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Fault Seal Potential Of The Sherbrook Group: Port Campbell Area, Otway Basin, Victoria.

Ryan, Lisa M.

Honours Degree, 1999

University of Adelaide

Abstract

Fault sealing is recognised as one of the key factors in trapping hydrocarbon accumulations. An understanding of fault seal relationships within the Port Campbell area is considered essential as entrapment of most hydrocarbon accumulations in the area rely either totally or partially on fault seal. Therefore, it has become necessary to evaluate fault seal processes in the Otway Basin in order to provide a greater understanding of prospects and reduce the exploration risk for the region.

The sealing mechanism of the North Paaratte Fault was investigated to evaluate the entrapment process of the North Paaratte accumulation. Fault seal analysis, using FAPS (Fault Analysis Projection System) software was conducted on the North Paaratte Fault and the Wild Dog Road Fault to determine their sealing potential.

The fault seal evaluation strategy involved determination of the juxtaposition relationships between the footwall and hangingwall of the North Paaratte and Wild Dog Road faults to determine what stratigraphic unit the reservoir has been offset against. Second-order fault seal analysis involved calculation of the clay smear along the fault gouge, by using both the Shale Smear Factor (SSF) and Shale Gouge Ratio (SGR) empirical algorithms.

It is concluded that reservoir - non-reservoir juxtaposition relationships on the North Paaratte Fault are the primary sealing mechanism for the North Paaratte accumulation. Results from the fault seal analysis indicate that fault seal is not attributed to clay smear processes. Therefore, using the North Paaratte Fault for calibration of empirical fault seal prediction algorithms was not possible. SGR fault seal analysis also reveals there is a potential for cross fault communication and hydrocarbon leakage through small ?windows? of lower SGR values. Regions of low SGR (<25%) values on the fault plane are interpreted to represent phyllosilicate framework fault rocks that will exhibit reduced seal capacity relative to clay-rich fault processes.

Juxtaposition relationships on the Wild Dog Road Fault indicate that there is little or no potential for cross fault communication. This is because SGR and SSF ratios calibrated with known sealing faults suggest that the fault plane will be dominated by clay smear processes which are likely to seal.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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