Abstract: Basin Formation in the NIAS Area of the Sumatra Fore Arc, Western Indonesia
Although Sumatra includes the site of Indonesia's first oil field and continues to be one of the country's most important hydrocarbon producing regions, the fore-arc basin to the west remains a frontier exploration area. Gas has been found in a number of wells but commercial reserves have yet to be established. The possibility of their existence hinges on the presence of a complex of deep subbasins, but the development of these basins and their relationship to structures onshore Sumatra are still unclear. Although geological observations on the fore-arc islands are acquiring increasing importance with the recognition that the sediments exposed were deposited dominantly or entirely within the fore-arc basin, seismic reflection data remain the key to geological understanding. Reconnaiss nce surveys in the basin near Nias, the largest of the fore-arc islands, have defined two major depocenters, but interpretation has been hampered by poor data quality in some areas. Measurements of gravity field point to remarkable structural variations along the axis of the fore-arc basin and have been used to amplify and extend seismic interpretation. The combined analysis demonstrates that although some of the structural highs that straddle the fore-arc basin have been positive elements for considerable periods, at least one overlies a deep depression. The very poor quality of the seismic data in parts of this subbasin may be due to extensive shale diapirism, which must be recognized as a factor in future exploration.
AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994