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ABSTRACT: Seismic Stratigraphy Applications in the Pattani Basin, Gulf of Thailand

Lee Tung-Yi, Tang Chen-Hui

The Pattani trough in the Gulf of Thailand is a Tertiary extensional basin of Oligocene to Recent age. Five gas condensate fields are currently producing, and several more have been discovered. A large database of 450 wells and 55,000 line kilometers of 3-D seismic have been utilized for detailed seismic stratigraphic studies.

Five gross sequences are identifiable from both seismic data and well logs. The environments range from lacustrine through fluvial-deltaic to the current marine conditions. Only the fluvial and deltaic sequences produce significant quantities of hydrocarbons. The fluvial sequences are dominantly red beds comprising point bar sands and varicoloured red-brown shales. The deltaic sequence is gray colored with abundant coals and widespread low velocity, low resistivity shales. This sequence is usually overpressured.

Sands are low impedance relative to the shales and rarely exceed 70 ft in thickness. All sands fall in the seismic thin bed tuning range, but depending on data quality units as thin as 15 ft may be mapped. Although sands give discontinuous reflections when viewed on seismic lines they may be mapped for large distances across many fault blocks. The geometry of the mapped sands demonstrates that they are point bar acretions deposited in meanderbelts. Numerous examples demonstrate that depositional history can be deduced from seismic data in a nonmarine environment.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990