Shale Content Implementation on the Application of the Acoustic Impedance of the Upper Ordovician Mamuniyat Reservoir in Murzuq Basin, Libya

ABSTRACT Understanding the reservoir characteristics by integrating the petrophysical and elastic properties is a valuable procedure for hydrocarbon fields. Therefore, this work concerns an integration of petrophysical and elastic rock properties with the acoustic impedance (AI) and rock physics diagnostics (RPDs) of the Upper Ordovician Mamuniyat reservoir that provides a significant illustration of shale content influence. These interpretations are based on the processing of well‐logging data (spectral gamma ray [SGR], neutron, density, and photoelectrical factor (PEF), as well as shallow and deep resistivities), which are derived from four oil wells in the Murzuq Basin of Libya. Using spectral gamma‐ray (GR) data indicated that the formation comprises upper clean and lower shaly sandstone (SS) units with a spiky behavior of the lower unit due to the alternation between the sand and shaly sand causing a spiky variation of the total and effective porosities. The relatively high concentration of potassium (K) and thorium (Th) within the lower unit of the Mamuniyat Formation indicates a granitic basement as the parent rock. Plotting the Th/K versus the potassium and PEF values is used to define the clay type of the studied reservoir. The neutron‐density crossover is well presented in the upper clean sand unit and a few intercalations in the lower shaly sand unit. Increasing the deep resistivity values in the upper unit indicates its hydrocarbon content and its promising nature for oil extraction. Utilizing the RPDs revealed that plotting the AI versus the V p / V s ratio, the bulk density, and Poisson's ratio data points of the clean sand reservoir unit shows well‐aligned points rather than scattered plotting of the shaly SS unit. Furthermore, plotting the λρ and μρ against the effective porosity helped to find out the rock type and its interstitial fluid type that has been trapped in the pore spaces. This study adds more understanding of the Mamuniyat reservoir properties based on the RPDs.