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Abstract: Structural Geometry and Trapping Styles in a Back-Thrusted Detachment Fold, Moran Discovery, Papua New Guinea

KVETON, KEVIN J., Chevron Niugini Pty. Ltd.

Recent exploration in the Papuan fold-and-thrust belt resulted in an oil discovery with over 1200 m of vertical column in two fault compartments. Two wells with three side-tracks spanning over two km across the structure were drilled from a single surface location at the crest of a severely karsted anticlinal mountaintop. Without the aid of seismic data, these wells clearly define the fold geometry and related faults within the L. Jurassic to E. Cretaceous Toro and Digimu reservoir sands.

Folding dominates over thrust faulting in the surface anticlines of Miocene limestone in the Papuan belt and the dominance of folding at depth is evident from the well data. The first well and sidetrack revealed a tight to isoclinal detachment style fold.

These wellbores traversed the entire fold at the reservoir level, drilling from the upright back-limb, through the core of the fold and then back up-section across the inverted and dismembered forelimb. The down-dip sidetrack was drilled using geo-steering techniques and LWD to define the OWC within the Digimu sand discovery. Instead, a sealing back-thrust was encountered and a new oil discovery was made in the footwall of this back-thrust in both the Digimu sand and in the Toro sand, which was water-bearing in the hanging wall of the back-thrust. The second well deviated out one km from the surface location and encountered the water leg in both sands. The updip sidetrack of this well discovered oil in the Toro sand near the fold crest and also traversed into the inverted forelimb.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah