85 research outputs found
Effect of fertilization on reaction of soil in a long-term field experiment
No full textBakalaureusetöö eesmärk oli uurida, kuidas mõjutab väetamine mulla reaktsiooni
kolmeväljalises külvikorras. Saadud tulemusi võrreldi kirjanduslike tulemustega. Tartu
IOSDV katse rajati 1989. aastal. Katses oli viis erinevat mineraalväetise varianti (0, 40, 80,
120 ja 160 kg/haN) kolmel orgaanilise väetise foonil: orgaaniliste väetisteta, sõnnik (40 t/ha
igal kolmandal aastal enne kartulit) ja alternatiivsed orgaanilised väetised. Alates 2004.
aastast alternatiivse orgaanilise väetise katseribal mineraalväetisi ei kasutatud. Käesoleva töö
eesmärk oli uurida lupjamisjärgselt mulla aktiivse happesuse dünaamikat aastatel 2001-2015.
Külvikorras olid suvinisu, suvioder ja kartul. Katseandmete töötluseks kasutati kirjeldavat
statistikat, lineaarse regressioonimudeli parameetrite hinnanguid ja kovariatsioonanalüüsi
(ANCOVA). Tulemused näitasid, et mineraalne lämmastikväetis kiirendab mulla
taashapestumist, sõnnik aeglustab seda ning alternatiivsed orgaanilised väetised vähendavad
mulla happesust. Mineraalset lämmastikväetist kasutades taashapestuvad mullad 12 aastaga,
sõnnikuga väetades taashapestuvad mullad kaks korda aeglasemalt kui ainult mineraalse
lämmastikväetisega väetades.The aim of the thesis was to study how fertilizing affects the reaction of soil in three field
crop rotation. The results were compared with the results found in literature. The IOSDV
Tartu field experiment was established in 1989. The experiment contains five differet mineral
fertilizer treatments (0, 40, 80, 120 ja 160 kg N ha-1
) on three organic fertilizer background:
without organic fertilizers, with farmyard manure (40 t per ha-1
after each 3 years in autumn
before potato) and with alternative organic fertilizers. From 2004 mineral fertilizers were not
given to alternative organic fertilizer plots. The aim of the thesis was to research the dynamics
of soil acidity in 2001 to 2015 after liming in 2000. The crop rotation contains summer
wheat, summer barley and potato. For data analysis descriptive statistics, linear regression
parameter estimates and analysis of covariance (ANCOVA) was used. Results showed that
mineral fertilizers speed up soil acidification, organic fertilizers slow down soil acidification
protcesses and alternative organic fertilizers reduce soil acidity. Soils fertilized with mineral
fertilizers acidified to the levels of 2000 in 12 years, acidification of the soils fertilized with
farmyard manure was two times slower than of soils fertilized with only mineral fertilizers
Laboratory estimation of fracture compliance of a fluid-filled fracture using AVO response of a nonwelded interface
No full textWe explore the potential of multi-angle AVO inversion of P-P and P-S reflections from a fracture to estimate fracture proper- ties. Although AVO analysis of welded interface like geologi- cal layer boundaries is common, the use of AVO variations for nonwelded boundaries like fractures is yet to be investigated. We conduct laboratory experiments to measure reflection re- sponses of dry and wet fractures. The observed P-P reflec- tions of the fracture and the fracture aperture are very well pre- dicted by the nonwelded interface model. We invert the angle- dependent P-P reflectivity of the fracture to estimate both nor- mal and tangential fracture compliances. The estimated value of the normal compliance is accurate, and it is also possible to obtain the value of the non-zero tangential compliance. We find that supplementing the information of converted P-S re- flections in the AVO inversion greatly improves the estimate of the tangential compliance. The calculated compliance ra- tio clearly shows the existence of fluid in the fracture. This finding can be crucial for new applications in a wide range of scale - from earthquake seismology, deep and shallow seismic exploration, to nondestructive material testing.Applied Geophysics and Petrophysic
AVO inversion for a non-welded interface: Estimating compliances of a fluid-filled fracture
No full textThough well known for layer boundaries, the use of amplitude-versus-offset (AVO) variations for non-welded boundaries like fractures is not yet investigated. Depending on the seismic wavelength used, fractures can be regarded as thin, compliant zones in rocks, in different scales. We explore the potential of multiangle AVO inversion of P-P and P-S reflections from a fracture to estimate fracture properties.We conduct laboratory experiments to measure reflection responses of dry and wet fractures. The observed P-P reflections of the wet fracture and the fracture aperture are very well predicted by the non-welded interface model.We invert the angle-dependent P-P reflectivity of the fracture to estimate both normal and tangential fracture compliances. The estimated value of the normal compliance is accurate, and it is also possible to obtain the value of the non-zero tangential compliance.We find that supplementing the information of converted P-S reflections in theAVOinversion greatly improves the estimate of the tangential compliance. The calculated compliance ratio clearly shows the existence of fluid in the fracture. This finding can be crucial for new applications in a wide range of scale—from earthquake seismology, deep and shallow seismic exploration, to non-destructive material testing
