Controls on Methane Occurrences in Aquifers Overlying the Eagle Ford Shale Play,South Texas

Assessing natural vs. anthropogenic sources of methane in drinking water aquifers is a critical issue in areas of shale oil and gas production. The objective of this study was to determine controls on methane occurrences in aquifers in the Eagle Ford Shale play footprint. A total of 110 water wells were tested for dissolved light alkanes, isotopes of methane, and major ions, mostly in the eastern section of the play. Multiple aquifers were sampled with approximately 47 samples from the Carrizo‐Wilcox Aquifer (250‐1200 m depth range) and Queen City‐Sparta Aquifer (150‐900 m depth range) and 63 samples from other shallow aquifers but mostly from the Catahoula Formation (depth <150 m). Besides three shallow wells with unambiguously microbial methane, only deeper wells show significant dissolved methane (22 samples >1 mg/L, 10 samples >10 mg/L). No dissolved methane samples exhibit thermogenic characteristics that would link them unequivocally to oil and gas sourced from the Eagle Ford Shale. In particular, the well water samples contain very little or no ethane and propane (C1/C2+C3 molar ratio >453), unlike what would be expected in an oil province, but they also display relatively heavier δ¹³C_methane (>?55‰) and δD_methane (>?180‰). Samples from the deeper Carrizo and Queen City aquifers are consistent with microbial methane sourced from syndepositional organic matter mixed with thermogenic methane input, most likely originating from deeper oil reservoirs and migrating through fault zones. Active oxidation of methane pushes δ¹³C_methane and δD_methane toward heavier values, whereas the thermogenic gas component is enriched with methane owing to a long migration path resulting in a higher C1/C2+C3 ratio than in the local reservoirs.     

Controls on Methane Occurrences in Shallow Aquifers Overlying the Haynesville Shale Gas Field,East Texas

Understanding the source of dissolved methane in drinking‐water aquifers is critical for assessing potential contributions from hydraulic fracturing in shale plays. Shallow groundwater in the Texas portion of the Haynesville Shale area (13,000 km²) was sampled (70 samples) for methane and other dissolved light alkanes. Most samples were derived from the fresh water bearing Wilcox formations and show little methane except in a localized cluster of 12 water wells (17% of total) in a approximately 30 × 30 km² area in Southern Panola County with dissolved methane concentrations less than 10 mg/L. This zone of elevated methane is spatially associated with the termination of an active fault system affecting the entire sedimentary section, including the Haynesville Shale at a depth more than 3.5 km, and with shallow lignite seams of Lower Wilcox age at a depth of 100 to 230 m. The lignite spatial extension overlaps with the cluster. Gas wetness and methane isotope compositions suggest a mixed microbial and thermogenic origin with contribution from lignite beds and from deep thermogenic reservoirs that produce condensate in most of the cluster area. The pathway for methane from the lignite and deeper reservoirs is then provided by the fault system.     

Influence of Hydraulic Fracturing on Overlying Aquifers in the Presence of Leaky Abandoned Wells

The association between hydrocarbon‐rich reservoirs and organic‐rich source rocks means unconventional oil and gas plays usually occur in mature sedimentary basins—where large‐scale conventional development has already taken place. Abandoned wells in proximity to hydraulic fracturing could be affected by increased fluid pressures and corresponding newly generated fractures that directly connect (frac hit) to an abandoned well or to existing fractures intersecting an abandoned well. If contaminants migrate to a pathway hydraulically connected to an abandoned well, upward leakage may occur. Potential effects of hydraulic fracturing on upward flow through a particular type of leaky abandoned well—abandoned oil and gas wells converted into water wells were investigated using numerical modeling. Several factors that affect flow to leaky wells were considered including proximity of a leaky well to hydraulic fracturing, flowback, production, and leaky well abandonment methods. The numerical model used historical records and available industry data for the Eagle Ford Shale play in south Texas. Numerical simulations indicate that upward contaminant migration could occur through leaky converted wells if certain spatial and hydraulic conditions exist. Upward flow through leaky converted wells increased with proximity to hydraulic fracturing, but decreased when flowback and production occurred. Volumetric flow rates ranged between 0 and 0.086 m³/d for hydraulic‐fracturing scenarios. Potential groundwater impacts should be paired with plausible transport mechanisms, and upward flow through leaky abandoned wells could be unrelated to hydraulic fracturing. The results also underscore the need to evaluate historical activities.     

