ABSTRACT: Hydrodynamic Character of the Toro Sandstone, Iagifu-Hedinia Area, Southern Highlands, Papua New Guinea
EISENBERG, LEONARD I., Chevron Overseas Petroleum Inc., San Ramon, CA
Hydrocarbons in the Iagifu-Hedinia area are trapped in fault-propagation folds developed along the frontal portion of the Papuan fold and thrust belt. The Lower Cretaceous Toro (primary) and Upper Jurassic Digimu (secondary) reservoir sandstones are approximately 100 m and 25 m thick, respectively, and exhibit characteristics of shallow-marine barrier-bar deposition.
Drilling results and detailed pressure profiles through the reservoirs have shown that hydrodynamic flow in the Toro Sandstone has had a profound effect on oil distribution in the Iagifu-Hedinia anticline, having swept the northwest side free of moveable oil. In adjacent structures the Toro hydrodynamic effect is less pronounced; hydrocarbons are not shifted appreciably and fluid contact tilts are less than 0.5 degrees . In the Iagifu-Hedinia anticline, a structurally controlled
flow restriction causes a rapid drop in hydraulic potential, tilting local oil/water contacts up to 6 degrees . In the zone of restricted flow the three sandstone members of the Toro behave as separate reservoirs, each with its own hydrocarbon/water contact. The rapid loss of hydraulic potential, variously distributed through each sand member, results in a local differentiation of fluid contacts. Outside the restricted-flow zone the Toro members are near hydrostatic, whether saturated with water or hydrocarbon, and the low permeability sections which separate them, given sufficient time, allow fluid pressures to equilibrate between all three members.
On a regional scale, Toro waters appear to flow parallel to structural strike to a point 15 km southeast of Iagifu-Hedinia. There the flow exits to the lower hydraulic potential foreland structural province.
AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)