2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations CO2 Injection For Geological Storage Dr. Steven L. Bryant Associate Professor Dept. of Petroleum and Geosystems Engineering Director Geologic CO2 Storage Joint Industry Project The University of Texas at Austin Module Objectives INTRODUCTION TO CO2 SEQUESTRATION IN WATER-BEARING FORMATIONS Know the scale at which sequestration will have to operate Know key physical properties of CO2 Know several important physical, chemical phenomena in geologic storage Be able to estimate volume of structure needed for CO2 storage Be able to estimate safe rates of injection Demonstrate principle of safe structural storage STORE (Sequestration Training, Outreach, Research and Education) B-1 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Scale of CO2 sequestration is set by scale of fossil fuel consumption Approximate CO2 emitted by burning fossil fuel 2 ton CO2/ton coal 3 ton CO2/ton oil 2.75 ton CO2/ton natural gas 1 ton = one metric ton = 1000 kg 1 Mt = one megaton = 106 ton 1 Gt = one gigaton = 1000 Mt = 109 ton 1 Pg = one petagram = 1015 g = 1 Gt CO2 emissions from human activities CO2 emissions (PgC y-1) 10 3.7 ton CO2 = 1 ton C 8 Fossil fuel 6 4 Land use change 2 1960 1970 1980 STORE (Sequestration Training, Outreach, Research and Education) 1990 2000 2010 B-2 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations CO2 emissions from fossil fuel consumption Global emissions from fossil fuel consumption 35 30 Gt CO2 per year 25 20 Flaring Cement Gas Liquids Solids 15 10 5 0 1850 1900 1950 2000 CO2 emissions from human activities By source (in 2000, as CO2) Solid fuel Liquid fuel Gaseous fuel Subtotal: fossil fuel emissions As carbon Flaring + cement Land use change Total As carbon STORE (Sequestration Training, Outreach, Research and Education) 8.6 Gt 10.4 Gt 4.7 Gt 23.7 Gt ¾ of total 6.3 Gt 1.0 Gt 7.6 Gt 32 Gt 8.6 Gt B-3 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Global CO2 emissions by sector (2004 data) Electricity generation, heat 41% Transportation 20% Industry 18% Residential/Commercial 13% Other 8% CO2 emissions by sector Electricity generation: ~10 GT CO2/y About a third of anthropogenic emissions STORE (Sequestration Training, Outreach, Research and Education) B-4 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Exercise 1: CO2 emissions at the global scale In 2009 what was rate of CO2 emissions from coal, oil and natural gas consumption in China USA Compare CO2 emission rates from China and from USA per capita per $ GDP Population, 2009 (CIA World 3.07E+08 China 1.34E+09 US Approximate oil equivalents 2 ton coal = 1 ton oil equivalent GDP, 2009, purchasing powe 1.41E+13 China 8.75E+12 US Gas conversion 1 Mt gas = 48 BCF CO2 emissions from electricity generation 19900 TWhr generated in 2007 72 EJ 4000 GW generating capacity 10 GT CO2/y About a third of anthropogenic emissions 1 1 1 1 1 GW GW GW GW GW coal-fired Æ ~7.6 MT CO2/y gas-fired Æ ~3.9 MT CO2/y hydroelectric Æ ~0 MT CO2/y nuclear Æ ~0 MT CO2/y oil-fired Æ ~7.5 MT CO2/y STORE (Sequestration Training, Outreach, Research and Education) http://www.eia.doe.gov/oiaf /ieo/electricity.html B-5 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Conversion factors for CO2 0.379 MSCF per lbmol 0.00861 MSCF per lb 18.95 MSCF/ton 18.95 MMSCF/thousand ton 18.95 BSCF/million ton 18.95 TSCF/gigaton 1 ton = 1000 kg 3.7 ton CO2 = 1 ton C Geologic CO2 Sequestration: target formations CO CO22 Oil/Gas Producing Reservoir Aquifer/Depleted Oil or Gas Reservoir 1 mile Unmineable Coal Deep Saline Aquifer STORE (Sequestration Training, Outreach, Research and Education) B-6 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Geologic CO2 Sequestration: target formations IPCC SRCCS Technical Summary Where can we put that much CO2? OIL & GAS RESERVOIRS In NORTH AMERICA 140 GT CO2 STORE (Sequestration Training, Outreach, Research and Education) B-7 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Where can we put that much CO2? UNMINEABLE COAL SEAMS In NORTH AMERICA 175 GT CO2 Where can we put that much CO2? SALINE 9 DEEP AQUIFERS In NORTH AMERICA >3000 GT CO2 STORE (Sequestration Training, Outreach, Research and Education) B-8 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations CO2 density at conditions of shallow Earth’s crust (onshore) Exercise 2a: CO2 emissions at the local scale How much CO2 was produced from Fayette County Power Project per year? Suppose a pilot capture plant is retrofitted onto Fayette to capture 10% of emissions. Calculate