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1.
Three boreholes were drilled near the Nojima fault, which the 1995 Hyogoken–Nanbu earthquake occurred on. In order to research the properties and the healing process of the fault, water injection experiments were conducted every 3 years. In this report, we researched the permeability of the fault as a measurement of crack density or porosity of the fault zone. Pore water pressure changes in rock due to the water injections at one borehole were observed as discharge changes or groundwater level changes at the other borehole. Using numerical calculations, the permeability of the fault fracture zone was estimated for each experiment. The permeability has been decreasing as time passed, which is thought to show the fault healing process of the Nojima fault after the 1995 Hyogoken–Nanbu earthquake.  相似文献   

2.
The core from two boreholes (13.1 and 19.2 m depth) drilled 500 m apart in the fractured, welded tuff near the summit of the Snowshoe Mountain, Colorado (47°30′N, 106°55′W) had unique petrographic and hydrodynamic properties. Borehole SM-4 had highly variable annual water levels, in contrast to SM-1a, whose water level remained near the land surface. Core samples from both boreholes (n=10 and 11) were examined petrographically in thin sections impregnated with epoxy containing rhodamine to mark the pore system features, and were analyzed for matrix porosity and permeability. Core from the borehole sampling the vadose zone was characterized by open fractures with enhanced porosity around phenocrysts due to chemical weathering. Fractures within the borehole sampling the phreatic zone were mineralized with calcite and had porosity characteristics similar to unweathered and unfractured rock. At the top of the phreatic zone petrography indicates that calcite is dissolving, thereby changing the hydrogeochemical character of the rock (i.e. permeability, porosity, reactive surface area, and mineralogy). Radiocarbon ages and C and O stable isotopes indicate that calcite mineralization occurred about 30 to 40 ka ago and that there was more than one mineralization event. Results of this study also provide some relationships between primary porosity development from 3 types of fracture in a welded tuff.  相似文献   

3.
Beldih mine at the central part of the South Purulia Shear Zone (SPSZ) has been reported with low grade uranium-bearing formation within quartz-magnetite-apatite host in kaolinized formation. Therefore, the present integrated geophysical study with gravity, magnetic, radiometric, very low frequency electromagnetic (VLF) and gradient resistivity profiling methods around the known mineralized zones aimed at identifying the exact geophysical signatures and lateral extent of these uranium mineralization bands. The closely spaced gravity-magnetic contours over the low to high anomaly transition zones of Bouguer, reduced-to-pole magnetic, and trend surface separated residual gravity-magnetic anomaly maps indicate the possibility of high altered zone(s) along NW-SE direction at the central part of the study area. High current density plots of VLF method and the low resistive zones in gradient resistivity study depict the coincidence with low gravity, moderately high magnetic and low resistivity anomalies at the same locations. Moderate high radioactive zones have also been observed over these locations. This also suggests the existence of radioactive mineralization over this region. Along profile P2, drilled borehole data revealed the presence of uranium mineralization at a depth of ～100 m. The vertical projection of this mineralization band also identified as low gravity, low resistivity and high magnetic anomaly zone. Thus, the application of integrated geophysical techniques supported by geological information successfully recognized the nature of geophysical signatures associated with the uranium mineralization of this region. This enhances the scope of further integrated geophysical investigations in the unexplored regions of SPSZ.  相似文献   

4.
Boreholes drilled in the crystalline rocks of Nigeria have a reputation of failures and low yields. The performance of 256 boreholes drilled in different parts of the crystalline rocks of SW Nigeria were reviewed to determine their failure characteristics. 100% success was claimed for 105 boreholes constructed by one driller. Out of 111 other borehole records supplied by three other drillers 35 were abortive, representing a failure rate of 32%. In contrast, 24 owners of 40 boreholes reported 24 failures representing a failure rate of 60%.The common causes of borehole failure in the crystalline rocks of SW Nigeria are seasonal variations in water level, improper casing of the overburden, damage to pumps and other system failures such as blocked pipelines and malfunctioning tanks. Non-penetration into the water bearing horizon also features as a cause of borehole failure in this study.It is suggested that proper construction, operation and maintenance of boreholes will reduce the incidence of borehole failures in crystalline rocks of SW Nigeria.  相似文献   

