共查询到20条相似文献，搜索用时 11 毫秒
1.
In eastern England the Chalk aquifer is covered by extensive Pleistocene deposits which influence the hydraulic conditions and hydrochemical nature of the underlying aquifer. In this study, the results of geophysical borehole logging of groundwater temperature and electrical conductivity and depth sampling for major ion concentrations and stable isotope compositions (δ18O and δ2H) are interpreted to reveal the extent and nature of the effective Chalk aquifer of north Norfolk. It is found that the Chalk aquifer can be divided into an upper region of fresh groundwater, with a Cl concentration of typically less than 100 mg l−1, and a lower region of increasingly saline water. The transition between the two regions is approximately 50 m below sea-level, and results in an effective aquifer thickness of 50–60 m in the west of the area, but less than 25 m where the Eocene London Clay boundary is met in the east of the area. Hydrochemical variations in the effective aquifer are related to different hydraulic conditions developed in the Chalk. Where the Chalk is confined by low-permeability Chalky Boulder Clay, isotopically depleted groundwater (δ18O less than −7.5‰) is present, in contrast to those areas of unconfined Chalk where glacial deposits are thin or absent (δ18O about −7.0‰). The isotopically depleted groundwater is evidence for groundwater recharge during the late Pleistocene under conditions when mean surface air temperatures are estimated to have been 4.5°C cooler than at the present day, and suggests long groundwater residence times in the confined aquifer. Elevated molar Mg:Ca ratios of more than 0.2 resulting from progressive rock-water interaction in the confined aquifer also indicate long residence times. A conceptual hydrochemical model for the present situation proposes that isotopically depleted groundwater, occupying areas where confined groundwater dates from the late Pleistocene, is being slowly modified by both diffusion and downward infiltration of modem meteoric water and diffusive mixing from below with an old saline water body. 相似文献
2.
The Chalk aquifer is one of the main sources of water in South East England. The unsaturated zone in the aquifer plays an important role controlling the time and magnitude of recharge and is major pathway for contaminant transport to the water table. A range of previous work has addressed flow processes in the Chalk unsaturated zone, but physical understanding is still incomplete. Here we present the results of a study on flow mechanism in the Chalk unsaturated zone using a combination of statistical analysis and novel laboratory methods. The study was undertaken at three sites (North Heath Barn [NHB], Pyecombe East [PE], and Preston Park [PP]) on the Chalk of the Brighton block, South East England. Daily and hourly time series data of groundwater level and rainfall were correlated. The results show that a slower groundwater level response to rainfall occurs during dry seasons (summer and autumn) when the amount of effective rainfall is less than 4 mm/day, with a thicker and drier unsaturated zone. A faster response occurs during wet seasons (winter and spring) when the daily effective rainfall exceeds 4 mm/day with a thinner and wetter unsaturated zone. Periods of very rapid response (within 15 h) were observed during wet seasons at NHB and PE sites, with unsaturated hydraulic conductivity (Ku) inferred to reach 839 mm/day. A slower response was observed at an urbanized site (PP) as a result of reduction in direct recharge due to reduced infiltration, due to presences of impermeable infrastructure covering the area around PP borehole. Laboratory measurements of Ku of the Chalk matrix using a geotechnical centrifuge show variation from 4.27 to 0.07 mm/day, according to the level of saturation. Thus, the rapid responses cannot be linked to matrix flow only but indicate the contribution of fracture and karstic flow processes in conducting water. 相似文献
3.
Stephen M. Sellwood David J. Hart Jean M. Bahr 《Ground Water Monitoring & Remediation》2015,35(4):85-94
Recent research has demonstrated the use of in‐well heat tracer tests monitored by a fiber optic distributed temperature sensing (DTS) system to characterize borehole flow conditions in open bedrock boreholes. However, the accuracy of borehole flow rates determined from in‐well heat tracer tests has not been evaluated. The purpose of the research presented here is to determine whether borehole flow rates obtained using DTS‐monitored in‐well heat tracer tests are reasonable, and to evaluate the range of flow rates measureable with this method. To accomplish this, borehole flow rates measured using in‐well heat tracer tests are compared to borehole flow rates measured in the same boreholes using an impeller or heat pulse flowmeter. A comparison of flow rates measured using in‐well heat tracer tests to flow rates measured with an impeller flowmeter under the same conditions showed good agreement. A comparison of in‐well heat tracer test flow rate measurements to previously‐collected heat pulse flowmeter measurements indicates that the heat tracer test results produced borehole flow rates and flow profiles similar to those measured with the heat pulse flowmeter. The results of this study indicate that borehole flow rates determined from DTS‐monitored in‐well heat tracer tests are reasonable estimates of actual borehole flow rates. In addition, the range of borehole flow rates measurable by in‐well heat tracer tests spans from less than 10?1 m/min to approximately 101 m/min, overlapping the ranges typically measurable with an impeller flowmeter or a heat pulse flowmeter, making in‐well heat tracer testing a versatile borehole flow logging tool. 相似文献
4.
