Convection of two-phase fluid in a layered porous medium driven by the heat of magmatic dikes and sills

In order to quantify the rate of filtration of the liquid and gas phases of pore-water and hydrocarbon fluids, convection processes were explored in the framework of the two-dimensional problem of convective heat transfer, taking into account phase transitions under the influence of the heat of sheet igneous bodies. Various regimes of the convection of pore-water fluid were simulated. In the case of a homogeneous fluid (without boiling), regular convection cells are formed, showing periodicity with respect to flow velocity and temperature. When a sheet igneous body is emplaced near the surface, flow patterns and the evolution of the temperature field change dramatically owing to boiling of interstitial liquid. The cellular structure does not form, and heat advection is observed via an ascending flow of a gas or gas-liquid mixture in the form of a "mushroom" or a plume. The initial stage of heating of fluid-bearing rocks is accompanied by the generation of excess pressure below the lower contact of a sill. The lifetime of such anomalously high pressures is estimated for the watervapor system, where they may be higher than hydrostatic pressure by a factor of 1.5-1.8. Models including sills of finite extensions show the viability of mechanisms of long lateral fluid migration below impermeable igneous bodies toward discharge zones. The application of the results of modeling to oil- and gas-bearing sedimentary basins with flood basalt magmatism demonstrated that sheet intrusions played a significant role in the transformation of hydrocarbon matter and influenced the character of convection flows. Magmatic heat causes phase transitions of liquid hydrocarbons into gas phase in a country rock volume comparable with that of the igneous body (sill or dike).