MICROFACIES ANALYSIS AND PALEOENVIRONMENTAL TRENDS OF THE PALEOCENE FARRUD AND MABRUK RESERVOIRS, CONCESSION 11, WEST SIRT BASIN, LIBYA

Abstract

Investigation of thin sections taken from representative core samples under the petrological 
microscope reveals common petrographic and mineralogical characteristics with distinct faunal 
assemblages allow establishing the microfacies associations and deducing the paleoenvironmental trends 
of the Paleocene Farrud and Mabruk rock units. Recognition of the early and post diagenetic processes 
particularly dolomitization and micritization as well as dissolution and precipitation of spary drusy calcite 
as a newmorphism process affecting the reservoir rocks is established. The microfacies trends detected 
from the investigation of 46 core samples from Farrud Member (Lower Paleocene) representing six wells; 
QQQ1-11, GG1-11, LLL1-11, RRR1-11, RRR40-11 and RRR45-11 indicate that the deposition was started 
within the realm of shallow supratidal and intertidal subenvironments followed by deeper environments 
of the shelf bays with maximum sea level during inner shelf environment where fossiliferous bioclastic 
packstone dominated. The microfacies associations determined in 8 core samples from two wells LLL1and 
RRR40 representing Mabruk Member (Upper Paleocene) indicate paleoenvironmental trends marked by 
sea level fluctuations accompanied with a relatively marine shelf bay conditions intervened with short-lived 
shallow intertidal and supratidal warm coastal sedimentation. As a result dolostone, evaporitic dismicrites 
and gypsiferous dolostone of supratidal characters were deposited.