GSA 2018
Modeling Irrigated Pumping Data for the High Plains Aquifer in Western Kansas
ALEKSANDR GLAVNIK, WHEATON COLLEGE; SAMUEL J. SMIDT, UNIVERSITY OF FLORIDA
The High Plains Aquifer is a predominant resource for irrigated agriculture in Western Kansas. However, prolonged rates of pumping have depleted the supply faster than it can naturally be replenished. Here, we analyze pumping data from almost 5,000 wells from 1990-2013 to identify trends between water pumping and groundwater decline. We applied a water-balance sustainability model to extrapolate regional pumping rates to better inform water conservation strategies and end-user decision making. We found the correlation between pumping and water level change to be nonlinear, where a moderate amount of pumping led to the greatest water level decline. We then explore other degrees of complexity by applying a polynomial fit model to represent the data. Results from this study can be used as pilot data for research questions focused on water use decision making and aquifer sustainability.
GSA 2018 – BEST STUDENT POSTER AWARD – HYDROGEOLOGY DIVISION
Identifying Factors of Groundwater Consumption Across the High Plains Aquifer
LIBBY G. QUINN, WHEATON COLLEGE; SAMUEL J. SMIDT, UNIVERSITY OF FLORIDA
The water level of the High Plains Aquifer (HPA) continues to decline due to irrigation practices, leaving farmers in a dire situation; choosing to irrigate results in the depletion of the valuable water resource, and choosing to reduce irrigation results in lost current crop productivity.In this study, we analyzed key socio-agricultural system elements(e.g., market prices, groundwater legislation, and local management strategies) to identify predominate drivers to irrigation water use across the HPA. We collected county-level data in 2012 for each element and ran a linear regression model against aquifer groundwater levels to derive key correlations leading to groundwater decline. We found that the driving factors of groundwater decline include: total number of farms, acres of farmland, average farm size, total crop sales, largest crop commodity, average rainfall, per capita income, management district, recharge, and saturated thickness. According to our results, many of the variables tested do not significantly influence groundwater decline. These variables include: total population, population served by groundwater, and groundwater withdrawal type (fresh, saline, total, domestic). The results of this study may assist experts in focusing management plans and water use sustainability strategies across the HPA to extend the life of the aquifer.
Water Quality Assessment of Alternative Drinking Water Sources in Urban and Suburban Areas, Sierra Leone, Africa
GILLES V. TAGNE, WHEATON COLLEGE
The assessment of water quality for drinking purpose in Sub-Saharan Africa has been widely done using numerous criteria that usually vary from one country to another. In Sierra Leone, the Ministry of Water Resources has established a list of 34 criteria including biological (bacteria and pathogens), chemical and physicochemical properties that are used to assess the suitability of water for human consumption based on WHO recommendations. However, following the recent Ebola outbreak and the need to prevent the spreading of water-borne diseases associated with poor sanitation, both government and humanitarian aid efforts have focused their attention addressing the bacteriological component (Lapworth et al., 2015). As major concerns have been raised regarding groundwater chemistry in particular (elevated iron in the Freetown metropolitan area; naturally-occurring arsenic around mines in the Northeast), it is becoming clear that a more comprehensive picture of the quality of drinking water sources in the country should take into consideration other variables besides the biology. Ten biological, chemical and physicochemical criteria were used to assess the quality of drinking water collected from 142 alternative sources including packet water (73), communal water tank (36), groundwater samples (9), municipal grill (8), and retail bottled water (3). Although packet water is the most widespread and economically viable among all the other drinking water alternatives, it raises the biggest concern for public health among the 5 alternatives based on both biological and chemical criteria: 23% of samples falling above the WHO recommendations for coliform content; 15% above the recommended limit for iron content; maximum E-coli, Total Coliform and nitrate levels. To address the threat to human health presented by packet water, it is suggested a thorough assessment of its content (quality control) and a reinforcement of regulations and incentives to reduce their marketability.
Seismic Responses During Recharge Events in Karst Aquifers: Potential Records of Pressure Pulses?
