Online Journal for E&P Geoscientists

Sudakiewicz, Nikolai ^*1; Rees, Andrew J.¹; Kliischies, Ralf ²; Pearce, Tim ²; Zereik, Rachad ³
(1) Saudi Aramco, Dhahran, Saudi Arabia. (2) Chemostrat International Ltd., Welshpool, United Kingdom. (3) Halliburton Energy Services, al-Khobar, Saudi Arabia.

The Nuayyim Formation (formerly known as the Unayzah Formation) in Saudi Arabia consists of Early Permian continental clastics that were deposited on a regionally extensive unconformable surface referred to as the pre-Gharif Unconformity. The internal stratigraphy of the Nuayyim Formation is complex, with rapid lateral facies changes characterized by fluvio-aeolian and sabkha/wet interdune sandstones and siltstones with several significant intraformational unconformities.

The Nuayyim Formation and Basal Khuff Clastics (BKC) successions are proven prolific hydrocarbon bearing reservoirs. Exploration efforts are focused in targeting stratigraphic prospects. Despite excellent successes targeting these stratigraphic plays, a better understanding of the depositional model is required. Due to the barren nature of the aeolian dune reservoir units, correlation can be problematic. Consequently, our detailed understanding of lateral and stratigraphic variations in lithotypes and palaeogeographic distribution of facies, fairway prediction, and reservoir seal pairs is poor at best. A major problem with correlation within the Nuayyim Formation is an absence of fossils and the occurrence of thick sandstones with few shale interbeds. This results in a relatively poor undiagnostic E-log response that hampers confident wireline-based correlation, which inherently is lithostratigraphic in nature.

This paper summarizes the results of a chemostratigraphic study. The primary objective of this study was to clarify whether a chemostratigraphic zonation scheme could be attainable within “barren” aeolian sandstones of the Nuayyim Formation. Second, the study was designed to assess whether lateral lithological variations within the Nuayyim Formation represent an updip pinchout or reflect lateral facies variations as represented in dimming seismic response.

In summary, this study has identified a potential new stratigraphic play, based on the establishment of a high-resolution chemostratigraphic zonation of the Nuayyim Formation and BKC. Furthermore, chemostratigraphy has been demonstrated as an invaluable exploration tool that would not only aid correlation of other Nuayyim Formation/BKC successions, but also of the entire Unayzah in Saudi Arabia. In addition, chemostratigraphy will greatly assist with our exploration efforts that are progressively targeting much older and deeper targets with poor biostratigraphic control.