ABSTRACT: Promotion of early quartz cementation due to brine flow: Impact on porosity-depth prediction

Brincat, Mark P.¹, Peter J. Eadington², and Dariusz Jablonski³
(1) CSIRO Petroleum, Bentley WA 6102, Australia
(2) CSIRO Petroleum Resources, Sydney, Australia 
(3) Woodside Energy Ltd, Perth, Australia

Accurate porosity depth prediction is a requirement for play concepts that target deeply buried reservoirs as well as the economic viability of hydrocarbon bearing structures with a known bulk volume at intermediate depths.

Historically, such predictions have been achieved by reference to measured or log derived porosity values or through the application of increasingly more sophisticated basin modeling packages.

In this study fluid inclusion salinity analysis completed on 10 wells from the Northern Carnarvon Basin, Australia, suggest that brine migration exerts a strong control on the initiation of quartz cementation in the Mesozoic Sandstones.

The data show a distinct trend of increasing salinity with shallower palaeo-depths at the onset of quartz overgrowth crystallisation compared with those having lower salinities.

Evidence of brine migration is more pronounced in wells along the deep seated Rankin Trend and cross-formational flow from the Palaeozoic evaporites is suggested as a possible source for these fluids.

The results of this study suggest structures along the Rankin Trend are more likely to suffer advanced silica diagenesis than structures with similar burial/depth histories on the Legendre and Madeleine trends. These findings suggest that conventional porosity modeling may need to consider the effects of hydrology changes on prognosed porosity models.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia