Characteristics of Paleozoic tight gas sandstone reservoir: integration of lithofacies, paleoenvironments, and spectral gamma-ray analyses, Rub' al Khali Basin, Saudi Arabia

The glaciogenic Sarah Formation (Hirnantian) is a potential tight gas sandstone reservoir in the Rub' al Khali Basin and other basins in Saudi Arabia. This study investigated the facies heterogeneity and paleoenvironments of the Sarah Formation using cores, petrographic thin sections, and spectral gamma-ray (SGR) analyses. The study revealed four facies associations (FAs), including massive to ripple-laminated sandstone (FA1), gray massive sandstone (FA2), diamictites (FA3), and partially deformed, massive-graded sandstone (FA4), interpreted to have been deposited in fluvial, glaciofluvial, glaciolacustrine delta, and subglacial outwash environments, respectively. The sandstone varies from fine-, to medium-, and coarse-grained and is a moderately to poorly sorted quartz arenite, subarkose, and to sublithic arenite. The integration of facies analysis with SGR analysis allowed us to classify the facies further into low matrix and argillaceous sandstones in the fluvial and glaciofluvial facies, mixed sandstones in the glaciolacustrine delta facies, and clast-supported and matrix-supported diamictites with shales in the subglacial facies. The results of this study might provide guidelines for facies identification and the prediction of reservoir-quality targets in the tight sandstone in the subsurface. This classification could facilitate the identification of and distinction between the glaciogenic lithofacies of tight gas reservoirs in the subsurface and provides a tool for correlating the lithofacies. This work might also provide guidelines for the exploration and development of Paleozoic tight gas sandstone reservoirs in the subsurface that are deeply buried and show a wide range of facies, paleoenvironments, and paleogeographic settings.