Qatar Fm

Q.P.C. Well Dukhan No. 28, lat. 25°17’12” N, long. 50°48’46” E, elevation 32 m (106 ft), completed 1.5.1952, between drilled depths 1903 and 1990 m (6245 and 6529 ft). The formation takes its name from the Qatar Peninsula, since it contains the first commercial oil reservoir discovered in that country. First named by W. Sugden, 1953 in an unpublished report.

Synonym: None. (The A, B, C and upper, anhydrite, unit of the D Member of the Arab Formation, R.W. Powers et al., 1966).

Reference Section:

Top. 1. Limestone, light brown, varying from fine-grained, partly dolomitic and compact to a dolomitised and porous pellety limestone. 11 m (36 ft). 2. Anhydrite, white or light grey, with frequent stringers of brown dolomite near the top and bottom. 12 m (41 ft). 3. Limestone, brown, pellety and dolomitic, and dolomite, brown, porous. 5 m (17 ft). 4. Anhydrite, grey, massive, dolomitic near the top and bottom. 15 m (51 ft). 5. Limestone, grey-brown and brown. 20 ft of dolomitic, anhydritic limestone is underlain by some 40 ft of pellet grainstone and packstone interbedded with lime mudstones. These pass down into a basal oolitic grainstone. 25 m (83 ft). 6. Anhydritic, light brown or light grey, with a 4 ft bed of anhydritic dolomite near the bottom. 17 m (56 ft). Bottom. Its thickness is 87 m (284 ft).

The three limestone members of the Qatar Formation can be correlated with the A, B, and C Reservoirs of the Arab Formation of Saudi Arabia (R.W. Powers, 1968). In Qatar these members are informally named the Number 1, Number 2 and Number 3 Limestone from top to bottom. No name has been applied to the anhydrite members which separate the limestones.

In 1. Salpingoporella annulata Carozzi, Favreina salevensis (Parejas). In 3. F. salevensis. In 5. F. salevensis, S. annulata, Trocholina palastiniensis Henson, Kurnubia jurassica (Henson), Nautiloculina oolithica Mohler, Cerithium ursicinum de Loriol, Helicryptus cf. pusilus (Roemer), Retusa pellati Cossman, Ovacteonina pilleti (de Loriol), Isocyprina boonei Cossman

The equivalent of the Qatar Formation can be traced in the subsurface of large areas of Saudi Arabia, where it includes important oil reservoirs. The lowest member, the number 3 Limestone, was the first commercial oil producing reservoir to be discovered in Qatar.

The combined Qatar and Fahahil Formations of Qatar are the lateral equivalents of the Arab Fm of Saudi Arabia. The Fahahil Fm (No. 4 Limestone) has also been included with the overlying cyclical carbonate-anhydrite development in the offshore Qatar area. The name Qatar Fm has here been erroneously applied instead of the synonymous, earlier published name Arab Fm.

The practice of including all four “Arab Zone” limestones within one formation has many facts to recommend it. It is not customary in onshore Qatar for historical reasons and also because it was believed that the contact of the Fahahil and Qatar Formations marks a fundamental change from continuous carbonate deposition to the later, cyclical, anhydrite-limestone regime. This fact becomes more obvious to the east of Qatar, where it is often impossible to distinguish the contact of the Fahahil Fm with the underlying Darb Fm. The base of the Qatar Fm can still be recognized in such cases, as the base of the lowest significant anhydrite development.

The Number 1, Number 2 and Number 3 Limestones were assigned the names Jaleha Member, Juh Member and Umm Bab Member respectively. These names have never been published nor have they been applied locally. They are considered to be redundant.