Overview of potential CO 2 /brine leakage rates along faults. Elizabeth Keating (Given by Rajesh Pawar) Los Alamos National Laboratory

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1 Overview of potential CO 2 /brine leakage rates along faults Elizabeth Keating (Given by Rajesh Pawar) Los Alamos National Laboratory

2 Why fault-leakage scenarios are important to consider Although presence of known faults would likely preclude a site from being selected for injection, there is always a chance that faults could be undetected by subsurface characterization Even if existing faults are benign flow barriers, CO 2 injection could potentially lead to change in fault permeability (stress changes along faults, geochemical changes)

3 Available methodologies for estimating CO 2 fluxes in leakage scenarios Studies of natural systems where CO 2 is rising along faults Multi-phase flow simulations based on measured or assumed architectures of fault systems measured or assumed reservoir pressures and CO 2 saturations Caine and Minor (2009)

4 Natural systems It is fairly common for CO 2 to flow upward along faults in locations where there is a natural source of CO 2 at depth These systems provide an opportunity to understand the mechanisms of CO 2 flow in faults and the impact of CO 2 on shallow aquifers The CO 2 flow rates observed in these natural systems may not necessarily be comparable to rates that we might expect in a CCUS fault leakage scenario

5 Numerical Simulations Can quickly consider a wide range of scenarios, evaluate risks, monitoring and mitigation strategies Physical and chemical properties of faults will necessarily be vastly simplified It is very difficult to evaluate the veracity of model results Pasala et al., 2013

6 Context for flow rate/flux Assumptions: 1 GW plant, creates 30kT CO 2 /day Inject 75% over 50 years Leaky fault with 1000 m X 10 m footprint Worst case (total failure): fault leak rate = injection rate = 2250 kg/day/m 2 Best case (meets IPCC standards for 99% storage over 1000 years): fault leak <= kg/day/m 2

7 Observations in natural settings (permeable fault systems) Springerville, AZ 4.3 kg/day/m 2 deposits (Allis et al., 2004) (created extensive travertine Mammoth Mtn, CA 8 kg/day/m 2 (Rogie et al., 2001) Central Italy 3.8 kg/day/m 2 (Chiodini et al., 1999) Chimayo, NM 0.14 kg/day/m 2 (Keating et al., 2013) Crystal Geyser, UT 0.1 kg/day/m 2 (Moore et al., 2001) Some of the observed rates would be acceptable by IPCC standards (99% retention) e.g. Chimayo, Crystal Geyser. The others are above the standards but in the same ballpark. Note: The acceptable rates would probably be not acceptable if the regulatory criterion was no change over background.

8 Necessary conditions for upward leakage of CO 2 along faults Upward driving force Over-pressurization at depth Buoyancy Permeable pathway within fault structure or associated damage zone Final steady-state flow rate (if scaled to a 1km long fault) is ~613 kg/s Preuss and Garcia 2002 Or 2118 kg/day/m 2

9 NRAP Chuanhe Lu, Yunwei Sun, Joshua A. White, Laura Chiaramonte, and Susan Carroll kg/day/m 2 Over-pressurization in reservoir ~ 10 Mpa Includes a number of conservative assumptions

10 Brine leakage Upward driving force must overcome density effects ΔP = 0.2MPa Salinity of 17%: brine is pushed up conduit where it is held in static equilibrium Salinity 8% can push column of brine up into shallow aquifer Oldenburg and Rinaldi (2011)

11 Impact on shallow water quality due to brine leakage will exceed that due to CO 2 leakage Fault in the Santa Fe Group Keating et al. (2009)

12 Fault geometry will affect the likelihood that brine will be displaced upward Comparative study of brine and CO 2 upwelling along fault zones (Keating et al., Environmental Science and Technology, 2012) Broad fault systems are less likely to leak brine upwards (Springerville, AZ) Narrow fault systems are more capable of displacing brine vertically (Chimayo, NM) 1 km 10 m

13 Post-injection caprock breach scenarios Perhaps an existing benign fault becomes activated at some point in time after CO 2 has been sequestered If a permeable fault pathway becomes available, how much of the buoyant CO 2 will leak upward?

14 Post injection 17 MT of free-phase CO 2 sequestered in two saline aquifers Shallow aquifer Caprock Caprock Caprock Reservoir is not over-pressurized

15 Fault pathway opens (as a result of an event) CO 2 rapidly escapes

16 Some CO 2 rapidly escapes

17 The large majority of the CO 2 remains sequestered

18 Further questions Of the CO 2 that does escape, what would the environmental impact be? How would the system behave with Over-pressurized reservoir Alternative fault geometries Leaky wellbore

19 Conclusions Risk assessment calculations are assuming CO 2 mass flow rates along faults >>> natural CO 2 mass flow rates along faults in highly active systems Is it possible for fault systems to transmit this much CO 2? Many natural CO 2 release sites are emitting approximately as much CO 2 as would be deemed acceptable by IPCC standards, and so are worthy of further study as analogs Ongoing studies suggest unintended caprock breach by fault activation would not necessarily release the majority of sequestered CO 2.