Biostratigraphic and petrological characteristics of Lower Oligocene sediments in the Northeastern Cuu Long basin

Abstract

Oil and gas exploration and production activities, the evaluation of petroleum systems, modelling of geological, field structures and oil and gas reservoirs are carried out by various research. In which, studies on stratigraphy, sedimentary environment, petrographic features are considered as core studies, performed in great detail and the results are updated over time. In the Cuu Long Basin, the objects of exploration in the clastic sedimentary rocks are mainly the Lower Miocene and Oligocene, in which the Lower Oligocene sediments are attracting the attention of oil and gas companies. Therefore, this study was carried out for Lower Oligogcene sediments in the Northeastern Cuu Long Basin. Stratigraphic studies were performed by the method of palynology and palynofacies; the petrological characteristics was studied on thin section, SEM, XRD. Research results, lower Oligocene sediments are divided into two sequences (E, F) and two parasequences (E1, E2) of sediments, which are deposited in freshwater lake environment with frequently changing energy conditions from low-to-high. The lower Oligocene sandstone is significantly influenced by strongly compaction and highly cemented by authigenic minerals like calcite and zeolite, which fill up intergranular pores, pore throats, and cracks. Visible porosity is very poor, so the reservoir quality of lower Oligocene sandstone is estimated to be poor. Most of these sandstones are being at advanced diagenetic.