Impact of the demise mechanisms of the Cretaceous rudist buildups in the Arabian Plate on their reservoir characteristics

Abstract

Rudist buildups form the major oil-producing reservoirs in the Cretaceous carbonate strata of the Arabian Plate. They are the main components of the Shuaiba and Mishrif and to lesser extent, the Natih, Mauddud, Simsima, and the Hartha Formations. The demise of the rudist buildups in the region was achieved either by destruction, clastic invasion, or drowning. These processes are found to influence the resultant rocks and their reservoir properties. Destruction may lead to wide-scale scattering and deposition of thick, porous, and permeable strata of rudist-bearing grainstone/packstone beyond the buildup areas, whereas, those covered by clastic fronts are subjected to meteoric water and tend to be well-cemented. Drowned buildups tend to be compact and have more argillaceous materials. Both poroperm and capillary pressure data of these rock suites reflect such differentiation. Recognizing these processes may help predicting locations of the best-developed rudist-bearing reservoirs and enhance our understanding of their reservoir characteristics.