Effect of a Freshwater Layer Overlying Salt Water on the Regime of Replacement in Confined Coastal Aquifers

A mathematical model of fresh groundwater flow from a semi-infinite confined aquifer into a sea (pool, trench, and the like) filled with salt water and having a freshwater layer above its horizon. To study this problem a mixed boundary-value problem of the theory of analytical functions is formulated and solved with the use of the Polubarinova-Kochina method. The obtained exact analytical relationships and numerical calculations are used to perform a detailed hydrodynamic analysis of the effect of the freshwater layer and other physical parameters of the model on the character and the extent of displacement.     

Testing and Sampling of Deep Brine Aquifers in the Palo Duro Basin, West Texas

The U.S. Department of Energy is investigating the Palo Duro Basin of West Texas along with locations in Nevada, Washington, Utah, Mississippi and Louisiana as potential sites for storage of high-level nuclear waste. Ten wells have been drilled to depths between 3,000 and 8,300 feet. Short-term testing has included conventional oil-field-type drill stem tests and drill stem equipment with surface pressure readout. Long-term testing has consisted of a series of production and recovery tests.
Fluid sampling was performed in two stages. The first was at the well head under an imposed pressure of several hundred psi. The second fluid samples were collected downhole at the production zone under pressures close to ambient pressure. The geochemical data and hydrologic data can be used as independent checks on each other in many cases. Test results from the well along with examination of recovered core provided maximum data from each well.     

Geomorphic effects of a 10-year storm on a small drainage Basin in the Texas Panhandle

Bedded Permian salt in the Palo Duro Basin of the Texas Panhandle is being considered for isolation of nuclear waste. Studies underway to evaluate the geomorphic processes affecting any waste repository that may be sited in the region include studies of the geomorphic events associated with individual storms. On 26 May, 1978, thunderstorms occurred near Canyon, Texas, which received 130mm of rain, and on a small instrumented watershed at Buffalo Lake, 16 km to the southwest, which received 71 mm of rain. Rainfall at Buffalo Lake was concentrated in a period of 3 hours, representing a return period of approximately 10 years and a maximum 30-minute intensity of 64 mm/hour. Erosion-pin fields, topographic surveys, and stakes for headcut monitoring had been established 2 to 3 months before the storm in a 640-m long tributary canyon to Tierra Blanca Creek downstream of Buffalo Lake. Canyon slopes of moderately to slightly calichified sands and gravels of the Ogallala Formation are capped by well-indurated caliche on the canyon rim. Erosion-pin fields showed average net erosion of 2·4 cm (0° to 9° slope) to 2·7 cm (10° to 19° slope) and a single-pin maximum value of 6·2 cm in the 20° to 29° slope class. Headcuts 1 to 2 m deep in alluvial-colluvial material on the floor of the canyon migrated as much as 12 m upstream. Canyon floor deposition occurred as a series of elongate bars, 16m long and longer, located at the mouth of tributary gullies, downstream from scours, and at slope breaks. Grain sizes ranged from boulders up to 70cm in intermediate axis deposited in the upper canyon to fine to very fine sand deposited as a sheet up to 25cm thick beyond the mouth of the canyon at Tierra Blanca Creek. In an adjacent canyon a sequence of irregular beds of caliche gravel, mixed sand and gravel, and fine sand up to 3 m thick is exposed. Comparison of this sequence with deposits resulting from the 26 May, 1978, storm suggests that the coarse fraction of the alluvial sequence is deposited by repetitive major storm events. Cobble and boulder units 30 to 70cm thick can evidently be deposited in a few hours. Under the continental climate of the Texas Panhandle, erosion, deposition, and stream incision are taking place primarily in discrete steps related to episodes of intense rainfall.     

