PERSON, MARK¹, SHERLY FILBY¹, and PETER EADINGTON²

¹ University of Minnesota, Minneapolis, MN
² CSIRO, North Ryde, Australia

Abstract: Oil and Brine Migration within the Papuan Fold Belt

We have initiated a study to assess how saline ground water and petroleum have migrated in response to the structural evolution of the Papuan Fold Belt. Reconstruction of the subsurface "plumbing" of this compressional regime is complicated by the numerous thrust sheets and duplex structures which disect permeable strata. We use finite element models of basin-scale fluid flow, heat, oil, and solute transport to assess how groundwater flow affects the entrapment of oil, brine flushing, and sediment thermal history of this compressional terrain. A unique feature of our cross sectional models is that they honor the complex geology of the fold belt down to 13 km. Preliminary mathematical models have been constructed along a 120 km long, northeast-southwest trending transect extending from the topographic maximum of the fold belt through the Juha oil fields across the Fly platform towards the coastline.

Our results indicated that the configuration of fault severed aquifers and water table topography produce a surprisingly complex flow system with many reversals in groundwater flow direction at depth. Because few permeable units are laterally extensive, groundwater circulation has only reduced temperatures by 10-20°C below the fold belt. Groundwater hydrodynamics, on the other hand, have had a first order effect on the hydrodynamic entrapment of oil within Toro sandstone. Contour plots of petroleum potentials, which integrate both buoyant and hydrodynamic driving forces on oil, suggest that petroleum is being trapped in some places today by groundwater flow. Calculated travel times suggest that brine flushing within deep lying carrier beds occur on time scales of tens of thousands to millions of years.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas