Theoretical substantiation of application of the hydrocarbon accumulation prospecting technique in Western Siberia based on the study of water-gas equilibria

Abstract

Computer simulation of physicochemical equilibria and evasion-invasion processes in the water-gas system enables modeling gas saturation degree variability and the physical nature of gaseous diffusion redistribution at the hydrocarbon accumulation – formation waters interface and in the transition zone from hydrocarbon accumulation to the peripheral waters. Aquifers with waters characterized by low (< 0.2) to maximum saturation (0.8-1.0) with gases have been established within Cretaceous, Jurassic and Paleozoic deposits of the West Siberian sedimentary basin (WSSB), along with an increase in the saturation degree of formation waters with gases as the occurrence depth of reservoir intervals increases, and a relationship between gas saturation of formation waters and their total gas saturation value. All waters with total gas saturation exceeding 1.8 L/L become ultimately saturated with gases (Kg = 1.0), providing thereby theoretical prerequisites for the formation of hydrocarbon accumulations. The zone of Kg values spanning from 0.8 to 1.0 is associated with major gas condensate accumulations, while less saturated waters – with oil accumulations. The simulation results allow to assess the current state of the petroleum system of the West Siberian sedimentary basin, its part or a separate horizon within its limits, and to substantiate forecasts of its oil and gas potential at regional, zonal or local levels. The application of modeling techniques to water-gas equilibrium enables significant improvement of the reliability of oil and gas reserves assessment and largely contributes to the solution of problems with respect to searches of skipped accumulations in multi-reservoir fields during their further exploration.