GCCC Theses and Dissertations
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Browsing GCCC Theses and Dissertations by Department "Earth and Planetary Sciences"
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Item The behavior of dissolved organic carbon (DOC) at geological sequestration sites(2015-05) Patson, Michael Edwin; Breecker, Dan O.; Larson, Toti Erik; Bennett, Philip CGeologic carbon sequestration has been proposed as a means of mitigating anthropogenic greenhouse gas emissions. At depth, supercritical CO₂ may rise above the surrounding fluid. Detecting leaks from CO₂ storage reservoirs is important to evaluate the effectiveness of carbon sequestration and address public concern for negative environmental impacts. Other attempts have been made to detect leaks, such as changes in pH, pressure and direct observation of CO₂ in the AZMI (Above Zone Monitoring Interval). Each has limitations and here we investigate dissolved organic carbon (DOC) as a potential indicator for fugitive CO₂. This study uses a series of batch experiments to evaluate the interaction between dissolved CO₂ and DOC. The batches consist of homogenized and sieved 250 micron to 425 micron matrix samples of varying mass and type, 2mL of DI water and a headspace of pure carbon dioxide or air. The three different rock samples analyzed are Buffalo River Sediment, illite and Barnett Shale. A pure CO₂ headspace results in lower amount of DOC in solution than an air headspace. All matrix samples demonstrated this effect. The proposed mechanism to describe the observed results is that a lowered pH shifts speciation of weak organic acids and protonated humic substances causing decreased solubility and increasing the adsorption of these compounds. These results suggest that a decrease in DOC concentrations could be used to detect CO₂ leakage and that CO₂ leakage would not deteriorate water quality by releasing DOC.Item Carbon capture and storage network optimization under uncertainty(2018-05) Tutton, Peter Mark; Leibowicz, Benjamin D.; Hovorka, Susan D. (Susan Davis)Carbon capture and storage is a method for emissions reductions that can be applied to both the electric sector and industrial sources. Significant uncertainties surround the technologies, policy and extent to which CCS will be deployed in the future. For widespread deployment, future CCS demand should be considered during infrastructure planning. This study presents a novel model that considers spatial information and uncertainty in generating an optimal CCS network. The two-stage stochastic model, utilizes both geographic information systems (GIS) and mixed integer programming (MIP), to generate an optimal near-term hedging strategy. The strategy considers one discrete uncertainty distribution: the future demand for CO₂ storage. A case study in the Texas Gulf Coast demonstrates the value of considering uncertainty of future demand. The optimal solution is selected from a candidate network consisting of twelve sources and five reservoirs that can be linked via a network of pipelines and ship routes. The results demonstrate that optimal hedging strategies lead to transportation cost savings of up to 14% compared to a ‘naive approach’ in which only the expected value is considered. The transportation selection also highlights the benefit of utilizing ship transport in uncertain scenarios due to their ability to be reassigned to a different route or sold.Item Carbon dioxide storage in geologically heterogeneous formations(2013-12) Chang, Kyung Won; Hesse, Marc; Nicot, Jean-Philippe, 1958-Geological carbon dioxide (CO₂) storage in deep geological formations can only lead to significant reductions in anthropogenic CO₂ emissions if large amounts of CO₂ can be stored safely. Determining the storage capacity, which is the volume of CO₂ stored safely, is essential to determine the feasibility of geological CO₂ storage. One of the main constraints for the storage capacity is the physical mechanisms of fluid flow in heterogeneous formations, which has not been studied sufficiently. Therefore, I consider two related problems: a) the evolution of injection-induced overpressure that determines the area affected by CO₂ storage and b) the rate of buoyant fluid flow along faults that determines the leakage of CO₂. I use a layered model of a sandstone reservoir embedded in mudrocks to quantify the increase in storage capacity due to dissipation of overpressure into the mudrocks. I use a model of a fault surface with flow barriers to constrain the reduction in the buoyancy-driven leakage flux across the fault. Using the layered model with injection at constant rate, I show that the pressure evolution in the reservoir is controlled by the amount of overpressure dissipated into ambient mudrocks. A main result of this study is that the pressure dissipation in a layered reservoir is controlled by a single dissipation parameter, M, that is identified here for the first time. I also show that lateral pressure propagation in the storage formation follows a power-law governed by M. The quick evaluation of the power-law allows a determination of the uncertainty in the estimate of the storage capacity. To reduce this uncertainty it is important to characterize the petrophysical properties of the mudrocks surrounding the storage reservoir. The uncertainty in mudrock properties due to its extreme heterogeneity or limited data available can cause large variability in these estimates, which emphasizes that careful characterization of mudrock is required for a reliable estimate of the storage capacity. The cessation of the injection operation will reduce overpressure near the injector, but regional scale pressure will continue to diffuse throughout the whole formation. I have been able to show that the maximum radius of the pressure plume in the post-injection period is approximately 3.5 times the radius of the pressure plume at the cessation of injection. Two aquifers can be hydraulically connected by a fault cutting across the intermediate aquitard. If the upper aquifer contains denser fluid, an exchange flow across the fault will develop. The unstable density stratification leads to a fingering pattern with localized zones of upwelling and downwelling along the fault. Due to the small volume of the fault relative to the aquifers, the exchange-flow will quickly approach a quasi steady state. If the permeability of the fault plane is homogeneous, the average number of the quasi-steady plume fingers, (nu), scales with the square root of the Rayleigh number Ra and the exchange flux measured by dimensionless convective flux, the Sherwood number, Sh, is a linear function of Ra. The dispersive flux perpendicular to the flow direction induces the