Mutual Dynamics of Heat Dissipation and Oil Displacement Fronts during In-Situ Oil Combustion. One-Dimensional Simulation

Abstract

One-dimensional axis-symmetrical and plane-symmetrical problem of propagation of the combustion and displacement fronts in oil-containing layer in situ has been considered numerically. Two combustible components, viz. liquid (oil) and solid (kerogen, oil sorbate), were considered. The influence of the blast rate, liquid component viscosity, oxygen concentration in blasted air and heat losses (the width of the oil-containing layer) on the dynamics of the heat dissipation and displacement fronts is investigated. In the cylindrical system the oxidizer flow to the combustion front is reducing over time; and the shift-down of the maximum temperature from the solid combustion front to the oil displacement front takes place (the combustion front “jump”). The time of the “jump” may vary from tenths to hundreds of days and the distance of the shift, – up to 10 or more meters, depending on the parameters of the system. After the “jump”, the combustion rate and maximum temperature continue to deteriorate and after the period of time close to the time lapse before the “jump” the chemical reaction ceases. Herewith the transition of combustion to the liquid phase after the “jump” doesn’t influence notably on oils displacement front speed. The time of the “jump”, as well as the velocity of the mutual combustion (maximum temperature) front and displacement front removal nearly linearly depends on incoming gas blast rate and non-linearly – on oil viscosity. When viscosity is low, the displacement front rapidly runs away from the combustion front, time of the “jump” retards and the distance between the fronts at the instance of the “jump” may reach 10 m or more. The oxygen concentration in the gas being blasted influences significantly on the mutual dynamics of the combustion and displacement fronts since combustion front velocity is proportional to oxygen concentration and displacement front velocity is independent on it. Oxygen enrichment of the gas being blasted just after the “jump” may help localize the area of heat release (combustion) near the oil displacement front. The mentioned manipulation may be utilized for sustainability control of the displacement front. However for its practical implementation it is necessary to have information on concentration and temperature fields inside the layer, which may be obtained from indirect data and via modeling. The results of investigation may be utilized for development of technical projects of oil recovery via in-situ combustion.