The time-domain induced polarization (IP) of saturated Sherwood Sandstone correlates significantly with the intergranular permeability and the matrix conductivity but only at low electrolyte concentrations (< 500 p.p.m. NaCl). An increase in the magnitude of sandstone IP with increase in the valence of the electrolyte cation is pronounced but occurs only at intermediate concentrations, i.e., between 100 and 2500 p.p.m. Surface IP and resistivity depth sounding measurements, supplemented by data from laboratory measurements, can be used to estimate the groundwater conductivity and hence the salinity in a moderate to strongly saline sandstone aquifer. 相似文献
5.
Shear waves can provide valuable information about seismic anisotropy. On entering an anisotropic medium, a shear wave generally splits (shear-wave splitting) into a fast and a slow quasi-shear wave with polarizations fixed by the elastic properties of the medium and direction of travel. If the medium contains planar discontinuities with common normals, the fast shear wave will be suitably propagated if its polarization lies in the plane of the discontinuities. Measuring this polarization, using a VSP geometry with oriented three-component geophones in the borehole, offers the possibility of monitoring the orientation and density of the discontinuities as a function of depth. Such a shear-wave VSP was carried out in an uncased 0.3 m diameter borehole drilled to a depth of 120 m in the north of The Netherlands. The upper 80 m of the sequence, consisting of a glacial till and sands and clays of Pleistocene age, was studied. The clays in this sequence have been subjected to glacial deformation and as a result are overconsolidated and locally fissured. In our shallow VSP experiment, shear-wave splitting and therefore anisotropy was identified at various geophone depths for one source offset. Hodograms showed a consistent polarization of the fast shear-wave component over a large depth interval. Under the assumption that the anisotropy was caused by planar discontinuities with common normals, this polarization direction gives the strike of the fissures in this interval. The polarization direction of the fast S-wave did not correspond exactly with the strike which was obtained from geological information on the fissures. The geological information was from undisturbed oriented 70 mm core samples taken at 3 m intervals in the borehole. The discrepancy, however, could be explained in terms of dipping fissures, and such a dip was confirmed by the geological and geotechnical information. The orientation of fissures is an important factor in the directional deformation and strength characteristics of clays as far as geotechnical behaviour is concerned. This study thus illustrates a practical application of shear-wave splitting observed in shallow shear-wave VSP for geology and geotechnical engineering. 相似文献
6.
Resistivity of partially saturated Triassic Sandstone 总被引：1，自引：0，他引：1
The variation in resistivity with saturation of poorly cemented Triassic Sandstone samples from a site in the English Midlands has been measured. The measurements were obtained using an adapted four‐electrode technique, which utilizes conductive gelling agents between electrodes, avoiding the need to sputter electrodes directly on to samples – a difficult process with such friable samples. The measurements provide important information regarding the way in which resistivity varies with saturation in the Triassic Sandstone. The resulting variation in the observed resistivity versus saturation curves indicates the presence of significant pore‐scale variation between samples. Measurements have also been conducted on fully saturated samples. These indicate significant variation in the matrix conductivity between samples. The results have important implications for field‐scale monitoring of the unsaturated zone. 相似文献
7.
Geophysical well logging has been applied for fracture characterization in crystalline terrains by physical properties measurements and borehole wall imaging. Some of these methods can be applied to monitor pumping tests to identify fractures contributing to groundwater flow and, with this, determine hydraulic conductivity and transmissivity along the well. We present a procedure to identify fractures contributing to groundwater flow using spontaneous potential measurements generated by electrokinetic processes when the borehole water head is lowered and then monitored while recovering. The electrokinetic model for flow through a tabular gap is used to interpret the measured data and determine the water head difference that drives the flow through the fracture. We present preliminary results at a test site in crystalline rocks on the campus of the University of São Paulo. 相似文献
8.
