ABSTRACT: Exploration of the Frontal Trend of the Papuan Fold Belt, Papua New Guinea
HEBBERGER, JOHN J., JR., Chevron Overseas Petroleum Inc., San Ramon, CA
For over a decade Chevron/Gulf has been exploring a 350 km long portion of the Papuan Fold Belt, a mountainous, densely rainforested area with no infrastructure. Intense pinnacle karst precludes seismic acquisition over much of the area. Data include surface geological traverses and remote imagery, from which geologic maps, serial balanced cross sections, and objective horizon maps are constructed to define general fold belt structure and specific drillable prospects.
Chevron's exploration effort has been concentrated on the segment of the fold belt centered around the 200+ MMBO Iagifu-Hedinia discovery. The structures here are interpreted as generally parallel folds formed by flexural slip and simple shear. The sequence of deformation in "normal" from hinterland to foreland, although there is overlap between structural components. The 1300 m thick, massive Darai limestone (Miocene) acts as the dominant structural member of the sedimentary sequence, generally controlling the structural style of the rest of the sequence. Two significant levels of detachment have been recognized, one above and one below the lowermost Cretaceous Toro sandstone reservoir. First order structures are thrusts with strike lengths on the order of 100 km. Ramp anticlines and a single fault-propagation fold trend over 120 km long are associated with the thrusts.
All oil discoveries to date have been along the fault-propagation fold trend. The localization of discoveries may be due to greater exploration effort, greater trap integrity of four-way closures, the presence of a detachment above the Toro Reservoir along fault-bend fold trends, the timing of trap development relative to migration, hydrodynamics, or a combination of these factors.
AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)