A THIN SKINNED MODEL FOR THE PAPUAN THRUST BELT AND SOME IMPLICATIONS FOR HYDROCARBON EXPLORATION

Abstract

In the Papuan thrust belt the main risk in hydrocarbon exploration lies in identifying structural traps which are detached below the level of the primary reservoir. Because of the difficulty in obtaining usable seismic in the remote, inaccessible terrain, identification of prospects has been based on the interpretation of structural cross-sections drawn from geological maps. The structural models commonly used have been geometrically inadmissible, and as a result, some wells have penetrated thrusts at depth, before reaching the reservoir horizon.

More rigorously constrained regional cross sections through the thrust belt may be constructed using the principles of thin skinned tectonics. These may be used to identify structural provinces, characterised by different types of thrust pattern. In turn, the probability of reservoir involvement in a particular structure is directly related to its location in a particular province.

The cross-sections show that there has been as much as 100 km of shortening in the hinterland of the thrust belt. Restored versions of the cross sections may be used to reconstruct the shape of the basin and ideally to identify regions favourable for source and reservoir sediment distribution. In Papua New Guinea, palinspastic maps are currently feasible only for Miocene strata, but with the present level of exploration activity increased stratigraphic information should soon permit reconstructions for older formations.