Pressure and Basin Modelling in Foothills: A Study of the Kutubu Area, Papua New Guinea Fold and Thrust Belt

Abstract

During the last decade, the Papua New Guinea fold and thrust belt has been the locus of renewed exploration. In that frame, a study of the PNG petroleum system has been undertaken along a 200km long transect in the frontal fold and thrust belt, based on a regional balanced cross section. The scenario integrates the Jurassic rifting and passive margin stage, the uplift related to Coral Sea rifting and the Plio-Pleistocene shortening, together with a moderate amount of erosion during the Upper Cretaceous (600 to 1300m), and an early growth of the Hedinia anticline. Calibration of the section boundary conditions and properties was done by comparison with data from 7 wells and field data. Apart from the high pressure trend in the Kutubu structures, all data are accounted for with a good to very good fit, and the modelled section appears quantitatively predictive. Water flow away from the topographic highs in the pervious Darai carbonates is decoupled from the underlying low velocity fluid in the Ieru Shale creating a delay in the pressure equilibrium between the deep escape of the fluids from the highs and the slow recharge from above. The are three major pathways for water: (1) topographically driven flow, from the onset of mountain building until present, (2) deep basinal flux, flowing along the flexed reservoirs at the onset of thrusting, and (3) across fault escape from connected reservoir bodies during late stage of basement fault inversion. The petroleum system evolution shows that the deep type III source rock explains the small extent of its maturation. Type II or mixed type II/III are used to model the Cretaceous source rock shales. Maturation starts in the mid Cretaceous, increases regularly during burial, with a strong increase during the late tectonic burial (50% increase during the last 7Ma). The saturation shows three main accumulations: (1) the deep part of the Mubi zone, with vertical migration along faults; (2) the Hedinia anticline charged during Orubadi deposition and the Kutubu anticline charged during Era deposition; and (3) less important, the Darai plateau, cutoff from lateral charge by the early growth of the Hedinia anticline.

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