Construction of 2-D and 3-D Models of the Kutubu Oilfield, Papua New Guinea Fold Belt

Abstract

The Kutubu Field in the jungle-covered mountains of PNG, comprises the Hedinia Anticline containing mainly gas and the oil-bearing Iagifu Anticline. Together they hold reserves of >1 tcf gas and >350MMBL oil in a basal Cretaceous Toro Sandstone reservoir overlain by 1 km of Cretaceous shale and 1 km of karstic Miocene limestone. Over 70 wells and sidetracks have been drilled but there are only 7 2D seismic lines which are of poor quality. In 2D, sequential balanced cross-sections along seismic lines were constructed and revealed that the structure formed as a large detachment fold cored by the Jurassic syn-rift facies of a pre-existing half-graben. This was then cut by forethrusts and backthrusts making a pop-up structure with hydrocarbon reserves both in the gently folded hangingwall and the separate 1 km vertical forelimb. A 3D model was constructed of the hangingwall revealing the many small faults that compartmentalise the structure. The model relied on detailed correlation of all base Cretaceous and Upper Jurassic horizons, determination of their TSTs and rigorous analysis of the well dipmeter data tied to surface geological maps and dips. As most wells are highly deviated each stratigraphic horizon could be projected in 3D to make a construction panel at reservoir level, resulting in several hundred panels representing top Toro. The panels could be trimmed and joined where appropriate but also connected by faults as necessary. It is important to note that this was done directly in 3D without sections and that the 3D orientation of the faults was revealed by the panels, not by pre-conceived ideas. In areas away from dense well data, the model was infilled by projection along plunge tied to the seismic data and regional sections. The model revealed a transverse fault through a saddle in the centre of the structure that separated an area with gas on water to the west from gas on a 250m oil column on water to the east. Furthermore, the oil-filled syncline in the east is cut by several axial faults creating many compartments with different pressures and perched water. The model has allowed optimal depletion of the reservoir and together with detailed production simulation, has defined areas of untapped potential. It has also increased our understanding of the timing and nature of deformation in the Fold Belt of Papua New Guinea.

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