formation of wider fingers and subsequently the less convective flux parallel to the flow direction. In the flow system with larger Ra, even the same increase in transverse dispersivity [alpha]T causes stronger impact of the mechanical dispersion on the vertical exchange flow so that (nu) and Sh reduce more with larger [alpha]T . Both measured characteristics, however, follow the same scaling for the non-dispersive homogeneous case by using a modified Rayleigh number, Ra*, considering the mechanical dispersion. The presence of flow barriers along the fault triggers unsteady exchange flow and subsequently controls the growth of the plume fingers. If the barriers are sufficiently wide to dominate the flow system, they create preferential pathways for exchange flow that determines the distribution of the quasi-steady fingers, and (nu) converges to a constant value. In addition, wider barriers induce substantial lateral spreading and enhance the efficiency of structural trapping, and reduce the exchange rate but still follows a linear relationship function of the effective Rayleigh number, Raeff , defined by the vertical effective permeability. This study is motivated by geological CO₂ storage in brine-saturated aquifer, but the effect of geological heterogeneity is also important in many other geological and engineering applications, in particular the risk assessment of the injection operations or the migration of hydrocarbons in tectonic-driven or hydraulically developed faults in reservoirs. Better understanding of fluid flow in geologically heterogeneous formations will allow more precise estimate of the reservoir capacity as well as more efficient operation of injection or production wells.Item Characterization and prediction of reservoir quality in chlorite-coated sandstones : evidence from the Late Cretaceous Lower Tuscaloosa Formation at Cranfield Field, Mississippi, U.S.A.(2013-05) Kordi, Masoumeh; Fisher, W. L. (William Lawrence), 1932-; Hovorka, Susan D. (Susan Davis)The effectiveness of CO₂ injection in the subsurface for storage and EOR are controlled by reservoir quality variation. This study determines the depositional processes and diagenetic alterations affecting reservoir quality of the Lower Tuscaloosa Formation at Cranfield Field. It also determines the origin, time and processes of the grain-coating chlorite and its impacts on reservoir quality. Moreover, by integrating depositional and diagenetic characteristics and by linking them to sequence stratigraphy, the distribution of reservoir quality, could be predicted within a sequence stratigraphic framework. The studied sandstones are composed of medium to coarse-grained, moderately sorted litharenite to sublitharenite with composition of Q76.1F0.4L23.5. Depositional environment of this formation in the Mississippi Interior Salt Basin is interpreted as incised-valley fluvial fill systems. The cross sections and maps at the field show trend of the sandy intervals within channels with a NW-SE paleocurrent direction. During burial of the sandstones, different digenetic alterations including compaction, dissolution, replacement and cementation by chlorite, quartz, carbonate, kaolinite, titanium oxides, pyrite and iron-oxide modified the porosity and permeability. Among these, formation of chlorite coats plays the most important role in reservoir quality. The well-formed, thick and continuous chlorite coatings in the coarser grain sandstones inhibited formation of quartz overgrowth, resulted in high porosity and permeability after deep burial; whereas the finer grain sandstones with the poorly-formed, thin and discontinuous chlorite coatings have been cemented by quartz. The optimum amount of chlorite to prevent formation of quartz overgrowths is 6% of rock volume. The chlorite coats are composed of two layers including the inner chlorite layer formed by transformation of the Fe-rich clay precursors (odinite) through mixed-layer clays (serpentine-chlorite) during early eodiagenesis and the outer layer formed by direct precipitation from pore waters through dissolution of ferromagnesian rock fragments during late eodiagenesis to early mesodiagenesis. In the context of the reservoir quality prediction within sequence stratigraphic framework, the late LST and early TST are suitable for deposition of chlorite precursor clays, which by progressive burial during diagenesis could be transformed to chlorite, and thus results in preserving original porosity and permeability in deep burial.Item Characterization of the High Island 24L Field for modeling and estimating CO₂ storage capacity in the offshore Texas state waters, Gulf of Mexico(2019-07-25) Ruiz, Izaak; Meckel, Timothy AshworthCarbon, Capture, and Storage (CCS) is considered an essential technology that can contribute to reaching the IPCC’s target to limit global average temperature rise to no more than 2.0°C. The fundamental purpose of CCS is to reduce anthropogenic CO₂ emissions by capturing gas from large point sources and injecting it into deep geologic formations. In the offshore Texas State Waters (10.3 miles; 16.6 kilometers), the potential to develop CO₂ storage projects is viable, but the size of storage opportunity at the project level is poorly constrained. This research characterizes the High Island 24L Field, a relatively large historic hydrocarbon field, that has produced mainly natural gas (0.5 Tcf). The primary motivation for this study is to demonstrate that depleted gas fields can serve as volumetrically significant CO₂ storage sites. The stratigraphy of the inner continental shelf in the Gulf of Mexico has been extensively explored for hydrocarbon for over 50 years, and this area is well suited for CCS. Lower Miocene sandstones beneath the regional transgressive Amphistegina B shale have appropriate geologic properties (porosity, thickness, extent) and can be characterized utilizing 3D seismic and well logs in this study. Identifying key stratigraphic surfaces, faults, and mapping structural closure footprints illustrates the field’s geologic structure. The interpreted stratigraphic framework can then be used to model three different lithologic facies and effective porosity to calculate CO₂ storage capacity for both the ~200-ft (60-m) thick HC Sand (most productive gas reservoir) and the overlying thicker 1700 ft (520 m), but non-productive, Storage Interval of Interest. Four different methodologies are utilized to achieve confidence in the CO₂ storage capacity estimates. A storage capacity of 15 – 23 MT is calculated for the HC Sand and 108 – 179 MT for the Storage Interval of Interest by applying interpreted efficiency factors. This study evaluates the accuracy of these storage capacity methodologies to better understand the