The Optimization of Gas/ Steam Injection Using Numerical Simulation

Simultaneous injection of heated exhaust gas (mainly CO2 and N2) and steam is one of EOR methods used in Russia for heavy oil recovery. In this case the energy released by gas-steam generator is used more efficiently compared to pure steam injection. Another benefit of using this EOR method is an additional reduction of the oil viscosity caused by exhaust gases solution in oil. This technology is particularly efficient when used for the small reservoirs being developed by a single well. Practical implementation of this technology is not always successful. One of the main reasons of failure is that parameters of the injected gas-steam mixture are far from being optimal. This study presents results of numerical simulation of the gas-steam injection process, so called huff-and-puff injection. The aim of the modeling was to estimate an influence of reservoir geometry and heterogeneity as well as huff-and-puff injection parameters on oil recovery factor. The reservoir's and oil properties were typical for Volga-Ural oil province of Russia. The radial geometry was used in numerical simulation with model radius equal to 400 meters. The main results of this study can be summarized as follows: heavy oil reservoir development based on primary depletion is not profitable; EOR methods are needed;efficiency of the huff-and-puff gas-steam injection increases with oil column thickness increasethere is optimal time for well being shut-in after gas-steam injection, this time is dependant on volume of injected energy;the reservoir heterogeneity plays significant role in thermal oil recovery process.