Abstract
The Upper Oligocene-Middle Miocene Al Faidiyah Formation occurs as the uppermost unit in the Darnah-Tubruq area. At the base of this unit, immediately above the underlying Al Abraq Formation, is a layer of clay. This clay unit is composed of varying amounts of montmorillonite and other clays, along with glauconite, gypsum, carbonates, and other minor minerals. In several samples, microfossils have been identified, while another contains ostracods, sharks’ teeth and nodules and pseudomorphs of phosphate minerals.
The physical properties of muds made up of varying amounts of this clay with water vary from sample to sample. The different mixtures behave as pseudo-plastic fluids, and show many of the required properties of drilling fluids. Their properties do, however, vary from place to place, and vertically within the section. Samples from the lower parts of the section generally have better properties than those from the upper half. Muds have been prepared from the samples having yields as high as 25 m³/tonne, and viscosities as high as 73 centipoises. Results of tests using caustic soda and Carboxy-Methyl-Cellulose (CMC) to control filter loss and viscosity are also reported.