Descreening of Field Effect in Electrically Gated Nanopores

This modeling work investigates the electrical modulation characteristics of field-effect gated nanopores. Highly nonlinear current modulations are observed in nanopores with non-overlapping electric double layers, including those with pore diameters 100 times the Debye screening length. We attribute this extended field-effect gating to a descreening effect, i.e. the counter-ions do not fully relax to screen the gating potential due to the presence of strong ionic transport

Possible quadrupolar nematic phase in the frustrated spin chain LiCuSbO4_4: an NMR investigation

The frustrated one-dimensional (1D) quantum magnet LiCuSbO$_4$ is one rare realization of the $J_1-J_2$ spin chain model with an easily accessible saturation field, formerly estimated to 12~T. Exotic multipolar nematic phases were theoretically predicted in such compounds just below the saturation field, but without unambiguous experimental observation so far. In this paper we present extensive experimental research of the compound in the wide temperature (30mK$-$300K) and field (0$-$13.3T) range by muon spin rotation ($\mu$SR), $^7$Li nuclear magnetic resonance (NMR) and magnetic susceptibility (SQUID). $\mu$SR experiments in zero magnetic field demonstrate the absence of long range 3D ordering down to 30mK. Together with former heat capacity data [S.E. Dutton \emph{et al}, Phys. Rev. Lett. 108, 187206 (2012)], magnetic susceptibility measurements suggest short range correlated vector chiral phase in the field range $0-4$T. In the intermediate field values (5$-$12T), the system enters in a 3D ordered spin density wave phase with 0.75$\mu_B$ per copper site at lowest temperatures (125mK), estimated by NMR. At still higher field, the magnetization is found to be saturated above 13T where the spin lattice $T_1^{-1}$ relaxation reveals a spin gap estimated to 3.2(2)K. We narrow down the possibility of observing a multipolar nematic phase to the range 12.5$-$13T.Comment: 12 pages, 15 figure

Predictions of Groundwater Levels and Spring Flow in Response to Future Pumpage and Potential Future Droughts in the Barton Springs Segment of the Edwards Aquifer

A two-dimensional numerical groundwater-flow model was developed for the Barton Springs segment of the Edwards aquifer to evaluate groundwater availability and predict water levels and spring flow in response to increased pumpage and droughts from 2000 through 2050. A steady-state model was developed on the basis of average recharge for a 20-yr period (1979 through 1998) and pumpage values for 1989. Hydraulic conductivity zones (10) were adjusted to obtain good agreement between measured and simulated hydraulic heads. Zones of hydraulic conductivity ranged from 1 to 1,000 ft/d. We conducted transient simulations using recharge and pumping data for a 10-yr period from 1989 through 1998 that includes periods of low and high water levels. Good agreement was found between measured and simulated flow at Barton Springs (root mean square error [RMSE, average of squared differences in measured and simulated discharges] 17 cfs) and between measured and simulated water levels in many of the monitoring wells (mean RMSE 40 ft). The simulation results overestimate spring discharge by about 10 cfs during low flow periods. To assess the impact of future pumping and potential future droughts on groundwater availability, we conducted transient simulations using extrapolated pumpage for a 10-yr period (2041 through 2050) and using average recharge for a 3-yr period and recharge from the 1950s drought for the remaining 7 yr. Results for this scenario predict that flow in Barton Springs will become very low ( 4 cfs) toward the end of the drought. Because of the bias in the simulation results, the combination of drought and future pumpage could result in no discharge at Barton Springs. Additional scenarios were simulated that included current pumpage and no pumpage. These simulations indicate that with current pumpage, spring discharge will decrease to levels similar to those calculated for the end of the 1950s drought (11 cfs). No pumpage resulted in discharges as low as 17 cfs. Actual flows, which may be about 7 cfs because of the bias in the simulation results, indicate that drought conditions similar to those of the 1950s will require no pumpage if spring discharges similar to those of the 1950s are to be maintained.Bureau of Economic Geolog