key geologic factors that influence CO₂ storage in a depleted hydrocarbon field for CCSItem Characterizing reservoir quality for geologic storage of CO2 : a case study from the Lower Miocene shore zone at Matagorda Bay, Texas(2021-05-10) Hull, Harry Lejeune; Meckel, Timothy AshworthThe geologic storage of anthropogenic CO₂ through Carbon Capture, Utilization, and Storage (CCUS) is necessary to reduce the emissions produced as a biproduct of fossil fuel combustion. This process of injecting CO₂ into the subsurface is known as carbon sequestration and requires the assessment of geologic reservoirs. Depositional processes and the resulting facies and stratigraphic architectures have great influence over reservoir volumetrics and behavior. The objective of this study is to constrain the depositional controls on storage capacity. A subsurface Lower Miocene 2 strandplain/barrier bar complex of the Texas Gulf Coast at Matagorda bay is interpreted and modeled using well data and 3D seismic. These data reveal the presence of a major shore zone that experienced initial progradation through the late highstand and into the lowstand before later retrogradation. The LM2 is then capped by a thick regional shale. A stratigraphic framework is built that captures these changes in shoreline position at both the systems tract and parasequences level. Sediments were strike fed and wave-dominated processes are apparent. Petrophysical properties of this region including porosity are modeled from with machine learning from log data. Machine learning to predict porosity is carried out using a random forest regression in which porosity is a function of lithology and depth. Finally, a 3D reservoir model is built integrating the stratigraphic, facies, and petrophysical properties. Static storage capacity estimates and storage capacity maps are created from the 3D model. Storage capacity is observed to occur at a strike parallel geometry. This “axis” of highest storage capacity tracts with the position of the shore zone in vertical succession highlighting a dependence on the balance between the generation of accommodation and sediment supply. At a higher resolution storage capacity is observed highest within the foreshore where beach ridges are interpreted from seismic stratal slices. High wave energy processes at this position in the shoreline profile are known to create well sorted and therefore highly porous sandstones. Storage capacity is then a direct function of the high wave energy paleo-depositional processes occurring at the shorelineItem Compositional changes of light hydrocarbons during migration through overburden : proxy for assessing potential leakage from Geological Carbon Storage(2017-12) Anderson, Jacob Spencer; Young, Michael H.; Lavier, Luc L; Hesse, Marc A; Breeker, Daniel O; DiCarlo, David ALight hydrocarbon compositions evolve during migration through geologic media, but our understanding of geochemical alteration is limited because of the challenges with analyzing fluids in the sedimentary column. Understanding fluid evolution is timely because of the possibility of upward fluid migration from Geologic Carbon Storage (GCS) operations. The first goal of this research is to identify to what extent hydrocarbons migrate to shallower intervals. Addressing this goal is challenging because microbial hydrocarbon production commonly occurs in the near-surface. Light hydrocarbon compositions are investigated in soil gas above a hydrocarbon system and in offshore sediment above a gas chimney. In both cases, the fluid sources are interpreted as microbial in origin. However, these geochemical datasets are relevant to attributing future light hydrocarbon seeps and anomalies above GCS sites. The second goal is to quantify alteration processes when migration has occurred. I hypothesize that phase changes and sorption are the primary alteration processes. To test this hypothesis, I numerical simulation these processes to compare with field datasets that are interpreted as migration. The models indicate that sorption has the most significant influence on light hydrocarbons, although more lab work is warranted to improve these models. Forward models of CO₂ migration show that phase changes are important in attenuating CO₂ and can be identified with noble gas compositions. This conclusion may be valuable to determining the source of CO₂ anomalies above GCS sites.Item Empirical analysis of fault seal capacity for CO₂ sequestration, Lower Miocene, Texas Gulf Coast(2012-05) Nicholson, Andrew Joseph; Meckel, Timothy Ashworth; Tinker, Scott W. (Scott Wheeler); Trevino, Ramon H.; Steel, Ronald J.The Gulf Coast of Texas has been proposed as a high capacity storage region for geologic sequestration of anthropogenic CO₂. The Miocene section within the Texas State Waters is an attractive offshore alternative to onshore sequestration. However, the stratigraphic targets of interest highlight a need to utilize fault-bounded structural traps. Regional capacity estimates in this area have previously focused on simple volumetric estimations or more sophisticated fill-to-spill scenarios with faults acting as no-flow boundaries. Capacity estimations that ignore the static and dynamic sealing capacities of faults may therefore be inaccurate. A comprehensive fault seal analysis workflow for CO₂-brine membrane fault seal potential has been developed for geologic site selection in the Miocene section of the Texas State Waters. To reduce uncertainty of fault performance, a fault seal calibration has been performed on 6 Miocene natural gas traps in the Texas State Waters in order to constrain the capillary entry pressures of the modeled fault gouge. Results indicate that modeled membrane fault seal capacity for the Lower Miocene section agrees with published global fault seal databases. Faults can therefore serve as effective seals, as suggested by natural hydrocarbon accumulations. However, fault seal capacity is generally an order of magnitude lower than top seal capacity in the same stratigraphic setting, with implications for storage projects. For a specific non-hydrocarbon producing site studied for sequestration (San Luis Pass salt dome setting) with moderately dipping (16°) traps (i.e. high potential column height), membrane fault seal modeling is shown to decrease fault-bound trap area, and therefore storage capacity volume, compared with fill-to-spill modeling. However, using the developed fault seal workflow at other potential storage sites will predict the degree to which storage capacity may approach fill-to-spill capacity, depending primarily on the geology of the fault (shale gouge ratio – SGR) and the structural relief of the trap.Item Experimental analysis and modeling of perfluorocarbon