Influence of faulting on reservoir overpressure distribution in the Northern Carnarvon Basin
Edward Hoskin A , Stephen O'Connor A , Stephen Robertson B , Jurgen Streit C , Chris Ward A , Jack Lee A and David Flett AA Ikon Science
B Santos Ltd
C Woodside
The APPEA Journal 55(1) 35-48 https://doi.org/10.1071/AJ14003
Published: 2015
Abstract
The Northern Carnarvon Basin has a complicated geological history, with numerous sub-basins containing varying formation thicknesses, lithology types, and structural histories. These settings make pre-drill pore pressure prediction problematic; the high number of kicks taken in wells shows this.
Kicks suggest unexpected pore pressure was encountered and mudweights used were below formation pressure. The horst block penetrated by the Parker–1 well is focused on in this peer-reviewed paper. This horst is one of many lying along Rankin Trend’s strike. In this well, kicks up to 17.2 ppg (pounds per gallon) were taken in the Mungaroo reservoir. The authors investigate whether the kicks represent shale pressure—or rather, represent pressure transferred into foot-wall sandstones—by using well data from Forrest 1/1A/1AST1 and Withnell–1, and wells located in the Dampier Sub-basin and the hanging-wall to the horst. This anomalous pressure could result from either cross-fault flow from juxtaposed overpressured Dingo Claystone or transfer up faults from a deeper source.
Using a well data derived Vp versus VES trend, the authors establish that the kicks taken in Parker–1 are more likely to result from pressure transfer using faults as conduits. These data lie off a loading trend and appear unloaded but likely represent elevated sand pressures and not in situ shale pressure. Pressure charging up faults in the Northern Carnarvon Basin has been recognised in Venture 1/1ST1, however, this paper presents a focused case study.
Pressure transfer is noted in other basins, notably Brunei. From unpublished data, the authors believe that buried horst blocks, up-fault charging and adjacent overpressured shale may explain high reservoir pressures in other basins, including Nam Con Son in Vietnam.
Ed Hoskin is a Team Leader and senior geologist at Ikon Geopressure, and has worked at the company since 2008. He previously held roles in other companies as a junior engineering geologist and as a support geoscientist. Ed graduated from the University of Southampton in 2003 with a MGeol (Master of Geology). Member: European Association of Geoscientists and Engineers (EAGE) and Petroleum Exploration Society of Great Britain (PESGB). |
Stephen O’Connor is responsible for all technical aspects of Ikon GeoPressure globally. He oversees the entire lifecycle of pressure prediction projects and regional pressure studies from concept to completion. Technically, he leads and mentors the GeoPressure team. Stephen has more than 20 years of experience, and his background as a petroleum geologist has lead him to work with many types of oilfield data, particularly in the areas of reservoir quality, structural geology—with particular reference to geomechanics—fault seal and pore pressure. After graduating from Leeds University with a BSc in geological sciences he started his career working on exploration assignments for Unocal and BP/Amoco before returning to university to undertake a MSc in sedimentology at Reading University. Following this Stephen worked for service companies on sedimentology/diagenesis in areas such as the United Kingdom Continental Shelf (UKCS) including the Atlantic Margin, and the Middle East before specialising in areas such as pore pressure and fault seal. |
Stephen Robertson graduated from the Queensland University of Technology (QUT) after completing a Bachelor of Applied Science (Geology) in 1996. The following year he completed a Bachelor of Applied Science (Honours) degree in Petroleum Geology and Geophysics at the National Centre for Petroleum Geology and Geophysics (NCPGG) through the University of Adelaide. Joining Santos in 1998 Stephen has since worked a number of basins both onshore and offshore Australia, and internationally, for the company in primarily exploration geologist roles. Stephen now works as a geologist in the Santos Geomechanics team after switching roles from Northern Carnarvon Basin exploration to subsurface services in early 2014. Member: Petroleum Exploration Society of Australia (PESA) and the American Association of Petroleum Geologists (AAPG). |
Jurgen Streit is a Geohazards Manger at Woodside Energy Ltd where he leads a team working on shallow hazards, pore pressure, borehole stability and reservoir geomechanics. He has previously held geomechanics positions with Geomechanics International (GMI; 2004–07) and the Australian CO2CRC (2000–04). During his academic career as a lecturer and researcher in geomechanics (1994–2004), Jurgen established a publication record on earthquake and fault mechanics, fluid-rock interaction and CO2 storage. Jurgen holds a PhD in Earth sciences (1994, Australian National University, Canberra). Member: American Geophysical Union (AGU) and the Society of Petroleum Engineers (SPE). |
Chris Ward is a graduate geologist who has been working for Ikon GeoPressure since 2012. He has worked on a variety of studies, from small scale to regional-scale Roknowledge studies (which are regional-scale pressure studies involving many hundreds of wells, of which the Australian North West Shelf Pressure Study: Carnarvon Basin is one). Chris graduated from the University of Durham with a BSc (Hons) in geology. This degree included specialisms in petroleum geosciences and structural geology, as well as large amounts of fieldwork and mapping across Europe. Chris is a Fellow of the Geological Society. Member: PESGB. |
Jack Lee is a graduate geologist who has been working for Ikon GeoPressure since 2012. He has worked on a variety of studies, from small scale to regional-scale Roknowledge studies. Jack studied at the University of Durham reading a BSc in geology. His dissertation involved the geological and structural mapping of the Lizard Peninsula, Cornwall; an area of highly variable polyphase deformation and serpentinisation of an ophiolitic sequence. |
David Flett commenced his geological career with honours at Leicester University and subsequently Sheffield University in the UK. He moved to the Far East in 1985 and became the regional Asia Pacific Managing Director of Roberston Research based in Jakarta, Indonesia, in 1988. In 1992, a move to Mincom—Australia’s largest software developer—saw David head-up the Petroleum Technology Division, initially in Asia and subsequently in the Europe, Africa and Middle East (EAME) region from 1992–99, developing a business around the company’s flagship petrophysical product, GEOLOG. Following the acquisition of GEOLOG by Paradigm, David became Regional Vice President of the Asia Pacific Region for Paradigm before moving into the muticlient seismic business as the global head of sales for Searcher Seismic in Perth in 2008. David joined Ikon in the Kuala Lumpur regional headquarters as Asia Pacific President in October 2011. |
