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1.
本文采用Rayleigh理论描述纵波激励下非饱和岩石中气泡的局域流体流动,从经典力学的哈密顿原理导出了双重孔隙介质中的波传播方程,即Biot-Rayleigh方程.方程的格式简洁,参数少,所有相关参数物理可测,因此,方程具有较好的物理可实现性.基于相同的岩石与前人理论对比,初步验证了本理论的有效性.对三个地区的砂岩储层进行了分析,结果显示:地震频段内纵波对储层是否含气非常敏感,但对含气饱和度指示性不佳,且随着孔隙度降低,纵波频散与衰减在中低频段更为显著;含甲烷与含二氧化碳的砂岩储层均呈第三类AVO响应特征,很难从叠前分析技术中鉴别;理论预测的纵波频散随饱和度与频率变化的趋势与特征,与多频段实验观测结果一致.  相似文献   

2.
海洋含水合物沉积层的速度频散与衰减特征分析   总被引:2,自引:1,他引:2       下载免费PDF全文
随着水合物含量的增加,往往会引起纵、横波速度的增加,同时也会引起衰减的变化.针对含水合物沉积层的速度频散与衰减特征分析,有助于水合物含量的估计.本文以有效介质理论模型(EMT)为基础,研究了海洋未固结含水合物沉积层的纵、横波速度的非线性变化趋势.同时采用BISQ模型替代有效介质模型中的Gassmann方程,具体分析了全频带范围内海洋含水合物沉积层的速度频散与衰减特征.采用该模型,速度与衰减均随着水合物含量的增加而增加,且岩石孔隙度与泥质含量对衰减系数的影响较小.针对大洋钻探计划(ODP)164航次的实际数据,运用该模型方程计算采用声波测井数据(20 kHz)与VSP数据(100 Hz),分别获取了水合物稳定带的饱和度数据,平均在5%~7%之间,由于速度频散的影响,VSP估算结果要弱低于声波测井估算数据,均与实测保压取芯的甲烷含量数据、他人研究成果以及神经网络趋势预测结果均有着较好的一致性.对南海神狐海域三口钻位开展了水合物含量预测,与保压取芯结果有着较好的吻合关系.同时基于层剥离法提取该区域某地震测线BSR层的等效Q值,采用本文方法估算了该区域的等效天然气水合物含量15%~30%.数值模拟与实际应用结果表明:含水合物沉积层的速度频散与衰减特征均随着水合物含量的变化而变化,联合利用这一些变化特征,有助于天然气水合物含量的估计.  相似文献   

3.
Natural fractures in hydrocarbon reservoirs can cause significant seismic attenuation and dispersion due to wave induced fluid flow between pores and fractures. We present two theoretical models explicitly based on the solution of Biot's equations of poroelasticity. The first model considers fractures as planes of weakness (or highly compliant and very thin layers) of infinite extent. In the second model fractures are modelled as thin penny-shaped voids of finite radius. In both models attenuation is a result of conversion of the incident compressional wave energy into the diffusive Biot slow wave at the fracture surface and exhibits a typical relaxation peak around a normalized frequency of about 1. This corresponds to a frequency where the fluid diffusion length is of the order of crack spacing for the first model and the crack diameter for the second. This is consistent with an intuitive understanding of the nature of attenuation: when fractures are closely and regularly spaced, the Biot's slow waves produced by cracks interfere with each other, with the interference pattern controlled by the fracture spacing. Conversely, if fractures are of finite length, which is smaller than spacing, then fractures act as independent scatterers and the attenuation resembles the pattern of scattering by isolated cracks. An approximate mathematical approach based on the use of a branching function gives a unified analytical framework for both models.  相似文献   

4.

