This work is devoted to CO2 Huff-n-Puff studies on heavy oil. Oil recovery for heavy oil reservoirs is sufficiently small in comparison with conventional reservoirs, and, due to the physical limitation of oil flow through porous media, a strong need for better understanding of tertiary recovery mechanisms of heavy oil exists. Notwithstanding that the idea of Huff-n-Puff gas injection technology for enhanced oil recovery has existed for dozens of years, there is still no any precise methodology for evaluating the applicability and efficiency of this technology in heavy oil reservoirs. Oil recovery factor is a question of vital importance for heavy oil reservoirs. In this work, we repeated Huff-n-Puff tests more than three times at five distinct pressure points to evaluate the applicability and efficiency of CO2 Huff-n-Puff injection to the heavy oil reservoirs. Additionally, the most critical factor that affects oil recovery in gas injection operation is the condition of miscibility. Experimental data allowed to distinguish the mixing zone of the light fractions of studied heavy oil samples. The experimental results showed that the pressure increase in the Huff-n-Puff injection process does not affect the oil recovery when the injection pressure stays between miscibility pressure of light components of oil and minimum miscibility pressure. It was detected that permeability decreases after Huff-n-Puff CO2 tests.
The paper discusses two technologies for implementation of gas methods used in oil field development. -alternating gas-water injection and water-gas stimulation in which combined injection of displacement agents (gas and water) is used.OJSC "RITEK" is successfully implementing the enhanced oil recovery by means of water-gas injection into the formation.Water-gas stimulation is stimulation of the oil-bearing formation in which oil is displaced by a maximum possible wide frontal gas fringe followed by water injection. Gas flood ensures high displacement efficiency, while water flood ensures high sweep factor.Two approaches to water-gas stimulation can be distinguished depending on the injection method of displacing agents, which can be either alternating or combined.Alternating water-gas injection turns out to be economic viable when applied in small fields if deposits of high pressure natural gas and oil are close to each other. It allows reduction of compression stages in the procedure and, as a result capital and operating costs.To work out the alternating injection technology we have chosen the western dome of the Vostochno-Perevalnoye field since the noncommercial gas deposit in the Cenomanian bed has been found on its territory. Gas pressure from the deposit is insufficient for its direct injection into the formation, thus gas from the gas well is pumped to the specially OJSC"RITEK" developed booster unit operating under the principle of a single-stage "compressor with hydraulic seal" The principal lay-out drawing of the Vostochno-Perevalnoye western dome construction for application of water-gas technology is shown in Figure 1. Figure 1 -The principal lay-out drawing of the Vostochno-Perevalnoye western dome construction for application of water-gas technology (alternating water and gas injection)
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