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ABSTRACT: Characteristics and origins of 'graben shift' geometries, Funan Field, Pattani Basin, Thailand

A. Kornsawan and C. K. Morley
(1) Unocal Thailand, Ltd, Bangkok, Thailand, [email protected] 
(2) Department of Petroleum Geoscience, University of Brunei Darussalam, Jalan Tungku Link, Bandar Seri Begawan, BE 1410, Brunei

Hydrocarbon traps in the Pattani basin, Gulf of Thailand most commonly occur within conjugate sets of normal faults in the middle Miocene-Recent 'post-rift section'. The axes of isopach thicks associated with the conjugate faults undergo jumps along strike, informally known as graben shifts. These shifts are accompanied by reversal in dominant conjugate fault dip. 3D seismic reflection data around the Funan Field was used to investigate 1) how along-strike fault dip reversals were accommodated (i.e. interfingering, overlapping faults, or cross-faults) and 2) what factors influenced transfer zone location (e.g. active strike-slip faults, basement fabrics, random development). Fault displacement diagrams, structure and isopach maps show the main boundary fault and secondary faults in the lower syn-rift sequence (Oligo- Early Miocene) are influenced by the same trends that affect the post-rift conjugate faults. Fault patterns for the upper syn-rift package (Early Miocene) do not show the same influence. Some conjugate faults show multiple displacement maxima indicating linkage of several faults, including vertical linkage of higher displacement maxima in the post-rift section with lower displacement maxima in the syn-rift section. Adjacent faults of opposite dip in the transfer zone show laterally restricted, slightly overlapping geometries. Transfer zones in the conjugate faults appear to be affected by passive basement fabrics that also influenced the lower syn-rift faults. There is no indication that the conjugate fault geometries have been influenced by active strike-slip faulting.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia