Interpretation Of Tracer Tests Research Articles

Study on the adsorption mechanism of fluorescent nano-tracer in sandstone core

Chemical tracer testing technology has increasingly become the preferred method for reservoir monitoring in oil fields due to its low cost and high efficiency. Understanding the migration behavior and adsorption mechanisms of chemical tracers in porous media is crucial for designing tracer injection processes and enhancing the accuracy of tracer test interpretation. This study employs an enhanced Stöber sol-gel method to synthesize fluorescent silica nanoparticles. After surface modification with the silane coupling agent γ-(methacryloyloxy) propyltrimethoxysilane (KH570) and doping with two fluorescent dyes, a multicolor fluorescent nano-tracer (PMFN) was synthesized. This study conducted dynamic and equilibrium adsorption experiments to investigate the adsorption behavior of PMFN on sandstone surfaces. To elucidate the adsorption mechanism of PMFN, we fitted the adsorption equilibrium experimental data using the Langmuir, Freundlich, and Temkin isothermal adsorption models. The adsorption kinetics were studied using the Lagergren, Elovich, and pseudo-first-order kinetic models. Additionally, we assessed the influence of ionic strength and particle size on the adsorption of PMFN by calculating the DLVO interaction forces between PMFN and the sandstone surface. The results showed that PMFN adsorption on sandstone primarily occurs in the pre-contact stage and is characterized by monolayer adsorption. When the ionic strength of the solution is 0.001 mol/L, the maximum repulsive energy barrier between PMFN and the sandstone surface hinders adsorption.

Численно-аналитическая модель для интерпретации результатов индикаторных исследований нефтяных пластов: решение прямой задачи при наличии каналов низкого фильтрационного сопротивления

The article considers the problem of interpretation of tracer tests in oil reservoirs, into which a specific chemical substance - tracer - is injected via an injection well for flow monitoring and tracer concentration measurements in surrounding production wells. The testing data provide evidence of the existence of low resistance channels in the reservoirs, along which the tracer moves at velocities several orders of magnitude higher than in the reservoir. The nature and properties of these channels are unknown, and a semi-analytical model involving two small parameters is proposed to solve this problem. This makes it possible to construct two non-conjugate solutions: universal numerical and analytical. Such an approach allows us to solve both direct and inverse problems. The present article is devoted to solving the direct problem. The problem of pressure distribution in a rectangular reservoir pattern is solved in dimensionless coordinates and is universal, i.e., it does not depend on the size of the area and the pressure drop. This solution is approximated by power functions and is further used to determine the mass transfer between channel and reservoir. The problem of tracer slug propagation through the channel obeys the law of conservation of tracer mass and Darcy's law. Its solution is found by the methods of characteristics under the condition of smallness of the parameter reflecting the ratio of reservoir permeability to channel permeability. The results of the semi-analytical solution are compared with the numerical solutions previously obtained by other authors. The fundamental difference between these solutions is the presence of numerical diffusion when using the finite-difference method of solution, which leads to the «dissipation» of the trace slug edges.

Advanced workflow for multi-well tracer test analysis in a geothermal reservoir

Interpretation of tracer tests in geothermal reservoirs is carried out by fitting the measured data either with simplified two-dimensional (2-D) analytical solutions or with complex numerical models. Available analytical solutions commonly only describe isotropic conditions in 1-D or 2-D, which is generally unsatisfactory to construct realistic reservoir models. Moreover, due to the large spatial and temporal scale of a tracer test in deep reservoirs, the concentration levels measured in the field are relatively low due to dispersion that complicates the assessment of breakthrough curve tailing and residence time. Fitting tracer data with fully resolving 3-D numerical models thus may be more appropriate, but even with a rich set of field data, reliable calibration is often compromised by the high computational effort and data hunger of such models. In this study, an advanced workflow is presented for evaluating tracer test data. Firstly, a 3-D analytical model in which solute transport is considered in anisotropic porous media is developed. Green's function method is applied to obtain a moving line source solution of the convection-dispersion-diffusion equation for solute transport in a 3-D porous medium. In addition, Green's function equation is analytically convoluted with a rectangular pulse function, which represents tracer injection. Secondly, the analytical model results are fitted to the tracer test data by Monte-Carlo simulations to obtain feasible ranges of flow velocities, as well as longitudinal and transversal dispersivities. Finally, the derived parameter values are implemented in a 3-D numerical model to evaluate the solute residence time in a large-scale reservoir. The results applied to field data from the Kızıldere field in Turkey demonstrate that the workflow provides robust estimates of effective parameters from well-to-well data in complex reservoir systems with anisotropic flow paths. Thus, despite the higher effort of applying convolution and stochastic parameter estimation, the preceding analytical step of the workflow substantially eases numerical model set-up.

