Tertiary tectonic evolution and related hydrocarbon potential in the Natuna area

Three major tectonic elements were present during early Oligocene time in the Natuna area—the West Natuna Basin, the East Natuna Basin, and the Natuna Arch. The arch is a N-S trending basement high that separates the two basins. Basin development in the West Natuna area began during early Oligocene time where rifting and pull-apart action produced predominantly SW-NE half-grabens filled with nonmarine sediments. These features probably formed due to the extrusion of the Malay Peninsula from Asia during the early stages of the India-Asia collision. The tensional forces in the West Natuna area, however, had little effect on the East Natuna Basin, where Oligocene sediments are uniform and only thicken regionally eastward toward the basin center. Compressive forces began to dominate in the West Natuna Basin during early Miocene time, resulting in reverse movement of once normal faults and corresponding uplift of areas that previously were half grabens. Simultaneously, the East Natuna Basin was influenced by predominantly tensional forces that produced NW-SE right lateral movements coupled with SW-NE-trending normal faulting. The differences in tectonic regimes between the West and East Natuna Basins during early Miocene time can again be explained by the extrusion of Indochina from Asia during later stages of India's collision with Asia. The hydrocarbon potential of the West Natuna Basin is enhanced by the presence of locally thick sequences of both Oligocene and Miocene sediments that were tectonically controlled. Both sections offer good potential for source and reservoir rocks. In the western part of the East Natuna Basin the presence of thick, mature sediments is limited to early Miocene grabens.