A very first real data application of stochastic wave-equation based AVO inversion of seismic pre-stack data
No full textWave-Equation-Based Amplitude Vs Offset (WEB-AVO ) inversion solves the full elastic wave equation both for properties and for the total wavefield. It is a non-linear inversion technique that accounts for multiple scattering and mode conversions inside the target interval. When prior geological information interpreted from well logs is incorporated, stochastic inversion can be performed by honouring Bayes' theorem for probability density functions. The posterior function is proportional to the product of the likelihood function and the prior probability density function.The prior probability function is built from well logs and is a complex mixture of Gaussians that account for thicknesses, property values and their corresponding standard deviations.The likelihood function is built from the maximum likelihood estimator, the result of the deterministic inversion, and from the Hessian derived from the inversion kernel, scaled by the variance of the noise in the data. The present work proposes that the best estimate of the noise in the data can be extracted from the residual of the seismic-to-well match.The inaccuracy of the method can be quantified by taking the second derivative of the posterior function at the Maximum a Posteriori estimate. The present work also proposes that an additional source of inaccuracy is the intrinsic uncertainty, or non-uniqueness, of the method. It can be estimated with the help of random starting models on a perfect data set (synthetic data).The stochastic WEB-AVO inversion is a natural extension of the already existing deterministic WEB-AVO inversion workflow. The inversion result is constrained by the prior to honour the true geology observed in the wells.Applied Geophysics | IDEA Leagu
Stiffness of a Fracture from AVO Inversion Incorporating Linear Slip Boundary Condition - Experimental Investigation
No full textCharacterizing fracture is important in order to understand how groundwater is transported and stored in fractured environments, to assess contaminant transport through fractures, as well to evaluate the mechanical behaviour of a fractured rock mass. In this research, we have investigated through careful laboratory experiments the amplitude versus offset (AVO) response of seismic reflections from a fracture. We use the linear slip boundary condition at the fracture and estimate the angle-dependent reflection response due to a single fracture. The observed angle-dependent reflectivity is inverted to obtain the fracture compliance and aperture. Two detailed laboratory experiments are performed - one using laterally homogeneous fracture and another using laterally heterogeneous fracture (partly air-filled and partly water-filled). Our results demonstrate that normal compliance (inverse stiffness) of a fracture can be quite accurately estimated from the AVO inversion of P-P reflected waves. It is also possible to obtain the non-zero tangential compliance. The existence of fluid in the fracture can be predicted. Distinction of the fracture infills and quantification of the fracture aperture are possible. This finding will be crucial for numerous new applications in civil and geotechnical engineering, hydrogeophysics, as well as in other areas of earth sciences and non-destructive material testing.Applied Geophysics and Petrophysic
Obtaining angle-dependent reflectivity using the Marchenko redatuming method
No full textWhen reflection images are studied, often only the zero-offset reflectivity is considered, however, taking into account the angle-dependent reflectivity can add additional information about the subsurface. This additional information can be used to extract the properties of the subsurface using amplitude variation with offset (AVO) analysis. However, the presence of a complex overburden can significantly deteriorate the AVO response, especially for deep targets. To overcome this problem, the overburden effects can be removed by redatuming the reflection response at a depth level below the overburden. In this paper, we show that the Marchenko redatuming method has the potential to correctly retrieve the angle-dependent reflectivity in an acoustic medium without distortions due to multiple scattering. The retrieved angle-dependent reflection coefficients can be used as input in a subsequent inversion process to obtain the velocity and density of the subsurface.Accepted Author ManuscriptApplied Geophysics and Petrophysic
