Online Journal for E&P Geoscientists

Tang, David Z.^*1; Lawrence, Paul ¹; Tan, Wenbin ¹; Bakhiet, AbdelFattah ¹; Gregory, Greg ¹; Wharton, Stanley R.¹; Shokair, Khalid ¹
(1) Exploration Resource Assessment, Saudi Aramco, Dhahran, Saudi Arabia.

The Middle and Upper Jurassic (Late Callovian-Oxfordian-Early Kimmeridgian) Tuwaiq Mountain and Hanifa formations contain both significant oil reservoirs (Hanifa and Hadriya reservoirs) and world-class hydrocarbon source rocks. Understanding the regional stratigraphic framework and exploration concepts of these formations is extremely important for unlocking the hydrocarbon exploration potential of the Jurassic system.

The Tuwaiq Mountain and Hanifa formations comprise two separate composite third-order sequences. Following almost complete fill of the Dhruma Basin during Bathonian time, a renewed differential subsidence in the early Callovian established the Late Jurassic Arabian carbonate platform along the southwest margin of the Tethys Ocean. Two major intrashelf basins were developed within the Arabian carbonate platform interior: the central Arabian intrashelf basin and the north Arabian intrashelf (Najmah) basin. Grainy carbonates of the Hadriya reservoir were developed in higher energy and shallow-water environments along the southwest and northeast margins of the central Arabian intrashelf basin. The time-equivalent Tuwaiq Mountain muddy carbonates, mudstones and organic-rich source rocks were deposited in relatively deeper water and basinal environments. The Hanifa reservoirs (skeletal/oolitic limestones and packstones) were developed as prograding clinoforms during the highstand of the Hanifa Sequence. The Hanifa margin grainstone complexes shifted further basinward as a result of continuous carbonate growth and progradation. The organic-rich mudstones of both the Tuwaiq Mountain and Hanifa formations are proven to be the primary source-rocks that supplied most of the hydrocarbons for the exceptionally prolific Jurassic petroleum systems. An early Kimmeridgian base-level fall, as revealed from core and 3D seismic stratigraphic analysis generated using the Wheeler Diagram approach, terminated the Hanifa carbonate platform and resulted in substantial subaerial exposure of previous shoaling grainstone complexes and proximal areas, with thin-layers of evaporates (e.g. anhydrites) in further distal and basinal areas. A variety of new exploration concepts (e.g. stratigraphic traps) has emerged through the building of a robust regional stratigraphic framework of the Tuwaiq Mountain and Hanifa formations in Saudi Arabia.