Southern shoulder of Urals Trough: additional petroleum potential
In 1970-1980s, active exploration and prospecting works in the northern flank of the Caspian depression and in the Urals trough resulted in discovery of large oil and gas condensate fields Karachaganak and Orenburgsky, and a number of oil and gas fields having small size and reserves. However, the zone of the Urals trough’s southern flank closure appeared to be underexplored in terms of both seismic studies and deep drilling. This may have been due to the USSR breakdown, and the border sections of two administrative zones remained unexplored. After drilling two deep wells in Koblanky and Shirak structures, geological exploration conducted in 2008-2012 within the Koblandy-Tamdinsky swell and Aktyubinsky zone of dislocations allow reassessing petroleum potential of the region. The author presents the results of seismic works in the Shirak area and lithofacies characteristics of ШР-1 well column in accordance with the results of core studies; the well penetrated the Palaeozoic sedimentary sequence. According to well logging and mud logging data, four structural and formational sequences interesting in terms of oil and gas occurrence are identified in the section. In accordance with the formation microimager (FMI) and core analysis data, high fracture and good reservoir quality are typical of the sandstones. In the course of drilling, high gas indications were reported in them (up to 100 % of total gas). By the example of the Shirak area, petroleum potential of the Kazakhstan sector of the trough is discussed. The author has identified the new Azir structure in the Palaeozoic sedimentary sequence, which may become the priority exploration target in this region