Steven Lingrey1, Dean Johnstone2
(1) ExxonMobil Upstream Research Company, Houston, TX
(2) Esso Australia Limited, Melbourne, Australia
ABSTRACT: Seismic Interpretation of Structural Traps in the Papuan Foldbelt, Papua New Guinea
The Papuan Foldbelt records late Cenozoic contraction associated with the collision between the Australian and Caroline plates. Current physiography outlines many broad, elongate ridges of high relief (>1000 m) whose profiles loosely mimic underlying fold shapes in the Miocene Darai Limestone. A Jura-Cretaceous shale dominant passive margin succession underlies the Darai. Within these sequences, the sandstone dominated Lower Cretaceous Toro Formation forms the main hydrocarbon reservoir. Interpretation of Toro structural patterns, however, is complicated by the local disharmony between the Darai expressed at the surface and the Toro concealed in the subsurface. Detachment faulting and variable amounts of tectonic thickening within the intervening Cretaceous Ieru Formation cannot be consistently predicted from surface geology. Unfortunately, seismic data show very poor signal to noise and are difficult to interpret. This is due to high relief and karst topography, crooked line paths, an irregularly developed low velocity zone in weathered, near-surface limestone, and a folded surface of velocity inversion where 5000 m/s Darai Formation overlies 3300 m/s Ieru Formation. Various processing approaches all yield noisy data containing weak, hard to recognize reflections. Migration of the stacked images is problematic; a variety of approaches have been tried, but none yield interpretable images. This paper describes an interpretation approach developed for the Paua-Moran area that uses forward and inverse raytrace modeling to correlate, depth convert, and properly position the stack section reflections. Using this procedure, it is possible to infer a likely subsurface structure map that is constrained by the combination of surface geology, well data, production data, and seismic reflection data.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado