PESA Journal No 28 P59-66

File Size15.8 MB
AuthorPeter van Ruth, Richard Hillis, Richard Swarbrick and Peter Tingate
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Article Title:

Mud weights, transient pressure tests, and the distribution of overpressure in the North West Shelf, Australia

PUBLICATION: PESA Journal No 28 P59-66

AUTHORS: Peter van Ruth, Richard Hillis, Richard Swarbrick and Peter Tingate

REFERENCE TYPE: Journal Article

DATE: December, | FILESIZE: 15.8 MB

Document Abstract:

Pore pressure data from drill-stem tests, wireline
formation 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.