Experimental verification of spatially varying fracture-compliance estimates obtained from AVO inversion coupled with linear slip theory
No full textThe elastic compliance of a fracture can be spatially varying, reflecting the variation of microscale properties of the fracture, e.g., aperture, contact asperities, and fracture infill. Characterizing the spatial heterogeneity of a fracture is crucial in explaining the apparent frequency dependence of fracture compliance and in addressing the spatially varying mechanical and hydraulic properties of the fractured medium. Apparent frequency dependence of the estimated fracture compliance is caused when the used seismic wavelength is very large compared to the scale of heterogeneity. We perform ultrasonic laboratory experiments, and characterize the spatially varying compliance along a fluid-filled fracture. We simulate a horizontal fracture, and introduce heterogeneous fluid distribution along the fracture. We perform AVO inversion of the P-P reflections, where we obtain the theoretical angle-dependent reflection responses by considering the linear-slip model. The estimated compliance distribution clearly separates the dry region from the wet region of the fracture. The effective bulk modulus of the fluid is estimated using the derived values of the compliance. We find that the obtained bulk modulus is well explained by the presence of minute quantity of air bubbles in the water. We find also new evidences of the existence of scattered waves generated at the boundary representing a sharp change in fracture compliance. The estimated boundary between the dry and the wet regions of the fracture, which is detected by AVO inversion, is slightly shifted compared to the actual location. This is possibly due to the interference of the scattered waves that are generated at the boundary. The linear-slip model can represent thin structures in rocks in a wide range of scale. Therefore, the methodology, results and discussion presented in this study will be useful in developing new applications for assessing laterally varying mechanical and hydraulic properties of thin nonwelded discontinuities, e.g., fractures, joints, and faults.Applied Geophysics and Petrophysic
Estimation of changes in saturation and pressure from 4D seismic AVO and time-shift analysis
No full textA reliable estimate of reservoir pressure and fluid saturation changes from time-lapse seismic data is difficult to obtain. Existing methods generally suffer from leakage between the estimated parameters. We propose a new method using different combinations of time-lapse seismic attributes based on four equations: two expressing changes in prestack AVO attributes (zero-offset and gradient reflectivities), and two expressing poststack time-shifts of compressional and shear waves as functions of production-induced changes in fluid properties. The effect of using different approximations of these equations was tested on a realistic, synthetic reservoir, where seismic data have been simulated during the 30-year lifetime of a water-flooded oil reservoir. Results found the importance of the porosity in the inversion with a clear attenuation of the porosity imprint on the final estimates in case the porosity field or the vertically averaged porosity field is known a priori. The use of a first-order approximation of the gradient reflectivity equation leads to severely biased estimates of changes in saturation and leakage between the two different parameters. Both the bias and the leakage can be reduced, if not eliminated, by including higher-order terms in the description of the gradient, or by replacing the gradient equation with P- and/or S-wave time-shift data. The final estimates are relatively robust to random noise, as they present fairly high accuracy in the presence of white noise with a standard deviation of 15%. The introduction of systematic noise decreases the inversion accuracy more severely.Geoscience & EngineeringCivil Engineering and Geoscience
Frequency-dependent reflection response of a laterally varying fracture, represented as a nonwelded interface