ANDREW J. LUHMANN, WHEATON COLLEGE; SUSAN L. BILEK, NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY; RONNI GRAPENTHIN, NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY
Seismic signals have been recorded during recharge events in karst aquifers, including responses to both anthropogenic injection experiments and natural recharge events. Here, we highlight records that were collected near Bear Spring in southeastern Minnesota, USA. Temperature and electrical conductivity monitoring during a natural recharge event suggest that the spring is sourced by at least a couple of conduit flow paths. During this natural recharge event, surface displacements of up to 2 µm were recorded. The largest displacement corresponded to a time when spring discharge underwent a significant increase. It is likely that this displacement was caused by a pressure pulse or surge signal within one of the conduits in response to the recharge event, either from the conduit transitioning from open channel to full pipe flow or by a flood wave arriving at an already, fully submerged conduit. While both velocity and discharge generally increase as water levels rise in a conduit with open channel flow, both decrease as water levels approach and reach full pipe flow conditions. If this transition happens quickly, pressure increases, potentially producing a pressure surge or a water hammer effect. Regardless of whether the measured displacement resulted from the transition of open channel to full pipe flow or from a flood wave reaching a conduit full of water, pressure perturbations would travel at ~1500 m/s in conduits full of water. This particular displacement was first recorded at seismometers near the spring and successively later at seismometers further from the spring and at higher elevations, potentially suggesting much faster signal propagation through the water in the conduit than through the thin overlying rock and soil. Another series of displacements were recorded during one of the artificial recharge events, but the order of arrival times at the seismometers was reversed, likely due to lower water levels and only portions of the flow path full of water that led to slower pressure transmission through the conduit. Environmental seismology enables monitoring of dynamic flow processes in karst aquifers, and ongoing research is assessing how this information may be used to improve karst aquifer characterization.
Unraveling the Age of HT Metamorphism in Eastern Senegal: Evidence from U-Pb in-situ Analyses on Monazite and Sm-Nd Garnet Geochronology
J. KONE, L. BARATOUX, K.A. MANEIRO, E.F.BAXTER, O. VANDERHAEGHE, S. DUCHENE, P.M. NDIAYE, P. PITRA, G. DUFRECHOU, O. BRUGUIER
Metasediments of the Paleoproterozoic Diale Dalema Basin are affected by a polyphase metamorphic evolution during the Eburnean Orogeny (2.25 - 2.00 Ga). The garnet-staurolite-sillimanite metapelites contain two generations of garnet. Garnet porphyroclasts wrapped in the S3 schistosity contain inclusions of chlorite, epidote, biotite, ilmenite, plagioclase, and quartz that delineate the S2 schistosity. The development of S3 is coeval with the growth of inclusion-free rims around the garnet porphyroclasts and by garnet neoblasts. Garnet porphyroclast displays a zoning pattern typical of prograde metamorphism associated with decompression from 9 to 6 kbar and an increase in temperature from 550 to 620°C. Monazite neoblasts in the S3 schistosity yield LA-ICP-MS U-Pb ages of 2052 ± 7 Ma and 2048 ± 8 Ma, whereas inclusions in staurolite yield an older age at 2090 ± 16 Ma. Sm-Nd garnet geochronology yields a bulk garnet age of 2080.2 ± 7.7 Ma on garnet porphyroclasts and 2049.1 ± 3.1 Ma on neoblasts. The results highlight an agreement between U-Pb ages from monazites and Sm-Nd ages from metamorphic garnets. The oldest ages are interpreted as the age of the prograde regional metamorphism during burial, while the youngest are attributed to the thermal peak.
