Application of chemostratigraphy to the Mungaroo Formation, the Gorgon field, offshore northwest Australia
Ken Ratcliffe A , Milly Wright A , Paul Montgomery B , Andy Palfrey C , Adam Vonk C , Jösta Vermeulen C and Michael Barrett CA Chemostrat Inc
B Chevron Energy Technology Company
C Chevron Australia Pty Ltd
The APPEA Journal 50(1) 371-388 https://doi.org/10.1071/AJ09022
Published: 2010
Abstract
The Mungaroo Formation in the Gorgon Field is a stratigraphically complex fluvial system of Triassic age. It is also a major hydrocarbon reservoir, therefore understanding its internal stratigraphic architecture is of paramount importance to exploitation of its reserves. Here, the technique of chemostratigraphy is used to construct a correlation framework for the Mungaroo Formation of the Gorgon Field.
Chemostratigraphy is a tool that employs variations in inorganic whole rock geochemistry to enable the characterisation and subsequent correlation of sediments. For this study, a total of 1,514 cuttings and core samples from eight wells in the Gorgon Field have been analysed. Using data derived from both claystone and sandstone lithologies, the Mungaroo Formation is divided into nine chemostratigraphic packages, 22 geochemical units and 19 sand units. Additionally, three surfaces identified as time lines (T1–T3) are geochemically defined.
Changes in values of Ga/Rb and Al2O3/(CaO+ MgO+K2O+Na2O) indicate that during deposition of the Mungaroo Formation, the paleoclimate became warmer and wetter, resulting in increasingly intense hydrolytic weathering. Steps in the values of these ratios allow three surfaces to be identified (T1–T3), at which there is a marked and sustained change in the paleoclimate. These three surfaces represent time lines that provide a quasi-chronostratigraphic framework for the formation. Values of Cr/Al2O3, Cr/Na2O and Nb/Al2O3 are related to changes in sediment provenance and indicate that during deposition of the Mungaroo Formation the provenance became more mafic and less intermediate. It is variations in paleoclimate and provenance modelled from the geochemical data that allows the packages, units and sand units to be characterised and correlated.
The chemostratigraphic correlation is more detailed than is available from other stratigraphic techniques. Although in most instances the lithostratigraphic correlation of sand units based on wireline log correlation matches the one defined using chemostratigraphy, there are some significant differences between the two that influence reservoir models and gas production.
Bruce James is a principal reservoir engineer at Woodside and has been there for four years. Before that he worked for Unocal and Shell. Bruce holds BASc and PhD degrees in geological engineering from the University of Waterloo and University of British Columbia, respectively and a MS in engineering economic systems and operations research from Stanford University. Member: SPE. kenratcliffe@chemostrat.co.uk |
Milly Wright graduated from the University of Leicester with an honors degree in geology in 2000. She is studying for a MS at University of Houston and is hoping to extend that research and gain a doctorate at the same university. Her research is on chemostratigraphic application to mud rocks of the Ferron Sandstone, Utah. Milly is also a director of Chemostrat International Ltd, in charge of US-based business development and proprietary project work. Member: AAPG, CSPG and SEPM. millywright@chemostrat.co.uk |
Paul Montgomery graduated from the University of Birmingham with an honours degree in geological science in 1987 and a masters degree in engineering geology from Durham University in 1988. He went on to gain his PhD on the magnetostratigraphy of cretaceous chalk of southern England from the University of Southampton in 1995. After conducting stratigraphic research at the University of East Anglia and the University of Kansas, Paul joined Chevron as stratigrapher in 2002 working in the USA, Australia and the UK. He is based in Aberdeen, working as a stratigrapher for the Chevron Energy Technology Company and is an adjunct research fellow in the Department of Geological Sciences and Geography, University of Western Australia. PMontgomery@chevron.com |
Andy Palfrey graduated from The University of Leeds with an honours degree in geological sciences in 1985 and The University of London with an MSc in stratigraphy in 1994. Andy joined Chevron UK in 1990 and worked principally in appraisal and asset development roles in the UK offshore sectors. He spent six years with Chevron in Houston where he was lead development geologist for several deepwater Angolan development projects. He is a senior development geologist with Chevron Australia, focussing on the characterisation and modelling of fluvial reservoirs of the Northern Carnarvon Basin. Member: AAPG, EAGE, PESGB and Geological Society of London. A.Palfrey@chevron.com |
Adam Vonk graduated from the University of Waikato, New Zealand, with a BSc degree in 1997 and an MSc (Tech) (Hons) degree in 1999 in earth sciences. Adam’s interests include stratigraphy, sedimentology, sequence stratigraphy, basin analysis and palaeogeographic reconstructions, having worked on Neogene strata in western North Island (New Zealand) sedimentary basins. Adam joined Chevron Australia in 2008 and is a geologist in the regional exploration team, working on fluvial reservoirs of the Northern Carnarvon Basin. Member: PESA and the Geological Society of New Zealand. Adam.Vonk@chevron.com |
Jösta Vermeulen graduated from University College Dublin, Ireland, with a BSc honours degree in geology in 1994 and a MSc in petroleum geology in 1995. Jösta joined Chevron UK in 1999 and worked in exploration and asset development roles in the U.K, Irish and Norwegian offshore sectors. He is a regional geologist with Chevron Australia, focussing on the fluvial reservoirs of the Northern Carnarvon Basin. Jösta is an honorary research fellow at the University of Western Australia. Member: PESA, PESGB and Geological Society of London. jvermeulen@chevron.com |
Michael Barrett graduated from Durham University in 1987 with an honours degree in geology and geophysics and gained his MSc from Imperial College RSM in 1990. Michael joined Chevron UK as a geophysicist in 1990 and worked in the UK until 1996 when he pursued an international career with Chevron Overseas Petroleum Inc. Michael has worked in the US, Angola, Norway and Australia for Chevron and is the regional project team leader for Chevron Australia. |
