Exploration for a Frontier Salt Basin, Oman159GeoArabia, Vol. 6, No. 2, 2001 Gulf PetroLink, Bahrain159Exploration for a Frontier Salt Basin in Southwest OmanMark F. Blood Phillips Petroleum CompanyABSTRACTAn undrilled Infracambrian-lower Paleozoic salt basin is interpreted as being present in the Dhofar area of southwest Oman. A re-evaluation of the existing seismic and gravity data indicated that the basin is located immediately north of a major NE-orientated basement feature known as the Ghudun-Khasfah High. The basin is centered in the southern part of the Al Hashman Block 36 and the northern part of Mudayy Block 38, both operated by Phillips. Studies conducted by Phillips suggest that the basin has a similar structural history and pre-Silurian stratigraphy to the known salt basins of Oman. New stratigraphically deeper Paleozoic and Infracambrian exploration plays that are proven in the other Oman salt basins are proposed for this undrilled basin. The new plays rely on an unproven Infracambrian Huqf source. Source and reservoir degradation through widespread post-Huqf deformation is possible, but structural modeling and seismic facies analysis, together with the detection of significant micro-seepage anomalies, suggest otherwise. In addition, the identification and gravity modeling of what appear to be salt features on seismic lines support the presence of Lower Cambrian salt swells and piercement structures. The salt features are believed to be age equivalent to the Ara salt section of the upper Huqf Supergroup present in the other salt basins. Phillips has named this potential salt basin the Ghudun Salt Basin.INTRODUCTIONA new regional tectonic model has been developed by Phillips (Webster, 2000), which allows for the development in central and southern Oman of Infracambrian salt basins that are considered to have evolved with similar structural and depositional histories. In the late 1980s and early 1990s, southwest Oman was believed to have been affected by Early Cambrian regional deformation due to the collision of two Precambrian continental blocks. The deformation resulted in what has been described as the Western Deformation Front (see Loosveld et al., 1996) that loosely delineated the western margin of prospectivity in Oman. Recent work by Phillips suggests that the deformation was likely to be of an intra-cratonic nature and to be much more localized than previously thought. As a result of the Phillips work, the prospectivity of southwest Oman has been upgraded.The paper focuses primarily on the two concessions (Block 36, Al Hashman; and Block 38, Mudayy) that Phillips operates in southwest Oman (Figure 1) in association with Maersk Oil and Gas and Berkley Petroleum. It attempts to demonstrate through a re-evaluation of the existing reprocessed seismic and gravity data the presence of a fourth, as yet undrilled, Infracambrian salt basin in this part of Oman. Several exploration plays are proposed for the new salt basin that are analogous to plays proven in the known salt basins of Oman.Blocks 36 and 38 have a combined area of approximately 36,000 sq km (8.5 million acres). Immediately to the west is the Republic of Yemen, to the north the Kingdom of Saudi Arabia and the Rub Al Khali Basin and to the east lies the prolific South Oman Salt Basin (SOSB). Separating the SOSB from Blocks 36 and 38 is a NE-trending linear basement feature known as the Ghudun-Khasfah High. The High is represented on gravity and seismic data as a positive anomaly and is one of several such features in Oman. As a structural high, it dates from the later stages of the formation of the Arabian Plate in the late Neoproterozoic (Webster, 2000). It has had a strong influence on the depositional history of the adjacent basins.Blood160136-86-50-250255075100125FAHUD SALT BASINGHABA SALT BASINSOUTH OMAN SALT BASINGHUDUNBlock 36Block 38SALT BASINHU QF HAU SH IUP LI FTOMAN MOUNTAINSGHUDUNK HASFA HHIGHSAUDI ARABIAUNITED ARAB EMIRATESGULF OF OMANRub Al Khali BasinMuscatARABIAN GULFSalalahIRAN0100kmTERTIARYANDSUNEINAHFOREDEEPS52E5456586026N22201824525456582622201824mgalsYEMENOil shows Dry holeFasad-1Ghudun-1Ahboot-1Al Hashman-1Block 36Block 38Figure 3Figure 4Figure 12Figure 11Figure 7Figure 9NFigure 1: Bouguer Gravity Map of Oman (after Ravaut and Warsi, 1977) showing the locations of Blocks 36 and 38.Exploration for a Frontier Salt Basin, Oman161Blocks 36 and 38 were formerly part of the Dhofar Concession that covered much of southern and southwestern Oman. This large area had previously been operated and explored by Cities Services Petroleum, BP, and Petroleum Development Oman (PDO) from the early 1950s to the early 1990s. In that time, however, only four wells were drilled in what are now Blocks 36 and 38 (see Figure 1 inset). Moreover, three of them were drilled in the late 1950s and early 1960s on either surface and/or gravity anomalies before the acquisition of modern seismic data.