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The storage potential of hydrocarbon reservoirs in the central Gulf of Mexico (GOM) makes future development of CO2 storage projects in those areas promising for secure, large-scale, and long-term storage purposes. Focusing on the producing and depleted hydrocarbon fields in the continental slope of the central GOM, this paper analyzed, assessed, and screened the producing sands and evaluated their CO2 storage potential. A live interactive CO2 storage site screening system was built in the SAS® Viya system with a broad range of screening criteria combined from published studies. This offers the users a real-time assessment of the storage sites and enables them to adjust the filters and visualize the results to determine the most suitable filter range. The CO2 storage resources of the sands were estimated using a volumetric equation and the correlation developed by the National Energy Technology Laboratory (NETL). The results of this study indicate that 1.05 gigatons of CO2 storage resources are available in the developed reservoirs at the upper slope area of the central GOM. The Mississippi Canyon and Green Canyon protraction areas contain the fields with the largest storage resources. [ABSTRACT FROM AUTHOR]

• We quantify wettability of resedimented clay mudrocks immersed in scCO2 at t ≥ 60 °C and P C O 2 ≥ 25 MPa. • Imbibition results indicate mudrocks remain water-wet to CO2 at typical storage conditions. • Results validate expectations of buoyant CO2 structural trapping by capillary forces. Structural trapping provided by seals is one of the key components of CO 2 geological storage systems. Clay-rich caprocks and fault gouge are expected to be water-wet at supercritical CO 2 conditions and to create a positive capillary pressure P C O 2 − P w > 0 MPa to ensure trapping of buoyant CO 2. This paper presents the results of water imbibition experiments in resedimented clay mudrocks immersed in supercritical CO 2 at temperature T ≥ 60 °C and pressure P C O 2 ≥ 25 MPa. The samples used in this work include kaolinite clay and Anahuac shale from the Gulf of Mexico Coast. Additional validation tests include Berea sandstone and silane-treated Berea sandstone. The results show spontaneous and rapid imbibition of water droplets into resedimented and rock samples initially saturated with wet supercritical CO 2 for all cases. This outcome provides indirect evidence that typical siliciclastic caprock building minerals remain water-wet to CO 2 at typical storage pressure and temperature conditions. The results and analysis indicate that siliciclastic caprock and fault gouge are expected to develop a positive capillary entry and breakthrough pressure to hold buoyant CO 2 by capillary forces. These results validate expectations of buoyant CO 2 structural trapping and field observations from natural analogues. [ABSTRACT FROM AUTHOR]

Structural fault trapping of buoyant fluids, such as hydrocarbons and CO 2 , relies on fault sealing capacity. The traditional approach to quantifying the sealing capacity of fault zone materials is Shale Gouge Ratio (SGR), which implicitly homogenizes fault properties. However, a large range of fault throw and the presence of fault heterogeneity can lead to different trapping capacities for the same structure. This paper presents a stochastic study to statistically determine the possible range of CO 2 column height at a normal fault in sand-shale sequences. We present the procedures of two stochastic models including the continuous shale gouge model (CSGM) and the discrete smear model (DSM). The models are applied in an example case for the High Island field in the Gulf of Mexico (GOM) basin combining borehole geophysical data and measurements from laboratory experiments. Both one-dimensional and two-dimensional cases are discussed. The results show that more than 50% of the realizations predict negligible fault sealing capacity. The CSGM method shows that CO 2 column height is overall proportional to SGR and breakthrough pressure. The DSM model suggests that clay smear continuity may significantly affect fault sealing capacity. Large fault throws (>100 m) result in smear breaches and therefore in highly variable maximum CO 2 column heights, varying from 0 m to a maximum of ∼95 m. Both the DSM method and the CSGM method proposed in this paper permit explaining geologic uncertainties and the resulting variability of column heights observed in the field. Our results together with the field data from the literature demonstrate the utility of combining both methods to help improve column height prediction. Uncertainty quantification of clay ductility, smear location, and fault heterogeneity is important for determining fault sealing capacity and improving reservoir risk management associated with carbon dioxide geological storage. • The presence of leak points in faults provides CO 2 leak paths and decreases the likelihood to trap a tall CO 2 column. • Ductile clays have the potential to produce continuous smears and result in large column heights. • Both discrete smear model and continuous shale gouge model permit explaining variability of CO 2 column heights. [ABSTRACT FROM AUTHOR]

