Petroleum systems of the Timan–Pechora sedimentary basin (including the offshore Pechora Sea)

Abstract

The sedimentary cover of the Timan–Pechora petroleum basin records several phases of tectonic activity in the area: rifting and incipient ocean opening; a passive margin setting with intracontinental rifts and aulacogen, an intrashelf depression and inversion swells; collisional orogeny with the development of a foredeep; vertical isostatic movements associated with the development of a late syneclise and renewed orogenic movements. The deposition of source and reservoir facies occurred during the divergent phases of the tectogenesis (Ordovician–Tournaisain). The formations that accumulated during a convergent tectonic regime (Visean–Triassic) comprise mostly reservoir rocks. Because of thermal maturity of organic matter, the sedimentary rocks in the area span the broad range of oil and gas generation zones. The identified hydrocarbon kitchen areas were developed in different geodynamic settings: in the east of a passive margin, within rift-related troughs, and in the Ural foredeep. The first two were more liquids-prone fairways, with predominant oil and condensate generation, whereas the latter was largely a gas- and gas-condensate-generative source. The change of structural settings, the extension of oil and gas kitchens, variation of the regional dip, and recurrent faulting caused both the formation of new play fairways and the destruction of existing ones. The new oil-prone fairways that formed synchronously with the onset of intense oil generation might have later evolved into oil- and gas-prone fairways or even oil-, gas-, condensate-prone fairways at the expense of the gas component of petroleum systems, which is thought to increase as a source rock generating mostly oil became capable of generating oil, gas, and condensate. In addition, tectonically active zones may provide the most favorable conditions for the formation of gas and gas-condensate accumulations due to a decrease in formation pressure and expulsion of a free gas phase or due to its updip migration from great depths. Analysis of hydrocarbon generation and accumulation conditions provided insights into the evolution of a petroleum system of each play and transformation of a sedimentary basin into a petroleum basin. The study revealed the areal distribution patterns for oil and gas plays. The long-lived oil-prone plays are confined to a series of paleouplifts within the Izhma–Pechora and Khoreiver tectonically stable blocks. Oil-, gas-, and condensate-prone plays are associated with a tectonically active setting (Pechora–Kolva aulacogen and Timan block), whereas mostly gas- and condensate-prone plays are found within the Ural foredeep.