THE ROLE OF TECTONICS AND FAULTING IN BRINE FLUSHING WITHIN THE PAPUAN FOLD BELT

Comparison of paleo-pore fluids chemistry with present-day groundwater salinity within the Toro Sandstone, Papuan Fold Belt, Paupua New Guinea suggests that pore water salinity has changed substantially during the past 5 million years. Salinity of present-day groundwater within the Toro Sandstone underlying oil reservoirs ranges between 5000-15,000 mg/l. Paleo salinities estimated from Toro Sandstone aqueous fluid inclusions range between 2,000 to 277,000 mg/l. Inclusions with observable oil phase display less chemical variability (50,000 to 85,000 mg/l). These inclusions must have formed during reservoir charging. Higher salinity brines trapped in fluid inclusions probably formed early in the basins history during sedimentation, burial and diagenesis under marine conditions. Diagenetic reactions and dissolution of evaporite minerals could explain fluid inclusion salinities above 100,000 mg/l. The reduction of brine salinity since Pliocene time is probably due to the introduction of meteoric recharge during Pliocene tectonic uplift.

In this study, we have reconstructed the tectonic evolution of the Papuan Fold Belt using the structural restoration software package 2DMove at 1 million year increments along a northwest-southeast cross-sectional transect which cuts through the Muller anticline. Finite element representations of fluid flow, heat, and brine transport were then used to study the brine flushing history of the fold belt at 1 million year increments. The goal of these models is to assess the role of faults in brine flushing and determine how basin hydrodynamics has affected tilting of the oil/water contact during basin structuring.