Safety issues in the exploitation of sedimentary basins of hydrocarbon deposits

Numerical simulation of fluid motion in the formation of hydrocarbon deposits allowed to identify complex self-oscillating modes of this process. To describe the motion of liquids and gases in a porous medium, filtration equations are used under the assumption of the feasibility of Darcy's law in the field of gravity, non-mixing phases (for example, gas-water), isothermicity and neglect of capillary forces. It is a complex system of nonlinear partial differential equations. According to one of the variables – pressure – it has properties close to the equations of parabolic type, on the other – saturation – of hyperbolic properties, including – formation of discontinuity surfaces – saturation jumps. The area in which the system is solved, usually has a high degree of heterogeneity, consists of layers with different reservoir properties (porosity, permeability), faults, depositional lithologic discontinuities and other features that complicate as the filtration processes and their numerical modeling. To study such problems, the support operator method provides great opportunities, allowing the use of unstructured grid with cells, the sizes of which may differ by several orders of magnitude. The numerical study by this method revealed that in the problems corresponding to the processes of migration of hydrocarbons in the formation of deposits, self-oscillating gravitational reverse regimes can occur. The characteristic cycle is as follows: the pressure of accumulated gas under a poorly permeable area at some point in time may exceed a critical value. Then there is a gas breakthrough, and if this critical pressure is below the rock strength limit, then the breakthrough does not occur as a result of cracks, but due to the rapid movement of the gas through the site with poor collector properties due to filtration instability. The gas rushes up, the pressure in this area falls, there is a depression funnel, which causes a new influx of gas – until the next critical pressure.