© Commonwealth of Australia (Geoscience Australia) 2017. This material is released under the Creative Commons Attribution 4.0 International Licence. (http://creativecommons.org/licenses/by/4.0/legalcode)

Integrated petroleum systems analysis and

the source of fluids in the Browse Basin

For Further Information: Client Services

Email: clientservices@ga.gov.au

Ph: +61 2 6249 9111 Web: www.ga.gov.au

Browse Basin petroleum systems analysis The Browse Basin is a proven hydrocarbon province (Fig. 1a) hosting gas with

associated condensate and where oil reserves are typically small. This study

combines a pseudo-3D petroleum systems model with a review of source rock

characteristics to gain an understanding of source rock distribution, quality,

maturity and generation potential. Integration of this assessment with fluid

characteristics provides insight into the oil and gas prospectivity of the basin.

A regional 3D geological model of the Browse Basin was developed from new

seismic interpretation (Rollet et al., 2016; Fig. 1b and c) and forms the basis of a

pseudo-3D petroleum systems model. A total of 34 wells were modelled to

calibrate (Fig. 2) the 3D model to produce results displayed in Fig. 3.

T Palu, L Hall, E Grosjean, D Edwards, N Rollet, K Higgins, C Boreham, A Murray, D Nguyen, K Khider and T Buckler

GA PP-451 | eCat 104620

Fluid and phase behaviour Pressure-volume-temperature (PVT) data and fluid analyses in the Browse Basin

indicate that most fluids belong to dew-point petroleum systems (Fig. 4a), where

gas-liquid-ratios (GLR) are high (>10,000 scfs/bbl), consistent with sourcing from

gas-prone source rocks. This substantiates the lack of significant oil-prone facies in

the penetrated Jurassic and Cretaceous sections, as shown by the geochemistry

of source rocks and petroleum systems model. While the search for oil

traditionally relies on the presence of oil-prone source rocks, light oil can also

be found in basins where the primary hydrocarbon type is a gas-condensate

migrating into reservoirs at pressures below their dew point pressure. Most

reservoired fluids in the Browse Basin are liquid-undersaturated gas-condensates

(Fig. 4b). However, some accumulations are close to their saturation pressure in

the reservoir and slightly lower pressure would result in oil-rim formation.

Conclusions Petroleum systems analysis indicates that most hydrocarbon fluids found in the

Browse Basin are single-phase dew point fluids (gas-condensates). However,

these fluids are expected to drop out oil rims if they migrate into lower pressure

(shallower) traps and this may result in light oil spilling up-dip or being present as a

residual column after gas loss through leaking seals.

Key references Rollet, N., Abbott, S.T., Lech, M.E., Romeyn, R., Grosjean, E., Edwards, D.S., Totterdell, J.M., Nicholson, C.J., Khider, K., Nguyen, D.,

Bernardel, G., Tenthorey, E., Orlov, C. and Wang, L. 2016. A regional assessment of CO2 storage potential in the Browse Basin: Results of a

study undertaken as part of the National CO2 Infrastructure Plan. Record 2016/17. Geoscience Australia, Canberra.

http://dx.doi.org/10.11636/Record.2016.017

Acknowledgements Thanks to Andrew Murray (Murray Partners Ltd.) for help and advice on workflow development. Thank you to Irina Borissova for providing

internal review and to Theo Chiotis for his help with figure production. Petroleum systems modelling work was conducted using the Trinity-

Genesis-KinEx software suite (http://www.zetaware.com). The Jurassic and older seismic horizon interpretation has been provided by

Bradshaw Geoscience Consultants, the specific details of which can be found at http://www.cgss.com.au/products.html. This poster is

published with the permission of the CEO, Geoscience Australia.

Source Rock TOC (%) HI (mg HC/ g TOC)

Kerogen type Onset of initial expulsion P10 P50 P90 P10 P50 P90

K20-K30 Echuca Shoals Formation

1.1 1.6 2.4 63 139 246 D/E (with significant

marine influence) Caswell: middle Eocene

Barcoo: late Eocene

J30-K10 Vulcan Formation

1.1 1.4 2.3 58 168 304 D/E (with some

marine influence) Caswell: latest Cretaceous Barcoo: Early Cretaceous

J10-J20 Plover Formation

1.1 1.8 15.1 31 107 215 D/E (with some

marine influence) Caswell: Late Jurassic

Barcoo: Middle Jurassic

Table 1. Browse Basin petroleum systems analysis results showing source rock amount, quality, typical kerogen and

timing of initial expulsion. TOC and HI are quoted in 10, 50 and 90 percentiles. TOC less than 1% are not considered a

source rock and have been excluded from these analysis.

Figure 4 a) Gas-liquid-ratio (GLR) vs saturation pressure plot for available fluid data. Solid lines show global trends of dew

point and bubble point thresholds. b) Saturation pressure vs measured reservoir pressure for the same data.

Source rocks and charge history Bulk geochemical characteristics for the main source rocks in the basin are based

on an updated compilation of quality-controlled total organic carbon (TOC) and

Rock-Eval pyrolysis (Table 1). Jurassic and Cretaceous supersequences

predominantly comprise gas-prone kerogen and, where penetrated, the marine

shales within the J30–K10 and K20–K30 supersequences do not have sufficient

organic richness and quality to expel significant amounts of oil. All modelled

source rocks within the Caswell Sub-basin have reached sufficient maturities to

have transformed most of the kerogen into hydrocarbons, with the majority of

expulsion occurring from the Late Cretaceous until present. Within the Barcoo Sub-

basin, only the source rocks within the J10–J20 supersequences have reached

sufficient maturity for significant generation.

Figure 3 Browse Basin petroleum systems analysis results. Rows: 1) K20-K30 Echuca Shoals Fm, 2) J30-K10 Vulcan Fm,

and 3) J10-J20 Plover Fm. Columns: a) total sequence thickness, b) net source rock thickness, c) source rock

geochemical characteristics (Hydrogen Index - HI vs Tmax), d) transformation ratio, e) maturity, and f) total gas expelled.

Figure 2 Burial history at the Caswell 2 ST2 with associated calibration data (palaeo-temperature and bottom hole

temperature).

Figure 1 Browse Basin a) regional setting, b) supersequences and petroleum systems elements, and c) 3D perspective of

the basin model, showing the top J50 horizon, 2 cross sections and location of the modelled wells. Information on the

regional petroleum systems elements of the basin is limited below the Middle Triassic, hence source rocks are only

modelled down to the top Triassic (TR30). Top Permian (P50) is used as the lower thermal boundary for the model.