--> Using Pressure Data To Aid Exploration In The Dampier Sub-Basin, Australia

AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

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Using Pressure Data To Aid Exploration In The Dampier Sub-Basin, Australia

Abstract

The extensive pressure data for the mature Dampier Sub-Basin offshore northwestern Australia has been used as an additional exploration tool to: • Understand pressure baffling/ connection in the basin; • Identify areas of higher trapping confidence and potential larger hydrocarbon columns; • Identify faults and onlap surfaces that separate pressure cells and thereby provide increased potential for trapping hydrocarbons in 3-way closures. Hydrodynamic differential cannot be used to quantify trap potential or column heights because only baffling can be concluded, not sealing. Three main aquifers have been identified and their pressures mapped as hydraulic head to display pressure trends: • The sandy deep water Tithonian (J50) Angel Formation; • The sandy shallow marine Bathonian to Callovian (upper J20) Legendre Formation; • The interconnected TR27 sand (Norian) of the upper Mungaroo Formation; The northern part of the study area is sandier and has the three aquifers interacting at onlaps and fault juxtapositions, reflected in pressure equilibration on the structural highs which reduces potential for trap integrity. In spite of this, significant pressure differential and hydrocarbon trapping still occurs, especially where the muddy Early Jurassic (lower J20) aquitard is involved. The southern area exhibits a more restricted reservoir distribution which coincides with very large pressure differentials that suggest increasing potential trap integrity and confidence in intersecting larger column heights. This work provides an innovative approach to the evaluation of exploration prospectivity in a mature basin.