A stricter approach where cut-off values were applied for each property showed that sweet-spot maps are only prospective in the southern flanks of the middle Barbwire Terrace of Goldwyer I.

Environmental conditions and microbial community structure during the Great Ordovician Biodiversification Event; a multi-disciplinary study from the Canning Basin, Western Australia

The Great Ordovician Biodiversification Event (GOBE) is regarded as one of the most significant evolutionary events in the history of Phanerozoic life. The present study integrates palynological, petrographic, molecular and stable isotopic (δ13C of biomarkers) analyses of cores from four boreholes that intersected the Goldwyer Formation, Canning Basin, Western Australia, to determine depositional environments and microbial diversity within a Middle Ordovician epicontinental, tropical sea. Data from this study indicate lateral and temporal variations in lipid biomarker assemblages extracted from Goldwyer Formation rock samples. These variations likely reflect changing redox conditions between the upper (Unit 4) and lower (Units 1+2) Goldwyer, which is largely consistent with existing depositional models for the Goldwyer Formation. Cryptospores were identified in Unit 4 in the Theia-1 well and are most likely derived from bryophyte-like plants, making this is the oldest record of land plants in Australian Middle Ordovician strata. Biomarkers in several samples from Unit 4 that also support derivation from terrestrial organic matter include benzonaphthofurans and δ13C-depleted mid-chain n-alkanes. Typical Ordovician marine organisms including acritarchs, chitinozoans, conodonts and graptolites were present in the lower and upper Goldwyer Formation, whereas the enigmatic organism Gloeocapsomorpha prisca (G. prisca) was only detected in Unit 4. The correlation of a strong G. prisca biosignature with high 3-methylhopane indices and 13C depleted G. prisca–derived chemical fossils (biomarkers) is interpreted to suggest an ecological relationship between methanotrophs and G. prisca. This research contributes to a greater understanding of Ordovician marine environments from a molecular perspective since few biomarker studies have been undertaken on age-equivalent sections. Furthermore, the identification of the oldest cryptospores in Australia and their corresponding terrestrial biomarkers provides further insight into the geographical distribution and evolution of early land plants.

A New Method to Estimate Total Organic Carbon (TOC) Content, an Example from Goldwyer Shale Formation, the Canning Basin

Background:There is an increasing interest in the Goldwyer Formation of the Canning Basin as a potentially prospective shale play. This Ordovician shaly formation is one of the most prominent source rocks in the Canning Basin. One key property to evaluate the prospectivity of any shale oil or gas is its total organic carbon (TOC) richness.Objectives:This study investigates different TOC estimation techniques and validates the reliability of each, aiming to provide a best estimating approach for local and global applications.Method:The limited well distribution in the large area of the Canning Basin makes a basin-wide study not warranted at this stage. A focused look into the Barbwire Terrace was carried out instead. General TOC estimation methods, such as Schmoker and ∆logR were employed for TOC calculation. TOC relationships of single and multivariate regressions were also derived from wireline data and TOC rock sample measurements.Results:Both Schmoker and ∆logR methods tend to overestimate TOC when compared to the available Rock-Eval pyrolysis TOC measurements. The regression approach have shown to provide the best TOC estiamtes for wells in the Barbwire Terrace, where the best multiple regression approach for the terrace and global application was found to be the one derived from gamma-ray (GR), bulk density (RHOB), and sonic log transit time (DT).Conclusion:The generalized nature of the Schmoker method, as it provides a global relationship between density and TOC is probably the main reason why this approach does not provide a good fit in the case of the Goldwyer Formation. Furthermore, the uncertainty associated with the ∆logR method factors, such as the level of maturity (LOM), and resistivity and sonic baselines greatly influence the TOC estimation in this method, and hence, sometimes do not merit a reliable TOC estimation. The multiple regression approach have shown to be most accurate once lithology and compaction information (GR, RHOB, and DT) were incorporated in the regression process. TOC was reliably estimated for wells inside and outside the Barbwire Terrace, and also for wells of a global lacustrine shale. Such derivation have provided a more accurate technical assessment of the shale play and its prospectivity as a potential unconventional hydrocarbon resource.

