In 1939 the largest oil field in Qatar was discovered by Iraq Petroleum Company. Dukhan field is located in the western part of Qatar. The 44 mi long Dukhan anticline trends north to southeast with an average width 5 mi. The field currently produces from three reservoirs: Uwinat, Arab C, and Arab D. The four dome culmination forms the major divisions; these are Khatiyah, Fahahil, Jaleha, and Dyab as shown in the figure below. (Stephens et al, 2009)
The Arab Formation constitute of four members named alphabetically Arab A, Arab B, Arab C and Arab D. Each of these members is separated by anhydrite layer which forms seals for the hydrocarbons in the producing reservoirs. Among the four subdivisions, Arab C and Arab D are of greater importance. It is not surprising that regional fields like Ghawar and Berri in Saudi Arabia produce from these two formations. The Arab C reservoir is 70 to 100 feet thick and it occurs between anhydrite intervals. The reservoir is capped by the Middle Qatar anhydrite which forms the seal and the most restricted condition for the progradational succession. The Arab C and D intervals have been deposited on a low angle carbonate ramp and because of that most of the stratigraphic surfaces are mostly sub parallel across the field. Within Dukhan field, 23 environments of deposition types can be attributed to five facies. (Stephens et al, 2009)
Outer-Mid Ramp Facies: These facies represent the deepest water environment which is only found in the lower Arab D. The two EODs in the Outer-Mid Ramp facies are the Distal Ramp which is associated with deeper water and exhibit little to no porosity In contrast to the Middle Ramp which is often micro porous with over 10% porosity and less than a milidarcy permeability . (Stephens et al, 2009) Ramp Crest Facies: These facies is composed of shallow-water high-energy EODs like Distal Gran Flat, Shoal, and Biostome/ Bioherm. Ramp Crest Facies are restricted to the middle portion of Arab D....
Cited: Stephens, N., Puls, D., Albotrous, H., Al-Ansi, H., and Al-Tamimi,F.,2009, Sequence Stratigraphic Framework of the Arab Formation Reservoirs, Dukhan Field, Qatar: International Petroleum Technology Conference, Doha, Qatar, 7-9 Dec 2009, IPTC 13631, P 1-12
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