New Chronostratigraphic Model for the Lower Qusaiba Member—Shale Gas Exploration Areas of Northern Saudi Arabia

Abstract

In light of the shale-gas developments of North America, the organic-rich Lower Silurian fine-grained deposits that occur across much of North Africa and the Middle East (Le Heron et al. 2009) came into focus as potential unconventional gas targets (Hayton et al. 2010; Alexeyenko et al. 2013; Loydell et al. 2013). As part of the initial phase of shale-gas exploration in northern Saudi Arabia, cores were commonly taken over the lower section of the Qusaiba Member, within the Base Qusaiba Hot Shale (BQHS) in particular. For the first time, this allowed a comprehensive analysis of the nature and age of the lower Qusaiba in the subsurface of northern Saudi Arabia. Due to the excellent preservation of graptolites within many of the cores and the large number of cores that were obtained, in the initial phase of the shale-gas program, high resolution chronological data for the lower part of the Qusaiba, especially the BQHS, was available at numerous locations across northern Saudi Arabia. The graptolite identification and interpretation was undertaken and provided the chronological framework from which the lithostratigraphy could be correlated with certainty. The resulting identification of isochronous surfaces enabled significant advances to be made in understanding the development of the lower Qusaiba through time. We present, for the first time, a chronostratigraphic model for the lower Qusaiba Member that has been developed for subsurface shale gas exploration in northern Saudi Arabia, which includes two new lithofacies within the lower Qusaiba, the Qusaiba Black Chert (QBCH) and the Qusaiba Transgressive Siltstone (QTSS). We identify multiple, genetically distinct phases of hot shale development. It should be noted that this work is ongoing and the proposed model is the first attempt at building a comprehensive chronostratigrahic model for the lower Qusaiba in northern Saudi Arabia.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015