孔隙尺度的喷射流流动是引起地震波速度频散和衰减的重要机制之一. 目前,大多数喷射流模型仅考虑硬孔隙与微裂隙之间的局部流动,而忽略了具有不同孔隙纵横比微裂隙间的喷射流作用. 为了研究各种类型孔隙间的流体流动效应,本文对经典喷射流模型进行了扩展,通过结合等效介质理论和孔隙结构模型,根据从干燥岩石超声速度-压力曲线中提取的微裂隙孔隙纵横比分布,求取出岩石中各种微裂隙的体积压缩系数,并在此基础上,利用孔隙空间的压力松弛效应对微裂隙间的喷射流效应进行了模拟,并运用Biot理论描述了硬孔隙间的宏观流动效应. 扩展后的理论模型不仅考虑了微裂隙与硬孔隙间的局部流动、硬孔隙与硬孔隙间的Biot宏观流,还加入了微裂隙与微裂隙间的喷射流作用,且模型的高、低频极限始终与Mavko-Jizba理论和Gassmann方程保持一致. 模型应用分析发现,对于砂岩和大部分致密灰岩样品,扩展模型均能给出与超声实验测量数据吻合良好的估计结果. 此外,扩展模型预测的速度频散及衰减表明,喷射流机制在地震和测井频段发挥着重要作用,其速度频散曲线由低频至高频呈逐渐增大趋势,不具有明显的快速变化特征,与经典频散曲线形态存在显著差异;在低有效压力下,频散和衰减程度较大,喷射流机制发挥主要作用,而随着有效压力的增加,Biot宏观流机制开始占主导,频散和衰减程度逐渐减小.

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5.
王斌  陈祥忠  陈娟  姚军  谭开俊 《地球物理学报》2020,63(12):4528-4539
近年来围绕四川盆地侏罗系陆相致密砂岩已取得了勘探突破,其中川中—川西过渡带具备形成大气田的地质条件,但对该套致密砂岩弹性性质变化规律的研究还较少,致使利用地震方法进行"甜点"储层预测的精度不高.本文利用四川盆地侏罗系沙溪庙组32块样品开展了系统的声学测量,在此基础上,分析了样品弹性性质的变化规律.结合X射线衍射矿物组分分析、扫描电镜、铸体薄片和岩石薄片特征确定了不同成岩作用对岩石储集性能的影响.研究结果表明,研究区致密砂岩储层表现为孔隙型储层,受差异性成岩作用影响,黏土含量、钙质含量和硅质含量的差异以及它们分布特征之间的差异对岩石弹性性质造成了很大的影响.在研究区对岩石物性及弹性性质有明显影响的成岩作用包括早期的钙质胶结作用、压实作用和溶蚀作用,因此针对不同时期的成岩作用对岩石弹性及物性的影响,利用接触-胶结模型、微分等效模量模型和临界孔隙度校正的Hashin-Shtrikman上限模型建立了研究区致密砂岩的岩石物理模型.  相似文献   

6.
王斌  陈祥忠  陈娟  姚军  谭开俊 《地球物理学报》1954,63(12):4528-4539
近年来围绕四川盆地侏罗系陆相致密砂岩已取得了勘探突破,其中川中—川西过渡带具备形成大气田的地质条件,但对该套致密砂岩弹性性质变化规律的研究还较少,致使利用地震方法进行"甜点"储层预测的精度不高.本文利用四川盆地侏罗系沙溪庙组32块样品开展了系统的声学测量,在此基础上,分析了样品弹性性质的变化规律.结合X射线衍射矿物组分分析、扫描电镜、铸体薄片和岩石薄片特征确定了不同成岩作用对岩石储集性能的影响.研究结果表明,研究区致密砂岩储层表现为孔隙型储层,受差异性成岩作用影响,黏土含量、钙质含量和硅质含量的差异以及它们分布特征之间的差异对岩石弹性性质造成了很大的影响.在研究区对岩石物性及弹性性质有明显影响的成岩作用包括早期的钙质胶结作用、压实作用和溶蚀作用,因此针对不同时期的成岩作用对岩石弹性及物性的影响,利用接触-胶结模型、微分等效模量模型和临界孔隙度校正的Hashin-Shtrikman上限模型建立了研究区致密砂岩的岩石物理模型.  相似文献   

7.
Fluid pressure diffusion occurring on the microscopic scale is believed to be a significant source of intrinsic attenuation of mechanical waves propagating through fully saturated porous rocks. The so-called squirt flow arises from compressibility heterogeneities in the microstructure of the rocks. To study squirt flow experimentally at seismic frequencies the forced oscillation method is the most adequate, but such studies are still scarce. Here we present the results of forced hydrostatic and axial oscillation experiments on dry and glycerine-saturated Berea sandstone, from which we determine the dynamic stiffness moduli and attenuation at micro-seismic and seismic frequencies (0.004–30 Hz). We observe frequency-dependent attenuation and the associated moduli dispersion in response to the drained–undrained transition (∼0.1 Hz) and squirt flow (>3 Hz), which are in fairly good agreement with the results of the corresponding analytical solutions. The comparison with very similar experiments performed also on Berea sandstone in addition shows that squirt flow can potentially be a source of wave attenuation across a wide range of frequencies because of its sensitivity to small variations in the rock microstructure, especially in the aspect ratio of micro-cracks or grain contacts.  相似文献   