GOLDSCHMIDT 2018 CONFERENCE
Earth’s Oldest Garnet: 3.20 Ga Garnet Ages Robustly Constrain the Timing of Early Metamorphism
K.A. MANEIRO, K. CUTTS, E.F. BAXTER, AND G. STEVENS
Earth’s earliest metamorphic stories have been told using zircon and monazite ages with thermodynamic modeling, but the Archean garnet record has remained largely untapped. Garnet’s role as a rock-forming mineral directly tied to growth during metamorphic reactions provides an attractive target for direct determination of linked ages, pressures, and temperatures for Earth’s earliest metamorphism. Earth’s Oldest Known Garnet Age To our knowledge, the only location with published direct garnet ages exceeding 3.0 Ga is the Barberton Granite Greenstone Belt (“BGGB”). A previous study in the BGGB indicated the presence of garnet of extreme age, but Sm/Nd ratios were low, Nd concentrations high, and the garnet textures indicate polymetamorphism leaving room for speculation about the accuracy and averaging of the age. This study provides robust, new Sm-Nd garnet ages for two samples from the Inyoni Shear Zone, bordering the Stolzberg and Badplaas blocks of the BGGB. Sample 115-13 is 3201.6 +/- 5.2 Ma (MSWD = 1.12), and Sample 21-13 is 3200.7 +/- 5.3 Ma (MSWD = 0.46). Both Sm-Nd garnet isochron ages yield relatively high Sm/Nd ratios (>0.6) and low Nd concentrations (<0.3 ppm) for garnet, mitigating concerns about age inaccuracy due to mineral inclusions. Garnet ages from the BGGB represent the oldest known garnet ages and provide a solid age constraint for the formation of the Inyoni Shear Zone at 3.20 Ga.
The Inyoni Shear Zone’s Metamorphic Story
Updated thermodynamic modeling for the region yields metamorphism at approx 600° C and 8 kbar. The presence of 3.20 Ga garnet ties garnet growth conditions to a prominent Archean structural boundary and robustly constrains metamorphic timing. These P-T-t conditions support interpretation of the Inyoni Shear Zone as an early example of accretionary tectonics potentially tied to early subduction.
AGU 2018
Seismic Monitoring of Artificial and Natural Recharge Events in Karst Aquifers
ANDREW J. LUHMANN, WHEATON COLLEGE; SUSAN L. BILEK, NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY; RONNI GRAPENTHIN, NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY
Seismology is now being used to study a variety of Earth surface processes in rivers, hill slopes, and glaciers, leading to the new field of environmental seismology. We have begun to expand this field to the study of various processes that occur in karst aquifers, reporting on observations during artificial and natural recharge events near Bear Spring in southeastern Minnesota, USA. Artificial recharge experiments were conducted by injecting water directly into the conduit system via a dry overflow spring, whereas the natural recharge event involved seismic monitoring of a rainstorm that yielded more than two inches of rain over a couple of hours. We observe a variety of seismic signals associated with the different recharge events. The largest amplitude ground motions occurred during the rain of the natural recharge event, with multiple large amplitude pulses occurring within several seconds of each other and during the period of rapid discharge increase at Bear Spring. These pulses arrived first at the seismometers near the spring, which may be due to the details of the conduit geometry relative to the surface topography or a rockfall or collapse near the spring. We find different behavior for the artificial recharge events, with the large ground motion signals arriving first at the seismometers near the location of the water input, suggesting signals generated from or near the water fall into the conduit system. We also
find differences in frequency content of the seismic signals, with peak power in the higher frequencies during time periods of subsurface flow and peak power in the lower frequencies during time periods of surface flow. Ongoing seismic monitoring of recharge events in karst aquifers will hopefully be used to locate the conduit network, to characterize the aquifer, and to monitor for flow and transport processes.
Diagenetic Capillary Heterogeneity Influences Multiphase Flow, Enhanced Oil Recovery,and CO2 Storage in a Depleted Brownfield Reservoir
THOMAS A. DEWERS, LINDSEY RASMUSSEN, WILLIAM AMPOMAH, JASON E. HEATH, ERIC BOWER, ANDREW J. LUHMANN, MARTHA CATHER, AND PETER MOZLEY
Pennsylvanian Morrow Sandstones, part of the Southwest Regional Partnership on Carbon Sequestration’s (SWP) Farnsworth Unit CO2 injection project in the Texas Panhandle, USA, have been targets of decades of enhanced oil recovery with both water and CO2 flooding. We investigate CO2-brine relative permeability in core obtained through the SWP at both in situ residual oil saturation and cleaned via Dean-Stark extractions. SEM, optical microscopy, laser scanning confocal microscopy, and mercury porosimetry show that all core contain abundant diagenetic microporosity, and that most residual oil resides within the microporosity, commonly associated with abundant kaolinite and illite-filled pores. We classify the pore heterogeneity within the Morrow-B unit at well 13-10A in terms of five hydraulic flow units based on mercury porosimetry, gas permeability, and porosity of cleaned core. Using dual focused on/scanning electron beam and micro-CT analysis, we quantity properties and three dimensional distributions of macro- and microporosity in the five units, and show via pore network modeling how micropore distribution, and not just extent of heterogeneity, controls effective stress-dependent absolute permeability and flow paths in and around hydrocarbon-containing micropores. A parallel experimental effort involves co-injection of brine and super-critical CO2 into core at in situ conditions. Tests at capillary numbers near the viscous limit yield brine curves that follow a Corey-type relative permeability curve, whereas CO2 curves during drainage do not. CO2 -flooding at similar injection rates near irreducible water saturation yield capillary numbers approaching the capillary limit, apparent flow-rate dependent relative permeability, and low end point CO2 permeability related to the degree of capillary heterogeneity in the flow units. These observations are linked to influences of microporosity. We examine effects of extreme capillary heterogeneity with reservoir simulations of CO2 injection into a model Farnsworth reservoir using a five-spot injection-producer well pattern. Relative permeability relationships derived from low capillary number data generally show poor sweep and storage efficiency compared to history-matched relative permeability models, corresponding to much higher capillary numbers. We discuss the potential for fast paths, residual CO2 trapping, and enhanced oil recovery in light of these results.
Three-Phase Compositional Simulation Modeling Coupled with Reactive Transport: Application to Farnsworth Field CO2-EOR and Storage Project
EUSEBIUS J. KUTSIENYO, WILLIAM AMPOMAH, ROBERT S. BALCH, MARTHA CATHER, AND ANDREW J. LUHMANN
This poster presents field-scale numerical compositional simulations of CO2 storage mechanisms in the Morrow B sandstone of the Farnsworth Unit (FWU) located in Ochiltree County, Texas. The study examines structural-stratigraphic, residual, solubility and mineral trapping mechanisms. The reactive transport modeling incorporated evaluates the field’s potential for long-term CO2 sequestration and predicts the CO2 injection effects on the pore fluid composition, mineralogy, porosity and permeability. The dynamic CO2 sequestration simulation model was built from an upscaled geocellar model for the Morrow B. This model incorporated geological, geophysical, and engineering data including well logs, core, 3D surface seismic and fluid analysis. We calibrated the model with historical CO2 -WAG miscible flood data and used it to evaluate the feasibility and mechanisms for CO2 sequestration. We used the maximum residual phase saturations to estimate the effect of gas trapped due to hysteresis. In addition, gas solubility in the aqueous phase was modelled as function of pressure, temperature and salinity. Lastly, the coupled geochemical reactions, i.e., the characteristic intra-aqueous and mineral dissolution/precipitation reactions were assimilated numerically as chemical equilibrium and rate-dependent reactions respectively. Additional scenarios that involve shut-in of wells were performed and the reservoir monitored for over 1000 years to understand possible mineralization. Changes in permeability as a function of changes in porosity caused by mineral precipitation/dissolution were calibrated to the laboratory chemo-mechanical responses. The study validates the effects of Morrow B petrophysical properties on CO2 storage potential within the FWU. Study results shows: EOR at the tertiary stage of field operations, total amount of CO2 stored in aqueous-gaseous-mineral phases, evolution and dissolution/precipitation of the principal accessory minerals and the time scale over which mineral sequestration took place in the FWU. This study relates the important physics and mechanisms for CO2 storage in the FWU and illustrates the use of the coupled reactive flow. The study serves as a is benchmark for future field-scale reactive transport CO2 -EOR projects in similar fields throughout the world.