Petrophysical Properties of the Late Carboniferous and Early Permian Glaciogenic Reservoirs: An Example from Al Khlata Formation, Block 56, Eastern Flank of South Oman Salt Basin

Abstract

The Late Carboniferous and Early Permian Al Khlata Formation represent the lower unit of the Haushi Group, related to the third glacial event in the Arabian Plate. Al Khlata Formation, which is deposited in proglacial fluvial and deltaic systems, is an important hydrocarbon target in Oman. The accurate estimation of the amount of hydrocarbon that can be produced from Al Khlata reservoirs is very challenging because the rock properties between wells in the Block 56 vary significantly, and the distribution of the petrophysical properties is poorly understood. This study aims to construct a petrophysical model and predict the vertical and lateral distribution of the petrophysical properties of the Al Khlata sandstones in Block 56 within depositional facies and sequence stratigraphy. This study is based petrophysical analysis using wireline logs and drilling cuttings. However, the study revealed that the Al Khlata Formation consists of two sandstone bodies: sand 2 and sand 1, (from oldest to youngest), characterized by significant heterogeneity in lithology and petrophysical properties. The thickness of the correlatable sandstone bodies within the Al Khlata Formation varies from one well to another because their deposition was highly controlled by the salt movement during the Late Devonian to the Late Carboniferous hiatus. Moreover, this study has revealed that the correlation between wells allowed the prediction of the influence of the glacial environments on the petrophysical properties of sandstone bodies. There is no consistent trend for the lateral and vertical distribution of porosity and permeability of the lacustrine and deltaic proglacial sandstone bodies, due to the complexity of the glacial environment. The degree of comparison between the two oil-bearing sandstones in terms of petrophysical properties is obvious. For example, sand 2 has good to excellent reservoir quality because of low average shale volume, and good average porosity. Sand 1 is a tight reservoir because it is enriched with shale, has poor porosity, and is very hard to drill because of diamictite. Subsequently, all of that has a significant impact on the hydrocarbon potentiality of each sand. Such modeling will help in drawing more efficient drilling, production, and recovery strategies.