Please use this identifier to cite or link to this item: https://hdl.handle.net/2440/110469
Type: Thesis
Title: In-situ stress and natural fracture networks in the Carnarvon Basin, North West Shelf, Australia
Author: Jepsom, G. M. M.
Issue Date: 2014
School/Discipline: School of Physical Sciences
Abstract: A total of 517 naturally occurring fractures are identified on 12 resistivity image logs in Carnarvon Basin on the North West Shelf of Australia. A range of fracture orientations were present. The fractures can be divided in to two sets using image logs. 1) Electrically resistive and conductive fractures orientated NE-SW, 2) electrically resistive and conductive fractures orientated E-W. There are 235 electrically resistive fractures that are considered to be cemented with electrically resistive cements. These electrically resistive fractures dominantly orientated NE-SW. There are 282 conductive fractures that are considered to be uncemented and filled with drilling mud. Thus, these fractures are considered to be open for fluid flow. The conductive fractures are dominantly orientated E-W. The in-situ stress field is a major control on the ability for fractures to transmit fluid. 123 drilling induced tensile fractures and 175 borehole breakouts present in 12 image logs, determined a mean maximum horizontal stress orientation of 110°. Leak-off tests and density logs were used to calculate the in-situ stress magnitudes with a vertical stress (𝑆𝑣) of 21.7 MPa/km, a minimum horizontal stress (𝑆ℎ𝑚𝑖𝑛) of 16.8 MPa/km and a maximum horizontal stress of 23.4 MPa/km (𝑆𝐻𝑚𝑎𝑥), this indicates a strike-slip faulting stress regime (𝑆𝐻𝑚𝑎𝑥 > 𝑆𝑣 > 𝑆ℎ𝑚𝑖𝑛) in the Carnarvon Basin. Using fracture susceptibility plots and Mohr circles constrained by the in-situ stress values, we show that the majority of E-W striking conductive fractures are optimally oriented within the in-situ stress field, demonstrating a high likelihood for fluid transmission. Additionally, several of these fractures demonstrate significant losses of drilling fluids at corresponding depths. It is likely that the identified conductive fractures are indeed open to fluid flow; demonstrating that these fracture networks provide secondary permeability the Carnarvon Basin subsurface.
Dissertation Note: Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2014
Where: Carnarvon Basin, North West Shelf, Australia
Keywords: Honours; Geology;in-situ stress; Carnarvon Basin; natural fractures; structural; geomechanics
Description: This item is only available electronically.
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the author of this thesis and do not wish it to be made publicly available, or you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals
Appears in Collections:School of Physical Sciences

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