Sweet-spot mapping of the Goldwyer Formation through formation evaluation and property modelling in the Canning Basin, Barbwire Terrace case study

The Goldwyer Formation of the Canning Basin has been regarded as a highly prospective shale petroleum play. This study assesses the potential prospectivity of this source rock as an unconventional hydrocarbon resource via property modelling. Considering the sparsity of wells penetrating the Middle Ordovician Goldwyer across the vast under-explored area of the Canning Basin, a basin-wide study of the source rock is not justified. Due to a higher well density, assessment of the Goldwyer Formation within the Barbwire Terrace, a sub-division of the Canning Basin, is carried out instead. This assessment includes the estimation of key shale play properties, such as, total organic carbon, total porosity, water saturation, and brittleness. Each property was estimated from available well wireline log data by testing multiple estimation methods. Total organic carbon values were derived from multiple regressions of different well data. A simplified Archie’s equation was used to estimate water saturation. Density porosity method was used for total porosity estimations. Sonic data along with density were utilised to estimate the brittleness index. Each property was then modelled across the Barbwire Terrace, which provided geostatistical estimates on the propagation of each parameter. In order to generate sweet spot maps, averaged maps of the properties were combined in a weighted manner. In the model, the Goldwyer Formation was divided into three layers based on dominant lithology. The uppermost shale dominated layer was predicted by the model to be the most prospective stratigraphic zone. The sweet spot maps highlight the southern flanks of the northern and western part of the Barbwire Terrace as the highest prospective geographic locations. This approach attempts to simplify the complexity of unconventional resource assessment, and has provided a single product evaluating the prospectivity of the Goldwyer as a hydrocarbon resource.

Texture and diagenesis of Ordovician shale from the Canning Basin, Western Australia: Implications for elastic anisotropy and geomechanical properties

Microstructural and textural measurements from two Ordovician shale units (Goldwyer and Bongabinni formations) within the Palaeozoic–Mesozoic Canning Basin indicate that the former unit was affected by mechanical compaction and clay mineral transformation whereas the latter preserves an early fabric due to syn-depositional precipitation of authigenic dolomite and anhydrite. Conventional petrographic analysis coupled with quantitative mineralogy, electron micro probe analyses, X-ray Texture goniometry (XTG) and cathodoluminescence spectroscopy of core samples were used to decipher the post-depositional evolution of marine and supratidal facies in the Goldwyer and Bongabinni formations, respectively. Differences in diagenesis are strongly reflected in the orientation of clay minerals as quantified by XTG: in both cases the c-axes of illite diffract strongest normal to the bedding plane but the measurements clearly illustrate that shale in the Goldwyer Formation has a stronger preferred orientation relative to the Bongabinni Formation, with multiple of random distributions (m.r.d.) values of 5.77 and 2.54, respectively.Laboratory measurements conducted at 10 MPa effective stress also indicate distinct rock physics signatures: the Bongabinni Formation shows very low anisotropy, whereas the Goldwyer Formation displays a higher degree of elastic anisotropy in terms of both P- and S- waves. The crystallographic preferred orientation of illite, highlighted by the XTG, is likely to contribute to the significant difference in elastic anisotropy observed in the two units. Therefore, the Bongabinni Formation is mechanically stronger and stiffer than the Goldwyer Formation, likely due to the early dolomite and anhydrite cementation of the former providing a rigid microstructure framework.

Emerging unconventional shale plays in Western Australia

Production of shale gas in the US has changed its position from a gas importer to a potential gas exporter. This has stimulated exploration for shale-gas resources in WA. The search started with Woodada Deep–1 (2010) and Arrowsmith–2 (2011) in the Perth Basin to evaluate the shale-gas potential of the Permian Carynginia Formation and the Triassic Kockatea Shale, and Nicolay–1 (2011) in the Canning Basin to evaluate the shale-gas potential of the Ordovician Goldwyer Formation. Estimated total shale-gas potential for these formations is about 288 trillion cubic feet (Tcf). Other petroleum source rocks include the Devonian Gogo and Lower Carboniferous Laurel formations of the Canning Basin, the Lower Permian Wooramel and Byro groups of the onshore Carnarvon Basin, and the Neoproterozoic shales of the Officer Basin. The Canning and Perth basins are producing petroleum, whereas the onshore Carnarvon and Officer basins are not producing, but they have indications for petroleum source rocks, generation, and migration from geochemistry data. Exploration is at a very early stage, and more work is needed to estimate the shale-gas potential of all source rocks and to verify estimated resources. Exploration for shale gas in WA will benefit from new drilling and production techniques and technologies developed during the past 15 years in the US, where more than 102,000 successful gas production wells have been drilled. WA shale-gas plays are stratigraphically and geochemically comparable to producing plays in the Upper Ordovician Utica Shale, Middle Devonian Marcellus Shale and Upper Devonian Bakken Formation, Upper Mississippian Barnett Shale, Upper Jurassic Haynesville-Bossier formations, and Upper Cretaceous Eagle Ford Shale of the US. WA is vastly under-explored and emerging self-sourcing shale plays have revived onshore exploration in the Canning, Carnarvon, and Perth basins.