Lateral Velocity Variations in the Darai Limestone, Papua New Guinea Foreland

Abstract

A combination of exploration and appraisal drilling results from wells on three adjacent discoveries in the Papuan Basin, western Papua New Guinea foreland, shows significant lateral velocity variation across the more than 1 km thick Darai Limestone. Investigation suggests that these are due to alteration, including dolomitisation, of the limestone. Most alteration appears associated with small scale faulting which is typically crestal. Seismic processing velocities are key to establishing the velocity profiles between wells required for depth conversion. Seismic forward modelling studies based on predicted high velocity bodies show processing velocities can develop an oscillatory behaviour in the vicinity of abrupt lateral velocity changes similar to those that may accompany dolomitisation. Similar results are observed on some of the field data.