Abstract The Nukhul Formation (Suez rift) consists of fluvial and tidally influenced shallow marine strata that were deposited in fault-controlled seaways and tidal embayments during rift initiation. In this study, we create a half-graben-scale, high-resolution (typical grid cell dimensions 20 m x 20 m x <1 m), geocellular outcrop model of the Nukhul Formation. The evolution of the normal fault system in the study area is associated with the development of fault-parallel and fault-perpendicular folds. The changing nature of the structural template, and the resulting geomorphology, during deposition led to complex syn-rift stratigraphic architecture and facies distributions. We use a LIDAR-based digital outcrop approach to map this geological complexity to a high degree of accuracy, for export to reservoir modelling software. Software developed in-house was used to integrate field observations with the digital dataset, aid interpretation, and create realistic surface meshes from outcrop data. Facies modelling used a combination of sequential indicator simulation and object-based modelling approaches. Sedimentary logs were attached to the dataset and used as conditioning data. 2D probability maps, source points, and flow lines constrained the geocellular outcrop model to match the known geology. The approach leads to improvements in three areas: (i) geological knowledge of the study area, (ii) data portability, and (iii) geocellular outcrop modelling. Comparison between the final geocellular outcrop model, outcrop geology, and inferred palaeogeography shows that the geology of the Nukhul Formation is realistically modelled. The final reservoir model can be used as an analogue for similar geological settings. It can be applied to improve the prediction of subsurface geology in analogous reservoirs and to increase the accuracy of static connectivity and flow simulations. Ultimately this will improve knowledge of the impact of facies heterogeneities on reservoir performance and lead to increased efficiency of reservoir drainage.

Abstract A field study focusing on fracture systems in a fault linkage zone from the Suez Rift, Egypt, is presented to elucidate the role of fault linkage zones in the permeability structure of segmented normal faults in tight carbonate rocks. Fracture systems in the linking damage zone show significantly increased structural complexity compared to that typical of isolated faults. The linkage zone is characterized by high fracture frequencies and multiple fracture sets of different orientations. Notably, pervasive fracture corridors strike at high angles to the fault trend and are interpreted to have formed during the latest evolutionary stages of what is interpreted as a breached relay. The structural observations indicate that along segmented normal faults in carbonate rocks, fault linkage zones represents locations of progressively increased cross- and along-fault permeability through the stages of relay growth and breaching. Our findings, in combination with previously published work, indicate that fault linkage zones represent localized conduits not only for increased fluid flow across faults, but also (vertically) within fault zones. Appreciating this has wide-ranging implications for understanding fluid transport in carbonate rocks and other naturally fractured lithologies.

Abstract The NW Red Sea-Gulf of Suez rift system was initiated during Late Oligocene time and underwent extension in a N65°E direction, almost orthogonal to pre-existing WNW-trending Pan African shear-zone fabrics in the crystalline basement of the Sinai-African plate. Earliest syn-rift sediments are Upper Oligocene continental clastic deposits with minor synrift basalts. Early Miocene sedimentation was dominated by shallow marine clastic deposits, which developed variable stratigraphic architectures as a response to the interaction of extensional faulting, sea-level changes, sediment supply and dispersal. Analysis of fault geometries, fault kinematics and sedimentation patterns indicates that rift-normal extension predominated throughout the Late Oligocene-Early Mid-Miocene evolution of the rift. Reactivation of the Precambrian basement fabrics was the main factor controlling the fault architecture, fault linkage and evolution of the NW Red Sea-Gulf of Suez rift. Individual faults were initially strongly segmented and offset across ‘soft-linked’ relay structures. With increased extension these faults became linked by breaking down relay structures with the development of local ‘hard-linked’ transfer faults, thus giving rise to the rhomboidal fault pattern of the rift system. In Mid-Miocene time, the Levant–Gulf of Aqaba transform boundary was established, linking the Red Sea rift plate boundary to the convergent Bitlis–Zagros plate boundary. This resulted in a dramatic decrease in extension rates within the Gulf of Suez whereas the northern Red Sea continued to extend, with significant syn-rift sediments deposited in Late Miocene–Pliocene time in offshore fault-bounded basins.

Abstract This paper examines the stratal geometries and facies stacking patterns associated with forced regressions around fault-propagation folds in extensional and compressional settings. Case studies are documented from: (i) the Miocene of the Suez rift and (ii) the Eocene of the Ainsa piggyback basin, Pyrenees. Despite the different tectonic settings, the stratal geometries and facies stacking patterns are remarkably similar. Distinctive sharp-based shoreface sandstones, formed as a result of forced regression, were deposited around growth anticlines. The forced regressive shoreface sandstones ‘shale-out’ rapidly basinward away from the growth anticlines and sit abruptly within offshore mudstones of highstand (HST) and transgressive (TST) systems tracts along the flanks of the growth anticlines. As fold amplification proceeded, older sandbodies were rotated to dip more steeply, and there is commonly a 2–5° angular difference between successive forced regressive sandbodies. This progressive tilting, coupled with marine erosion during relative sea-level fall has completely removed HST and TST deposits near anticline crets, and led to vertical amalgamation of individual forced regressive sandbodies. The resulting stratal geometries clearly result from the tectonic enhancement of forced regression.

Abstract Six distinctive tectonic episodes punctuate the stratigraphic record of the Gulf of Suez area. These episodes include the Pan-African event (late Proterozoic), which resulted in the development of the continental lithosphere of the area, a Cambrian extensional event, the Hercynian event (late Paleozoic), the Neo-Tethyan rift event (Jurassic), the Syrian Arc event (Late Cretaceous-early Tertiary) and the Gulf of Suez rift event (Oligocene[?]-Miocene). The structural fabrics imparted to the continental crust during the late Proterozoic and Cambrian appear to have played an important role in controlling the subsequent structural development of the Gulf of Suez area. The first evidence of Tertiary rifting that led to the present-day expression of the Gulf of Suez is manifest by Oligocene-Miocene basaltic volcanism and in poorly age-constrained, continental to shallow-marine clastics of the Abu Zenima and Nukhul formations. The Nukhul Formation was deposited over much of the present-day extent of the rift basin, suggesting that subsequent extension experienced by the crust was constrained to the initial area of deformation. Subsidence during the initial phase of extension was slow. Accelerated subsidence and extension is recorded in the deep-marine lithologies of the Rudeis Formation. This subsidence was disrupted midway through the deposition of the Rudeis Formation by the "mid-Rudeis" event, which resulted in the structural reorganization of the rift. This event correlates roughly in time with the onset of significant motion on the Dead Sea wrench system and marks the progressive abandonment of the Gulf of Suez as a site of active extension. After the mid-Rudeis event, variable and reduced tectonic subsidence rates prevailed in the gulf. The onset of significant evaporite deposition is recorded in the Belayim Formation, and evaporites subsequently become the major lithology of the South Gharib and Zeit formations as tectonic subsidence diminishes and basin restriction increases. Open-marine conditions and a change from dominantly Mediterranean to Indo-Pacific fauna took place in the Pliocene as a link was established to the Indian Ocean through continued extension in the Red Sea. Four distinct fault populations are documented in the rift and show varying amounts of both strike-slip and dip-slip motion, depending on their orientation relative to the principal direction of extension. The major faults establish domains in their dip direction, subdividing the Gulf of Suez rift into three major structural subbasins with alternating structural asymmetry along the axis of the rift. Extension increases along the axis of the rift from northwest to southeast. Associated with this increase are increases in fault-block dip, the number of faults with large throw, and geothermal gradient. Fault-block size decreases with increasing extension to the south along the rift axis.