Long-term temperature monitoring was carried out in a borehole drilled for investigation of the Nojima fault, an active fault in SW Japan, using the distributed optical fiber temperature sensing (DTS) technique. Temperatures in the borehole had been measured every 1 m along an optical fiber cable with a resolution of about 0.1 K over a period of 6 years. Water injection experiments were conducted in this borehole in 1997, 2000 and 2003. Monitoring of the temperature profile was started after the first injection experiment, and the temperature profile remained very stable until the start of the second injection experiment. During the second and third experiments, the temperatures in the borehole dropped due to cooling by the injected water but no appreciable temperature change was observed below about 580 m. It clearly shows that the water leaked out of the hole around this point and the leaking depth is estimated to be about 540 m based on the shape of the temperature profile. After the injection was stopped, the recovery of the temperature to the undisturbed profile was exceptionally slow around the leaking point, resulting in a local temperature anomaly, probably because the water leaking out of the hole had cooled the surrounding formations extensively. A very similar temperature anomaly was observed at the beginning of temperature monitoring, which suggests that water leaked out at the same depth in the first injection experiment as well. Between the second and third injection experiments, the top of the borehole was kept open to allow groundwater discharge for about 1 month in 2000 and 2003. In both periods, groundwater flowed out continuously and the shapes of the observed temperature profiles indicate that the groundwater entered in the hole at the same depth as the leaking point during the injection experiments. The temperature records also show that the rate of discharge had been nearly constant through the two test periods. The water discharge appears to have been little affected by the water injection. These results demonstrate that the optical fiber temperature monitoring system is a very effective tool for hydrological experiments. 相似文献
9.
Permeability measurements are critical to the calculation of water‐flow within hillslopes. Despite this, errors in permeability measurements are often ignored, and can be very large particularly in disturbance‐sensitive gley soils. This work compares the uncertainties associated with six field methods of permeametry applied to a gleyed soil in upland Britain. Slug tests, constant‐head borehole permeametry, and falling‐head borehole permeametry were undertaken on established piezometers. Additionally, ring permeametry and two types of trench tests were evaluated. Method‐related uncertainty due to proximity of impeding layers of high sorptivity soils produces under‐ and over‐estimates of permeability by a factor of up to 0·2 and 5, respectively. This uncertainty band is smaller than the observed effects of anisotropy and temporal variability. Had smearing and soil‐ring leakage errors not been minimized, the methodological uncertainties would have been so large that they would have distorted the true spatial field of permeability and its estimated impact on the balance of vertical and lateral flow. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
10.
An approach to characterization of multilayer aquifer systems using open well borehole dilution is described. The approach involves measuring observation well flow velocities while a nearby extraction well is pumped by introducing a saline tracer into observation wells and collecting dilution vs. depth profiles. Inspection of tracer profile evolution allows discrete permeable layers within the aquifer to be identified. Dilution profiles for well sections between permeable layers are then converted into vertical borehole flow velocities and their evolution, using an analytic solution to the advection-dispersion equation applied to borehole flow. The dilution approach is potentially able to measure much smaller flow velocities that would be detectable using flowmeters. Vertical flow velocity data from the observation wells are then matched to those generated using a hydraulic model of the aquifer system, "shorted" by the observation wells, to yield the hydraulic properties of the constituent layers. Observation well flow monitoring of pumping tests represents a cost-effective alternative or preliminary approach to pump testing each layer of a multilayer aquifer system separately using straddle packers or screened wells and requires no prior knowledge of permeable layer depths and thicknesses. The modification described here, of using tracer dilution rather than flowmeter logging to obtain well flow velocities, allows the approach to be extended to greater well separations, thus characterizing a larger volume of the aquifer. An example of the application of this approach to a multilayer Chalk Aquifer in Yorkshire, Northeast England, is presented. 相似文献
11.
倾斜观测已在地球物理领域以及地震部门获得广泛应用。有时,由于种种原因井下倾斜仪难以定向,这会对倾斜观测资料的解释带来困难,本文阐明一种利用潮汐信号进行井下倾斜仪定向反演的方法。 相似文献
12.
