Structural Characterization of the Phitsanulok Basin, Onshore Thailand, and Inverted Pull-Apart Basin Sandbox Analog Models

The Phitsanulok basin is the largest onshore rift basin in Thailand and has been a major hydrocarbon producer for over 30 years. Due to its proximity to the India-Asia collision, the Phitsanulok basin was subjected to transtensional rifting, transtensional to transpressional reactivation, post-rift thermal subsidence, and late inversion between the early Miocene to present. It is recognized that the northern Phitsanulok basin is predominantly extensional whereas the southern Phitsanulok basin has experienced inversion that has produced unconformities, folding, and reverse faults. However, the transition between these domains has not been well-quantified, nor are the possible hydrocarbon implications. This study had two aims: (1) structurally characterize the Phitsanulok basin from an extensive 2D and 3D seismic petroleum industry dataset and examine the basin structure within a regional tectonic context; and, (2) structural analysis of the complex, internal geometry of inverted pull-apart basin sandbox models through the development of a new 3D analog model reconstruction method using Petrel software. In Study 1, analysis of structural styles, time structure and isochron maps, fault patterns, fault dip angles, fault throws, and fault azimuths, newly define a Northern and Southern structural domain across 16°50’N latitudes. Our interpreted 16°50’N structural boundary occurs near the southern limit of major earthquakes, changes in regional fault trends, and a possible terrane boundary, which suggests the structural domains could be controlled by deep structures. We compare our structural domains to Phitsanulok Basin hydrocarbon data (i.e. hydrocarbons in place, production rates) and show the hydrocarbon implications. In Study 2, we found that inverted pull-apart basins formed rhomboidal basins that hosted complex border faults and a throughgoing cross-basin fault system. 3D analysis of the internal sandbox model geometries using our newly developed workflow revealed two distinct fault azimuth populations (0° - 5° and 35° - 40°) relative to the master strike-slip faults, changes in fault-dip angles, and increased inactive faults during pull-apart basin inversion.