transport in the vadose zone : implications for monitoring CO₂ leakage at CCS sites(2013-05) Gawey, Marlo Rose; Breecker, Dan O.; Romanak, Katherine Duncker; Larson, Toti ErikPerfluorocarbon tracers (PFTs) are commonly proposed tracers for use in carbon capture and sequestration (CCS) leak detection and vadose zone monitoring programs. Tracers are co-injected with supercritical CO₂ and monitored in the vadose zone to identify leakage and calculate leakage rates. These calculations assume PFTs exhibit “ideal” tracer behavior (i.e. do not sorb onto or react with porous media, partition into liquid phases or undergo decay). This assumption has been brought into question by lab and field evaluations showing PFT partitioning into soil contaminants and sorbing onto clay. The objective of this study is to identify substrates in which PFTs behave conservatively and quantify non-conservative behavior. PFT breakthrough curves are compared to those of a second, conservative tracer, sulfur hexafluoride (SF₆). Breakthrough curves are generated in 1D flow-through columns packed with 5 different substrates: silica beads, quartz sand, illite, organic-rich soil, and organic-poor soil. Constant flow rate of carrier gas, N₂, is maintained. A known mass of tracer is injected at the head of the columns and the effluent analyzed at regular intervals for tracers at picogram levels by gas chromatography. PFT is expected to behave conservatively with respect to SF₆ in silica beads or quartz sand and non-conservatively in columns with clay or organics. However, results demonstrate PFT retardation with respect to SF₆ in all media (retardation factor is 1.1 in silica beads and quartz sand, 2.5 in organic-rich soil, >20 in organic-poor soil, and >100 in illite). Retardation is most likely due to sorption onto clays and soil organic matter or condensation to the liquid phase. Sorption onto clays appears to be the most significant factor. Experimental data are consistent with an analytical advection/diffusion model. These results show that PFT retardation in the vadose zone has not been adequately considered for interpretation of PFT data for CCS monitoring. These results are preliminary and do not take into account more realistic vadose zone conditions such as the presence of water, in which PFTs are insoluble. Increased moisture content will likely decrease sorption onto porous media and retardation in the vadose zone may be less than determined in these experiments.Item Fault seal and containment failure analysis of a Lower Miocene structure in the San Luis Pass area, offshore Galveston Island, Texas inner shelf(2016-05) Osmond, Johnathon Lee; Meckel, Timothy Ashworth; Gulick, Sean; Marrett, Randall; Eichhubl, PeterFaults that displace siliciclastic reservoirs have been observed to either seal hydrocarbon accumulations in structural traps or serve as conduits for buoyant fluid migration. While many faults located along the Texas Inner Shelf in the Gulf of Mexico do provide adequate lateral seals for the Lower Miocene petroleum system, oil and gas operators targeting the large antiformal structure roughly 7 mi offshore from San Luis Pass have been highly unsuccessful in discovering commercial amounts of methane gas. Images interpreted from 12 mi2 of high-resolution 3-D seismic reflection data (HR3D) has revealed an apparent gas chimney feature directly above the target structure that previously acquired lower-resolution conventional 3-D data failed to identify. Furthermore, the available seismic data show that the 55,000 foot-long normal growth fault displacing the San Luis Pass structure (Fault A) has propagated into the shallow Late Pleistocene (~140 ka) and younger sediment, suggesting recent movement of the hanging wall block has occurred. These three observations call into questions the ability for Fault A to properly seal and contain hydrocarbon accumulations, assuming the structure was sufficiently charged with methane, similarly to the surrounding Lower Miocene structures that have produced. An analysis of fault seal and potential containment failure mechanisms affecting the San Luis Pass structure is conducted here in order to address how hydrocarbons may have escaped into the shallow overburden sediments. 3-D geologic modeling of the Lower Miocene 2 (LM2) reservoir interval and Amph. B Shale top seal against Fault A yields fill-to-spill closure capacities of approximately 686 ft and 992 ft for the footwall and hanging wall closures, respectively. Fault seal membrane limited methane column height estimations are 300 ft and 325 ft from footwall to hanging wall, and were obtained by way of empirically calibrated equations that attempt to account for capillary entry properties of a fault through the estimation of its clay mineral content using the Shale Gouge Ratio (clay volume/fault throw). Although capacity estimations appear to be geologically reasonable in this region, they fail to explain the lack of hydrocarbons in the system, so four potential across-fault migration and leakage scenarios are considered for the purpose of determining pathways from the reservoir interval to the shallow subsurface. Areas where sandstone on sandstone juxtapositions generally pose the greatest risk of across-fault leakage, and 23 individual Lower Miocene 2 and Middle Miocene (MM) sandstone units juxtaposed against Fault A are evaluated. While the ability of Fault A to seal hydrocarbons may be feasible in static conditions, additional mechanisms evaluated using the available data include: top seal membrane leakage, top seal mechanical failure and fault reactivation mechanisms. Top seal thickness ranges between 500 ft and 1,000 ft in the study area, and analogous Lower Miocene mudstones are shown to retain methane columns of about 936 ft. Data limitations significantly reduce the ability to thoroughly investigate top seal mechanical failure and fault reactivation at this time, however, apparent vertical displacement measurements from overlapping seismic datasets suggest that movement along Fault A continued since it originally formed, and that two pulses of increased throw rate may have occurred in Early Miocene, and the Pleistocene. The apparent Pleistocene throw rates range from 0.010 mm/year to 0.125 mm/year, and are significant because the Early Miocene pulse occurred before the formation of the Amph. B top seal. Thus, it is interpreted that fault reactivation may represent the primary containment failure mechanism for the San Luis Pass structure, and that the increased apparent throw rate in the Pleistocene may symbolize a period of hydrocarbon leakage from the LM2 reservoir interval.Item Geochemical effects of elevated methane and carbon dioxide in near-surface sediments above an