Multi-scale Discontinuities Characterization of the Arab-D and Upper Jubaila Tight Carbonates Outcrop, Central Saudi Arabia

Abstract

Stratigraphically equivalent outcropping strata to the Arab-D carbonate reservoir, which is one of the most prolific hydrocarbon reservoirs in the world, are well exposed around Riyadh in central Saudi Arabia. This study investigates lithofacies and discontinuities types of the Upper Jurassic Arab-D Member of Arab Formation and the underlying Upper Jurassic Upper Jubaila Formation based on outcrop analogs in central Saudi Arabia. The study describes the lithofacies and characterizes the discontinuity properties. The Arab-D Member and Upper Jubaila Formation vary in their lithofacies types, thicknesses, abundances, and stacking patterns. Lithofacies include mudstone/wackestone, packstone/grainstone that deposited within a tidal flat, skeletal banks and shallow to deep lagoonal paleoenvironments. The Upper Jubaila Formation shows several fracture sets that are oriented north–west, north $$20{^{\circ }}$$ east, and north $$40{^{\circ }}$$ east. Most of these fracture sets exhibit near horizontal (5–15) to near-vertical dipping (70–90). The Arab-D member is intersected by four fracture sets oriented north $$20{^{\circ }}$$ east, north–south, east–west and north–west. These fractures also exhibit near near-vertical (70–80) dipping. In both the Arab-D and Upper Jubaila Formation, the northwest-oriented sheared fractures show small vertical displacements. Regional and local controls seem to have affected fractures within the Jurassic carbonate rocks. Regionally, the fractures appear to be structurally controlled by the Central Arabian Graben System, which affected central Saudi Arabia. Locally, at the outcrop scale, stratigraphic, depositional and diagenetic factors have also affected the fracture development and intensity. Bed perpendicular fractures sets were interpreted to be formed at three separate stages: the first stage is associated with the initiation of Central Arabian Graben System during Quaternary which lead to formation of NW–SE-oriented fractures set, the second stage the NE–SW-oriented set, this set is associated with the abutting of the older fracture set along beds and sequence boundaries forming several types of fractures deflections along these boundaries, the last stage is the E–W-oriented set that cross-cut the previously existed set. The integration of discontinuities characteristics revealed from the Arab-D outcrop with subsurface data might help to understand and predict discontinuity properties and patterns of the Arab-D reservoir in the subsurface.