NEW TYPE OF RESERVOIR IN CRYSTALLINE BASEMENT ROCK

Abstract

The shelf deposits off South Vietnam are dominated by Oligocene-to-Miocene clayey carbonate sandstones and argillites, generally resting on a silicic crystalline basement. Penetration of the basement yielded oil flows from wells in quartz-kaolinite rocks that were initially interpreted as a granite weathered crust. But additional studies using the Superprobe-733 electron microprobe, a Link Systems energy dispersion analyzer and a JSM-50A scanning electron microscope suggested a new interpretation. To summarize, our detailed analysis of the alteration of crystalline basement rocks in the shelf zone off South Vietnam has identified a fundamentally new hydrothermal type of reservoir, which will probably be increasingly encountered as deep-sea drilling in this area is expanded.