Characterization Of A Carbonate Reservoir Formed In A Low Energy Environment

The Cretaceous oil and gas reservoir located in the Middle East is one of the most important reservoirs in the world. However, it is highly inhomogeneous and porous and displays low permeability. These characteristics affect is potential as high quality reservoir. The present research integrated conventional petrophysical tests, high-pressure mercury intrusion analysis, scanning electron microscopy (SEM) and petrological analysis to determine the rock characteristics of the Kh2 upper cretaceous oil field. With this information we classified the reservoir in different types. The results showed that the reservoir was formed in a low energy environment, is an open platform running from above the wave base level to below the low tide line. The lithology was dominated by foraminiferal biomicritie, echinate biomicritie, micritie, pelsparite, algae biopelmicrite, algal biomicritie, and algal fossiliferous micrite. Based on the regional structure and palaeogeodetic sedimentary background, the presence of open sea (MF1), high-energy pellets shoal (MF2), intershoal sea (MF3), low-energy pellets shoal (MF4), and low-energy bioclastic shoal (MF5) were identified. The porosity ranged from 10% to 29%, with an average of 23.73%. The permeability varied between 0.4 mD and 490 mD, with an average value of 21.21 mD. In addition, the petrophysical properties were controlled by sedimentary microfacies and diagenesis, and the quality of these properties decreased in the order MF2, MF4, MF5, MF3, MF1. Diagenesis transformed the reservoir; however, the basis for diagenesis was the sedimentary environment. The reservoir was divided into 3 types, which corresponded to 3 types of pore structures. The first type (pore throat structure I) mainly developed in MF2 and MF4, where the average throat radius was larger than 2.2 mu m, and the permeability higher than 20 mD. The second type (pore throat structure II) was identified in MF4 and MF5, presenting an average throat radius between 0.5 mu m and 2.2 mu m, and a permeability between 5 mD and 20 mD. The third type (pore throat structure III) occurred in MF1 and MF3, presented average throat radius smaller than 0.5 mu m, and permeability smaller than 5 mD. The Kh2 layer was a type II reservoir. The results presented herein will be of great significance for the identification of po tential oil research and development areas.