Geologic Carbon Storage of Anthropogenic CO₂ under the Colorado Plateau in Emery County, Utah

Round 1

Reviewer 1 Report

This paper has been submitted to as special issue for Geologic CO2 Sequestration and its potential impacts on the environment, in a section on environmental mineralogy and biogeochemistry. Under that heading, this paper does not meet that subject matter area. On that basis the office may decide to reject the paper and redirect it to a more appropriate title.

Rather this is an initial modelling study to determine the potential of an area that has not previously been evaluated as a potential geological carbon storage site. It is very high level, and provides limited information on the location geologically and there is an oblique reference to Petrel as the possible software used for the modelling (but not explicit). 

I think that there could be a broader range of reference materials used, as there is the risk that newer rel perm curves or other data might improve the models. 

Some of the assumptions struck me as odd and I have flagged them in the marked up pdf. 

I suggest you have a look at some of the work conducted on the South West Hub CCS site in south west Western Australia for information on a storage site where residual and dissolution trapping were believed to be the potential major mechanisms to store CO2. In that case there was no outcrop risk, but it might give you more information to compare your results or help tweak the models. Most of the data is open file and can be found at https://wapims.dmp.wa.gov.au/WAPIMS/Search/SwHubCarbonStorage 

Please also make sure you've got your units as SI units for publication.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer #1

