Petroleum Geologic Characteristics and Exploration Fields in the Eastern Margin of Pre-Caspian Basin

The Pre-Caspian Basin experienced the geological history from the Late Paleozoic craton margin-Mesozoic to Cenozoic depression-superimposed Ural Foreland, and has a long exploration history. It is the most important oil and gas producing area of Kazakhstan and a large number of oil and gas fields have been discovered in it. Major oil and gas discoveries are located in the clastic rocks and platform carbonates below the Lower Permian salt domes. The Aktobin Uplift is developed between the central depression of the Pre-Caspian Basin and the Ural Ocean. The uplift to the Ural Ocean side is what is currently called the eastern edge of the Pre-Caspian Sea. It is between the platform and the lagoon, with the deposits of carbonate rocks and mudstones. In the Carboniferous, four sets of carbonate rocks were developed, including the KT-I/II/III and D3. The source rocks of the eastern margin are mainly the Devonian, Carboniferous and Lower Permian are the main source rocks in the region. The oil and gas is distributed in the Carboniferous carbonate reservoir, and the major exploration layers are the Carboniferous KT-I and KT-II layers. The caprocks are mainly the Lower Permian subsalt gypsum rock and interlayer tight layers. It constitutes a good combination of source rock, reservoir, and caprock.