Many coastal estuaries have experienced declines in pH over the past few decades due to coastal acidification. However, mean monthly water column pH values (collected during daylight hours) have increased in Tampa Bay, Florida over recent decades concurrent with seagrass recovery. We measured changes in carbonate system and water quality variables in Tampa Bay and the nearcoastal Gulf of Mexico environment to quantify diurnal to seasonal trends, drivers, and controls of carbonate chemistry; identify exposure periods to low pH conditions; and to examine the potential for seagrasses to buffer acidification in Tampa Bay. Autonomous sensor packages deployed in Tampa Bay and the Gulf of Mexico from December 2017 to June 2020 recorded hourly measurements of seawater temperature, salinity, pressure, pHT (total scale), carbon dioxide (pCO2), dissolved oxygen (DO), and photosynthetically active radiation. Results indicated strong temperature and biological influence on DO, pHT, and pCO2 in Tampa Bay during the dry season, and only weak to moderate correlation of these variables with temperature and salinity during the wet season. Strong influence from biological processes during the wet season was coincident with spring-to-summer periods of maximum seagrass growth rates. Gulf of Mexico results indicated higher pHT and DO, and lower pCO2 than in Tampa Bay, with similar but attenuated seasonal variation. Results suggest potential benefits from seagrass photosynthesis increasing pHT, DO, and decreasing pCO2 in Tampa Bay, and delivery of high pHT, low pCO2 Gulf of Mexico water to Tampa Bay during flood tides. Approximately 30% of pHT and pCO2 data records collected in Tampa Bay were below pHT 7.900 and above pCO2 of 600 patm, primarily during the wet season, indicating potential for dissolution of carbonate sediments that may also help buffer acidification conditions in Tampa Bay. [ABSTRACT FROM AUTHOR]

• The tailored methodology accounts for changes in CO 2 density and sediment behavior. • The calculator accounts for unique offshore features (i.e., water depths). • Domain storage estimates ranged from 0.5 to 10,000 Gigatons of CO 2. • Saline efficiency was a significant factor when calculating storage capacity. • The methodology and calculator are applicable at multiple geographic scales. The world produces approximately 50 billion tonnes of greenhouse gases annually. This is measured in CO 2 -equivalents, and geologic CO 2 storage has the potential to advance decarbonization and mitigate greenhouse gas emissions. New technologies to assess offshore carbon storage are needed to address resource, regulatory, and commercial needs. Although most efforts to assess storage resources focus on onshore criteria, offshore reservoirs offer significant storage potential and distinct development challenges. Potential advantages of offshore carbon storage include being further from human population centers and less potential to interact with groundwater. The U.S. Department of Energy's method for evaluating storage capacity in non-oil-bearing saline reservoirs has been enhanced to support assessments for offshore environments in the Offshore CO 2 Saline Storage methodology (OCSS). This methodology applies data-driven capabilities to estimate saline storage capacity while accounting for features specific to offshore reservoirs. Features include changes in CO 2 density and sedimentary differences that impact estimates of permanence and capacity. The Offshore CO 2 Saline Storage Calculator mechanizes OCSS to estimate storage capacity. This paper presents the methodology and estimates for 18 geologic domains in the Gulf of Mexico. Potential storage distributions, sensitivity analyses, and the incorporation of spatial data and tools to support safe site selection are also discussed. [ABSTRACT FROM AUTHOR]

