A systematic approach to unconventional play analysis: the oil and gas potential of the Kockatea Shale and Carynginia Formation, North Perth Basin, Western Australia
Gareth Cooper A , Roger Xiang A , Nick Agnew A , Phil Ward A , Mark Fabian A and Neil Tupper AAWE Limited
The APPEA Journal 55(1) 193-214 https://doi.org/10.1071/AJ14015
Published: 2015
Abstract
Key formations throughout the North Perth Basin have been mapped from 3D and 2D seismic data to define depth grid inputs to a 3D basin model calibrated with temperature and maturity data from 45 wells, plus an additional 27 pseudo well models. The Permian Carynginia Formation and Early Triassic Hovea Member of the Kockatea Shale have been defined in this model as unconventional shale reservoir targets.
Basin-wide pyrolysis data have been used to construct kinetics curves for both the Carynginia Formation and Kockatea Shale, which define Type D/E and mixed B, and D/E kerogen types, respectively. When combined with thermal history inputs, these source rocks expel and retain significant volumes of hydrocarbons, of which the free hydrocarbons in the retained components reach 22 BCF/km2 for the Carynginia Formation gas and 8 MMBBLS/km2 and 21 BCF/km2 for the Hovea Member liquids and gas, respectively. The defined kinetics relationships allow the estimation of kerogen-specific oil and gas windows, which have been applied across the study area to map unconventional play fairways for both formations, and to calculate the initial total organic carbon (TOC) and hydrogen index (HI) for each unit prior to significant maturation. This study employs a mass balance approach through basin modelling as a means of estimating likely retained hydrocarbon volumes in key unconventional reservoirs in the basin.
Sonic and density data from 28 wells in the basin have been used to calculate theoretical porosity to determine likely areas of overpressure. When combined with observed connection gas peaks and modelled maturity, there is a reasonable correlation suggesting that the basin exhibits modest overpressure of 2–6 MPa associated with the main gas window at 1.2 Ro% and this observation is applied to the play fairway mapping process.
Play fairways are further constrained through geomechanical and stress considerations from mechanical earth models (MEMs) built from log and image data for wells in the basin. These data define an overall strike-slip stress regime with SHmax consistently oriented east to west with the exception of local perturbations. Dynamic rock strength calculated from the same MEM process shows target zones in the Kockatea Shale and Carynginia Formation ranging from ~60–130 MPa unconfined compressive strength (UCS), calibrated against available static data. The net thickness of rock with a UCS >75 MPa is mapped and overlain on retained in place hydrocarbon maps to restrict the area of likely economically extractable resource.
While unconventional play cut-offs in the Perth Basin are notably lower than those commonly used in shale gas plays in the US, successful stimulation of Perth Basin rocks has been demonstrated by substantial flows from wells such as Arrowsmith–2. This study outlines a new workflow for mapping unconventional resources and suggests that Australian rocks are unique in both depositional environment and mechanical properties such that unconventional assessment using US play cut-offs may be misleading.
Gareth Cooper is a structural geologist at AWE Limited, with a background in basin modelling, heat flow and organic petrology. He has worked as a geologist for Santos Ltd, New Guinea Energy Ltd and Hot Dry Rocks Pty Ltd. Gareth graduated with a BSc (Hons) from the University of Wollongong in 1990, and a PhD from Monash University in 1995. Gareth is an Associate Member of the International Committee for Coal and Organic Petrology (ICCP). Member: Petroleum Exploration Society of Australia (PESA) and The Society for Organic Petrology (TSOP). |
Roger Xiang graduated from the University of New South Wales with a BSc (Hons) degree in geology and a BA in international relations. He joined AWE’s Shale Resources Group in 2011 and is now working as a project geologist on AWE’s operated onshore Perth Basin projects. Member: PESA, the Society of Petroleum Engineers (SPE) and the Formation Evaluation Society of Australia (FESAus). |
Nick Agnew is a geologist with AWE. He graduated with a Master of Geoscience from Macquarie University in 2012, with commendation for academic excellence. He joined AWE in 2011 and has worked on various projects, including the Perth Basin, new ventures and regional unconventional assessments. He graduated from the University of Technology, Sydney with a Bachelor of Information Technology in 2003, and worked in computer programming and systems design roles prior to embarking on a geoscience career in oil and gas. Member: PESA and FESAus. |
Phil Ward is a geoscientist with AWE. He graduated with a Bachelor of Science from the University of Sydney in 2005, and a Master of Geoscience from Macquarie University in 2012. Member: PESA. |
Mark Fabian graduated from the University of Adelaide with a BEng (Hons) in 1982. He has worked in a variety of roles, initially as a petroleum reservoir engineer, and more recently in asset, engineering and subsurface management roles. During his career Mark has worked for Santos Ltd, Canadian Occidental Petroleum Ltd, Santos Europe Ltd, Mobil E&P Australia Ltd, Newfield Exploration Australia Ltd, and ARC Energy Ltd. Mark is presently Subsurface Manager – Onshore WA with AWE. |
Neil Tupper has more than 30 years of industry experience having worked in a variety of technical and managerial positions for AWE, Santos, Enterprise Oil, Sagasco Resources and BP. He has a BSc (Hons) in geology from Hull University and a MSc in sedimentology from the University of Reading, UK. Neil has worked primarily on the basins of Australia and Southeast Asia, and has specific expertise in strategic planning, portfolio analysis, prospect evaluation and reserves assessment. Member: PESA, the American Association of Petroleum Geologists (AAPG) and SPE. |
