Seismic delineation of near-field exploration opportunities in the Papuan thrust belt: examples from the SE Gobe Area

Abstract

Hydrocarbon exploration within the Papuan thrust belt has traditionally relied on non-seismic techniques to resolve the complex subsurface structure. Subsequent appraisal drilling for most PNG discoveries has defined a complex pattern of fault-bounded compartments which show differing fluid contacts and pressure isolation. The Gobe Anticline forms a frontal hangingwall fold at the leading edge of the Papuan thrust belt, with the SE Gobe field forming the easternmost compartment. Experimental seismic data were first acquired over the Gobe area in 1996 with the recording of dip line PN96-204 and in 1998 by acquisition of the SE Gobe experimental dip line PN98- 206. This resulted in the successful appraisal of the SE Gobe 7 well, which targeted the southern extent and cutoff of the Iagifu reservoir at depth. Following this success, further seismic acquisition and reprocessing were undertaken during 1999 and 2001 over selected areas of the Papuan thrust belt resulting in over 130 km of 2D seismic data along strike of the SE Gobe trend to define near- field exploration opportunities. This high-quality seismic dataset significantly enhanced the ability to accurately determine the subsurface structure and identified additional low-risk hangingwall plays at Saunders and Bilip and defined an additional high-risk sub-thrust structure within a footwall play underlying Bilip. These prospects were drilled in 2001 by Chevron (operator for PDL4) and Santos (operator for PPL190) in 2002. Both hangingwall targets proved successful in encountering hydrocarbons. Saunders-1 resulted in a discovery sharing a common OWC at 1260 mss with SE Gobe and extended the known southeast limit of the field. Bilip-1 encountered a deeper down-plunge structural compartment with a GOC established at 1722 mss and an OWC at 1735 mss. The footwall Iagifu sub-thrust target at Bilip was encountered at 2527 mss and was water wet. Geophysical modeling indicates remaining updip attic potential. These results highlight the increasing value of seismic definition in accurately imaging the subsurface and defining additional exploration opportunities within the Papuan thrust belt.