f Impact of Regional Tectonics on Structure Development in Pm309, Eastern Malay Basin

Movement and collision of the Indian-Australian plate on the Eurasian plate has played a major role on the formation of the structural style seen in the Tertiary basins throughout Southeast Asia. The December 2004 earthquake, off northern Sumatra in the Indian Ocean confirmed the high mobility of the plates. The earthquake not only brought about the catastrophic tsunamis that devastated large area of South and Southeast Asia, but its geological effect has also been felt in the eastern Malay Basin in PM309. Geodetic measurement recorded in one of the platform reveals that there has been some lateral displacement. Although the displacement is small and does not impact the structural integrity of the facilities, over geological time, the collective displacements of the collisions has considerable imprint on the geological structures in the sedimentary basins of the area. Based on analogy to plasticene modeling work carried out by Tapponier et. al. (1982), indentation of the hard Indian sub-plate into the soft Eurasian plate, not only caused the deformation and uplift of the Himalaya Range, but also resulted in the extrusion of Indo-China sub-block between the Red River Fault and Three Pagodas Pass Fault. The southeast movement on the Indo-China sub-block in conjunction with the northward movement of the Indian-Australian plate to the west of Sumatra and in the Andaman Sea has caused the presence of a right lateral wrench couple in the region. From the experimental work of Harding (1974), a wrench couple would result in the formation of a set of stress fields that can be depicted on a strain ellipsoid inclined to its direction of wrenching. Compression or folding will be set up in the shorten axis while extension or normal faulting will occur in the lengthen axis of the strain ellipsoid. Further, there will be two sets of strike slip faults formed, a synthetic right lateral set at an oblique angle and its conjugate antithetic left lateral set at near-perpendicular to the wrench direction. Work carried out by PCSB has revealed the presence of a series of grabens and half grabens bounded by N-S striking faults in the Malay Basin. Block PM309 is located in the Eastern Graben of the Malay Basin (Suhaileen 2006, personal comm.). Recent 3D seismic surveys acquired in PM309 have better our understanding on the fault systems in PM309 and the eastern Malay Basin. Within Block PM309, interpretation of the seismic data not only confirms the presence of major compressional features running in the east west direction which form the traps of the many large oil and gas fields in the Malay Basin, it also shows the presence of a system of strike slip faults in the area set up as a result of the right lateral couple directed to the area. The right lateral synthetic strike slip faults predicted in the strain ellipsoid, is represented<br>by the NW-SE right strike slip faults present in the western part PM309. Its antithetic NE-SW left lateral strike slip faults is present in the eastern part of the block. A set of N-S faults is also prominent in the western part of the block, its origin probably extensional, as predicted in the strain ellipsoid, but over geological time, has seen reactivation and taking up some of the right lateral movement and imparting the NW-SE orientation of the Malay Basin.