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Development of Gas/Oil Miscibility in Water and Gas Injection

Development of Gas/Oil Miscibility in Water and Gas Injection . Tara LaForce, and Franklin M. Orr, Jr. (Stanford) Second Nature Sample Poster Dec. 3, 2008. Abstract.

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Development of Gas/Oil Miscibility in Water and Gas Injection

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  1. Development of Gas/Oil Miscibility in Water and Gas Injection Tara LaForce, and Franklin M. Orr, Jr. (Stanford) Second Nature Sample Poster Dec. 3, 2008

  2. Abstract • We use analytical solutions for a one-dimensional model to study water and gas injection strategies into an oil reservoir. The model accounts for three-phase flow of four components through porous rocks and uses a cubic equation of state to model gas/oil phase behavior. In oil reservoirs super-critical CO2 may generate a multi-contact miscible displacement of hydrocarbons, so both miscible and immiscible injection of CO2 is studied. We consider the implications of using CO2 in order to improve oil recovery, and find that this is often a competing goal with storing CO2 far from production wells. –Mixtures which create efficient miscible displacements result in earlier breakthrough of injected CO2, while mixtures that have delayed arrival of CO2 in production wells have less favorable oil recovery.

  3. Background • Depleted oil reservoirs are excellent candidates for CO2 storage. • When CO2 is stored in oil reservoirs it is of critical importance to maximize the reservoir volume containing CO2. • CO2 can behave as a miscible gas in many reservoirs, which means displacement efficiency of hydrocarbons is optimal • Injecting water simultaneously with CO2 in aquifers has been shown to increase the volume of CO2 that can be stored as a trapped phase because injected water inhibits the ability of CO2 to rise under buoyancy forces (SPE109905). • In an oil reservoir, a similar result is likely. Moreover, if there are active wells in the reservoir then injection of water to trap CO2 will prevent excessive gas cycling. • But can we store CO2 securely and improve oil recovery at once?

  4. Displacement Efficiency • Can be thought of as flow along a streamline in the reservoir • This is a 1D problem 1 Gas Saturation 0

  5. CO2 Injection in 2D and 3D • The drawback in injecting CO2 alone is that the sweep efficiency is poor • By injecting water and gas (WAG) simultaneously, it is possible to get good sweep efficiency AND optimal displacement efficiency … or is it?

  6. Vaporizing Gas Drive Phase Behavior Phase behavior in full system at MMP (only three-phase regions are shown) Phase behavior in ternary subsystems at MMP (three-phase region shown in light blue) • Peng-Robinson EOS is used to model the gas/oil phase behavior • Henry’s Law is used to model hydrocarbon/aqueous phase partitioning • Water does not partition into gas or oil

  7. shock • rarefaction Vaporizing Gas Drive at MMP • Injection of CO2 into a mixture of C3 and C16 results in a miscible vaporizing gas drive. • Water/CO2 mixtures C-E behave like miscible gas drives, but A and B are immiscible. • Injection of water/CO2 mixtures have miscible displacements as long as injected CO2, is more mobile than water and flows ahead of injected water. • Mobility of the CO2 is determined by the relative permeabilities of the water and CO2 phases. E E Injection Conditions D C D C B A B A Initial Condition • Volume of CO2 injected: E=100%D=25%C=19.84%B=15%A=0%

  8. shock • rarefaction Tertiary Vaporizing Gas Drive Water in the initial condition causes the miscible front to accelerate: • If no water is present initially then the MGF = 19.84% • If 12% residual water is present initially then the MGF = 20.77% • If 25% water is present initially then the MGF is about 22.17% JC = 75% water xD/tD Initial Conditions

  9. Results and Conclusions • In SWAG displacements a minimum gas fraction of CO2 must be injected to create a miscible gas bank • Miscible displacements that have optimal displacement efficiency result in an unstable displacement and early gas breakthrough • Relative permeabilities determine whether miscibility will be achieved • The failure to achieve miscibility will allow the design for injection strategies that will effectively trap the CO2 in the reservoir • A high fraction of CO2 can be injected in a water-flooded reservoir without creating a fast-moving miscible gas bank that will quickly reach production wells • This represents directly competing goals between optimizing oil recovery with a miscible gas flood and storing the CO2 far from production wells

  10. Many Thanks To: • Grantham Institute for Climate Change at Imperial College London • Shell Grand Challenge on Clean Fossil Fuels • UK Engineering and Physical Science Research Council

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