The impact of pore typing on saturation of carbonate reservoirs: Early Miocene carbonates, eastern Saudi Arabia

Significant pore system complexity occurs in carbonate lithofacies influencing its reservoir properties and efficiency. In this study, we attempted to disclose the response of carbonate pore system to the laboratory saturation procedures in gaseous and liquid phases by applying different experimental, spectral and imaging techniques. Thus, plug samples were obtained from two early Miocene, genetically-different carbonate lithofacies in eastern Saudi Arabia, namely; the skeletal oolitic peloidal grainstone and the stromatolitic boundstone. These lithofacies form prolific reservoirs in many petroleum fields in the Arabian Platforms. The skeletal oolitic peloidal grainstone was characterized by a laterally-extended uniform pore system, including fewer skeletal molds and dominant intergranular pores with significant pore bridging. In contrary, the stromatolitic boundstone revealed a complex pore system which varies laterally, with fewer interparicle, intraparticle, vuggy and moldic pores, and dominant isolated fenestral pores. This setting is believed to stand behind the under-saturation state as indicated by NMR porosimetry and visual analyses (SEM and micro-CT scan). The depositional and diagenetic settings of these lithofacies have contributed directly to the evolution of their respective pore types and geometries, which in turn influenced the gas flow, and to a higher degree; the liquid saturation procedures and its related properties derivations.