5.
Double Porosity Finite Element Method for Borehole Modeling   总被引：2，自引：0，他引：2  
Summary. This paper considers the mechanical and hydraulic response around an arbitrary oriented borehole drilled in a naturally fractured formation. The formation is treated as a double porosity medium consisting of the primary rock matrix as well as the fractured systems, which are each distinctly different in porosity and permeability. The poro-mechanical formulations that couple matrix and fracture deformations as well as fluid flow aspects are presented. A double porosity and double permeability finite element solution for any directional borehole drilled in the fractured porous medium is given. Compared with conventional single-porosity analyses, the proposed double-porosity solution has a larger pore pressure in the matrix and a smaller tensile stress in the near-wellbore region. The effects of time, fracture, mud weight, and borehole inclination in the double-porosity solution are parametrically studied to develop a better understanding of physical characteristics governing borehole problems.  相似文献   

6.
This paper presents the combination of two complementary methods, magnetic and joint inversion of resistivity/TEM data, as an effective approach to characterize groundwater reservoirs. Twenty stations of transient electromagnetic (TEM) and vertical electrical soundings (VES) were measured and interpreted using a joint inversion technique to evaluate the subsurface low resistivity zones connected to the groundwater reservoir. A complementary survey including 871 land magnetic stations was carried out at the same area to detect the upper surface of the basaltic sheet, which represents the bottom of the Miocene aquifer in the study area. The geological log from one borehole drilled in the zone was used to partially calibrate the calculated models. The results revealed that the study area consists of five different geological units with ages ranging from Paleogene (Oligocene) to Quaternary. The methodology provides good results at a very low cost when compared with drilling boreholes.  相似文献   

7.
As part of a larger regional research program “KarstEAU”, the authors have applied electrical resistivity tomography (ERT) techniques to characterize heterogeneities in the Port-Miou coastal karst aquifer (Cassis, SE France). Field surveys were carried out on intensely fractured and karstified Urgonian carbonates. Extensive research has characterized macro- and micro-scale geology of the Port-Miou area and particularly underground water-filled conduits and fault/fracture and karst systems within a former quarry. The authors applied 2D ERT along two surface profiles of length 420 and 595 m to test capability for delineating subsurface conduits and possibly relationship between conduit and fault/fracture/karst orientation; and 3D ERT with a dense 120 electrode array at 1 m spacing (11 × 10 m) was applied over an area of the quarry that had been profiled using 3D georadar and which has had intensive nearby structural geological interpretation. The 2D profiling imaged several underground conduits at depths to >50 m below ground surface and below sea level, including possibly the main Port Miou submarine spring and smaller springs. The 2D profiling within the quarry provided a better understanding of the connectivity between major fractures and faults on the quarry walls and secondary springs along the coast supporting flow of the secondary springs along interpreted fracture orientations. In addition, 2D inversion-derived conductivity models indicate that high resistivity zones above sea-level are associated with non-saturated zones and low resistivity anomalies in the non-saturated zone are associated with residual clays in paleokarsts. A partitioned lower resistivity zone below sea-level can be associated with a higher porosity/permeability zone with fractures and karstic features. Inversion models of the dense 3D ERT data indicate a higher resistivity volume within the larger surveyed block. The survey characterized the non-saturated zone and the ERT resistivities are correlated with karst features interpreted by 3D georadar and visible in the inferior wall of the quarry.  相似文献   

8.
Summary Currently under study by the Department of Energy are the geologic and hydrologic characteristics of the ash-flow deposits under Yucca mountain at the Nevada test site. Of interest at this site is the potential for disposal of high-level radioactive wastes in the unsaturated zone of the densely welded portions of the tuffs. These studies include the preformance-assessment of barriers and seals for boreholes, ramps, drifts and shafts at the Yucca mountain site. In-situ tests on standard Type II Portland cement and microfine cement as grout materials have been performed on a similar rock type to Yucca Mountain's near Superior Arizona. The tests were performed in a vertical borehole drilled in highly fractured and densely welded tuff (brown unit of Apache Leap) through a series of pressurized grout applications. Packer flow tests prior to and after each grout application measure the effectiveness of the grout application in reducing the permeability of the rock surrounding the borehole. Overall the grout applications have reduced the permeability of the test hole by three orders of magnitude.  相似文献   