8.
Abstract   Detrital composition and major element geochemistry of Jurassic sandstones in the south Hefei Basin, central China, show their provenance to be the Dabie Mountains, whose tectonic attributes are closely related to continent–island arc complexes. It was found that a provenance change, from recycled orogen signatures and mixed orogenic sandstones to arc orogen, occurs from the lower Middle Jurassic to the Upper Jurassic (the Zhougongshan Formation). Dissected magmatic arc sources were gradually exposed in the Dabie Mountains due to intensive exhumation during the Late Jurassic, particularly after the Fenghuangtai depositional phase. Furthermore, it can be infered that the magmatic arc was initially present in both the Early Paleozoic and the Triassic, according to isotopic dating studies in previously published reports. δ13C–δ18O tracing between existing marbles of different strata in the Dabie block and marble gravels of the Fenghuangtai Formation in the Hefei Basin indicate that partial lithostratigraphic units for the Jurassic provenances have entirely disappeared from the Dabie block; therefore, it is impossible to reconstruct integral orogenic processes from studies on the remaining Dabie block alone. These findings, together with basin-fill sequences, also suggest that the Hefei Basin was mainly subjected to compressive mechanical regimes rather than extensional regimes in the Jurassic, which resulted in reverse-grading clastic depositional sequences, and is probably related to the northward intracontinental deep subduction of the Yangtze Plate. Regional exhumation properties and a tectonic model of the Late Mesozoic Dabie orogenesis are discussed in this paper.  相似文献   

9.
Knowledge about the spatial distribution of the fracture density and the azimuthal fracture orientation can greatly help in optimizing production from fractured reservoirs. Frequency-dependent seismic velocity and attenuation anisotropy data contain information about the fractures present in the reservoir. In this study, we use the measurements of velocity and attenuation anisotropy data corresponding to different seismic frequencies and azimuths to infer information about the multiple fracture sets present in the reservoir. We consider a reservoir model with two sets of vertical fractures characterized by unknown azimuthal fracture orientations and fracture densities. Frequency-dependent seismic velocity and attenuation anisotropy data is computed using the effective viscoelastic stiffness tensor and solving the Christoffel equation. A Bayesian inversion method is then applied to measurements of velocity and attenuation anisotropy data corresponding to different seismic frequencies and azimuth to estimate the azimuthal fracture orientations and the fracture densities, as well as their uncertainties. Our numerical examples suggest that velocity anisotropy data alone cannot recover the unknown fracture parameters. However, an improved estimation of the unknown fracture parameters can be obtained by joint inversion of velocity and attenuation anisotropy data.  相似文献   

10.
A direct detection of hydrocarbons is used by connecting increased attenuation of seismic waves with oil and gas fields. This study analyzes the seismic attenuation of P- and S-waves in one tight sandstone gas reservoir and attempts to give the quantitative distinguishing results of gas and water by the characteristics of the seismic attenuation of P- and S-waves. The Hilbert–Huang Transform (HHT) is used to better measure attenuation associated with gas saturation. A formation absorption section is defined to compute the values of attenuation using the common frequency sections obtained by the HHT method. Values of attenuation have been extracted from three seismic sections intersecting three different wells: one gas-saturated well, one fully water-saturated well, and one gas- and water- saturated well. For the seismic data from the Sulige gas field located in northwest Ordos Basin, China, we observed that in the gas-saturated media the S-wave attenuation was very low and much lower than the P-wave attenuation. In the fully water-saturated media the S-wave attenuation was higher than the P-wave attenuation. We suggest that the joint application of P- and S-wave attenuation can improve the direct detection between gas and water in seismic sections. This study is hoped to be useful in seismic exploration as an aid for distinguishing gas and water from gas- and water-bearing formations.  相似文献   

