Abstract: The rift basins of Thailand exhibit remarkable diversity of fault displacement patterns, fault length–displacement characteristics and mapped fault patterns during late rift, and post-rift, stages. These patterns reflect influences by: (1) zones of strength anisotropy in the pre-rift basement; (2) syn-rift fault patterns on post-rift faults; (3) spatial stress deflection, commonly related to irregularities in major fault profiles, and the basement–sediment interface; (4) temporal stress rotation, usually related to changes in the regional plate setting; and (5) varying strength properties (strain hardening or softening) of fault zones during their life. These influences created strongly segmented boundary faults, and long, low-displacement post-rift fault trends. The former are commonly strongly over-displaced, while the latter can be strongly under-displaced with respect to their length compared with typical length:displacement distributions. Seismic interpretation of multi-rift fault patterns requires 3D data to identify the complexities, otherwise the linkage pattern between deeper and shallower faults, and the changing fault strike-directions with depth, may be incorrectly mapped. Incorrect identification of fault patterns as breached relay structures may also arise. Oblique extension, the influence of pre-existing trends and stress rotation in multi-phase rifts provides a more comprehensive explanation for the observed features than the strike-slip interpretation of previous studies.

Abstract Many of the important Gulf of Thailand reservoirs are fluvial sandstones within the early to late Miocene. The fluvial sandstones vary considerably with respect to channel size, orientation, and sinuosity, making accurate reservoir characterization difficult as many of them are below seismic resolution. The stratigraphic architecture of the Miocene to Pleistocene succession in The Gulf of Thailand has been investigated by integrating seismic geomorphology, well logs, and biostratigraphic data. The Oligocene to early Miocene depocenter was controlled by synrift faulting and was adjacent to the large basin bounding faults. Oligocene lacustrine sediments are overlain by an early Miocene fluvial succession consisting of sinuous, broad (average width 2 km) northwest–southeast channel belts in the basin center. Channel belts became straighter and narrower (0.65 km) and change orientation to northeast–southwest in the middle Miocene when the main depocenter shifted eastward after the main phase of rifting ceased. Tidal creeks observed on seismic images supports biostratigraphic data that indicate a marine influence in the middle Miocene, the incursion coming from the northeast. Wide (1 km), northwest–southeast sinuous channels again dominate in the post-rift succession that comprises the top middle Miocene through Pleistocene. The general temporal variations indicate that tectonics was the main control on channel morphology until late early Miocene, whereas, in the middle Miocene short-lived marine incursions are present locally.

Abstract The intracratonic, supra-subduction zone setting of the Thailand rift basins caused the rifts to evolve in several ways differently from other intracratonic rifts. Key differences include: widespread occurrence of low-angle normal faults; basin inversion alternating with rifting; diachronous initiation and cessation of rifting; rapid post-rift subsidence; and extensive, low-displacement post-rift faults. These characteristics are related to hot, weak continental lithosphere, rapid evolution of the plate boundaries and stresses during the Cenozoic, and the history of subduction and accretion. Low-angle normal faults impacted the Sirikit Field by controlling the location of fluvio-deltaic reservoirs interfingering lacustrine shales (source and seal). Basin inversion alternating with syn-rift section is detrimental to prospectivity of the southern half of the Phitsanulok Basin by destroying syn-rift structure, and halting hydrocarbon maturation early in the basin history. The diachronous timing of basin development resulted in large, gas-dominated hydrocarbon accumulations in the eastern Gulf of Thailand basins, but was detrimental for younger basins that lack the post-rift section, and the greater variety of petroleum systems and traps that post-rift basins offer. The extensive low displacement–length ratio post-rift faults form significant hydrocarbon traps in the Pattani and North Malay basins. They represent a structural style not usually found in post-rift basins.