EOR/CCUS site(2013-05) Hingst, Mary Catherine; Young, Michael H.; Romanak, Katherine DunckerCarbon capture, utilization and storage (CCUS) aims to reduce CO₂ emissions by capturing CO₂ from sources and injecting it into geologic reservoirs for enhanced hydrocarbon recovery and storage. One concern is that unintentional CO₂ and reservoir gas release to the surface may occur through seepage pathways such as fractures and/or improperly plugged wells. We hypothesize that CO₂ and CH₄ migration into the vadose zone and subsequent O₂ dilution and Eh and pH changes could create an increased potential for metal mobilization, which could potentially contaminate ground and surface waters. This potential has not been addressed elsewhere. Goals of this study are to understand how the potential for metal mobilization through soil pore water may increase due to CO₂ and CH₄ and to assess potential impact to aquifers and/or the biosphere. The study was conducted at a CCUS site in Cranfield, MS, where localized seepage of CH₄ (45%) from depth reaches the surface and oxidizes to CO₂ (34%) in the vadose zone near a plugged well. Four sediment cores (4.5-9m long) were collected in a transect extending from a background site through the area of anomalously high soil gas CO₂ and CH₄ concentrations. Sediment samples were analyzed for Eh and pH using slurries (1:1 vol. with DI water) in the field and for occluded gas concentrations, metal (Ba, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) concentrations, moisture content, organic carbon content, and grain size in the laboratory. Data from the background reference area (no gas anomaly: occluded gas ~21% O₂, <1% CO₂, 0% CH₄) showed oxidized conditions (Eh from 464-508mV) and neutral pH (7.0-7.8) whereas samples collected near the gas anomaly (13-21% O₂, 0.1-5% CO₂, <0.1% CH₄) were more reducing (Eh 133-566mV) and more acidic (pH = 5.3-8.0). Significant correlations were found between Eh and O₂ (r = 0.95), pH and CO₂ (r = -0.88), and between these parameters and acid-leachable metals in samples from within the soil gas anomaly. Correlations quickly weaken away from the anomaly. Statistically, total metal concentrations, except for Ba, are similar in all cores. Acid-mobile metal concentrations, above 5m, increase toward the gas anomaly. The percent of water-mobile metals is very low (<2%) for all metals in all cores, indicating freely-mobile metals are not affected by elevated CO₂/CH₄. Conclusions are: 1) oxidation of CH₄ to CO₂ depletes O₂ causing reducing conditions; 2) high CO₂ and low O₂ affect Eh and pH of sediments which in turn alters mineralogy and bond strength between sediments and adsorbed ions; 3) intrusion of strongly acidic fluids (pH of acid used was 0.39) into these sediments could potentially remove weakly bonded metals or dissolve minerals. Implications from this study are that Eh needs to be considered along with pH when analyzing contamination potential, and that exposure of sediments to reducing, followed by acidic conditions, increases the potential for metal mobilization in the vadose zone. More research is needed to determine the concentration of gases (CO₂, CH₄ and O₂) that will create Eh and pH levels that could affect the mineralogy and sorption mechanism potentially leading to metal mobilization. Methods for assessing potential metal mobilization may be useful for site characterization and risk assessment.Item Geochemical evolution of karst vadose water and brush clearing impacts on recharge in central Texas(2008-12) Wong, Corinne; Banner, Jay L.Groundwater geochemistry is used to investigate flow paths, water residence times, and rock-water interaction processes, which is especially important in central Texas where groundwater flow is unpredictable and difficult to study due to the anisotropic nature of karst terrains. The first part of this study is a multiyear monitoring study that identifies and quantifies the processes controlling vadose drip water evolution in a cave, Natural Bridge Caverns, central Texas. Three different types of drip water are identified. Group 1 drip sites (n=3) are characterized by strong seasonal variations in Mg/Ca and Sr/Ca that are driven by seasonal fluctuations in calcite precipitation related to winter cave ventilation. Group 2 drip sites (n=4) exhibit correlations between drip water composition (Mg/Ca, Sr/Ca, and ⁸⁷Sr/⁸⁶Sr) and measures of water flux (rainfall and drip rate). Mass balance modeling demonstrates rock-water interactions (i.e., dissolution-reprecipitation processes involving carbonate minerals comprising host Cretaceous carbonate rocks) can account for drip water compositions. Group 3 sites (n=2) exhibit limited geochemical, physical or temporal correlations. Group 3 sites likely reflect a combination of Groups 1 and 2 processes, as drip water composition suggests both varying extents of rock-water interaction and calcite precipitation. The results of this study provide insight on the processes controlling the geochemical evolution of vadose karst waters and can be applied toward uncoding the paleoclimate signals recorded in speleothems. More specifically, in areas where cave-air CO₂ fluctuates seasonally, speleothem Mg/Ca and Sr/Ca variations may serve as chemical indicators of annual laminae, and speleothem growth may be biased. The second part of the study uses changes in drip rate and drip water geochemistry to evaluate the affects of brush clearing on recharge. Brush clearing is commonly used to increase stream and spring flow in central Texas even though it is not clear whether or not brush clearing enhances recharge. Drip rate and drip water composition were monitored every four to six weeks from May 2004 to April 2008. Brush clearing above the cave was conducted from April 2007 to July 2007. Drip rate and drip water compositions were compared at nine drip water sites, five of which are directly beneath an area cleared during this study. There were no changes in drip rate, Mg/Ca, Sr/Ca, or ⁸⁷Sr/⁸⁶Sr at drip sites beneath the cleared area that could be attributed to the brush clearing. The lack of change in drip water compositions and drip rates indicate that the brush clearing did not have a discernible impact on recharge to the cave, and suggests brush clearing does not have an impact on vadose recharge.Item High order stratigraphic framework of intraslope growth faulted subbasins offshore Matagorda Bay, Texas(2021-12-09) Franey, John D.; Meckel, Timothy AshworthCarbon capture and storage (CCS) is currently one of the leading atmospheric emission mitigation technologies. To have meaningful impact on the atmosphere CO₂ concentrations, megatons (10⁶) of CO₂ must be removed from the carbon cycle permanently. This requires a subsurface geologic storage