1. Are there examples of ccs projects where, at commercial scale, the reliance on only solubility and residual trapping have occurred? There are significant risks and it may not be legislated to be able to do so... so backing this up with an example or whether this possible should be considered here as it may be subject to significant debate.
   2. There are not any commercial scale CCS operations that use residual, solubility, and mineral trapping to contain CO2. A reviewer pointed to a similar study done in western Australia, called the South West Hub, indicated that their target of 220 Mt could be successfully stored below a cap rock that was not intact, with vertical migration pathways. I have included the following txt in the manuscript:
   3. The Navajo Sandstone crops out along the spine of the San Rafael Swell south of the Drunkards Wash field and east of the Buzzards Bench field. Therefore, the area to the east of the Hunter Power plant and Buzzards Bench field lacks a structural trap, suggesting the potential for CO₂ to migrate away from the injection zone and leak back into the atmosphere. Thus, areas to the west of the San Rafael Swell, including the Buzzards Bench site, would rely on solubility trapping, residual gas trapping, and long-term mineralization to permanently store the CO₂. A feasibility study in western Australia explored the idea of relying on capillary trapping, residual trapping, and mineral trapping to secure the 220 Mt of CO₂ [13], [14]. The characterization and simulation study indicated that it was possible to store that volume of CO₂ for greater than 1000 years without an intact stratigraphic trap [13], [14]. On the northern and eastern flanks of the San Rafael Swell there are several natural CO₂ sources, such as Farnham Dome that has produced nearly 267,000 metric tons of CO₂ during its lifetime [11]. Near the town of Green River, Utah, to the east of the study area, there is evidence of past CO₂ seeps and geysers, along with a CO₂ geysers created during exploration drilling that now serve as tourist attractions [11], [15].
2. it may come up later, but how old is the well, how deep is the formation here, are there any instruments for monitoring, any signs of seismic events induced during disposal... etc etc??
   96. They have not instrumented the SWD 1 well for seismic detection and I do not know of any events associated with produced water injection in this area. The well was completed in February ’96. The well TDs below the Wingate and into the Chinle at a measured depth of 2314 meter We re-wrote the site characterization section and added more details about the wells and logs data used in the modeling work.
3. You do not explain or discuss these 3 horizons but they are mentioned in Figure 3. This needs more background explanation given that you have presented results from each of them.
   1. Added text and a redid figure 3 to show the well logs for SWD1 well with the three horizons identified and the relative permeability and capillary pressure curves are plots next to the horizon they were assigned too in the model.
4. Consider looking at more up to date relative permeability data if available. There's been a bit of work on trying to improve these values for CO2 in more recent years.
   1. We understand that more recent work may have more accurate curves for the formations being modeled, but the curves presented in Bennion and Bachu’s manuscript are already in the format needed by the simulator and are a good approximation of the formation they represent. The reference is for the shale curves in their manuscript which we were able to use directly in the simulator.
5. Could you also include the depth in meters as an SI unit?
   1. Modified figure 2 to show all depths in meters. Change all units throughout the manuscript to SI units.
6. krw, krg, Pc are not explained in the figure caption and are not mentioned anywhere else. Perhaps consider explaining the three horizons more fully
   3. Addressed in response to question 3.
7. Please use SI units here for the primary unit and you can include these imperial measurements in brackets. Further, it will help with the comparison at the end of this paragraph, which is in different units....
   1. We considered your point here and have changed all the units in the manuscript from imperial to SI units. When we reported this data to the DOE it was all in imperial units, including all mass reporting in US tons.
8. Why 73 years of monitoring? I appreciate that 27+73 make a nice round number, but current thinking is that only 5-10 years post injection monitoring would be required, depending on the regulatory environment. Is the extra time purely from a modelling perspective? Its unlikely much will happen after injection stops (i.e., the highest risk activity).
   2. We thought that a total of 100 years would be sufficiently long enough to be able to gauge the long-term migration possibilities of the CO2. We had to simulate +50 years past the end of injection as part of the EPA’s requirement from their PISC (post injection site care) monitoring guidance documents and we wanted to understand the general long-term plume movement potential, especially around the Buzzards Bench area as it had the potential to leak to the surface.
9. I do not agree with this statement. The regulations will still apply irrespective of who owns the land. There may be less of an issue with respect to dealing with landholders (as the land is owned by the emitter) but all environmental, CCS and any other regulations will still apply.
   1. This statement was indeed referring to ease of dealings with landholders.
   2. Changed to:
      1. “The ideal location for the project injection well would be on the HPP site as it would make land ownership easier and minimize surface infrastructure, such as pipelines.”
   3. How shallow is too shallow? Be explicit. Also how have you defined "too close" to outcrop?? What are the assumptions??
      1. Expanded this section to address your comment.
      2. “The Navajo Sandstone is 1300 meters deep directly below the plant but crops out about 15 km to the southeast. The reservoir hydrostatic pressure 6.4 km up-dip from the power plant is above 7.4 MPa (near the triple point of CO₂) causing a potential phase change from supercritical to gas. Preliminary simulations showed that under certain conditions the CO₂ had the potential to migrate up-dip to this area of the reservoir within 50 years of ceasing injection, indicating that this area was not appropriate for long-term CO₂”
   4. Are these gas fields still in use? Which formations? Are there conflicts of resources? Are the operators onboard? Are there conflicting regulations? How do you manage monitoring if you already have activity in the subsurface etc?
      2. We added more information about the Buzzards Bench and Drunkards Wash gas fields in section 2.1 Study Site. As this was a pre-feasibility study, we did not have the budget or time to engage the operators in either of these fields to gage their interest in a CCS operation. If this project were to progress to commercialization, then we would have to engage all operators in the area and show how our operations might or might not interfere with their current operations, as well as to gage any level of cooperation in building a regional CO2 storage hub. If commercial operations were to happen then we would need to drill monitoring wells in areas where we thought the plume might migrate to as well as preform surface 4D seismic for plume monitoring and model calibration. The following text was modified:
      3. “Two injection sites were evaluated, the primary site is located west of Castle Dale in the Buzzards Bench gas field, and a secondary site just south of Price in the Drunkards Wash gas field (Figure 1). Both sites are currently producing gas and water from the Ferron coal and sandstone horizons, Cretaceous aged sandstone and coal formations covering much of the area to the north and west of the Swell. The produced water from the Ferron production operations are injected into the deeper Navajo and Wingate formations for disposal, with injection operations currently ongoing [10].”
   5. Is there a reference for this?
      1. No, it was a guideline given to the simulation team by the engineers. It is likely that a well can take up to 1.5 Mt/yr of injection but we opted for a more conservative 1 Mt/yr injection rate limit. If the project had moved ahead then this number would have been carefully calculated by the drilling engineers and then provided to the simulation team.
   6. I really like how you have considered the fact that the volumes will not be static and are anticipated to reduce as part of the energy transition!
      1. Thank you! We had a good breakdown of how much CO2 each of the heavy industries and power stations emitted per year and an idea of how long some of the power stations had left, so we thought it would be interesting to leverage this data in our simulations. It would give an idea of how a storage complex would react over long term CO2 storage activities.
   7. Have these wells been evaluated to see if they reach the appropriate depth intervals, have they been reviewed to see if they have maintained integrity? etc etc. and if they have, can you reference the report/materials?
      1. These wells were selected because they penetrated the Navajo, were more than 20km from any Navajo outcrop, and were situated in an area that has road access. They were not evaluated realistically as potential injection wells. They provided guidance on areas where injection wells could be located as there is some areas where geography would prohibit a well site. This is addressed further down in the manuscript in Section 4 Discussion.
   8. Are there no more recent studies or evaluations based on active projects??
      1. I added two more recent studies to the citations.
   9. Is it possible to make any comment on the impact on injectivity and mobility of CO2 that these heterogeneities might cause? Are there case studies that could help?
      1. Not aware of any other studies of co2 injectivity into the Navajo sandstone. Other projects I have worked on, we have seen a reduction in volumes injected and increases in pressure when heterogeneities are added into the model. Results have shown differences but the homogeneous cases do not grossly overestimated volumes and pressure. We added the following text to address your comment.
      2. “The smaller-scale Navajo Sandstone depositional morphology would lead to complex CO₂ flow paths that were not captured in the current model. These small-scale heterogeneities could cause reduced injectivity and increased pressure around the injection wells leading to either a longer injection timeline or more injection wells to accomplish the project’s goals.”
   10. I'm not sure if this is a safe assumption, depending on the timeline - but you may have knowledge of the location that the reader does not... may be worth providing a little more background here. Alternatively, just do not mention these sorts of assumptions given your statement about the pre-feasibility nature of the work.
       1. Removed that text. You are right, we don’t need to mention those sorts of assumptions in this study.
   11. Was there specific pressure data or a hydrogeological study that provided additional context and comfort here?
       2. Addressed in section 2.4 Model Domain and Initial Conditions.
          2. The San Rafael Swell infiltrates roughly 3,000 acre-ft/year of rainfall into the Navajo Sandstone along about 93,000 acres of outcrop area [12]. This infiltration rate was modeled by setting the top layer of cells along the outcrop to a constant flux of 2.7e-5 m3/day of water.
       3. Addressed again in section 3 Results.
          1. There is a clear path up-dip at the Buzzards Bench location for the CO2 to migrate towards the outcrop area and potentially escape containment. However, this is not seen in any of the simulation cases. The CO2 does spread laterally around the wells, but it stays in the vicinity of the injection wells and does not move up-dip towards the outcrops. This is due to the simulated surface water infiltration into the Navajo Sandstone along the outcrop area of the model, creating an above hydrostatic pressure gradient up-dip of the injection site. This pressure gradient impeded the buoyancy-driven upwards migration of the CO2 plume, keeping it trapped near the injection well

