Acoustics and petrophysical investigations on upper cretaceous carbonate rocks from northern Lebanon
Résumé
Carbonate rocks represent significant aquifers and reservoir rocks in many parts of the world. In this study, twenty-one carbonate samples collected from the exposed rocks at Batroun and Chekka, northwestern Lebanon, are studied to investigate their lithological characteristics, nannofossil content, and their acoustic and petrophysical properties. Four microfacies are recognized in the studied rocks including packstone, wackstone, wackmudstone, and the wack-packstone. Nannofossils are detected in the top part of the studied section indicating marine-type depositional conditions for the upper Cretaceous carbonate rocks. The Petrographic analysis revealed also that the studied rocks have moderate to high porosity which is consistent with the measured porosity on core samples. The low porosity of some samples is induced by cementation, which also reduced their permeability. The bulk density varies widely because of the many diagenetic processes that impacted the studied rocks. Moreover, because the primary and secondary wave velocities (Vp, and Vs) are greatly influenced by porosity and density, the samples exhibit extreme variations in acoustic velocities from low values which characterize soft, highly-porous, rocks to higher velocities 2 which are characteristic of compact, massive, and highly-cemented carbonates. Some relationships between the measured petrophysical and acoustic parameters are studied to investigate their mutual dependence, and discuss the impacts of rock composition and diagenetic alterations on the petrophysical properties of the collected rocks. The obtained results are also important in characterizing their mechanical strength, and in the analysis of seismic reflection profiles acquired for equivalent offshore limestone reservoirs in the Levant and the Eastern Mediterranean regions.
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