Mapping Sub-Surface Geology From Magnetic Data in the Hides Area, Western Papuan Fold Belt, Papua New Guinea

Abstract

Integration of seismic data with potential field data is valuable in the exploration for hydrocarbons in volcanic provinces, like the Papuan Fold Belt. Use of magnetic data in this area is challenging due the very rugged terrain, presence of thick volcanic cover, nearby volcanoes, weak magnetic susceptibility contrasts within the sedimentary layers and very complex thrust geology. By applying Energy Spectral Analysis (ESA) and Automatic Curve Matching (ACM) methods to high resolution aero-magnetic data, we test the possibility of mapping sedimentary horizons and faults in this region where there are no surface volcanics. An initial project area of 114km² in the vicinity of Hides, was chosen, as it was without volcanic cover and had a relatively simple anticline structure. The horizon mapping technique, developed from ESA, was used to detect magnetic susceptibility contrasts that were laterally merged to form magnetic interfaces corresponding to geological horizons derived from seismic and well data. The ACM technique was used to delineate structures such as major faults. The magnetic data was used to successfully detect and map generally shallow-dipping magnetic horizons in the Hides anticline structure and to define steep-dipping magnetic discontinuities in 3D interpreted as major faults, along with smaller associated structures. The combination of folded shallow horizons and steep faults was used to suggest an interpretation of the very complex overthrust structure, intersected at the Karius 1 well. The magnetic horizons could broadly be correlated to sedimentary interfaces, including magnetic markers (volcanic layers) within the weakly magnetic Darai Limestone. The base of the Darai Limestone/Top of the Ieru Formation correlated well with one magnetic horizon, the morphology of which was consistent with structures mapped from seismic and well data. Other horizons loosely correlated to the Top of Toro Formation, which contains magnetic sediments, and five deeper sedimentary interfaces within the Imburu formation or below. Using very limited geological information and constraints with magnetic data, we built a 3D structural model of the Hides anticline, that is overthrust to the southwest. This project has been a successful proof of concept and we propose, therefore that a similar approach may be applied with some confidence to more complex geology underlying thick volcanic cover, however, attenuating the influence of volcanics requires great care.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015