Author Response File: Author Response.pdf

Reviewer 2 Report

The article is entitled "GCS of anthropogenic CO2 under the Colorado Plateau in Emery County, UT". It is well written and quite easy to follow. Results could be presented more clearly by adding other tables and figures supportig the text of chapter 3.  Here are the only few remarks/comments I noted during my reading/review:

Line 19: replace anthropomorphic by anthropogenic.

Line 28: put “member of the Glen Canyon group” between comas. Replace “member” by “belonging to".

Line 40: please refer to a country by adding “U.S.” between “latest” and “national”.

Line 50: add a coma after “United States”.

Line 77: to which area lacking a structural trap are you referring to? The cropping area? Please, be more precise and do not use “this” here.

Line 81, figure 1: add a small US map to help locate Utah for non-US people.

Line 82, figure 1: use plural form, add a “s” to “site”.

Line 112: Chinle layer is said to be a seal but does not appear in red on figure 2. Modify figure 2?

Line 115: please give further details on the 3 considered zones: names, depths, etc. Details could be given in the text or in a new table.

Line 117, figure 2: column “depth” is not clear. The are 2 values for some formations. Can you explain these 2 values? Ex. Navajo sandstone is said to have a depth between 4915 ft. and 8238 ft., but depth of the underlying Kayenta formation is 5342 ft., which is higher than the deeper value for the Navajo sandstone. Please give further details to help understand the figure. Indicate from which well the depth values were determined.

