High Resolution Stratigraphy of the Khartam Member of the Permo-Triassic Khuff Carbonate: Outcrop Reservoir Analog from Central Saudi Arabia

A.M. Adam¹, O. Abdullatif¹, M. Abdelgadir¹, A. Abdelraziq¹, M. Osman¹, M. Bashiri¹, H. Eltom¹, and L. Babaloa¹

Abstract

This study aims to construct an outcrop-based high resolution stratigraphic scheme for Khartam member of Khuff Formation. Such scheme will help to provide an integral base to understand the spatial lithofacies distribution and the 3D reservoir architecture. Field outcrop sections were investigated to achieve the objective of this study. Four major depositional sequences were defined. Generally, these sequences fall within an overall regressive pattern (a composite Highstand System Tract), and this was inferred from the upward increase in grainstone/mudstone beds thicknesses ratio (37%, 50%, 72%, and 65% respectively). Each of the four sequences was defined by a basal sequence boundary (SB), transgressive system tract (TST), maximum flooding surface (mfs), and highstand system tract (HST). SBs were associated with scoured surface, poorly sorted and reworked bed (mud galls and breccia), imbricates, and vugs. The mfs were defined by the change in the depositional trend from TST to HST. The basal sequence composed of 30 elementary beds. The TST is dominantly composed of massive mudstone interbeded with thinly fissile mudstone, whereas the HST was associated with thick planar to trough cross-bedded oolitic grainstone beds. The second sequence composed of 31 elementary beds. The HST composed of uniformly interbedded thick grainstone with thinly fissile mudstone. Localized scoured surfaces, trough cross-beds, and herringbone structures may indicate tidal channel influences. The third sequences is a highstand dominated sequence (grainstone/mudstone bed ratio is 72%). This sequence composed of 18 elementary beds. The fourth sequence is composed of 50 elementary beds; the depositional pattern of this sequence indicates final stage of the composite HST. The upper part of this sequence contains abundant mud galls, breccia, imbricates, vugs, and marine fauna, these associations indicates a regional sequences boundary, this boundary corresponds to the upper most boundary of the composite HST sequence. The high resolution outcrop analog model provides better understanding of the reservoir stratigraphic hierarchy and depositional patterns that might help to understand and predict the Khuff reservoir quality and architecture in the subsurface.

AAPG Search and Discovery Article #90188 ©GEO-2014, 11th Middle East Geosciences Conference and Exhibition, 10-12 March 2014, Manama, Bahrain