Numerical modeling of a long-term in situ chemical osmosis experiment in the Pierre Shale,South Dakota

We have numerically modeled evolving fluid pressures and concentrations from a nine-year in situ osmosis experiment in the Pierre Shale, South Dakota. These data were obtained and recently interpreted by one of us (C.E.N.) as indicating a potentially significant role for chemical osmosis in media like the Pierre Shale. That analysis considered only the final pressure differentials among boreholes that were assumed to represent osmotic equilibrium. For this study, the system evolution was modeled using a recently developed transient model for membrane transport. The model simulates hydraulically and chemically driven fluid and solute transport. The results yield an estimate of the thickness of the water film between the clay platelets b of 40 Å, which corresponds to an osmotic efficiency σ of 0.21 for the ambient pore water salinity of 3.5 g/l TDS. These values largely confirm the results of the earlier equilibrium analysis. However, the new model analysis provides additional constraints suggesting that intrinsic permeability k = 1.4 × 10⁻¹⁹ m², specific storage S_s = 1.7 × 10⁻⁵ m⁻¹, and diffusion coefficient D* = 6 × 10⁻¹¹ m²/s. The k value is larger than certain independent estimates which range from 10⁻²¹ to 10⁻²⁰; it may indicate opening of microcracks during the experiments. The fact that the complex transient pressure and concentration behavior for the individual wells could be reproduced quite accurately, and the inferred parameter values appear to be realistic for the Pierre Shale, suggests that the new model is a useful tool for modeling transient coupled flows in groundwater systems.     

Methane in the hyporheic zone of a small lowland stream (Sitka, Czech Republic)

Methane concentrations and selected chemical parameters in interstitial water were examined along subsurface flowpath in two subsystems (hyporheic and parafluvial sediments) in the Sitka stream, Czech Republic. Interstitial methane concentrations exhibited a distinct spatial pattern. In the hyporheic downwelling zone where the sediments are relatively well oxygenated due to high hydrologic exchange with the surface water, low interstitial methane concentrations, averaging 9.3 μg CH₄/l, were found. In contrast, upwelling sediments and parafluvial sediments (active channel sediments lateral to the wetted channel) had significantly higher methane concentrations (p < 0.05, and p < 0.01, respectively), averaging 43.2 μg CH₄/l and 160.5 μg CH₄/l, respectively. Dissolved oxygen was the highest where surface water entered hyporheic/parafluvial sediments and decreased with water residence time in the sediments (p < 0.01). Nitrate concentrations decreased along the flowpath and were significantly lower at downstream end of the riffle (p < 0.001). Sulfate concentrations also show a slight decline with the water residence time, but differences were not significant. Effect of both nitrate and sulfate on methanogenesis is also discussed. The interstitial methane concentration significantly increased with surface water temperature (p < 0.001) and was negatively correlated with redox potential (p < 0.01) and dissolved oxygen (p < 0.05).     

云南建水跃进水库宏观异常研究

2001年8月初，云南省建水县跃进水库出现特大宏观异常——激烈的翻花冒泡现象，历时50多天。事后研究结果表明：该异常为区域断裂活动的表现，标志该区地应力增强，并非地震短临前兆。     

Performance of a conceptual and physically based model in simulating the response of a semi‐urbanized watershed in San Antonio,Texas

The need for accurate hydrologic analysis and rainfall–runoff modelling tools has been rapidly increasing because of the growing complexity of operational hydrologic and hydraulic problems associated with population growth, rapid urbanization and expansion of agricultural activities. Given the recent advances in remote sensing of physiographic features and the availability of near real‐time precipitation products, rainfall–runoff models are expected to predict runoff more accurately. In this study, we compare the performance and implementation requirements of two rainfall–runoff models for a semi‐urbanized watershed. One is a semi‐distributed conceptual model, the Hydrologic Engineering Center‐Hydrologic Modelling System (HEC‐HMS). The other is a physically based, distributed‐parameter hydrologic model, the Gridded Surface Subsurface Hydrologic Analysis (GSSHA). Four flood events that took place on the Leon Creek watershed, a sub‐watershed of the San Antonio River basin in Texas, were used in this study. The two models were driven by the Multisensor Precipitation Estimator radar products. One event (in 2007) was used for HEC‐HMS and GSSHA calibrations. Two events (in 2004 and 2007) were used for further calibration of HEC‐HMS. Three events (in 2002, 2004 and 2010) were used for model validation. In general, the physically based, distributed‐parameter model performed better than the conceptual model and required less calibration. The two models were prepared with the same minimum required input data, and the effort required to build the two models did not differ substantially. Copyright © 2012 John Wiley & Sons, Ltd.     

