OIL AND GAS FIELDS

OIL AND GAS FIELDS, areas of sedimentary layers, rarer crystalline crust rocks containing one or several industrial oil‑and‑gas reservoirs. There are geological and recoverable reserves. By contiguity to geol. structures, there are structural (arched), lithological and reef reservoirs. By presence of free gas and condensate, fields are divided into oil, oil‑gas and gasoil fields. By the size of recoverable reserves of oil, there are unique (over 300 million t), large (60—300), medium (15— 60), and small (up to 15 million t) oil fields. The largest quan‑tities of highly productive reserves are contained in the horizons of the Devonian Terrigenic Oil and Gas Bearing Complex within the South‑Tatar and Bashkir arches, in the Chekmagush‑Ufa Zone; the fields of the coal oil and gas bearing complex are developed within the Upper Kama Depression, the Birsk Saddle and the edge part of the Bashkortostan Arch, they are confined to the areas of sandstone, terrigenic‑carbonate and mainly to carbonate layers (Mrakovskaya Depression, the western slope of the Yuryuzano‑Sylvenskaya Depression and the southern part of the Shikhano‑Ishimbayskaya Saddle); the Lower Permian Oil and Gas Bearing Complex is composed of terrigenic‑carbonate and sedimentary rocks within the Pre‑Urals Foreland Basin, the Belskaya Depression and the Shikhano‑Ishimbayskaya Saddle; they are also developed in the carbonate and sedimentary strata of the reef zone; in the platform part of the Republic — everywhere. The first oil field in the RB was discovered in 1932 — the Ishimbay Oil Field. Arlanskoye and Tuymazinskoye oil fields are unique; Shkapovskoye Oil Field is large; Chetyrmanskoye, Mancharovskoye, Serafimovskoye oil fields are medium‑sized, etc.