Twenty-nine field sections measured along 135 km distance to identify the depositional, diagenetic, and stratigraphic nature of the Cyrenaican Miocene of Ar-Rajmah Group carbonate rocks, northeastern Libya. Four sections were sampled every 0.5 m for sedimentology, petrography and diagenesis. Petrographic study focused on identifying facies textures, grain types, cements and mud content that block pore spaces, and pore-creation processes dissolution and fracturing. Combined the sequence stratigraphy, sedimentology, and petrography indicates three carbonate facies characterized by high porosity values, considerable vertical thickness and lateral continuity. These reservoir-analogue facies are coralline red algal packstone, microbial reefs, and oolitic grainstones. 

The Miocene Ar-Rajmah Group carbonate succession is of 97 m maximum thickness and made up of six 3^rd-order sequences. The Ar-Rajmah Group depositional facies are peritidal facies (evaporites, microbialites, pelletal wackestone/packstone, porites reefs and bioclastic packstone, very fine to fine quartz sandstone, and green shale facies), ramp crest oolitic grainstones facies, and subtidal facies (bioclastic carbonates, reworked bioclastic carbonates, coralline red algae, and reworked red algae).

The petrographic analysis shows that the lower Miocene interval (Langhian and older) is dominated by biomoldic and frame-growth porosity in the bioclastic-rich, bryozoan, and coralline red algal packstone facies. The upper Miocene interval (Serravallian and younger) is dominated by oomoldic and fenestral porosity in the oolitic grainstone, microbial-bioclastic-oolitic grainstone.

The porosity values of the Cyrenaican Miocene carbonate rocks are considerably enhanced through multiple dissolution and fracturing events. In addition, the presence of the open factures considerably enhanced the permeability of these rocks by connecting the open pores together. The Upper Miocene has the lowest average porosity values due to cementation, where the Middle Miocene has the highest average porosity values due to dissolution and the dominance of grainstone texture, and the Lower Miocene has medial average porosity values due to mud content in the packstone texture. 

The studied Cyrenaican Miocene potential reservoir rocks are made of coralline red algal packstone, microbial reefs, and oolitic grainstones facies. The high secondary porosity, fracturing permeability, vertical thickness, and lateral continuity characterizations make these Cyrenaican rocks as good analogues of subsurface reservoirs.