9.
底板岩巷穿层钻孔抽采技术和本煤层定向长钻孔抽采技术是目前高瓦斯和突出矿井回采工作面最为主要的瓦斯治理措施。晋城矿区赵庄矿煤层具松软低透气性特点,主要采用岩巷穿层钻孔消突为主,本煤层顺层钻孔消突为辅的瓦斯治理方法。但底板岩巷穿层钻孔存在工程量大、施工周期长及成本高等缺点,本煤层钻孔存在钻孔抽采不均匀、钻孔覆盖密度不足等技术缺陷。为对比考察底板梳状长钻孔与底板岩巷穿层钻孔的抽采效果,在赵庄矿1307采面开展了2种瓦斯治理方法。结果表明:抽采条件和抽采范围相同条件下,5个底板梳状长钻孔的瓦斯抽采总量占到底板岩巷穿层钻孔瓦斯抽采总量的75.4%,而底板梳状长钻孔的经济投入仅占底板岩巷穿层钻孔经济投入的29.2%。由此得出,研究区梳状长钻孔替代穿层钻孔的瓦斯抽采技术是可行的。该研究为底板梳状长钻孔替代底板岩巷的技术可行性提供了实践参考,为松软低透的高瓦斯和突出矿井的瓦斯治理提供了更为经济可行的治理方案。   相似文献   

10.
With a view towards understanding the evolutionary history of the complex South Indian shield, several geological and geophysical studies have been carried out. Recent geophysical studies include magnetotelluric (MT), deep seismic sounding (DSS), gravity, magnetic and deep resistivity soundings (DRS). In the present study, MT results along 140 km Andiyur-Turaiyur east-west profile is presented. The data are subjected to Groom-Bailey decomposition and static shift correction before deriving a 2-D model. The 2-D modeling results have shown that the upper crust (up to about 15 km) towards western part of the profile have exhibited high resistive character of about 40, 000 ohm-m as compared to the eastern part (less than 5, 000 ohm-m). The mid-lower crust has shown a decrease in resistivity in western part of the profile, the order of resistivity being 2, 000 ohm-m. An anomalous steep conductive feature (less than 100 ohm-m) is observed near Sankari at mid-lower crustal depths (>20 km) towards middle part of the profile. This feature is spatially correlatable with the well-known Moyar-Bhavani Shear Zone (MBSZ). The features obtained in the present study are consistent with earlier MT studies in this region and correlatable with other geophysical studies. DSS studies near the study region gave an evidence for differing crustal structure on either side of MBSZ. Variation in geoelectric character along the profile both in the upper crust and mid-lower crust indicate a block structure in the SGT with shear zones acting as boundaries. The new evidence in the form of distinct geoelectric structure and also variation in seismic structure indicate a continent-continent collision zone in this region and plays an important role for the Gondwana reconstruction models of South Indian shield.  相似文献   

11.
Rock failure is observed around boreholes often with certain types of failure zones, which are called breakouts. Laboratory‐scale drilling tests in some high‐porosity quartz‐rich sandstone have shown breakouts in the form of narrow localized compacted zones in the minimum horizontal stress direction. They are called fracture‐like breakouts. Such compaction bands may affect hydrocarbon extraction by forming barriers that inhibit fluid flow and may also be a source of sand production. This paper presents the results of numerical simulations of borehole breakouts using 3D discrete element method to investigate the mechanism of the fracture‐like breakouts and to identify the role of far‐field stresses on the breakout dimensions. The numerical tool was first verified against analytical solutions. It was then utilized to investigate the failure mechanism and breakout geometry for drilled cubic rock samples of Castlegate sandstone subjected to different pre‐existing far‐field stresses. Results show that failure occurs in the zones of the highest concentration of tangential stress around the borehole. It is concluded that fracture‐like breakout develops as a result of a nondilatant failure mechanism consisting of localized grain debonding and repacking and grain crushing that lead to the formation of a compaction band in the minimum horizontal stress direction. In addition, it is found that the length of fracture‐like breakouts depends on both the mean stress and stress anisotropy. However, the width of the breakout is not significantly changed by the far‐field stresses. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

12.
Deep Crustal Electrical Signatures of Eastern Dharwar Craton, India   总被引：1，自引：0，他引：1  
Wide band magnetotelluric (MT) investigations were carried out along a profile from Kavali in the east to Anantapur towards west across the Eastern Ghat Granulite Terrain (EGGT), Eastern Dhanvar Craton (EDC) and a Proterozoic Cuddapah Basin. This 300 km long profile was covered with 20 stations at an interval of 12–18 km. The MT data is subjected to robust processing, decomposition and static shift correction before deriving a 2-D model. The model shows a resistive crust (−10,000–30,000 ohm-m) to a depth of 8–10 km towards west of the Cuddapah basin. The mid crust is less resistive (about 500 ohm-m) and the lower crust with a slight increase in resistivity (about 1,500 ohm-m) in the depth range of 20–22 km. The resistivity picture to the east of the Cuddapah basin also showed a different deep crustal structure. The resistivity of upper crust is about 5,000 ohm-m and about 200 ohm-m for mid and lower crust. The sediment resistivity of Cuddapah basin is of the order of 15–20 ohm-m. MT model has shown good correlation with results from other geophysical studies like deep seismic sounding (DSS), gravity and magnetics. The results indicate that the lower crustal layers are of intermediate type showing hydrous composition in Eastern Dhanvar Craton.  相似文献   

