INFILL SEISMIC IN THE SOUTHEAST JAVA FOREARC BASIN: IMPLICATIONS FORPETROLEUM PROSPECTIVITY

摘要

Reconnaissance long-offset 2D marine seismic reflection data, acquired in 2009 along the Java forearc, successfully imaged 3+ seconds two-way time (TWT) of unexpected block-faulted parallel-bedded sediments, with similarities in seismic character to Mesozoic sections from the Australian NW Shelf, buried under 2+ seconds TWT of mid-late Tertiary forearc fill.Subsequent infill surveys acquired in 2010, including gravity data, have provided a grid of about 20-25km spacing and defines the along-arc distribution of the probable Mesozoic section which seems to be restricted to the area between the deeper Southwest Java and Lombok Basins, both probably underlain by crust of ophiolitic and/or island arc affinity.Perpendicular to the forearc, the area south of East Java can now be morphologically and structurally divided into the following zones:1. Java Trench (JT): 6 to 9 seconds TWT water depth2. Accretionary Prism (AP): 1.5 to 3.5 seconds TWT water depth along the crest3. Outer Forearc Basin (OFB) with deep possible Mesozoic section: 3.5 to 4.5 sec TWT water depth with flat-lying and folded Late Tertiary sediments overlying possible Mesozoic sediments. Rotated Late Tertiary dip slopes show evidence of slumping with possible tsunamigenic implications.4. The OFB is separated from the IFB by a steep slope (Forearc Slope - FS) in 1.5 to 3.0 seconds TWT water depth, with a late Tertiary sediment package dominated by submarine canyon cut and fill, in places______________having well-defined up-dip extensions of the possible Mesozoic strata in the OFB zone. 5. Flatter lying Inner Forearc Basin (IFB): from 0.5 to 2.0 seconds TWT water depth; with variably thick, flatter lying Upper Tertiary sediments including pinnacle reefs overlying half graben of probable Paleogene age similar to those found further west by Shell in the 1970's.Within the Outer Forearc basin, temperatures should be high enough to expel hydrocarbons from possible Mesozoic source rocks, if present. While there are local structures within the OFB, strong updip migration may be expected into the IFB zone, where reefs and other structural traps are seen. Finally, the Paleogene half-graben in the IFB zone may be deeply enough buried to locally expel hydrocarbons from potential Ngimbang equivalent lacustrine source rocks.