Identification And Evolution Of Clay Minerals In The Sand-shale Reservoirs Of The Berkine Basin (algeria)

Porosity data and natural y-ray spectrometry well logging were used to identify the type and the nature of the clay minerals present in the Berkine basin sand-shale reservoirs. To highlight the character of the prevailing argillaceous cement, the porosity pb-At, At-N Z-plots are used. They make it possible to note: 1) the shale-sandy nature of the studied reservoirs, 2) the influence of these clays on the whole of the reservoir. The results showed that, in the Berkine Basin reservoirs, the cement is rather complex. The pb-K and U-K Z-plots were used to examine the influence of non-clayey cements on the studied reservoirs intervals. Mineralogy, particularly of clay minerals, was carried out by using the litho-density and natural y-ray spectrometry well logging data to establish Pe-K, Pe-Th/K and Th-K Zplots. The shale minerals evolution was then made for the Silurian reservoirs Al , A2, B1 and B2 and the Triassic reservoirs TAGI (Lower Trias Argillaceous Sandstones) and TAGS (Upper Trias Argillaceous Sandstones). This study shows that, for the old reservoirs, the dominating minerals are Chlorite and Kaolinite whereas, for the recent TAGI reservoirs, we find the presence of Montmorillonite and Illite and their mixed layers.