Abstract

The Middle Permian to Lower Triassic Khuff Formation is one of the world's most prolific hydrocarbon reservoirs. This study is part of a research project on Khuff outcrop equivalents whose overall aim is to investigate the reservoir architecture on different scales. The present paper focuses on heterogeneities in Khuff‐equivalent grainstones at the near well scale.An outcrop in the Oman Mountains, where the Khuff‐equivalent Saiq and Mahil Formations are exposed in an area 1800 m long by 100 m high, was studied to map lateral and vertical depositional heterogeneities. The investigated section represents parts of three third‐order sequences: the upper part of Khuff sequence (KS)3 (grain‐dominated), the whole of KS2 (mud‐dominated), and the lower part of KS1 (grain‐dominated). Real‐Time Kinematic GPS, satellite imagery, outcrop gamma‐ray and digitized sedimentary logs were used for outcrop description and were integrated into a three‐dimensional digital outcrop model.The resulting 3D facies model indicates that the apparently simple, layer‐cake geometry of the grainstone reservoir facies shows pinching and swelling with a standard deviation of 12.75% of bed thickness. These thickness variations may influence volume calculations during reservoir assessments. The heterogeneities of grainstone bodies are represented by compositional (ooid, peloid or intraclast‐dominated) and grain‐size variations.Muddy event beds at the cm‐scale were mapped out in detail in a 200 × 40 m outcrop window and together form a dense network of potential baffles to fluid flow. The thickness of these beds varies significantly due to syndepositional erosion.An important conclusion of this near well‐scale study is that the perceived simple, layer‐cake Khuff‐equivalent succession in the study area is in fact heterogeneous in mud‐rich deposits, while grain‐rich deposits extend over a wide area with some thickness variations. These findings can be directly applied in Khuff subsurface correlation and modelling attempts.

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