• Developed a screening method for ranking viable offshore CO 2 storage sites. • Evaluation incorporates disparate spatial GIS data in decision-making framework. • 14 GIS criteria aggregated over 2559 spatially balanced points across GOM OCS. • Highest ranking regions for storage located along LA coastline in shallow waters. • Highest ranking regions for EOR located in central GOM OCS and MS River Delta. Continued research into reservoir characterization along with offshore carbon dioxide (CO 2) transportation and infrastructure assets is needed to facilitate development of safe and successful carbon capture, utilization, and storage (CCUS) projects. This paper outlines a multi-criteria evaluation methodology that incorporates disparate sets of quantitative, spatially variable data into a decision-making framework for screening the Gulf of Mexico (GOM) outer continental shelf (OCS) for potentially viable CO 2 storage and enhanced oil recovery (EOR) sites. Criteria categories include favorable geologic characteristics, logistics, and potential risks. Data compiled for 14 criteria from several publicly available geographic information system (GIS) layers was aggregated over 2559 spatially balanced points across the study area using the National Energy Technology Laboratory (NETL)-developed Cumulative Spatial Impact Layers™ (CSIL) GIS tool. Criteria are weighted by qualitative expert opinion relative to their perceived importance to given scenarios— the output of combined criteria values and weights enables regional CO 2 storage suitability differentiation. The methodology considers both technical and non-technical factors impacting CCUS decision-making. The flexible methodology enables a systematic approach to regional ranking at high spatial resolution over a large study domain. Additionally, the framework enables high-grading of priority sites that warrant further characterization and follow-on analysis. Areas along the Louisiana coast and Mississippi River Delta consistently rank high for all scenarios largely a result of the favorable geology with the potential for stacked storage, as well as the density of existing pipelines and platforms, and proximity to several onshore CO 2 sources. High-graded regions for the CO 2 EOR-related scenarios are typically located further offshore towards the middle and edge of the OCS compared to higher priority regions for the geologic storage scenarios which fall closer to the Louisiana coastline. [ABSTRACT FROM AUTHOR]

The coastal ocean is affected by an array of co-occurring biogeochemical and anthropogenic processes, resulting in substantial heterogeneity in water chemistry, including carbonate chemistry parameters such as pH and partial pressure of CO 2 (p CO 2). To better understand coastal and estuarine acidification and air-sea CO 2 fluxes, it is important to study baseline variability and driving factors of carbonate chemistry. Using both discrete bottle sample collection (2014–2020) and hourly sensor measurements (2016–2017), we explored temporal variability, from diel to interannual scales, in the carbonate system (specifically pH and p CO 2) at the Aransas Ship Channel located in the northwestern Gulf of Mexico. Using other co-located environmental sensors, we also explored the driving factors of that variability. Both sampling methods demonstrated significant seasonal variability at the location, with highest pH (lowest p CO 2) in the winter and lowest pH (highest p CO 2) in the summer. Significant diel variability was also evident from sensor data, but the time of day with elevated p CO 2 and depressed pH was not consistent across the entire monitoring period, sometimes reversing from what would be expected from a biological signal. Though seasonal and diel fluctuations were smaller than many other areas previously studied, carbonate chemistry parameters were among the most important environmental parameters for distinguishing between time of day and between seasons. It is evident that temperature, biological activity, freshwater inflow, and tide level (despite the small tidal range) are all important controls on the system, with different controls dominating at different timescales. The results suggest that the controlling factors of the carbonate system may not be exerted equally on both pH and p CO 2 on diel timescales, causing separation of their diel or tidal relationships during certain seasons. Despite known temporal variability on shorter timescales, discrete sampling was generally representative of the average carbonate system and average air-sea CO 2 flux on a seasonal and annual basis when compared with sensor data. [ABSTRACT FROM AUTHOR]

Ocean acidification is thought to benefit seagrasses because of increased carbon dioxide (CO2) availability for photosynthesis. However, in order to truly assess ecological responses, effects of ocean acidification need to be investigated in a variety of coastal environments. We tested the hypothesis that ocean acidification would benefit seagrasses in the northern Gulf of Mexico, where the seagrasses Halodule wrightii and Ruppia maritima coexist in a fluctuating environment. To evaluate if benefits of ocean acidification could alter seagrass bed composition, cores of H. wrightii and R. maritima were placed alone or in combination into aquaria and maintained in an outdoor mesocosm. Half of the aquaria were exposed to either ambient (mean pH of 8.1 ± 0.04 SD on total scale) or high CO2 (mean pH 7.7 ± 0.05 SD on total scale) conditions. After 54 days of experimental exposure, the δ13C values were significantly lower in seagrass tissue in the high CO2 condition. This integration of a different carbon source (either: preferential use of CO2, gas from cylinder, or both) indicates that plants were not solely relying on stored energy reserves for growth. Yet, after 41 to 54 days, seagrass morphology, biomass, photo-physiology, metabolism, and carbon and nitrogen content in the high CO2 condition did not differ from those at ambient. There was also no indication of differences in traits between the homospecific or heterospecific beds. Findings support two plausible conclusions: (1) these seagrasses rely heavily on bicarbonate use and growth will not be stimulated by near future acidification conditions or (2) the mesohaline environment limited the beneficial impacts of increased CO2 availability. [ABSTRACT FROM AUTHOR]

