THE EAST ARGUNI BLOCK: HYDROCARBON PROSPECTIVITY IN THE NORTHERN LENGGURU FOLDBELT, WEST PAPUA

摘要

The BP operated East Arguni Block in the West Papua Province is located adjacent to the giant Tangguh gas discovery. In the southeast of the block is the Late Miocene-Recent Lengguru Fold Belt (LFB), while to the northwest basement-involved anticlines in the eastern Bintuni Basin host large hydrocarbon reserves. The LFB is poorly explored with only two onshore wells along its 250km NNW trend. Modern seismic data is restricted to rivers along the frontal fold belt, while older data and a number of well penetrations exist in the molasse basin to the west. Based on previous drilling results, the area was thought to have experienced deep burial resulting in extensive reservoir degradation and diagenesis. The Suga-1 well (Trend, 1983) recovered sidewall cores of Late Cretaceous and Paleocene(?) sandstones recording porosities of 0 and 5%, respectively. The Kamakawala-1 well (Mobil, 1991), to the south, reached the Jurassic Woniwogi Fm sandstone target to find tight reservoir and evidence of extensive diagenesis. Apatite fission track studies estimated a peak maximum burial of 7km for the Jurassic section, but using a very low temperature gradient. A combined geologic and seismic data acquisition program was undertaken during 2002 in the East Arguni Block. This work aimed to: 1) target potential structures defined by gravity anomalies along the front of the range, and 2) conduct a regional structural and field study to better define the timing of trap development and burial history. Extensive outcrops of thick Late Cretaceous sandstone (～Ekmai Fm equivalent) with good porosity and permeability were discovered in previously unmapped structures. The good reservoir potential of these sandstones suggests that deep burial did not occur in the northern LFB. New structural and depositional models of the East Arguni Block reflect the decreased reservoir risk. Traps are well placed to receive charge from the mature Miocene oil-prone source rocks in the Bintuni Basin and/or Mesozoic source intervals within the fold belt.