13.
Groundwater in eastern Uganda mostly occurs in fractures in the crystalline basement rocks and at the interface between the overburden and bedrock. The study was aimed at improving the success rate of boreholes through the use of complimentary geophysical siting procedures in 16 locations in Kamuli District, eastern Uganda. Boreholes that were sited after applying appropriate geophysical techniques yielded adequate quantities of water, whereas those sited where such procedures were not applied were out of service sooner than expected. Techniques to determine the precise location of resistivity anomaly and vertical electrical sounding (VES) models were used to locate water-bearing zones. VESs were undertaken to provide an overview of the geology. The apparent resistivities of the water-bearing zones both from VES and resistivity profiling data, had a relationship with the success rates of the boreholes. Electrical resistivities were correlated with hydrogeological parameters. The majority of successful boreholes had, within water-bearing zones, minimum apparent resistivity values less than 200 and 100 Ohmm, from the resistivity profiling anomalies and VES, respectively. The depth to bedrock was generally greater than 20 m below ground level, which indicates potential for medium yielding boreholes.  相似文献   

14.
淮南板集煤矿F512断层导水性分析及地面注浆加固   总被引：1，自引：0，他引：1  
板集煤矿F512断层落差70m,存在着导通上覆新生界松散层水与下伏太原组岩溶水的威胁,同时,断层带的破碎岩体也将对巷道掘进和支护带来困难。该矿先后施工了3个水文地质钻孔进行抽水和压水试验,根据岩心鉴定成果和岩石RQD值,认为断层带的岩心较为破碎;依据抽水过程中的流量变化、水位降深值和水位恢复值等指标及压水试验中透水率分析,发现该断层的导水性较差,具有弱渗透性。参考相邻矿区的经验,决定对断层破碎岩体采用地面注浆方法进行加固。整个工种注入水泥浆1 600m3,破碎岩体得到了有效加固,巷道掘进顺利通过了F512断层。  相似文献   

15.
The application of electrical imaging and very low frequency (VLF) electromagnetics was investigated for the purpose of delineating basement fracture zones, and to show how incorporating a priori information in numerical modelling would facilitate the location of fractured zones within a basement rock more precisely. To this end, direct current (DC) dipole–dipole resistivity and VLF modelling and inversion experiments were carried out to evaluate the efficacy of the methods in detecting low-resistivity fracture zones in a typical crystalline basement rock that is favourable for groundwater accumulation. Most wells drilled in such an environment usually have low yields. Results of the numerical experiment generally indicate that fractures covered by moderate overburden, and having considerable depth, extent, and thickness compared to the depth of fracture burial, produce good responses resulting in high-resolution resistivity images. Lower resolution resistivity images were obtained as the thickness of the overburden increased. Also, the model investigations indicate that width of the fracture zone plays a major role in controlling image resolution. Conclusions from the synthetic modelling were confirmed by resistivity and VLF data gathered across a suspected fault in a hard rock terrain of southwestern Nigeria. The results from the field data are in general agreement with the numerical modelling experiments.Integración de métodos geofísicos superficiales para la detección de fracturas en macizos rocosos cristalinos del suroeste de Nigeria.  相似文献   

16.
Groundwater movement and availability in crystalline and metamorphosed rocks is dominated by the secondary porosity generated through fracturing. The distributions of fractures and fracture zones determine permeable pathways and the productivity of these rocks. Controls on how these distributions vary with depth in the shallow subsurface (<300 m) and their resulting influence on groundwater flow is not well understood. The results of a subsurface study in the Nashoba and Avalon terranes of eastern Massachusetts (USA), which is a region experiencing expanded use of the fractured bedrock as a potable-supply aquifer, are presented. The study logged the distribution of fractures in 17 boreholes, identified flowing fractures, and hydraulically characterized the rock mass intersecting the boreholes. Of all fractures encountered, 2.5% are hydraulically active. Boreholes show decreasing fracture frequency up to 300 m depth, with hydraulically active fractures showing a similar trend; this restricts topographically driven flow. Borehole temperature profiles corroborate this, with minimal hydrologically altered flow observed in the profiles below 100 m. Results from this study suggest that active flow systems in these geologic settings are shallow and that fracture permeability outside of the influence of large-scale structures will follow a decreasing trend with depth.  相似文献   