Reevaluation of Ground-Water Resources on State Lands in Eastern El Paso County

A reevaluation of the groundwater resources on State (Permanent School Fund) lands in eastern El Paso County, Texas, has resulted in the delineation of three areas where further hydrogeologic investigations are justified. The three areas were delineated on the basis of water chemistry and depth to groundwater. In this reevaluation, the three areas delineated all had total dissolved solids of less than 1,000 mg/L and a depth to groundwater between 200 and 400 feet. On the basis of projected and reported consumption rates in other areas of the El Paso region, a range in cumulative production rates from 120 to 1,200 gallons per minute from 2 to 10 wells would meet local water needs. It is noted, however, that this reevaluation is based solely on readily available hydrologic and hydrochemical data. This reevaluation does not include any analysis concerning sustainable yield for the delineated areas based on site-specific hydraulic conductivity and specific storage data. The investigations described in the proposed scope of work will be required to provide these data, address sustainable yield, and target optimal drilling sites for water-supply wells.Bureau of Economic Geolog

Hydrologic and Hydrochemical Results from Pumping Tests Conducted at the 11-14 Pond, Pantex Plant, Texas

Results from pumping tests conducted in monitoring wells located at the 11-14 pond significantly increase our understanding of the hydrogeology of perched aquifers at the Pantex Plant, the U.S. Department of Energy weapons plant serving as the final assembly and disassembly point for the nuclear arsenal and also as a test facility for high explosives. The mean transmissivity and hydraulic conductivity calculated for all four wells based on delayed yield analyses were 488 ± 250 ft^2 d^-1 and 33.8 ± 17.9 ft d^-1 (45.3 ± 23.2 m^2 d^-1 and 10.3 ± 5.4 m d^-1), respectively. On the basis of these hydraulic conditions, a ground-water velocity in the 11-14 pond area of 0.85 ft d^-1 (0.26 m d^-1) was calculated. Results of chemical analyses on water samples collected at three different times during the pumping test were relatively consistent. This consistency indicates that, within the volume of the perched aquifer from which water was pumped, no compositional stratification or lateral compositional trends could be conclusively identified.Bureau of Economic Geolog

Geologic and Hydrogeologic Framework of Regional Aquifers in the Twin Mountains, Paluxy, and Woodbine Formations Near the SSC Site, North-Central Texas (Draft)

Water-utility districts and municipalities in North-Central Texas recently obtained as much as 100 percent of their water supply from deep regional aquifers in Cretaceous formations. Use of groundwater from the aquifers during the past century has resulted in water-level declines of as much as 800 ft (243.8 m) in Dallas and Tarrant Counties. Future continued water-level decline throughout North-Central Texas will depend on the amount of groundwater produced to help meet increased water-supply needs for municipal, industrial, and agricultural growth. It is probable that a significant part of the increased water demand will be met by groundwater. The objectives of this study were to develop a hydrologic model of the complex interrelations among aquifer stratigraphy, hydrologic properties, and groundwater availability and, given expected patterns of future groundwater demand, to predict water-level changes in the regional aquifers that underlie North-Central Texas. A cross-sectional model of both aquifers and confining layers was used to evaluate model boundary conditions and the vertical hydrologic properties of the confining layers. Results and insights from the cross-sectional model were used in a three-dimensional simulation of groundwater flow in the deep aquifers. The layers of a regional confining system were not explicitly included in the three-dimensional model. Hydrogeologic properties were assigned based on aquifer test results and stratigraphic mapping of sandstone distribution in the aquifer units.Bureau of Economic Geolog