Cross-borehole flowmeter tests have been proposed as an efficient method to investigate preferential flowpaths in heterogeneous aquifers, which is a major task in the characterization of fractured aquifers. Cross-borehole flowmeter tests are based on the idea that changing the pumping conditions in a given aquifer will modify the hydraulic head distribution in large-scale flowpaths, producing measurable changes in the vertical flow profiles in observation boreholes. However, inversion of flow measurements to derive flowpath geometry and connectivity and to characterize their hydraulic properties is still a subject of research. In this study, we propose a framework for cross-borehole flowmeter test interpretation that is based on a two-scale conceptual model: discrete fractures at the borehole scale and zones of interconnected fractures at the aquifer scale. We propose that the two problems may be solved independently. The first inverse problem consists of estimating the hydraulic head variations that drive the transient borehole flow observed in the cross-borehole flowmeter experiments. The second inverse problem is related to estimating the geometry and hydraulic properties of large-scale flowpaths in the region between pumping and observation wells that are compatible with the head variations deduced from the first problem. To solve the borehole-scale problem, we treat the transient flow data as a series of quasi-steady flow conditions and solve for the hydraulic head changes in individual fractures required to produce these data. The consistency of the method is verified using field experiments performed in a fractured-rock aquifer. 相似文献
13.
Jesus A. Uriarte Laura Damas Mollá Maialen Sagarna Arantza Aranburu Francisco García Iñaki Antigüedad Tomás Morales 《水文研究》2020,34(4):1004-1015
Locating and quantifying groundwater flow in many built-up areas are a priority with regard to its complete restoration. In this work, a hydrogeological survey of the surroundings of the Punta Begoña Galleries (Getxo, Bizkaia), built on a coastal cliff, was completed by using ground penetrating radar (GPR) testing. Thus, the preliminary characterization of soils and rocks in accessible areas of the cliff was first improved by hydrogeological information gathered from a single survey borehole, including permeability measurements by low pressure injection tests (LPTs) and continuous water level monitoring. As a complementary method, the non-destructive GPR technique was performed during both dry and wet hydrological periods and in tandem with the injection tests, providing more complete spatial and temporal images of water flows. Specifically, GPR allows mapping of flow paths in soils and assessing the continuity of fractures in rock masses. Altogether, this complementary approach provides greater knowledge of complex underground flow dynamics in built environments, thus making it easier to make decisions for their management. 相似文献
14.
In massive rocks ground waters mainly flow in fracture zones whose permeability greatly changes depending on their filling. When studying ground-water flow in fissures, the results of observations of the electric fields of filtrational origin—which, in this case, considerably differ from those in porous media—can be used. Therefore the authors have made experiments on fissured media models. The measurements have been made in a special filtration tube with the fissured media simulated by a system of quartz glass plates. The spacings between plates were regarded as fissure widths. The observations have been made in fully open “fissures” and in those partially filled with sand or sandy-clay material. These experiments have resulted in establishing a dependence between the values of streaming potentials and pressure drops. The SP values have particularly been found to decrease with the opening of “fissures”. The most intensive electro-filtrational fields were observed at 40 per cent filling with medium grained sand. Additions of argillaceous material to the sand filler brought about sharp reductions in the intensity of electro-filtrational potentials. 相似文献
15.
This paper examines the weathering processes that have combined to produce the distribution of soil‐regolith (SR) thickness across the Triassic Sherwood Sandstone Group outcrop (750 km2) in Nottinghamshire, UK. Archive borehole logs (n = 282) taken across the outcrop showed that SR thickness had mean and median depths of ~1·8 and 1·5 m, respectively. Cores were taken from a forested site to depths ~3 m for geochemical analysis. At this site the SR thickness was ~1·7 m. Analysis of the loss of elements, compared to bedrock using mass balance calculations (τ) showed that all the calcite and gypsum cement had been removed to depths of >3 m. Thus the major difference between the SR and the underlying saprolite was that the former exists as loose sand as opposed to a semi‐durable rock. Scanning electron microscopy (SEM) analysis of core samples suggested that the non‐durable rock or saprolite had greater cementation of clay particles. We propose that the mechanism through which the clay cement (and other interlocking grain bonds) was eased apart was through freeze–thaw processes associated with the summer ‘active layer development (ALD)’ during the last glacial activity in the UK. We tested this theory by developing a Monte Carlo simulation based on a simplified version of the Stefan equation. Current Arctic datasets of air and ground temperatures were obtained to provide reasonable starting conditions for input variables. These were combined with known data for thermal conductivity, bulk density and moisture content of the Sherwood Sandstone regolith. Model predictions (n = 1000) of the distribution of SR thickness accurately reflect the observed distribution thickness from the borehole logs. This is strong evidence that freeze–thaw and ‘ALD’ processes are major factors in determining the thickness of SR across this outcrop. British Geological Survey © NERC 2012 相似文献
16.
17.
