--> Timing of Diagenesis and Petroleum Entrapment in the Papuan Basin, Papua New Guinea, by J. P. Earnshaw, A. J. C. Hogg, N. H. Oxtoby, and S. J. Cawley; #90986 (1994).

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Abstract: Timing of Diagenesis and Petroleum Entrapment in the Papuan Basin, Papua New Guinea

J. P. Earnshaw, A. J. C. Hogg, N. H. Oxtoby, S. J. Cawley

A study of fluid inclusions and cementation history of the discoveries in the Papuan Fold Belt and Foreland of Papua New Guinea has been carried out. This study indicates that petroleum charging took place during the late Tertiary and Quaternary, synchronous with the thrusting that generated the traps. Fluid inclusions and diagenetic cements have been analyzed from the Toro Formation, Imburu Formation and Elevala sandstone in fourteen wells representing nine traps in the Papuan Fold Belt and Foreland.

Diagenesis is dominated by compaction and quartz cementation. Analysis of sandstone compactional porosities at the time of cementation and fluid-inclusion microthermometry suggests that quartz cementation occurred in all the traps studied at approximately maximum burial depths in the early Pliocene. Both aqueous and petroleum inclusions were observed. Primary fluid inclusions within quartz cements were exclusively aqueous, whereas petroleum inclusions were restricted to healed microfractures which cross-cut both detrital grains and diagenetic cements. The petrographic relationships indicate that petroleum emplacement occurred after quartz cementation, during the period of active thrusting in the late Pliocene to Recent.

The optical and spectral behavior of the petroleum inclusions indicates that the nine traps studied received both liquid and gaseous-phase charges and that the fold belt traps received a broader range of maturity products than the foreland traps. These results support a model where Cretaceous and Tertiary generated hydrocarbons have remigrated into the current traps as a result of Pliocene to recent thrusting.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994