thinkpool

Structure and Oil-Gas Prospects of Sub-Salt Complexes in South Emba Region of Peri-Caspian Depression V. M. Brenner, A. B. Sagingaliyev (Neftegazovaya Geologiya i Geofizika, no. 2, p. 8–12, 1982) Mesozoic sediments at the crests of salt domes have long been played for oil. Sediments beneath the Permian salt are now being targeted. Large sub-salt highs are being mapped by common depth point seismic surveys. The sub-salt, pre-Kungur section is divided into three seismostratigraphic complexes: pre-Upper Devonian (D1-2), Upper Devonian-Lower Carboniferous (D3-C1), and Middle Carboniferous-Lower Permian (C2-P1). The boundaries between these complexes are Φ (top of basement), Π3, Π2, and Π1 (top of pre-Kungur). Predominantly clastic rocks of the D1-2 complex occupy the central (sag on the surface of the basement) part of the region. See Fig. 1. These are bounded on the north by the flank of the Biikzhal basement high and on the south by a linear uplifted zone at the boundary of the Peri-Caspian depression and Turan platform. The sediments of the D3-C1 complex are the thickest (6.5-7.0 km) in the crest area of the South Emba high. On the north border of the North Ustyurt downwarp their thickness is 2.3-3.0 km. To the north with plunge of the surface of the Paleozoics and rise of the basement surface, this complex thins to 2.0-1.0 km. The sediments of C2-P1 are only 0.2-0.6 km thick over a large part of the region. The Primor-Tengiz block (A in Fig. 1) is very favorable for the carbonate sediments of C1-D3. See Fig. 2. Commercial oil has already been found here in the Tazhigali and Tengiz areas. These fields have not yet been outlined. Clastic sediments C1-D3 on the South Emba high are favorable in the crest area in the Tortay field, on the proximal flank on the Tabynay-Karaoy and Airshagyl steps, and on the south periphery on the Saztyube and Pioner highs. In the structurally high areas the carbonate C3-C1 plays are reefs that have been mapped by seismics. These now need to be drilled. By analogy with the Kenkiyak-Karatyube zone, pools can be present in the zone of greater thickness of the clastic sediments P1-C2 on the South Emba high in combination and stratigraphic traps. The commercial Shol’kra oil field is on this play. A large part of the South Emba region is thus very favorable for exploration of the sub-salt Paleozoics. © Petroleum Geology: A digest of Russian literature on Petroleum Geology, 2013