Fluid Geodynamics of Deeply Buried Zones of Oil and Gas Accumulation in Sedimentary Basins

Abstract

Abstract —We substantiate certain ideas concerning the key role of fluid-geodynamic processes in the evolvement of hydrocarbon accumulations at great depths, in the Earth’s crust. The presented geodynamic model of oil and gas accumulation is based on updated ideas of the structure of the Earth’s tectosphere, which includes plate, preplate, and folded complexes, and the model makes clearer the spatial scale of the organic matter transformation into hydrocarbons of the oil series. In the bottom layers of the Earth’s crust, we predict the existence of a special stagnation type of water-drive systems with the following distinguishing features: (a) different scales of manifestation, from local to regional; (b) a limited nature of processes of water exchange with the external environment; (c) absence of persistent drainage horizons (beds and interbeds); (d) alignment of hydrodynamic potentials in terms of depths and laterals; and (e) increasing importance of lithohydrochemical and organic-chemistry factors in the development of the void space of the fluid host medium. In their inner space, systems with difficult water exchange can exercise control over the evolvement and preservation of autoclave hydrocarbon systems for a long time, the key feature of the autoclave systems being spatial coincidence (localization) of the processes of oil and gas generation and accumulation. We assume that, in the settings of all-round compression, hydrodynamic instability, and no drainage, occurrence of productive zones is controlled by foci of low pore (reservoir) pressures rather than by local hypsometric highs. We present results of prediction of the development of water-drive stagnation systems occurring in the subsalt deposits of the Caspian depression within the unpenetrated areas of the subsalt profile. For the sedimentary cover at large (and ultralarge) depths, a prediction of reservoir pressures was made, which can be regarded as a necessary component in any prediction of oil and gas potential, since it makes it possible to contour some new (previously unknown) industrially significant zones of hydrocarbon accumulation.