Abstract
The Bahi Formation is diachronous in age, ranging from Cenomanian to Maastrichtian, and occurs in the subsurface of the Az Zahrah - Al Hufrah Platform in the western part of the Sirt Basin. The Bahi Formation onlaps the Al Hufrah Formation/Gargaf Formation and wedges out against the Az Zahrah Palaeo-high area. The Core samples from the studied wells record mainly sandstones units interbedded with shales and thin layers of dolomites in some parts. The uppermost portion of the formation is characterized by abundant glauconite, suggestive of a marine influence with an average thickness of about 30 feet (9 m). Petrographic investigation shows that the rock compositions of the uppermost Bahi Formation are mainly quartz with an average of 76%; feldspars make up to 22% mostly potassium feldspar (orthoclase and microcline) and minorPlagioclase (oligoclase) and rock fragments. The latter represent only 1.6% of the total rock framework composition, as a result, the uppermost Bahi Formation is classified as subarkose to arkosic-arenites. Accessory minerals such as pyrite, mica, iron oxides, zircon, tourmaline, rutile, ilmenite, and apatite are present in minor amounts. The presence of several kinds of clay minerals such as kaolinite, illite, and chlorite, in addition to other cements such as dolomite, calcite, and anhydrite, forming and growing of these minerals in-between sand grains, caused noticeable changes in the porosity of the studied part from the formation.