Anisotropy of magnetic susceptibility in welded tuffs: application to a welded-tuff dyke in the tertiary Trans-Pecos Texas volcanic province,USA

Consideration of published anisotropy of magnetic susceptibility (AMS) studies on welded ignimbrites suggests that AMS fabrics are controlled by groundmass microlites distributed within the existing tuff fabric, the sum result of directional fabrics imposed by primary flow lineation, welding, and (if relevant) rheomorphism. AMS is a more sensitive indicator of fabric elements within welded tuffs than conventional methods, and usually yields primary flow azimuth estimates. Detailed study of a single densely welded tuff sample demonstrates that the overall AMS fabric is insensitive to the relative abundances of fiamme, matrix and lithics within individual drilled cores. AMS determinations on a welded-tuff dyke occurring in a choked vent in the Trans-Pecos Texas volcanic field reveals a consistent fabric with a prolate element imbricated with respect to one wall of the dyke, while total magnetic susceptibility and density exhibit axially symmetric variations across the dyke width. The dyke is interpreted to have formed as a result of agglutination of the erupting mixture on a portion of the conduit wall as it failed and slid into the conduit, followed by residual squeezing between the failed block and in situ wallrock. Irrespective of the precise mechanism, widespread occurrence of both welded-tuff dykes and point-welded, aggregate pumices in pyroclastic deposits may imply that lining of conduit walls by agglutionation during explosive volcanic eruptions is a common process.     

Features in REE and Methane Anomalies Distribution in the East China Sea Water Column: a Comparison with the South China Sea

Water Resources - This paper presents review of dissolved Rare Earth Elements (REE) and methane anomalies distribution in the East China Sea water column. In general, the REE concentrations of the...     

Additional note on the isotopic composition of strontium in McCartys flow,Valencia County,New Mexico

Strontium isotopic analyses of additional samples of the McCartys basalt flow (Holocene) exhibit no evident correlation with distance from the source crater or with strontium content. This confirms our previous comments urging caution in sampling of one basalt flow in order to determine its “source” initial⁸⁷Sr/⁸⁶Sr.     

汶川大地震四川省青川县砖混结构村镇房屋震害分析

2008年汶川 8.0级大地震造成了大量的房屋破坏,尤其村镇房屋的破坏最为严重.本文基于对四川省青川县部分乡镇村镇房屋震害的实地调查,对砖混结构房屋的震害从地形、地基基础和结构三方面进行了震害总结,分析了典型震害的成因,指出了目前村镇房屋建设存在的问题,最后对提高村镇民房的地震安全提出了一些建议.     

Riparian influence on hyporheic‐zone formation downstream of a small dam in the Blackland Prairie region of Texas

Small‐order streams have highly variable flows that can result in large temporal and spatial variation of the hyporheic zone. Dam construction along these intermittent headwater streams alters downstream flow and influences the hydrologic balance between stream water and the adjacent riparian zone. A 3‐year site study was conducted along an impounded second‐order stream to determine the water balance between stream, unsaturated zone, groundwater and riparian vegetation. The presence of the upstream impoundment provided near‐perennial water flow in the stream channel. The observed woody plant transpiration accounted for 71% of average annual water loss in the site. The overall contribution of stream water via the hyporheic zone to site water balance was 73 cm, or 44% of total inputs. This exceeded both rainfall and upland subsurface contribution to the site. A highly dynamic hyporheic zone was indicated by high water use from woody plants that fluctuated seasonally with stream water levels. We found leaf area development in the canopy layer to be closely coupled with stream and groundwater fluctuations, indicating its usefulness as a potential indicator of site water balance for small dam systems. The net result of upstream impoundment increased riparian vegetation productivity by influencing movement of stream water to storage in the groundwater system. Copyright © 2006 John Wiley & Sons, Ltd.     

