Lithological characteristics and petroleum capacity of Oligocene - Early Miocene sandstones
in the Northwestern region of the Red River basin

Nguyễn Thị Phương Thảo, Trần Nghi, Đinh Xuân Thành

The Northwestern region of the Red River basin is a part of the Red River basin, extending from the mainland to the submerged part of the Northernwest region of the basin with a symmetrical shape running in the Northwest - Southeast direction. The Red River basin, in general, and the northwest region, in particular, have been studied by many Vietnamese and international authors, mainly on geological structure, tectonics and stratigraphy. In the field of petroleum geology’s sedimentary, the research and assessment of colecto quality of sandstone by quantitative methods has not been paid enough attention. The paper introduces research results on petrographic characteristics, lithophysical properties and quality of sandstone reservoir in Early Oligocene and Early Miocene. The lithological parameters (Md, So, Ro, Q, Li, Co and I) are the variables that affect the effective porosity (Me) as a function of linear correlation law; in which quartz coefficient (Q), cement matrix coefficient (Li), sorting coefficient (So) and the secondary change coefficient (I) have a very strong influence on the effective porosity. The variable- function correlation between effective porosity and lithological parametries is as follows: Me = F (Q, Li, So, I). Colecto quality of sandstone is divided into 3 levels: (1) good quality is Early Miocene sandstone with Me= 15-20%; Q > 0.8; So < 1.8; Li =0.08-0.15; I <0.5; (2) medium quality is Late Oligocene sandstones with following parameters: Me= 8-15%; Q = 0.6- 0.8; So = 1.8-2.2; Li < 0.05 and 0.15-0.25; I =0.5-0.7; (3) poor quality is Early Oligocene sandstone with Me<8%; Q<0.6; I=0.7-0.9.

Keywords: Grauvac, ackose, quartz-lithic, correlation analysis, textural coefficients, secondary change coefficient