Geologic Analysis of Primary and Secondary Tight Gas Sand Objectives, Phase C

Previous assessments of blanket-geometry tight gas sandstones led to the selection of the Travis Peak Formation of the East Texas and North Louisiana Basins and the Corcoran and Cozzette Sandstones of the Piceance Creek Basin as major research objectives. The anticipated outcomes of this study include increased availability of tight gas resources and advancements in technology with high transferability. The work reported here encompasses all aspects of the depositional systems and reservoir geology of these units as fundamental components of resource characterization, with an emphasis on understanding controls on reservoir facies distribution and their relevance to low-permeability reservoir development. Six lithofacies of the Travis Peak (Hosston) Formation in East Texas and North Louisiana have been identified using electric logs. These facies comprise sand-rich fluvial-deltaic, silt-rich delta-front, clay- and carbonate-rich shelf, carbonate reef, and clay-rich open marine facies. The most well-developed facies in the East Texas area are the fluvial-deltaic and delta-front facies. Travis Peak rocks from the Clayton Williams #11 Sam Hughes well, Panola County, Texas, were primarily deposited in a fluvial environment within a coastal plain setting. Porosity and permeability control in the clean sandstones are primarily attributed to quartz overgrowths, chlorite cement, and solid organic matter, with approximately half of the remaining porosity being secondary, resulting from framework grain dissolution. Studies of Travis Peak gas production at Pinehill Southeast and Percy-Wheeler fields indicate an average permeability-thickness product of about 10 md-ft, with a range of 0.7 to 35 md-ft, indicating dry gas reservoirs. Well logs, core, and mud logs from Chapel Hill field in Smith County, Texas, were examined in preparation for a complete cooperative well program in the ARCO #11 Phillips well on the western margin of that field. Field studies of Corcoran-Cozzette Sandstones near Grand Junction, Colorado, suggest that the depositional environments of the Corcoran evolved from marine upper shoreface to non-marine, while the Cozzette sequence evolved from lower to upper shoreface. Porosity and water saturation calculations have been conducted by computer for seven Corcoran and Cozzette depositional units. A comparison of calculated water saturation with core-derived porosity and permeability indicates a fair to very good correlation of reservoir properties with clay content measured by gamma-ray log.Bureau of Economic Geolog

Preliminary Geologic Description S.A. Holditch & Associates SFE No. 2

Four intervals of the Travis Peak Formation were cored in the S. A. Holditch & Associates SFE No. 2 well, North Appleby field, Nacogdoches County, Texas. Core was recovered from 8,230.0 to 8,319.7 ft, 8,678.2 to 8,738.0 ft, 9,480.0 to 9,572.1 ft, and 9,806.7 to 9,942.1 ft. The top of the Travis Peak is at 8,000 ft (log depth), so the core samples are from 230 ft to 1,942 ft below the top of the formation.Bureau of Economic Geolog

Geology of the Lower Cretaceous Travis Peak Formation, East Texas: Characterization of a Tight Gas SandStone

Since 1982, the Gas Research Institute (GRI) Tight Gas Sands Project has supported geological investigations designed to develop knowledge necessary to efficiently produce low-permeability, gas-bearing sandstones. As part of that program, the Bureau of Economic Geology has conducted research on low-permeability sandstone in the Lower Cretaceous Travis Peak (Hosston) Formation in East Texas. The first phase of the study, which lasted from 1983 until 1986, involved extensive collection of core and production data in seven cooperative wells. Information gained from the cooperative wells, combined with geologic characterization of the Travis Peak throughout the study area, led to the drilling by GRI of three Staged Field Experiment (SFE) wells between 1986 and 1988. The SFE wells were drilled and completed by GRI specifically for the purpose of research on low-permeability gas reservoirs. This report summarizes the results of the geologic studies of the Travis Peak Formation, and it focuses on the contribution of geology to evaluation and completion of tight gas sandstone wells.Bureau of Economic Geolog

Geologic and Hydrogeologic Framework of Regional Aquifers in the Twin Mountains, Paluxy, and Woodbine Formations Near the SSC Site, North-Central Texas

Water-utility districts and many municipalities in North-Central Texas recently obtained as much as 100 percent of their water supply from deep regional aquifers in Cretaceous formations. Use of groundwater from the aquifers during the past century has resulted in water-level declines of as much as 850 ft (259 m), especially in Dallas and Tarrant Counties. Future water-level changes will depend on the amount of groundwater produced to help meet growing water-supply needs for municipalities, industries, and agriculture throughout North-Central Texas. It is probable that a significant part of the increased water demand will be met by groundwater although at less than historic rates. The objective of this study was to develop a predictive tool for studying the effect of future groundwater production from regional aquifers in North-Central Texas. To do this, we reviewed the history of groundwater development, hydrogeology of the regional aquifers, and constructed numerical models of groundwater flow. A cross-sectional model of both aquifers and confining layers was used to evaluate model boundary conditions and the vertical hydrologic properties of the confining layers. Results and insights from the cross-sectional model were used in a three-dimensional simulation of groundwater flow in the deep aquifers. The layers of the regional confining system were not explicitly included in the three-dimensional model. Hydrogeologic properties were assigned on the basis of aquifer test results and stratigraphic mapping of sandstone distribution in the aquifer units.Bureau of Economic Geolog