3BackgroundLong term fate, how can you be sure that the CO2 stays underground?
4Field scale - The streamline method Permeability fieldInitial saturationPressure solveSL tracingSaturation along SLSaturation for the next time step
5Streamline method for CO2 transport Phases (3)Components (4)HydrocarbonAqueousSolidCO2OilWaterSalt+Hydrocarbon phaseAqueous phaseTodd&LongstaffFingering model for CO2 in oil
6Streamline method for CO2 transport Trapping modelPore-scale model matches experimental data.Kr is from Berea sandstone, which matches Oak (1990)’sexperiments.CO2/water system is weakly water-wet (Chiquet et al., 2007)contact angle (θ) = 65º.New trapping model (Juanes et al., 2006)
7Design of carbon dioxide storage Mobility ratio between carbon dioxide/brine mixture and formation brineMobility ratio between chase brine and carbon dioxide/brine mixture during chase brine injectionMobility ratio = 1.0fgiThe ratio of the mobility of injected brine and CO2 to the formation brine as a function of the injected CO2-phase volume fraction, fgi.
8Design of carbon dioxide storage 1D analysis: Numerical simulation vs. analytical solutionfgi = 0.5fgi = 0.85
9Design of carbon dioxide storage Mobile CO2 saturationZ170mX3200mY2280mTrapped CO2 saturationInjectorProducerSPE 10 reservoir model, 1,200,000 grid cells (60X220X85), 7.8 Mt CO2 injected.Two years after chase water injection for fgi=0.85.
10Design of carbon dioxide storage 3D simulation: Storage efficiency vs. trapping efficiencyTrapping efficiency =the fraction of the injected mass of CO2 that is either trapped or dissolvedStorage efficiency =the fraction of the reservoir pore volume filled with CO2The storage efficiency is highest for fgi = 0.85, which also requires minimum mass of chase brine to trap 95% of CO2.
11Design Criterion Inject CO2+brine where mobility ratio = 1.0 (fgi=0.85 in this example).Inject chase brine that is 25% of the initially injected CO2 mass.90-95% of the CO2 is trapped.
12Issues arising from field scale simulation Streamline-based simulator has been extended to model CO2 storage in aquifers and oil reservoir by incorporating a Todd-Longstaff model, equilibrium transfer between phases (dissolution) and rate-limited reaction;Trapping is an important mechanism to store CO2 as an immobile phase. Our study showed that WAG CO2 injection into aquifer can trap more than 90% of the CO2 injected;We have proposed a design strategy for CO2 storage in aquifers, in which CO2 and formation brine are injected simultaneously followed by chase brine.Streamline-based simulation combined with pore-scale network modeling can capture both the large-scale heterogeneity of the reservoir and the pore-scale effects of trapping.
13Future work Injection strategy design Require better experimental data, since the trapping model used has a significant impact on the results.Design of an injection strategy to maximize CO2 storage and oil recovery.
14CT ScanningA homogeneous sandpack was compressed and the porosity was determined via mass balance (Φ = 38,93).n-Heptane was injected; when no more brine was produced, another CT scan was performed at the irreducible water saturation, Swi.CO2 was injected again. Gas injection was stopped when no more liquid production was observed. Another CT scan was taken.30 pore volumes (PV) of brine were injected and a final CT scan was taken at the residual gas saturation Sgr .resolution 9 µm
15Sandpack at irreducible water saturation Brine – blueSand – redOil - orangeOil penetrates on average mainly into the largerpores as expected by capillary pressureconsiderations.Thin water layer is visible on the rock surface asexpected for quartz.Oil has penetrated into the middle of some pores.
16Sandpack at residual gas saturation Brine –blueSand – redCO2 - yellowThe largest CO2 ganglia is continuously spread over thelargest available pore.Though overall gas accumulates in the larger pores, a randomdistribution between large and medium size pores isobservable.Several tiny gas bubbles are randomly distributed inthe pore volume. Though they might originate fromthe segmentation process, it is thought that they are real.
17Vertical column experiments – Sor vs. Soi Sand-packed columns were oriented vertically.5 pore volumes of de-aired brine were injected to reach full saturation.Decane reservoir connected to top of columns and brine allowed to drain under gravity from the base. Decane enters the top of the column. No pumping.Equilibrium reached where both columns have a (theoretically) identical oil saturation profile versus height.One column removed for slicing and sampling – Soi.Second column has brine injected from the base, Brine sweeps oil leaving an Sor. Coulmn sliced and sampled.brine flowOil flowCOLUMN A - SoiCOLUMN B - Sor
18Vertical column experiments – Sor vs. Soi - results