sites that are both volumetrically significant and secure over geologic time-scales. The northern Gulf of Mexico (GOM) has the ability to serve as a major location for CCS. Miocene strandplain systems in the GOM are an ideal stratigraphy for such storage due to their proximity to emissions sources, quality sand reservoirs, and depth relative to overpressure. This study focuses on a suite of strike parallel subbasins within the Lower Miocene offshore Matagorda Bay, TX. Each subbasin has potential to serve as a future carbon sequestration site. Accurate mapping of subbasins’ stratigraphy is necessary to understand the variable thickness and associated risk of reservoir-sealing shale intervals, recognizing that injection beneath thicker, more uniformly distributed shales is more favorable. These intervals must be mapped at high resolution (4th order cyclicity) to understand the individual components in assessment and risk analysis. This research generates a novel dip-steered seismic volume which is leveraged to improve seismic attribute calculations and mapping at the 4th order. The dip-steered seismic volume records the seismic dip in the inline and crossline direction of seismic features at the intersection of every inline, crossline, and seismic sample. This volume is used to generate a model of dense, 3D, auto-tracked horizons across each subbasin. The models better connect high resolution, but sparse, well log data and low resolution, but continuous, seismic data. Thickness distributions and shale interval maps generated from the models aid in risk assessment. Based on the resulting shale thicknesses, the suite of subbasins should be further considered as future storage sitesItem Offshore mapping and modeling of Miocene-Recent extensional basins adjacent to metamorphic gneiss domes of the D'Entrecasteaux Islands, eastern Papua New Guinea(2011) Fitz, Guy Gregory; Mann, Paul, 1956-The D'Entrecasteaux Island (DEI) gneiss domes are fault-bounded domes with ~2.5 km of relief exposing ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic gneisses and migmatites exhumed in an Oligocene-Miocene arc-continent collision and subduction zone subject to Late Miocene to Recent continental extension. To study the style of continental extension accompanying exhumation of the DEI gneiss domes, a grid of 1,518 km of 2-D multi-channel seismic (MCS) reflection data and well data is interpreted from the offshore areas surrounding the DEI, including the Trobriand basin and the Goodenough basin. The offshore study is combined with onshore geologic information to constrain the area's Oligocene to Recent basinal and tectonic evolution. MCS and well data show the Trobriand basin formed as a forearc basin caused by southward Miocene subduction at the Trobriand trench. Late Miocene basin inversion uplifted the southern and northern basin margins. Subduction slowed at ~8 Ma as the margin transitioned to an extensional tectonic environment. Since then, the Trobriand basin has subsided 1-2.5 km as a broad sag basin with few normal faults deforming the basin fill. South of the DEI, the Goodenough rift basin developed after extension began (~8 Ma) as the hanging-wall of the north-dipping Owen-Stanley normal fault bounding the southern margin of the basin. Rapid uplift of the adjacent footwall of the Owen-Stanley fault zone in the Papuan Peninsula accompanied the formation of the Goodenough submarine rift basin. The lack of upper crustal extension accompanying subsidence in the Trobriand and Goodenough basins suggests depth-dependent lithospheric extension from 8-0 Ma has accompanied uplift of the DEI gneiss domes. Structural reconstructions of seismic profiles show 2.3 to 13.4 km of basin extension in the upper crust, while syn-rift basin subsidence values indicate at least 20.7 to 23.6 km of extension occurred in the lower crust since ~8 Ma. Results indicating thinning is preferentially accommodated in the lower crust surrounding the DEI are used to constrain a schematic model of uplift of the DEI domes involving vertical exhumation of buoyant, post-orogenic lower crust, far-field extension from slab rollback, and an inverted two-layer crustal density structure.Item Pre-injection reservoir characterization for CO₂ storage in the inner continental shelf of the Texas Gulf of Mexico(2017-05) Sabbagh, Reinaldo Jose; Meckel, Timothy AshworthThe injection of CO₂ into the subsurface (carbon capture and storage; CCS) is the most viable approach to significantly reduce industrial emissions of greenhouse gasses to the atmosphere. The inner continental shelf of the northern Gulf of Mexico has incredible potential for CO₂ storage. This study quantitatively evaluates the CO₂ storage capacity of the Lower Miocene brine-filled sandstones in the inner continental shelf of the Texas Gulf of Mexico using 3D seismic and well log data. The first part of this work investigates the relationship between elastic properties and reservoir properties (e.g., porosity, mineralogy, and pore fluid) of the Lower Miocene section using rock physics modeling and simultaneous seismic inversion. The elastic properties are related to porosity, mineralogy and pore fluid using rock physics models. These rock physics transforms are then applied to the seismically derived elastic properties to estimate the porosity and lithology away from the wells. The porosity and lithology distribution derived using this quantitative method can be interpreted to predict the best areas for CO₂ storage in the inner continental shelf of the Texas Gulf of Mexico. The second part of this work studies the effect that CO₂ has on the elastic properties of the Lower Miocene rocks using fluid substitution, amplitude variation with angle (AVA), and statistical classification to determine the ability of the seismic method to successfully monitor CO₂ injected into the subsurface. The velocities and density well logs were modeled with different fluid saturations. To characterize the seismic properties corresponding to these different fluid saturations, the AVA responses and probability density functions were calculated and used for statistical classification. The AVA modeling shows a high sensitivity to CO₂ due to the soft clastic framework of the Lower Miocene sandstones. The statistical classification successfully discriminates between brine and CO₂ saturation using Vp/Vs and P-impedance. These results shows that the Lower Miocene sandstones have the capacity to host CO₂, and that the CO₂ injected in these rocks is likely to be successfully monitored using seismic methods.Item A question of capacity assessing CO₂ sequestration potential in Texas offshore lands(2012-12) Miller, Erin Noel; Tinker, Scott W. (Scott Wheeler); Meckel, Timothy