required CO2 storage rate Ton CO2/day MMSCF CO2/day Suppose the G-2 unit of the Wilcox formation is selected for injecting the captured CO2 Calculate pore volume required to store 3 y of pilot plant operation STORE (Sequestration Training, Outreach, Research and Education) B-9 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Petrophysical properties relevant to aquifer storage Porosity Permeability Multiphase flow properties Relative permeability Capillary pressure Drainage/imbibition hysteresis Petrophysical properties relevant to aquifer storage Porosity Fraction of bulk rock volume containing fluid Larger porosity means smaller footprint for given CO2 volume Smaller porosity could yield greater long-term security of storage Correlated to residual CO2 saturation STORE (Sequestration Training, Outreach, Research and Education) B-10 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Petrophysical properties relevant to aquifer storage Porosity Permeability Multiphase flow properties Relative permeability Capillary pressure Drainage/imbibition hysteresis Storage volume in aquifers: relative permeability (two-phase flow) is important Frontal saturation advance Buckley-Leverett theory Injected CO2 occupies only a fraction of the invaded pore volume STORE (Sequestration Training, Outreach, Research and Education) CO2 + brine brine B-11 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Exercise 2b: CO2 emissions at the local scale After a successful pilot plant run, the Fayette Project is retrofitted to capture 90% of emissions. Use your results from Exercise 2a to calculate required CO2 storage rate Ton CO2/day m3 CO2/day at reservoir conditions Calculate rock volume and areal extent required to store 30 y of captured emissions Need Wilcox G2 thickness, porosity Assume average saturation of CO2 is 0.5 Storage Efficiency: fraction of structure pore volume that actually contains CO2 Combination of Displacement efficiency Areal sweep efficiency Vertical sweep efficiency Gravity override efficiency Overall storage efficiency STORE (Sequestration Training, Outreach, Research and Education) B-12 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Modes of storage in sedimentary rocks Structural storage Dissolution trapping Residual phase trapping Mineralization trapping permanent Geologic CO2 Sequestration: several simultaneous modes of storage in aquifers Unmineable Coal Oil/Gas Producing Reservoir Aquifer/Depleted Oil or Gas Reservoir Bulk phase CO2 Deepdissolved Saline Aquifer Residual phase Structural trapping Overlying formation blocks upward flow Dissolution trapping CO2 solubility in brine ~ 1 mol% STORE (Sequestration Training, Outreach, Research and Education) Residual phase trapping Mineral trapping 1/3 to 2/3 of the void volume CaCO3, MgCO3, FeCO3 B-13 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Secure storage: capillary seal of overlying formation is important If Pentry of sealing formation > PCO2 – PH2O then CO2 remains in storage formation If Pentry of sealing formation < PCO2 – PH2O seal seal h CO2 Storage stratum formation then CO2 can leak from storage formation Pentry = 2 σ cosθ / rthroat Other strata Exercise 3: Capillary sealing capacity 1. Assume that CO2 is injected so that it fills the entire thickness of the G-2 unit. Determine the capillary pressure PCO2 - PH2O at the top of the G-2 formation You will need to recall the density of CO2 at storage formation conditions from previous problems. Assume the density of the brine is 1000 kg/m3. 2. The low-permeability base of the Lower Wilcox G-1 unit should act as a capillary seal for fluids in the Lower Wilcox G-2. Suppose that the pore throats in the G-1 unit have radius 0.25 microns, and that the interfacial tension between CO2 and the brine is 0.015 N/m. What is the capillary entry pressure of the G-1 unit for CO2? Assume the CO2/brine/rock contact angle is 45 degrees. 3. Will the G-1 provide secure structural storage if CO2 fills the G-2? 