Velocity Modelling and Depth Conversion Uncertainty Mitigation in GS327 Oil Field, in Gulf of Suez Basin

Abstract The Gulf of Suez rift initiated in the Late Oligocene, probably propagating northwards, and intersecting a major east-west structural boundary of Late Eocene age at the latitude of Suez City. North of Suez, extension was more diffuse but mostly focused on the Manzala rift that is presently buried beneath the Nile Delta. Earliest syn-rift, mainly continental sediments (Chattian-Aquitanian) consisted of red beds containing minor basalts. Marine Oligocene strata are presently only proven from the southernmost Gulf, at the juncture with the northern Red Sea. By the Aquitanian, a shallow to marginal marine environment prevailed in most of the rift. The prolonged Burdigalian sea-level rise enabled marine waters to flow freely between the Mediterranean Sea and the Gulf of Suez, resulting in deposition of thick Globigerina shales and deep-water carbonates. During the Langhian and early Serravallian, rapid eustatic sea-level changes resulted in pronounced facies changes within the rift. During the late Serravallian there was a significant fall in sea-levels. The Mediterranean water connection was either completely or intermittently blocked, leading to deposition of evaporites in the central and southern Gulf subbasins. Thick halite sections accumulated in the Late Miocene, and later loading resulted in the formation of salt diapirs and salt walls. Normal marine conditions were re-established during the Pliocene, but waters were then provided by the Red Sea – Gulf of Aden connection to the Indian Ocean, and a permanent land-barrier separated the Gulf of Suez from the Mediterranean. Analysis of fault geometries, fault kinematics and sedimentation patterns indicate that rift-normal extension predominated throughout the Oligocene to Early Middle Miocene evolution of the rift. In the Middle Miocene, the 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 across the Gulf of Suez and a clockwise rotation of stress fields in Sinai. During the Late Pleistocene, the intra-Gulf of Suez extension direction rotated counter-clockwise to N15°E.As common in GOS fields, the zone of interest is below SGH-Evapraites stratigraphic section and the trapping mechanism is structural trap, and the main producing reservoirs are Miocene clastics reservoirs, the late Cenozoic Gulf of Suez basin is one of the best exposed and studied examples of a continental rift. Several recent models of rift geometry and evolution have relied heavily on data and concepts derived here (e.g., Bosworth, 1994; Bosence, 1998). The Gulf of Suez was the first rift basin in which large-scale, along-axis segmentation into subbasins by accommodation zones was clearly recognised (Moustafa, 1976), has served as one of the premier models for Miocene carbonate platform development (James et al., 1988; Burchette, 1988; Cross et al., 1998), and is recognised as a superb example of the interplay between sedimentation and extensional fault development (Gawthorpe et al., 1997; Sharp et al., 2000 a, b). Recent studies evaluated the relative roles of hard- and soft-transfer in intra-basin fault linkage, and the significance of pre-rift structures in controlling the style of linkage (McClay et al., 1998; McClay and Khalil, 1998; Younes and McClay, 1998). The Gulf of Suez is also one of the best examples of the integration of outcrop and subsurface data to enhance hydrocarbon exploration and exploitation (Gawthorpe et al., 1990; Patton et al., 1994; Sharp et al., 2000 a, b). Despite these positive and important developments, we believe that two issues have not been satisfactorily addressed. First, no comprehensive analysis and integration of all areas of the rift has been published, in spite of abundant new stratigraphic and structural data for parts of the basin (e.g., Richardson and Arthur, 1988; Hughes et al., 1992; Patton et al., 1994; Bosworth, 1995; McClay et al., 1998). Specifically, the major differences in the tectonostratigraphic histories of the southern and central rift basins have never been adequately addressed. Second, despite the use of many aspects of outcrop and subsurface geology of this basin as a model for other rift settings, this extrapolation has not considered all the dominant factors that controlled overall evolution of the Gulf. Some of these factors, such as the activation of the Aqaba transform boundary, are actually specific to the geographical and temporal position of the basin, and may make some aspects of this rift unsuitable for a general model. Structurally The NW-trending Gulf of Suez is about 300 km long, and the complete rift basin, including the on-shore border fault systems, varies in width from about 50 km at its northern end to about 90 km at its southern end where it merges with the Red Sea, this has been traditionally referred to as the "Clysmic" rift, after the ancient Roman settlement of Clysma that occupied the present site of the city of Suez (Hume, 1921; Robson, 1971). The rift is characterised by a zigzag fault pattern, composed of N-S to NNE-SSW, E-W and NW-SE striking extensional fault systems both at the rift borders and within the rift basins (Garfunkel and Bartov, 1977; Jarrige et al., 1986; Moretti and Chénet, 1987; Colletta et al., 1988; Meshref, 1990; Moustafa, 1993; Patton et al., 1994; Schutz, 1994; Bosworth, 1995; Montenat et al., 1998; McClay et al., 1998). The field of study GS327 locates in the central of Gulf of Suez rift basin; it is one f different oil-producing fields in this basin fig (2). In 2020 a drilling campaign have been done by Gulf of Suez petroleum company, which included exploration, appraisal, and development wells, achieved excellent results across all activities. The campaign's success ratio was notably high, that leading to a substantial addition to the company’s reserves and contributing significantly to overall production growth.