Tuwaiq Mountain Escarpment in the Central Saudi Arabia exposes the Late Jurassic carbonates, which are one of the world’s most prolific oil-producing strata in the subsurface. The outcrops provide a window of opportunity to study the architecture of these strata that is found usually complex due to heterogeneous lateral and vertical facies. These heterogeneities are sub-seismic in scale, thus, the information from outcrops bridge the gap between seismic and core data. This virtual field trip focuses on the Late Jurassic Hanifa Formation outcrops at Wadi Birk, central Saudi Arabia with an objective to highlight and display interwell scale heterogeneities associated with depositional architecture. The Hanifa Fm is one of the major hydrocarbon reservoirs in the subsurface of Saudi Arabia and is also in many respects analogous to the even more prolific overlying Arab D reservoirs.

The virtual field trip will include a 4x4 km² 3D digital outcrop model (DOM). The VRGS (Virtual Geoscience) platform will be used to run this field trip. The participants will be taken to one of the most spectacular exposures of the Hanifa Formation at Wadi Birk in Central Saudi Arabia. Depositional facies (in outcrop and thin section), 3D Digital Outcrop Models, and geophysical (GPR, Seismic) and petrophysical datasets (Spectral Gamma Ray - SGR) will be discussed. The main learning outcome of this field trip is to show reservoir equivalent facies in the outcrops but also provide clues into the intricacies of the stratal architecture. It will be demonstrated that the layered architecture is actually not so layered (as usually observed and published). Depositional cycles will be defined based on geological, geophysical, and petrophysical datasets (measured sections, core, thin section, and SGR). The mapping of the depositional cycles within the 4x4 km² area at Wadi Birk will aid in demonstrating that vertically and laterally the depocenters (sediment production) were migrating. These depocenters are a product of high sediment production by the buildups (stromatoporoid/coral), and relatively low sediment production or current winnowing in the inter-buildups areas. Further, the variability in the shape and sizes of the stromatoporoid/coral build-ups laterally adds more complexity to the thickness of a depositional cycle and provides clues to environmental dynamics. Uneven topography is healed during the deposition of the next cycle with the areas of higher accommodation availability becoming natural depocenters.

The observations and results will be used as input into high-resolution static reservoir models to address the gap of our understanding in inter-well scale heterogeneities of similar subsurface hydrocarbon reservoirs.

The Wren's Nest National Nature Reserve, situated in the West Midlands, UK, is well known for its exposures of Silurian (Wenlock and Ludlow Series) carbonates. The Wren’s Nest was first recognised as a nature reserve in 1965, and in 2020 it became recognised as part of the part of the Black Country Unesco Geopark. The area has significant geological importance due to the superb preservation of its fossils, with more than 700 macro fossil species identified (including brachiopods, bivalves,corals, crinoids, trilobites, gastropods, cephalopods and bryozoans), and is particularly well known for the trilobite Calymene blumenbachii, locally known as the “Dudley Bug”.

The Wren’s Nest Hill forms a large elongated N-S anticlinal dome structure faulted along is main axis by the Wrens Nest Fault, with the structure forming in the Late Carboniferous as a result of the Variscan Orogeny.

The nature reserve also has an extensive industrial heritage with the limestone being mined since the 1700’s for building stones, lime, fertilizer and during the industrial revolution as a flux for iron smelting, with abundant coal being available locally from the surrounding coal measures. An extensive network of mines and tunnels exists, with Dark Cavern being the largest man-made cavern in the UK. These mines are linked together by a series of underground canals which in turn join the national canal network.

With the underground workings closed off to the public for safety reasons this field tour is constructed using surface data only and attempts to reconstruct as much as possible through information from the archives.