Factors Controlling Sedimentary and Petroleum System of Early Syn-Rift Plays in Faulted Margin of Continental Rift Basin: An Example in the Eastern Edge of Cuu Long Basin, Offshore Vietnam

Abstract

Abstract

Structural syn-rift reservoirs in faulted margins of continental rift basins are usually disregarded in exploration consideration due to concerns of absence of reliable top seal and diagenetic alterations that significantly reduce reservoir poro-permeable. Not an exception to this trend, Early Oligocene reservoirs in the eastern margin of Cuu Long Basin (CLB), offshore Vietnam were overlooked in the past since they were interpreted as small and scattered structures without top seals. Recent exploration results in the eastern edge of CBL differ from past assessment regarding early syn-rift reservoirs of the area. The new seismic and exploration wells data confirm existent of the thick black lacustrine shale layers distribute widely across the area, which are acting as source rocks as well as top seals for potential prospects in the CLB Eastern margin. The new data interpretation also put top of granitic basement at a deeper depth than previously interpreted. As a result, syn-rift reservoirs which were small and insignificant have become large scale and two- or three-way faulted structures. Key reservoirs discovered is the basal sandstones which deposited right on top and shared a similar topography with the underlying Pre-Cenozoic granitic basement, mainly composed of near source sediment, mostly granitic fragments. These basal sandstones' porosity and permeability have been preserved better than shallower reservoirs. This paper discusses on the major factors impact to the completeness of the petroleum system of the early syn-rift plays in the flank of continental rift basins based on an example of the eastern edge of CLB. The study results indicate the factors control the sedimentary and petroleum system of the faulted margin include: tectonic, paleo-climate, paleo-topography and original bedrock.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016