Ashworth; Flemings, PeterThe combustion of fossil fuels results in the release of carbon dioxide to the atmosphere, a known greenhouse gas. Evidence suggests that “most of the observed increase in global average temperatures…is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (IPCC, 2007). One solution currently being examined is carbon capture and storage (CCS). The advantage of CCS is that it does not require an actual reduction in the amount of carbon dioxide emissions created, but reduces emissions to the atmosphere by storing the greenhouse gases in the subsurface. Fundamentally, CCS works in the reverse of oil and gas production. Instead of extracting fluids from the subsurface, CCS injects carbon dioxide (CO2) into the pore spaces of developed oil and gas reservoirs, saline aquifers, or coal bed seams (Bachu, 2007), where it exists in a dense but low-viscosity phase (Supercritical state). The Gulf Coast Carbon Center, based at the University of Texas at Austin’s Bureau of Economic Geology, is currently evaluating the State of Texas Offshore Lands (STOL) in the Gulf of Mexico (GOM) in order to evaluate the carbon-storage capacity in the state owned lands. “Capacity is defined as the volume fraction of the subsurface within a stratigraphic interval available for [CO2] sequestration” (Hovorka, 2004). There are a variety of methods currently used to calculate capacity. With so many options, how does a project decide which method to employ in determining capacity? This paper discusses the methods, presents an analysis of the benefits and drawbacks of the various methods, and develops a process for future projects to utilize in determining which methodology to employ. Additionally, storage capacity is calculated using the various methods presented, in order to compare the methods and understand their various advantages and drawbacks. Reservoir specific simulations are expected to predict smaller capacities in comparison to more broad static methods. This will provide end member predictions of capacity, shedding light on what can be expected in best case and worst case scenarios. The lessons learned from this study can be applied to future endeavors and formations all over the world.Item Time-lapse seismic monitoring for enhanced oil recovery and carbon capture and storage field site at Cranfield field, Mississippi(2013-12) Ditkof, Julie Nicole; Bangs, Nathan Lawrence Bailey; Meckel, Timothy AshworthThe Cranfield field, located in southwest Mississippi, is an enhanced oil recovery and carbon sequestration project that has been under a continuous supercritical CO₂ injection by Denbury Onshore LLC since 2008. Two 3D seismic surveys were collected in 2007, pre-CO₂ injection, and in 2010 after > 2 million tons of CO₂ was injected into the subsurface. The goal of this study is to characterize a time-lapse response between two seismic surveys to understand where injected CO₂ is migrating and to map the injected CO₂ plume edge. In order to characterize a time-lapse response, the seismic surveys were cross equalized using a trace-by-trace time shift. A normalized root-mean-square (NRMS) difference value was then calculated to determine the repeatability of the data. The data were considered to have “good repeatability,” so a difference volume was calculated and showed a coherent seismic amplitude anomaly located through the area of interest. A coherent seismic amplitude anomaly was also present below the area of interest, so a time delay analysis was performed and calculated a significant added velocity change. A Gassmann-Wood fluid substitution workflow was then performed at two well locations to predict a saturation profile and observe post-injection expected changes in compressional velocity values at variable CO₂ saturations. Finally, acoustic impedance inversions were performed on the two seismic surveys and an acoustic impedance difference volume was calculated to compare with the fluid substitution results. The Gassmann-Wood fluid substitution results predicted smaller changes in acoustic impedance than those observed from acoustic impedance inversions. At the Cranfield field, time-lapse seismic analysis was successful in mapping and quantifying the acoustic impedance change for some seismic amplitude anomalies associated with injected CO₂. Additional well log data and refinement of the fluid substitution workflow and the model-based inversion performed is necessary to obtain more accurate impedance changes throughout the field instead of at a single well location.Item Use of 3-dimensional dynamic modeling of CO₂ injection for comparison to regional static capacity assessments of Miocene sandstone reservoirs in the Texas State Waters, Gulf of Mexico(2013-05) Wallace, Kerstan Josef; Young, Michael H.; Meckel, Timothy AshworthGeologic sequestration has been suggested as a viable method for greenhouse gas emission reduction. Regional studies of CO₂ storage capacity are used to estimate available storage, yet little work has been done to tie site specific results to regional estimates. In this study, a 9,258,880 acre (37469.4 km²) area of the coastal and offshore Texas Miocene interval is evaluated for CO₂ storage capacity using a static volumetric approach, which is essentially a discounted pore volume calculation. Capacity is calculated for the Miocene interval above overpressure depth and below depths where CO₂ is not supercritical. The goal of this study is to determine the effectiveness of such a regional capacity assessment, by performing refinement techniques that include simple analytical and complex reservoir injection simulations. Initial refinement of regional estimates is performed through net sand picking which is used instead of the gross thickness assumed in the standard regional calculation. The efficiency factor is recalculated to exclude net-to-gross considerations, and a net storage capacity estimate is calculated. Initial reservoir-scale refinement is performed by simulating injection into a seismically mapped saline reservoir, near San Luis Pass. The refinement uses a simplified analytical solution that solves for pressure and fluid front evolution through time (Jain and Bryant, 2011). Porosity, permeability, and irreducible water saturation are varied to generate model runs for 6,206 samples populated using data from the Atlas of Northern Gulf of Mexico Gas and Oil Reservoirs (Seni, 2006). As a final refinement step, a 3D dynamic model mesh is generated. Nine model cases are generated for homogeneous, statistically heterogeneous, and seismic-based heterogeneous meshes to observe the effect of various geologic parameters on injection capacity. We observe downward revisions (decreases) in total capacity estimation with increasingly refined