No full textDisplacement across the interface is not continuous in the case of a nonwelded interface. The stiffness of a nonwelded interface is a function of fracture properties, e.g., roughness, asperities, aperture and fracture infill. In this research, the fracture compliance has been estimated by AVO inversion of P-P reflected waves from a nonwelded interface. Laboratory experiments were carried out in order to measure the reflection response of dry and wet fractures. CMP data were acquired for homogeneous and heterogeneous fluid-fillled fractures. The objectives of the research are: 1) to capture in the laboratory and study the reflection response of a laterally varying heterogeneous fracture, 2) to investigate the effectiveness of linear slip theory in predicting the AVO response of a heterogeneous fracture and estimate the fracture properties, 3) to observe in laboratory and utilize in characterization the scattered seismic waves from a laterally varying heterogeneous fracture, and 4) to utilize the time-lapse seismic reflection response for monitoring a fluid-filled laterally heterogeneous fracture. AVO inversion was carried out to obtain the fracture compliances. In order to illuminate a fracture which is significantly thinner than the predominant seismic wavelength, one promising approach is to incorporate the linear slip theory in the AVO inversion. This has been successfully implemented in this research. As a result, we could characterize a fracture which is nearly 65 times thinner than the seismic wavelength that we availed in our laboratory experiments. Fracture compliance values obtained from AVO inversion coupled with the linear slip theory can distinguish between wet and dry surfaces within a fracture. The obtained values of fracture compliance show the reliability of the AVO inversion in characterizing heterogeneous fractures. The obtained P-P reflection coefficients for each CMP gather closely match the expected values calculated from the linear slip theory. The value of the average compliance for the fluid-filled fracture in our experiment, estimated from AVO inversion, is 7:4x10^-14m/Pa. This value is slightly higher than the theoretical value of 6:4x10^-14m/Pa. This difference can be explained by the presence of minute quantity of air bubbles that got trapped in the infill fluid in the fracture during our experiment. We calculated that the volume of trapped air that can cause this deviation is 0.001%, which agrees with earlier observations. The AVO inversion of a fluid-filled nonwelded interface can be successfully used to monitor the fractured reservoir properties, using the dry fracture response as a reference. The scattered seismic waves from a heterogeneous fracture, observed for the first time in laboratory, show that these events affect the primary reflections, and therefore, there is a need for inversion that takes into consideration both specular and nonspecular reflection events.Civil Engineering and GeosciencesGeoscience & EngineeringIDEA League Applied Geophysic
Accumulation of sulfonamides and fluoroquinolones from soil to plants
No full textSaabunud / Received 12.12.2022 ; Aktsepteeritud / Accepted 29.06.2023 ; Avaldatud veebis / Published online 15.08.2023 ; Vastutav autor / Corresponding author Merike Lillenberg ; [email protected] current study was conducted to determine the potential
for some antibiotics to be taken up by food plants from soil fertilized with
manure, sewage sludge or its compost containing antibiotic residues. The
plants (potato – Solanum tuberosum L., carrot – Daucus carota L., and
wheat – Triticum aestivum L.) were cultivated in greenhouse under natural
light conditions in the presence of three fluoroquinolones (ciprofloxacin,
ofloxacin, and norfloxacin), and two sulfonamides (sulfadimethoxine and
sulfamethoxazole). The uptake of antibiotics was demonstrated from two
different soils (loamy and loamy sand). The concentrations of each
antibiotic in soil were 0.01, 0.1, 0.5, 1.0, and 10 mg kg–1. The antibiotics
were extracted from the plants using the liquid extraction (LE) and cleaned
up by the solid phase extraction (SPE). The extracts were analyzed by
liquid chromatography electrospray ionization tandem mass spectrometry
(LC-ESI-MS/MS). The accumulation range depended on antibiotic con-
centration in soil, chemical properties of the antibiotic, soil type, plant
species and parts (overground or below-ground). At soil concentrations of
10 mg kg–1 antibiotics accumulated in edible parts of most plants in
amounts, which exceeded their maximum residue levels (MRL) set for
food of animal origin – 100 μg kg–1. The highest average content of
antibiotics was detected in potato tubers and carrot roots grown in the
loamy sand soil – 3897 μg kg–1 and 3400 μg kg–1 sulfamethoxazole. Plants
accumulated antibiotics (ciprofloxacin and ofloxacin) from soil even at
soil concentration of 0.01 mg kg–1. Mostly the highest concentrations of
antibiotics were detected in below-ground parts of the plants grown in the
loamy-sand soil
- …