17.
Electrical resistivity tomography (ERT), single-point-resistance logging with time-lapse, and geological and groundwater level data, are utilized to determine the mechanism of, and a hydrogeological model of, the Gangxianlane landslide in the west-central part of Taiwan. The rock surface and geometry of the colluviums were found by integrating ERT and borehole data. The iso-resistivity line in the bedrock broadly followed the bedding plane, indicating that the contribution of lithology to resistivity exceeds that of groundwater. The results of single-point-resistance logging with time-lapse and borehole data reveal that the bedrock has low permeability, which is associated with poorly developed joints and fractures. The fine grain content part (including the clayey layer), almost parallel to the bedding plane of the bedrock and between the colluvium and the bedrock in the upper part of the landslide, served as the slip surface and is believed to have been recently produced. It can block and retain water in the colluviums. Accordingly, this slip surface has the potential to re-slip in the future. Another slope failure involved rock collapse by a well-developed open release joint close to the Huoshaoping Terrace. It is also related to groundwater flow over a large gradient from the Huoshaoping Terrace. It is a key to determining whether this landslide will expand in the future.  相似文献   

18.
Measurements of spectral induced polarization for environmental purposes   总被引：2，自引：0，他引：2  
Hydraulic permeability is one of the most important parameters for the evaluation of sediments relevant to environmental and hydrogeological problems. Up to now, permeability could be determined only by time-consuming and expensive methods like pumping tests or sampling and laboratory investigations. The results are confined to few locations, and they depend on the scale of the investigation method. Measurements on rock samples in a laboratory can differ significantly from well test results. Geophysical measurements are performed on different scales from high resolution measurements in boreholes up to large-scale soundings. Variations in permeability are mainly caused by varying grain size and by changes in porosity. A decrease of average grain diameter results in an increasing internal surface area. Petrophysical investigations have shown a reliable correlation between the imaginary part of electrical conductivity and the porespace-related internal surface. The formation resistivity factor, which is related to porosity, can be determined by geoelectrical measurements if the electrical conductivity of the pore fluid is known. The internal surface area and the formation factor are the only two parameters used by a Kozeny-Carman-like equation to evaluate the permeability or hydraulic conductivity for the investigated representative volume. Complex electrical conductivity is determined by measurements of induced polarization in the frequency domain. Frequencies below 10 Hz are used to avoid electromagnetic coupling. The permeability values determined by electrical measurements in boreholes can well be compared with those derived from the grain size distribution of samples. The same algorithm can be applied to evaluate the hydraulic conductivity of subsurface layers by complex resistivity soundings. The high sensitivity of the imaginary conductivity component to changes at the internal surface may be used as an indicator for contaminations.  相似文献   

19.
Measurements of seismoacoustic emissions in boreholes allow researchers to identify fault zones and zones of cracking and rock shattering. These zones are usually identified from the maximal values of seismoacoustic emission. However, the permeability of the identified zones cannot be estimated solely from the seismoacoustic emission data, especially in the case when seismoacoustic emission sources are located in isolation in the vicinity of a borehole. The experiments have shown that dynamically active permeable zones of tectonic failures can be identified based on joint measurements of seismoacoustic emissions and helium concentrations in fluid.  相似文献   

20.
The western sector of the Tagliamento River basin (Friuli Venezia-Giulia Region; northern Italy) is characterized by important water resources, both superficial and underground. In particular, in the Quaternary deposits of the plain, up to a depth of 500 m, six artesian aquifer systems exist. A large amount of lithological, geomorphological, and hydrogeological data is presented, allowing for definition of (a) the principal aquifer system of the area to a depth of about 500 m; (b) geometrical characteristics of the aquifers (thickness, lateral extension, etc); (c) the hydraulic parameters (hydraulic conductivity, transmissivity); (d) chemico-physical characteristics of the water; and (e) vulnerability to pollution of the aquifer systems. In a test area, where many boreholes were drilled for fresh water supply, the conceptual hydrogeological model was integrated by a detailed and repeated three-dimensional (3D) resistivity survey using combined electrical resistivity tomography (ERT) and time-domain electromagnetic (TDEM) soundings. ERT investigation was mainly used to get detailed information about geometry and porosity of the overburden and to calibrate the shallowest TDEM information.  相似文献   

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