4. Experiment: Tubes packed with different sizes of beads are filled with a hydrocarbon phase (top third) and water (bottom two thirds). Half the tube is packed with one size of beads, the other half with a different size. When the tubes are inverted (so that the part containing hydrocarbon phase is at the bottom), buoyancy causes the hydrocarbon to rise and water to fall. Observe the distance that hydrocarbon rises in each tube, and explain any differences between the tubes. STORE (Sequestration Training, Outreach, Research and Education) B-14 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Rate of Geologic CO2 Storage Depends on Injectivity of Structure TOP SEAL q q q h STORAGE AQUIFER Average permeability k CONFINING LAYER Injectivity for single phase flow Injectivity for CO2 storage More complicated! Petrophysical properties relevant to storage rates Permeability Rock property that relates driving force (pressure gradient) to flux (flow of single phase fluid) Darcy’s empirical law Large permeability requires less pressure to inject a given CO2 rate Heterogeneous permeability can lead to CO2 plume moving unexpected directions or distances STORE (Sequestration Training, Outreach, Research and Education) B-15 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Petrophysical properties relevant to storage rate Multiphase flow properties Relative permeability Normalized hydraulic conductivity to one phase (CO2 or brine) when both phases are present in the rock Typically expressed as function of phase saturation Phase saturation = Fraction of pore volume occupied by that phase Petrophysical properties relevant to storage rates Multiphase flow properties Relative permeability Drainage: CO2 displaces brine Sw,irr STORE (Sequestration Training, Outreach, Research and Education) B-16 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Fluid properties relevant to storage rate: CO2 viscosity at conditions of shallow Earth’s crust CO2 and brine viscosities as function of depth of storage formation Geothermal grad=16.5 F/1000ft Viscosity (cp) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 3000 109.5 4000 129.5 5000 Depth (ft) 149.5 6000 7000 8000 169.5 CO2 water 9000 10000 189.5 209.5 Temperature (degrees F) 0 229.5 11000 STORE (Sequestration Training, Outreach, Research and Education) B-17 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Storage rates: Injectivity index depends on formation kh and CO2 properties skin factor Assume radial flow from each injector Assume for illustration that steadystate single phase flow equation applies relates injection pressure Pbh to injection rate q and pressure in aquifer P(r) Actual rate smaller because of relative permeability effects injection well radius CO2 rate (reservoir condition) Injectivity index (single phase flow) Bottomhole injection pressure Average formation pressure brine viscosity storage aquifer radius Storage rates: adjust injectivity index for multiphase flow effects (CO2 displacing brine) two-phase dry CO2 CO2 - saturated brine Rough estimate brine Watersaturated CO2 Injectivity index (two phase flow) STORE (Sequestration Training, Outreach, Research and Education) B-18 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Exercise 4a: Storage rates Estimate the CO2 injectivity of the Wilcox G-2 formation Need permeability, viscosity of brine Assume aquifer drainage radius 10 km Assume wellbore radius 0.1 m, skin S = 0 Consider a pilot project that will capture 10% of the CO2 emissions from the Fayette Co. Power Project. Estimate the pressure difference required to inject the captured CO2 during the pilot project Storage rates: fracture pressure limits injection rate into a well Injection pressure Pbh should not exceed formation parting pressure Pfrac Formation parting pressure typically a function of aquifer depth z If Pbh is limited, and if average formation pressure increases during injection, then rate of injection must decrease during storage Operating constraint for CO2 injectors constant STORE (Sequestration Training, Outreach, Research and Education) B-19 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Example: compute safe injection rate into the Wilcox G-2 effective injectivity index 9.3243E-12 m^3/Pa/s hydrostatic gradient 10 assume frac gradient 16 depth to Wilcox, Fayette Co 2164 frac pressure in Wilcox, Fayette Co 34.6 initial pressure in Wilcox 21.64 initial allowable DP 13.0 initial injection rate 0.00012107 6.8 MPa/km MPa/km m MPa MPa MPa m^3/s ton/d Storage rates: multiple injection wells offer obvious advantage over single injection well Good news: multiple injectors enable greater overall injection rate than single well Bad news: multiple injectors interfere with each other 1 well 2 well STORE (Sequestration Training, Outreach, Research and Education) 4 well B-20 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Storage rates: interference between multiple injection wells reduces injection rate per well Can approximate interference effect with “equivalent skin”* R Single “equivalent well” Seq depends on Number of injectors n