Line 118, figure2: porosity and permeability values are only given for the modeled formations and not for all the formations of the stratigraphic column. Revise figure caption accordingly.

Line 128: precise (for example in brackets) what is SimCCS.

Line 162: reference to figure 3 is wrong. Refer to figure 2 or 5?

Line 166: present before this paragraph the models you built. You first need to introduce what are “Regional GCS” and “BB&DW Capacity” models.

Line 167: I don’t understand what is the BB&DW Capacity scenario. You didn’t name your scenarios.

Line 167: explain “co-located” at the surface. Do you mean they are located on the same well pad?

Line 217: use singular form. Replace “wells” by “well”.

Line 235: use subscript for “2” in “CO2”.

Line 240: precise if volume in cubic meters is given in bottomhole conditions.

Line 258: to what are you referring to with “as described above”?

Line 277: as a reminder, precise again that produced water is injected in the Navajo sandstone (as already said line 183).

Line 283, figure 5: the upper figure is difficult to read (it is hard to read the well names and their indications). Please use a lighter red color. 

Line 356, table 3: what does 3118 mean in the table legend text? Is it a year? If yes, add in yr. 3118.

Line 356, table 3: add a title name to the first table column: “Model name”?

Line 375: use plural form for “it peaks”?

Line 380: ad “in year” before 2118.

Line 381: ad “in year” before 3118.

Line 369-367, figure 6: you don’t use the right sign when referring to cross sections. Please, use the apostrophe sign.

Line 400, figure 7: you don’t use the right sign when referring to cross sections. Please, use the apostrophe sign.

Line 403: replace “areas” by “hypothesis”.

Line 464: models only take into account actual/present CO2 sources. Thus, add “present’ between “all” and “point-source”.

Author Response

please see attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

Review of “Geological Carbon Storage of Anthropogenic CO2 under the Colorado Plateau in Emery County, Utah” by Moodie et al.”

General Comments

The authors conducted CO2 sequestration simulation and evaluated feasibility of multi-million CO2 injection in the Navajo Sandstone member of the Glen Canyon Group. Reduction of global carbon concentration is important topic and must be resolved to prevent on-going global warming. The manuscript is written well, and I would like to recommend “minor revision” as long as the author implement following suggestions.

Comment #1. Line #75-#80 “The Navajo Sandstone crops out along the spine of the San Rafael Swell south of the Drunkards Wash field and east of the Buzzards Bench field. Therefore, this area lacks a structural trap, suggesting the potential for CO2 to migrate away from the injection zone and leak back into the atmosphere. Thus, this potential GCS site would rely on solubility trapping and residual gas trapping as permanent storage mechanisms in certain areas.”

As I recognized, there was no reliable caprocks at one of the flagship CO2 sequestration project in Australia, called “South West CO2 Geosequestration Hub” project (https://www.ceg.uwa.edu.au/__data/assets/pdf_file/0008/2186846/South-West-Hub.pdf). Without effective caprock, they also rely on both residual and solubility trappings as primary CO2 storage mechanisms. I am not sure whether the project is still on-going in Australia. Nevertheless, I think that the SW Hub project is worth to be mentioned in the manuscript as similar example project. In addition, please discuss that CO2 can be effectively trapped without caprock.

Comment #2. I think that it is also worth to mention existence of natural CO2 reservoirs at east of San Rafael Swell. Additionally, please also mention some CO2 is leaking as geysers and natural springs but they are not harmful rather served as attractive tourist sites

Comment #3. Pease unify the unit to SI throughout the manuscript. For example, in Figure 2, depth is shown as feet; In Line 157, 44 miles by 62 miles; Line 168 a 10-kilometer radius; Line 175 3,000 acre-ft/year; Line 177 2.7 e-5 m3/day.

Author Response

Please see attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Hi all,

thanks for taking my comments and suggestions on board and taking them in the positive manner they were offered.

While I'm still a little concerned that the manuscript doesn't fit the brief of the special issue super-well, the manuscript is now suitable for publication. I leave it to the editors to decide. 

regards,