geologic data and scale. Results show that estimates of storage capacity can decrease significantly (by as much as 88%) for the single geologic setting investigated. Though this decrease depends on the criteria used for capacity comparison and varies within a given region, it serves to illustrate the potential overestimation of regional capacity assessments compared to estimates that include additional geologic complexity at the reservoir scale.Item Use of high resolution 3D seismic data to evaluate Quaternary valley evolution history during transgression, offshore San Luis Pass, Gulf of Mexico(2015-05) Mulcahy, Francis Joseph; Meckel, Timothy Ashworth; Mohrig, David; Gulick, SeanA novel, shallow-investigation, high-resolution 3D (HR3D) seismic acquisition system has been employed, for the first time in the Gulf of Mexico, to characterize CO₂ storage potential and de-risk targets for sequestration. HR3D data can image detailed depositional, architectural, and structural features in the shallow subsurface that have previously been below seismic resolution and/or excluded from industry surveys, which are optimized for deeper targets. One HR3D survey was collected in 2013 offshore San Luis Pass, TX and covers an area of 31.5 km². The dataset images the upper 500 meters of stratigraphy with unprecedented detail -- peak frequency of approximately 150Hz (eight 25m cables, spaced at 12.5m, 6.25m by 6.25m bin size). Imaged within this dataset at ~100ms TWTT, is a mappable erosional unconformity that is interpreted to be associated with the Brazos River system during the ~130ka glacial-eustatic lowstand and following transgression. Through the analysis of horizon slices and the geometries of the valley form and its dendritic features, the evolution history of the valley system during a transgressive episode can be characterized. Observations indicate that the system evolves from a lowstand meandering channel system with clear point-bar deposits to a transgressive estuary characterized by dendritic erosional features that is eventually flooded. These 3D data represent an exceptional example of a lowstand to transgressive transition and the sedimentary processes and architectures that characterize each interval. A seismically discontinuous zone is observed within the HR3D volume that is interpreted to be a gas chimney system emanating from a tested dry, 3-way structure in the lower Miocene (1.5km depth). Within the shallowest intervals (<100m) and at the top of the chimney zone, seismic attribute analysis reveals several high amplitude anomalies that are predominantly located within interpreted interfluvial zones. The anomalies fit into our stratigraphic and structural interpretation of the interval, in that they appear to sit at local structural, fault bounded highs within deposits interpreted to be coarser grained and are overlain by finer grained, transgressive deposits. These observations support the interpretation of these amplitude anomalies as shallow gas accumulations derived from a deeper, depleted gas reservoir. Interestingly, point-bar deposits as well as channel scour deposits within the same interval show no sign of charge, suggesting that these are either isolated from the migration flowpath, or too fine-grained to host significant saturations.Item Using analytical and numerical modeling to assess deep groundwater monitoring parameters at carbon capture, utilization, and storage sites(2013-12) Porse, Sean Laurids; Young, Michael H.Carbon Dioxide (CO₂) Enhanced Oil Recovery (EOR) is becoming an important bridge to commercialize geologic sequestration (GS) in order to help reduce anthropogenic CO₂ emissions. Current U.S. environmental regulations require operators to monitor operational and groundwater aquifer changes within permitted bounds, depending on the injection activity type. We view one goal of monitoring as maximizing the chances of detecting adverse fluid migration signals into overlying aquifers. To maximize these chances, it is important to: (1) understand the limitations of monitoring pressure versus geochemistry in deep aquifers (i.e., >450 m) using analytical and numerical models, (2) conduct sensitivity analyses of specific model parameters to support monitoring design conclusions, and (3) compare the breakthrough time (in years) for pressure and geochemistry signals. Pressure response was assessed using an analytical model, derived from Darcy's law, which solves for diffusivity in radial coordinates and the fluid migration rate. Aqueous geochemistry response was assessed using the numerical, single-phase, reactive solute transport program PHAST that solves the advection-reaction-dispersion equation for 2-D transport. The conceptual modeling domain for both approaches included a fault that allows vertical fluid migration and one monitoring well, completed through a series of alternating confining units and distinct (brine) aquifers overlying a depleted oil reservoir, as observed in the Texas Gulf Coast, USA. Physical and operational data, including lithology, formation hydraulic parameters, and water chemistry obtained from field samples were used as input data. Uncertainty evaluation was conducted with a Monte Carlo approach by sampling the fault width (normal distribution) via Latin Hypercube and the hydraulic conductivity of each formation from a beta distribution of field data. Each model ran for 100 realizations over a 100 year modeling period. Monitoring well location was varied spatially and vertically with respect to the fault to assess arrival times of pressure signals and changes in geochemical parameters. Results indicate that the pressure-based, subsurface monitoring system provided higher probabilities of fluid migration detection in all candidate monitoring formations, especially those closest (i.e., 1300 m depth) to the possible fluid migration source. For aqueous geochemistry monitoring, formations with higher permeabilities (i.e., greater than 4 x 10⁻¹³ m²) provided better spatial distributions of chemical changes, but these changes never preceded pressure signal breakthrough, and in some cases were delayed by decades when compared to pressure. Differences in signal breakthrough indicate that pressure monitoring is a better choice for early migration signal detection. However, both pressure and geochemical parameters should be considered as part of an integrated monitoring program on a site-specific basis, depending on regulatory requirements for longer term (i.e., >50 years) monitoring. By assessing the probability of fluid migration detection using these monitoring techniques at this field site, it may be possible to extrapolate the results (or observations) to other CCUS fields with different geological environments.