11.
裂缝是影响致密砂岩储层高产及稳产的关键,目前,对致密砂岩储层裂缝定性识别与表征仍很困难.在对致密砂岩裂缝研究现状系统调研的基础上,以鄂尔多斯盆地定边—志丹地区延长组岩芯、成像测井、常规测井资料为基础,分析裂缝发育类型,利用岩芯和成像测井标定,明确裂缝测井响应特征,优选对裂缝响应敏感的测井参数,建立有效的裂缝测井识别方法.研究表明:(1)定边—志丹地区裂缝按成因分有天然构造裂缝、钻具诱导裂缝、井眼崩塌裂缝、应力释放裂缝,按角度大小分为垂直裂缝、高角度裂缝、低角度裂缝、水平裂缝;(2)常规测井系列中对裂缝反映灵敏的参数依次为微电极、八侧向电阻率、声波时差、自然伽马、自然电位、双感应电阻率、井径;(3)通过裂缝敏感测井参数,分别构建曲线变化幅度参数(FIA)、曲线变化率参数(FIG),进而构建裂缝识别综合指数(FFA),结合电阻率侵入指数,在此基础上,采用人工判识方法,排除泥质条带、钙质砂岩等岩性变化所造成的影响,最终确定裂缝可能发育段,裂缝综合识别率为80.6%,能够对致密砂岩储层裂缝进行识别和预测.  相似文献   

12.
为了研究含气地层对地震波传播的影响,在地层温压条件下,用超声波测试了长庆油田苏里格气田砂岩样品在不同饱和度下的纵、横波速度和衰减Q值.实验表明砂岩样品的物性和流体含量对纵波的速度和衰减的影响均大于横波,含气饱和度大于60%时纵波Q值变化明显;物性越好,含气饱和度越高,纵波Q值越小,吸收越大.分析实验结果和相应的影响机理,给出了利用纵波的吸收衰减预测砂岩含气性的应用实例.  相似文献   

13.

含流体孔隙介质中地震波的速度频散和衰减在指导复杂储层含油气性识别领域具有重要意义.本文构建了包含微观挤喷流与介观层间流影响的跨尺度模型, 并使用求解介质等效模量的方式得到了模型中地震波的频散速度与衰减因子, 克服了前人在高频段计算结果出现异常值以及不同尺度衰减峰无法分离的缺陷.在该双尺度模型的基础上, 本文又综合考虑宏观尺度Biot流, 将三种地震波衰减理论耦合, 建立了相对统一的三尺度地震波衰减岩石物理模型.在Biot理论框架下, 分析了非均匀性流体、孔裂隙结构、微观挤喷流以及介观层间流对流体压力与弹性模量的影响, 得到了该三尺度模型中地震波的波动方程, 并求解得到了相应的地震波衰减与频散曲线, 分析了不同介质参数对衰减与频散曲线的影响.我们推导了在该模型上覆均匀各向同性介质情况下, 分界面处各类极性波的反射、透射系数特征方程, 并得到了随频率以及入射角变化的反射、透射系数三维曲面.

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14.
The presence of fractures in fluid‐saturated porous rocks is usually associated with strong seismic P‐wave attenuation and velocity dispersion. This energy dissipation can be caused by oscillatory wave‐induced fluid pressure diffusion between the fractures and the host rock, an intrinsic attenuation mechanism generally referred to as wave‐induced fluid flow. Geological observations suggest that fracture surfaces are highly irregular at the millimetre and sub‐millimetre scale, which finds its expression in geometrical and mechanical complexities of the contact area between the fracture faces. It is well known that contact areas strongly affect the overall mechanical fracture properties. However, existing models for seismic attenuation and velocity dispersion in fractured rocks neglect this complexity. In this work, we explore the effects of fracture contact areas on seismic P‐wave attenuation and velocity dispersion using oscillatory relaxation simulations based on quasi‐static poroelastic equations. We verify that the geometrical and mechanical details of fracture contact areas have a strong impact on seismic signatures. In addition, our numerical approach allows us to quantify the vertical solid displacement jump across fractures, the key quantity in the linear slip theory. We find that the displacement jump is strongly affected by the geometrical details of the fracture contact area and, due to the oscillatory fluid pressure diffusion process, is complex‐valued and frequency‐dependent. By using laboratory measurements of stress‐induced changes in the fracture contact area, we relate seismic attenuation and dispersion to the effective stress. The corresponding results do indeed indicate that seismic attenuation and phase velocity may constitute useful attributes to constrain the effective stress. Alternatively, knowledge of the effective stress may help to identify the regions in which wave induced fluid flow is expected to be the dominant attenuation mechanism.  相似文献   