Approximately 380,000 underway measurements of sea surface salinity, temperature, and carbon dioxide (CO2) in the Gulf of Mexico (GoM) were compiled from the Surface Ocean CO2 Atlas (SOCAT) to provide a comprehensive observational analysis of spatiotemporal CO2 dynamics from 1996 to 2017. An empirical orthogonal function (EOF) was used to derive the main drivers of spatial and temporal variability in the dataset. In open and coastal waters, drivers were identified as a biological component linked to riverine water, and temperature seasonality. Air-sea flux estimates indicate the GoM open (− 0.06 ± 0.45 mol C m−2 year−1) and coastal (− 0.03 ± 1.83 mol C m−2 year−1) ocean are approximately neutral in terms of an annual source or sink for atmospheric CO2. Surface water pCO2 in the northwest and southeast GoM open ocean is increasing (1.63 ± 0.63 µatm year−1 and 1.70 ± 0.14 µatm year−1, respectively) at rates comparable to those measured at long-term ocean time-series stations. The average annual increase in coastal CO2 was 3.20 ± 1.47 µatm year-1 for the northwestern GoM and 2.35 ± 0.82 µatm year−1 for the west Florida Shelf. However, surface CO2 in the central (coastal and open) GoM, which is influenced by Mississippi and Atchafalaya River outflow, remained fairly stable over this time period. [ABSTRACT FROM AUTHOR]

An important pathway for CO 2 sinking in the ocean is via the "biological pump", driven by the production of particulate organic carbon (POC) in the surface ocean and its subsequent export to the deeper ocean via vertical settling. Here we examine the vertical fluxes of POC in the continental slope of the northern Gulf of Mexico by utilizing the short-lived radionuclide pair 210Po - 210Pb. The total activities of 210Po and 210Pb ranged from 2.5 ± 0.35 to 16.52 ± 1.98 dpm 100 L-1 and from 3.47 ± 0.45 to 24.49 ± 3.42 dpm 100 L-1 respectively with the exception of higher activities of 210Po (87.36 ± 11.38 dpm 100 L-1) and 210Pb (32.25 ± 4.35 dpm 100 L-1) from the near bottom water in the hypersaline anoxic Orca basin. In the upper 150 m of the water column, the inventories of 210Pb were consistently greater than those of 210Po while the total overall water column inventories of 210Po and 210Pb were found to be near equilibrium. The 210Po fluxes varied between 9.8 ± 6.34 dpm m-2 d-1 and 30.7 ± 12.06 dpm m-2 d-1 with corresponding POC fluxes between 8.6 mg C m-2 d-1 and 37.65 mg C m-2 d-1. The fluxes showed a general decreasing trend further offshore, closely following a similar trend in net primary productivity across the slope. The export efficiency ratios "e-ratios" of the biological pump over this slope region was found to vary between 0.027 and 0.11 averaging at 0.05 ± 0.01, which is low. The 210Po based and the model-based e-ratio estimates were different but within the range of previous estimates. • 210Po has an average residence time of 2.18 ± 0.47 year in the continental shelf. • 210Po based POC fluxes varied between 8.59 and 37.65 mg C m-2 d-1 across the shelf. • The e-ratio varied between 0.027 and 0.11 (mean = 0.05 ± 0.01) for this region is found to be low. • Highest reported activities of 210Po and 210Pb for open ocean observed in the hypersaline Orca basin. [ABSTRACT FROM AUTHOR]