Publication Name: PESA Journal No. 28
Authors: Peter van Ruth, Richard Hillis, Richard Swarbrick and Peter Tingate
Publication Volume: 28
Date Published: December 2000
Number of Pages: 9
Reference Type: Journal Article
Abstract:
Pore pressure data from drill-stem tests, wirelineformation interval tests, kicks and mud weights show that
overpressure occurs in the Carnarvon and Bonaparte
Basins of the North West Shelf, Australia. The reliability of
mud weights as an indicator of overpressure was
determined by comparison with transient pressure tests
(dri ll-stem tests, and wireline formation interval tests). On
average mud pressure was 3.5 MPa (508 psi) greater than
the transient pressure tests. Mud pressure data were used
to interpret the rock as either overpressured or normally
pressured, and found to match 90 per cent of wireline
interval formation tests, and 81 per cent of dri ll-stem tests.
Hence mud weights are a reasonable indicator of
overpressure, in permeable formations where the transient
pressure tests were undertaken. In impermeable
formations transient pressure tests are unreliable if
avai lable, and mud weights may not be accurately
predicting pore pressure. In the Carnarvon Basin depth to
top overpressure varies from 2,350 m to 5,250 m. In the
Bonaparte Basin depth to top overpressure varies from
1,705 m to 4,349 m. Stratigraphic age of top overpressure
ranges from Tertiary to Permian in both Basins.