15.
Estimates of sediment yield are essential in water resources analysis, modelling and engineering, in investigations of continental denudation rates, and in studies of drainage basin response to changes in climate and land use. The availability of high resolution, global environmental datasets offers an opportunity to examine the relationships between specific sediment yield (SYsp) and drainage basin attributes in a geographical information system (GIS) environment. This study examines SYsp at 14 long‐term gauging stations within the upper Indus River basin. Twenty‐nine environmental variables were derived from global datasets, the majority with a 1 × 1 km resolution. The SYsp ranges from 194 to 1302 t km?2 yr?1 for sub‐basins ranging from 567 to 212 447 km2. The high degree of scatter in SYsp is greatly reduced when the stations are divided into three groups: upper, glacierized sub‐basins; lower, monsoon sub‐basins; and the main Indus River. Percentage snow/ice cover (LCs) emerges as the single major land cover control for SYsp in the high mountainous upper Indus River basin. A regression model with percentage snow/ice cover (LCs) as the single independent variable explains 73·4% of the variance in SYsp for the whole Indus basin. A combination of percentage snow/ice cover (LCs), relief and climate variables explains 98·5% of the variance for the upper, glacierized sub‐basins. For the lower monsoon region, a regression model with only mean annual precipitation (P) explains 99·4% of the variance. Along the main Indus River, a regression model including just basin relief (R) explains 92·4% of the variance in SYsp. Based on the R2adj and P‐value statistics, the variables used are capable of explaining the majority of variance in the upper Indus River basin. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

16.
The reservoirs of the Upper Triassic Xujiahe Formation in Sichuan Basin have the characteristics of low compositional maturity, low contents of cements and medium textural maturity. The general physical properties of the reservoirs are poor, with low porosity and low permeability, and there are only a few reservoirs with medium porosity and low permeability in local areas. Based on the diagenetic mineral association, a diagenetic sequence of cements is established: early calcites (or micrite siderites) →first quartz overgrowth→chlorite coatings→dissolution of feldspars and debris→chlorite linings→ second quartz overgrowth (quartz widen or filled in remain intergranular pores and solution pores)→dissolution→third quartz overgrowth (quartz filled in intergranular and intragranular solution pores)→intergrowth (ferro) calcites→dolomites→ferro (calcites) dolomites→later dissolution→veins of quartz and calcites formation. Mechanical compaction is the main factor in making the reservoirs tight in the basin, followed by the second and third quartz overgrowth. In a long-term closed system, only feld-spars and some lithic fragments are dissolved by diagenetic fluids, while intergranular cements such as quartz and calcit are not dissolved and thus have little influence on the porosity of the Xujiahe Formation. This is the third factor that may have kept the sandstones of Xujiahe Formation tight finally. The hydrocarbon was extensively generated from organic materials after the second quartz overgrowth, and selectively entered favorable reservoirs to form tight sandstone gas reservoirs.  相似文献   

17.
Groundwater beneath the alluvial plain of the Indus River, Pakistan, is reported to be widely polluted by arsenic (As) and to adversely affect human health. In 79 groundwaters reported here from the lower Indus River plain in southern Sindh Province, concentrations of As exceeded the WHO guideline value for drinking water of 10 μg/L in 38%, with 22% exceeding 50 μg/L, Pakistan's guideline value. The As pollution is caused by microbially‐mediated reductive dissolution of sedimentary iron oxyhydroxides in anoxic groundwaters; oxic groundwaters contain <10 μg/L of As. In the upper Indus River plain, in Punjab Province, localized As pollution of groundwater occurs by alkali desorption as a consequence of ion exchange in groundwater, possibly supplemented by the use for irrigation of groundwater that has suffered ion exchange in the aquifer and so has values >0 for residual sodium carbonate. In the field area in southern Sindh, concentrations of Mn in groundwater exceed 0.4 mg/L in 11% of groundwaters, with a maximum of 0.7 mg/L, as a result of reduction of sedimentary manganese oxides. Other trace elements pose little or no threat to human health. Salinities in groundwaters range from fresh to saline (electrical conductivity up to 6 mS/cm). High salinities result from local inputs of waste water from unsewered sanitation but mainly from evaporation/evapotranspiration of canal water and groundwater used for irrigation. The process does not concentrate As in the groundwater owing to sorption of As to soils. Ion exchange exerts a control on concentrations of Na, Ca, and B but not directly on As. High values of Cl/Br mass ratios (most ?288, the marine value) reflect the pervasive influence on groundwater of sewage‐contaminated water from irrigation canals through seepage loss and deep percolation of irrigation water, with additional, well‐specific, contributions from unsewered sanitation.  相似文献   