汶川地震甘肃省文县地震地质灾害遥感分析

2008年汶川地震诱发了大量的次生山地灾害.本文以多源、多时相的遥感影像(TM、ASTER、SPOT)作为信息源,基于地学知识,采用图像增强、人机交互的方式对甘肃省文县地区汶川地震引发的次生山地灾害进行解译.以ArcGIS软件为处理平台,运用空间分析技术,将解译结果与海拔高度、坡度、植被覆盖度和地震烈度进行空间分析,获得了研究区次生山地灾害的分布规律,其特点为:文县境内的次生山地灾害主要分布在20°～60°的边坡;多发生在1 000～2 500m的海拔高程范围内;主要分布在地震烈度Ⅶ度及以上区域.     

甘肃永登湿陷性新近堆积黄土的微观结构分析

甘肃永登县树屏村某工程场地土为第四纪新近堆积黄土,其工程性质较为特殊,具有较大的湿陷性,但在天然湿度下震陷性却很小。本文利用扫描显微镜对其微结构图象进行分析,同时结合土工试验结果,揭示了导致其特殊工程性质的微观机理。最后提出了在工程施工中应注意的问题。     

基于微博数据的西藏那曲比如县地震舆情分析

震后对网络舆情信息的监控与分析,对于相关部门开展震灾应急救援、掌握救灾动态、稳定民众情绪具有重要意义。本研究基于新浪微博数据,运用网络爬虫技术,获取西藏自治区那曲市比如县6.1级地震震后24小时及震后一周的相关微博及评论;利用Python中文分词组件“jieba”和ROST CM6软件,对数据进行分类、去重、分词等处理,得到结构化的分级、分类数据,并制成震后微博时间序列图、地理分布图、舆情热词词频表、情绪极性统计图等,实现微博舆情数据的可视化。研究结果表明,本次地震事件的微博舆情整体呈现积极情绪,微博活跃程度与当地经济发展程度密切相关。在本次地震舆情传播中,政府部门的舆情引导起到至关重要的作用,舆情传播中的防灾视频传播具有明确的正向引导作用。本研究对于中国西部欠发达少数民族地区的地震舆情分析及引导工作具有借鉴意义。     

Physical controls on septic leachate movement in the vadose zone at the hillslope scale,Putnam County,New York,USA

The fate and transport of contaminants in the vicinity of septic fields remains poorly understood in many hydrogeomorphological environments. We report hydrometric data from an intensive hillslope‐scale experiment conducted between 29 August and 11 November 1998 at a residential leach field in New York State. The objective of our study was to characterize water flux within the vadose zone, understand the physical controls on the flux, and predict how this ultimately will affect subsurface water quality. Soil‐water flux was calculated using matric potential measurements from a network of 25 tensiometer nests, each nest consisting of three tensiometers installed to depths of 10, 50 and 130 cm. Unsaturated hydraulic conductivity curves were derived at each depth from field‐determined time‐domain reflectometry–tensiometry moisture‐release curves and borehole permeametry measurements. Flownets indicated that a strong upward flux of soil water occurred between rainstorms. Following the onset of (typically convective) rainfall, low near‐surface matric potentials were rapidly converted to near‐saturated and saturated conditions, promoting steep vertical gradients through the near‐surface horizons of the hillslope. Lateral hydraulic gradients were typically 10 times smaller than the vertical gradients. Resultant flow vectors showed that the flux was predominantly vertical through the vadose zone, and that the flux response to precipitation was short‐lived. The flux response was controlled primarily by the shape of the unsaturated hydraulic conductivity curves, which indicated a rapid loss of conductivity below saturation. Thus, soil water had a very high residence time in the vadose zone. The absence of rapid wetting at 130 cm and the delayed and small phreatic zone response to rainfall indicated that water movement through macropores did not occur on this hillslope. These results are consistent with a Cl tracing experiment, which demonstrated that the tracer was retained in the vadose zone for several months after injection to the system. Copyright © 2002 John Wiley & Sons, Ltd.