Grain-Size Analysis of Middle Cretaceous Sandstone Reservoirs, the Wasia Formation, Riyadh Province, Saudi Arabia

Abstract

Grain-size analysis is a significant descriptive method to determine and evaluate depositional environments and hydrodynamic conditions in addition to classifying sedimentary rocks. In this study, grain-size analysis was conducted using dry-sieving procedures on fourteen representative sandstone samples from the Wasia Formation, a thick water aquifer and a hydrocarbon reservoir. Hydrodynamic conditions and depositional environments were determined using bivariate plots, linear discriminate function (LDF), log probability, and Passega diagram. The results reveal that the lower outcrop section consists of coarse- to medium-grained sandstone with a majority being poorly sorted, while the upper section is made up of medium- to medium-well-sorted fine-grained sandstone units. The sediments have a unimodal distribution of 2∅ (all the lower section) and 3∅ (most of the upper section), while two beds have a bimodal of 2 and 3∅. The lower section has wide range skewness with mainly mesokurtic curves, while the upper section is near-symmetrical to coarse-skewed but mostly leptokurtic. Additionally, log probability plots and the Passega diagram show that the majority of the indicative sediments were transported via one to two saltation levels, while fine-grains were transported via suspension. The results of the LDF method are predominantly indicative of aeolian, marine, and fluvial environments.