Effective stresses and shear failure pressure from in situ Biot's coefficient,Hejre Field,North Sea 
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下载免费PDF全文 J.B. Regel K.A. Andreassen N.C. Høegh van Gilse I.L. Fabricius 《Geophysical Prospecting》2017,65(3):808-822
We propose a combination of Biot's equations for effective stress and the expression for shear failure in a rock to obtain an expression for minimum pore pressure in a stable vertical well bore. We show that a Biot's coefficient calculated from logging data in the Hejre Field, North Sea, is significantly different from 1. The log‐derived Biot's coefficient is above 0.8 in the Shetland Chalk Group and in the Tyne Group, and 0.6–0.8 in the Heno Sandstone Formation. We show that the effective vertical and horizontal stresses obtained using the log‐derived Biot's coefficient result in a drilling window for a vertical well larger than if approximating Biot's coefficient by 1. The estimation of the Biot's coefficient is straightforward in formations with a stiff frame, whereas in formations such as shales, caution has to be taken. We discuss the consequence of assumptions made on the mineral composition of shales as unphysical results could be obtained when choosing inappropriate mineral moduli. 相似文献
18.
P. F. WORTHINGTON 《Geophysical Prospecting》1976,24(4):672-695
Laboratory studies of Bunter Sandstone specimens from Northwest Lancashire, Shropshire, West Cumberland, and the Vale of Clwyd have indicated that the parameters effective porosity, intergranular permeability, compressional wave velocity, formation resistivity factor, and effective matrix resistivity have significantly different distributions in each of these four regions. Regression analyses have shown that bivariate and trivariate expressions for the prediction of the two hydrological parameters from petrophysical data vary from region to region. It is concluded that, in quantitative geophysical investigations of these formations, each area must be investigated independently. For all four aquifers, and for both horizontally and vertically oriented specimens, effective porosity can be most reliably and readily estimated through a bivariate relationship involving formation resistivity factor. On the other hand, the best estimate of intergranular permeability from geophysical data is obtained through a trivariate expression involving both formation resistivity factor and effective matrix resistivity. The use of hydrogeophysical relationships to estimate hydrological parameters in situ is illustrated by reference to field examples. 相似文献
19.
Yuliy A. Dashevsky Semen Petrov Alexandr N. Vasilevskiy Oleg B. Bocharov Gleb V. Dyatlov 《Studia Geophysica et Geodaetica》2017,61(1):69-92
Reliable estimates of the fluid pressure in the pore space of rocks are critical for different aspects of petroleum exploration and production including injection operations and scenarios of water flooding. Numerous approaches are available for formation pore pressure evaluation, however, these measurements become a challenge inside a cased borehole, and a list of possible options is short: either the casing is to be perforated, or the production tubing needs to be disconnected to perform the pressure tests. We present a method for through-casing evaluation of formation pore pressure without shutting down production. We suggest equipping an observation well with a borehole gravimeter and acquiring time variations of the vertical component of the gravity field. Changes in gravity occur during gas production and are related to time variations of formation pore pressure. Gravity changes obtained in the observation well are supposed to be inverted for time-dependent formation pore pressure variations beyond the casing. Our results and recommendations are based on numerical modeling of pore pressure spatial distribution during gas field exploitation and relevant changes in borehole gravity. Benchmark models were elaborated in order to consider a dynamic process of pressure changes in time and space under conditions similar to those in the Medvezhye gas field (Russia). Different modeling scenarios are considered for early and late stages of gas field exploitation. The sensitivity analysis was performed to estimate quantitatively a sensitivity of borehole temporal gravity changes to variations in formation pore pressure behind the casing. Based on resolution analysis we justify the possibility to extract the gravity measurements directly related to changes in pore pressure from the total changes in the gravity field due to reservoir exploitation. The impact of pore pressure on the gravity field measured in boreholes during the water flooding is also evaluated, and obtained results are discussed. 相似文献
20.
油田注水开发中后期,井温测井在常规注水工艺的条件下,难以准确地反映注水剖面的实际情况．为此,本文根据注水井井筒与地层的传热机理,针对注水井多层注入的实际情况,建立了井筒及其周围地层的温度场数学模型．用该模型模拟计算了大庆油田某注水井的井下温度场分布,计算结果与实测结果接近,说明模型是适用的．通过对不同注入条件和地质条件的数值模拟,得出注水温度同井眼温度差别越大或注水速度越快,井温曲线越易于识别注入剖面．同时,对如何改善注水工艺,以提高井温测井识别注入剖面的能力提出了合理化建议． 相似文献