Distance of each injector from center of storage formation R Skin factor of each injector S Radius of each injector rw equivalent injector *Pooladi-Darvish et al., GHGT10 Energy Procedia, 2010 Storage rates: multiple injection wells increase overall rate, but not proportionately to well number Interference causes benefit of drilling additional wells to diminish as number of wells increases Benefit of multiple injection wells Benefit of multiple injection wells 10 injectivity index of equivalent well, relative to single injector injectivity index of equivalent well, relative to single injector 10 9 8 7 re = 30 km 6 rw = 0.1 m 5 R = 5 km 4 S=0 3 2 9 8 7 6 5 re = 15 km 4 rw = 0.1 m 3 R = 1 km 2 S=2 1 1 0 10 20 30 40 number of injection wells STORE (Sequestration Training, Outreach, Research and Education) 0 10 20 30 40 number of injection wells B-21 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Exercise 4b: Storage rates Consider a pilot project that will capture 10% of the CO2 emissions from the Fayette Co. Power Project. Consider strategies for storing the captured CO2 in the Wilcox G2 How many wells do you need? How far from center of the formation do you put them? What skin factor would you like them to have? Suppose you are limited to 10 injection wells What formation properties do you require? Permeability, thickness Suppose you are limited to 3 injection wells What formation properties do you require? Exercise 4b solution: can Wilcox G-2 work? 500 wells 18.5 km from center of 0.5 mD, 23 m thick Wilcox G-2 Use multiple injection wells in the Wilcox G2 permeability thickness brine viscosity at 2 km effective mobility drainage radius r_e wellbore radius r_w number of wells, n distance of each well to center, R skin of each injectino well, S equivalent skin for single injector skin to use (allows compare n=1) effective injectivity index emssions rate mass rate of CO2 for pilot (10% cap q_CO2_reservoir_conditions_pilot Pressure Difference needed to injec Limit on DP by fracture criterion STORE (Sequestration Training, Outreach, Research and Education) 0.5 5E-16 23 0.36 0.00036 1389 40000.0 0.1 500 18500 -2.000 -12.13 -12.127184 4.5542E-09 mD m^2 m cP Pa-s (Pa-s)^(-1) m m m^3/Pa/s 12.5 3425 3424658 5269 0.061 13390007 13.4 13 Mt CO2/y t CO2/d kg CO2/d m^3/d m^3/s Pa MPa MPa m Not a good use of space! B-22 2010 SPE International CO2 Conference Carbon Sequestration: Storage of CO2 in Geologic Formations Exercise 4b solution: Seek other storage formations with manageable well count 10 wells 1000 m from center of 50 mD, 23 m thick formation Use multiple injection wells in the Wilcox G2 Use multiple injection wells in the Wilcox G2 permeability 50 5E-14 23 0.36 0.00036 1389 10000.0 0.1 10 1000 0.000 -8.48 -8.476938 4.3901E-09 thickness brine viscosity at 2 km effective mobility drainage radius r_e wellbore radius r_w number of wells, n distance of each well to center, R skin of each injectino well, S equivalent skin for single injector skin to use (allows compare n=1) effective injectivity index emssions rate mass rate of CO2 for pilot (10% cap q_CO2_reservoir_conditions_pilot Pressure Difference needed to injec Limit on DP by fracture criterion 12.5 3425 3424658 5269 0.061 13890526 13.9 13 3 wells 750 m from center of 20 mD, 120 m thick formation mD m^2 m cP Pa-s (Pa-s)^(-1) m m m m^3/Pa/s Mt CO2/y t CO2/d kg CO2/d m^3/d m^3/s Pa MPa MPa permeability thickness brine viscosity at 2 km effective mobility drainage radius r_e wellbore radius r_w number of wells, n distance of each well to center, R skin of each injectino well, S equivalent skin for single injector skin to use (allows compare n=1) effective injectivity index emssions rate mass rate of CO2 for pilot (10% cap q_CO2_reservoir_conditions_pilot Pressure Difference needed to injec Limit on DP by fracture criterion 20 2E-14 120 0.36 0.00036 1389 10000.0 0.1 3 750 0.000 -6.33 -6.3260968 4.7205E-09 12.5 3425 3424658 5269 0.061 12918262 12.9 13 mD m^2 m cP Pa-s (Pa-s)^(-1) m m m m^3/Pa/s Mt CO2/y t CO2/d kg CO2/d m^3/d m^3/s Pa MPa MPa Module 2: Key Lessons Volumes and rates for substantive CCS are huge Deep saline aquifers needed CO2 is less dense than brine under typical geologic storage conditions Driving force for leakage Petrophysical properties – especially multiphase rock/fluid properties – strongly influence injection, longterm security of storage Need to characterize formation before project STORE (Sequestration Training, Outreach, Research and Education) B-23
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