Using Elemental Geochemisty to Improve Sandstone Reservoir Characterization: a Case Study From the Unayzah A Interval of Saudi Arabia

摘要

The sandstones of the Permian Unayzah A reservoir in Saudi Arabia are an active target for natural gas exploration and development. These sandstones were deposited mainly in eolian dune complexes and sand sheets, as well as in playas and ephemeral streams in interdune areas. The detri-tal mineralogy is, in most cases, relatively simple. Grains are dominated by quartz, with minor feldspars, lesser lithic fragments, and little primary clay. Diagenetic components, however, can make the bulk-rock mineralogy and reservoir quality much more variable; pore-filling cements can include quartz, carbonates, anhydrite, and illite. Anhydrite nodules can impart significant heterogeneity in mineralogy and porosity. Because of these factors, determination of fundamental reservoir-quality parameters using the typical triple- or quad-combo wireline log suites can be challenging. Measurements of rock matrix elemental concentrations performed on drill cuttings or obtained from wireline logs provide additional information related to the mineralogical composition of the formation that can improve log-derived determinations of reservoir parameters.