18.
Pure-path averages for group velocities and specific attenuation have been calculated from individual observations and from path averages for two regionalizations; one original to this study and the other previously devised by Wu. Both are based on four upper-mantle provinces: ocean basin, continent, island arc and mid-ocean ridge. Pure-path group velocities and specific attenuation have also been calculated for combinations of regions and provide well separated regional measurements for such composite regions.Shear-velocity models for pure and combined regions have been derived by a controlled Monte Carlo inversion procedure and indicates that a low-velocity zone is required beneath the oceans, but is not required beneath continents. Models have been produced for pure and combined ocean, ocean-ridge, continent and continent-arc provinces.Q?1R determined from pure-path average group velocities and attenuation coefficients has been regionalized successfully for 2- and 3-region combinations. The resulting pure-path Q?1R for continents is much lower than that for ocean basins and ocean-ridge provinces. Inversion of Q?1R for ocean-ridge provinces shows that the average Qβ for the upper 200 km of these regions is between 85 and 100.  相似文献   

19.
Wettability is an essential property of reservoirs that is of great importance for enhancing oil recovery(EOR) and oil migration. The wettability of reservoirs is generally believed to be strongly affected by mineral compositions but it is not always the case. An integrated study of petrography and wettability was carried out to determine the impact of chlorite minerals on the wettability of the sandstone reservoirs in the Upper Triassic Yanchang Formation. Chlorites are found to be commonly present in the reservoir sandstones as detrital grains, rim-shaped cements, and biotite-chloritized forms with the pore peripheries being largely coated by chlorite, which is the main mineral in direct contact with pores. At pore scale, the wetting state of chlorites can either be oil-wet or water-wet in the tight sandstone reservoirs depending on wettability alteration by oil charge. Chlorites in contact with pores occupy a large of proportions of oil-wet pore walls and are crucial for the formation of oil-wetting state of reservoir sandstones. At core scale, the contents of chlorites in direct contact with pores do not correlate well with the AmottHarvey index due to other factors such as heterogeneity, oil-bearing degrees of samples.  相似文献   

20.
Groundwater abstraction and depletion were assessed at a 1‐km resolution in the irrigated areas of the Indus Basin using remotely sensed evapotranspiration (ET) and precipitation; a process‐based hydrological model and spatial information on canal water supplies. A calibrated Soil and Water Assessment Tool (SWAT) model was used to derive total annual irrigation applied in the irrigated areas of the basin during the year 2007. The SWAT model was parameterized by station corrected precipitation data (R) from the Tropical Rainfall Monitoring Mission, land use, soil type, and outlet locations. The model was calibrated using a new approach based on spatially distributed ET fields derived from different satellite sensors. The calibration results were satisfactory and strong improvements were obtained in the Nash‐Sutcliffe criterion (0.52 to 0.93), bias (?17.3% to ?0.4%), and the Pearson correlation coefficient (0.78 to 0.93). Satellite information on R and ET was then combined with model results of surface runoff, drainage, and percolation to derive groundwater abstraction and depletion at a nominal resolution of 1 km. It was estimated that in 2007, 68 km3 (262 mm) of groundwater was abstracted in the Indus Basin while 31 km3 (121 mm) was depleted. The mean error was 41 mm/year and 62 mm/year at 50% and 70% probability of exceedance, respectively. Pakistani and Indian Punjab and Haryana were the most vulnerable areas to groundwater depletion and strong measures are required to maintain aquifer sustainability.  相似文献   

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