PETROPHYSICAL PROPERTIES OF THE SILURIAN SANDSTONE RESERVOIR IN THE A STRUCTURE OIL FIELD, GHADAMES BASIN, WEST LIBYA

Abstract

The assessment of low-resistivity reservoir pay in the Silurian Sandstone Formation presents significant challenges and has far-reaching ramifications for field development plan. Therefore, this study attempts to analyse and examine the petrophysical properties of the Silurian Reservoir (Lower Akakus fm.) in the A Structure based on two well logs data (A1 and A2) located in the Block NC-118 at Ghadames Basin. There are numerous studies have been undertaken in the Ghadames Basin of West Libya; a few researchers have highlighted the challenges of reservoir pay in the Lower Akakus Formation. The comprehensive examination of the Silurian Formation is divided into five distinct sand units, namely sand 1, sand 2, sand 3, sand 4, and sand 5 (SS1, SS2, SS3, SS4, and SS5), arranged in a stratigraphic sequence from upper to lower Silurian. Employing advanced petrophysical analysis techniques and Techlog software, the lithological composition of each sand unit in the Silurian Formation was identified, revealing a predominantly sandstone reservoir interspersed with shale formations with an average shale volume ranging from 0.2% to 15%. Sand 1 has roughly 2% porosity, sand 2 and sand 3 have around 22% porosity, sand 4 has 17% porosity, and sand 5 has 15% porosity. Furthermore, the average water saturation within these sand units varies, with sand 1 registering approximately 60% water saturation, sand 2 indicating 72% water saturation, sand 3 displaying 62% water saturation, sand 4 revealing 17% water saturation, and sand 5 exhibiting 56% water saturation. Despite initial indications of low resistivity in the interval (L.A) from well test logs analysis, the subsequent well test results conclusively confirm the presence of oil in the Lower Akakus zone.