Correction: A parsimonious approach for large-scale tracer test interpretation

Correction: A parsimonious approach for large-scale tracer test interpretation

A parsimonious approach for large-scale tracer test interpretation

Dye tracing is an efficient method for spring watershed delineation, but is also used in surface waters to assess pollution migration over several kilometers. The aim of this study is to develop a simple and parsimonious approach that accounts for a linear relationship between dispersivity and scale that could be used for the simulation of large-scale transport processes in aquifers. The analysis of 583 tracer recoveries is used to validate an inverse relationship between arrival time and peak concentration, which is shown to be a consequence of the linear relationship between dispersivity and scale. These results show that the tracer displacement through a given tracing system can be characterized at a large scale by a constant Peclet number. This interpretation is used to propose a new approach for tracer test design based on the analytical expression of the peak/time factor. It is also used for Peclet number assessment and simulation of the whole tracer residence-time distribution using a new method based on the ratio between the mode of the residence time distribution (hmod) and the corresponding time from injection (tmod), which is called the hmod/tmod method. This methodology is applied to two tracer tests carried out in a karst aquifer over 13 km between the same injection and detection points under distinct hydrological conditions. These results found practical applications in generalizing tracer test results to various flow conditions, or guiding the parameterization of physically-based vulnerability mapping methods.

Practical methodology for interwell tracer applications

Tracer technology has been used in the oil industry to investigate the fluid flow behavior into the reservoir. Using this technology is possible to obtain relevant data from the reservoir such as remaining oil accumulations, estimate volumetric sweep efficiency, define reservoir heterogeneities, identify flow channeling, and determine residual oil saturation (Sor).
 
 This technology has been one of the most useful tools for reservoir characterization for several decades. The tracer is injected in the injector well and then monitored in the producer wells through the tracer concentration measurements. Although many tracer studies have been documented for reservoir characterization, the available information and methodologies related to the design, implementation, and interpretation of tracer tests are limited or confidential.
 The goal of his article is to show a methodology for the design, execution, and interpretation of interwell tracer tests, which includes procedures for field implementation, sampling, and monitoring of these tests. Laboratory analysis using ultra-high-performance liquid chromatography is described in the experimental evaluation of tracer tests. Additionally, for a better understanding of the technology, examples of laboratory and field cases are presented.

Probabilistic inference of fracture-scale flow paths and aperture distribution from hydrogeophysically-monitored tracer tests

Fracture-scale heterogeneity plays an important role in driving dispersion, mixing and heat transfer in fractured rocks. Current approaches to characterize fracture scale flow and transport processes largely rely on indirect information based on the interpretation of tracer tests. Geophysical techniques used in parallel with tracer tests can offer time-lapse images indicative of the migration of electrically-conductive tracers away from the injection location. In this study, we present a methodology to invert time-lapse ground penetrating radar reflection monitoring data acquired during a push-pull tracer test to infer fracture-scale transport patterns and aperture distribution. We do this by using a probabilistic inversion based on a Markov chain Monte Carlo algorithm. After demonstration on a synthetic dataset, we apply the new inversion method to field data. Our main findings are that the marginal distribution of local fracture apertures is well resolved and that the field site is characterized by strong flow channeling, which is consistent with interpretations of heat tracer tests in the same injection fracture.

Transfer function approach for artificial tracer test interpretation in karstic systems

Summary A karstic formation consists in a three-dimensional hydrological system which involves horizontal and vertical, diphasic or saturated water transfers characterised by a large range of velocity. These subsurface flow processes correspond to various water pathways through fractured, fissured, and underground streams or conduits leading to a nonlinear global behaviour of the system. An efficient way of investigating of a karstic system behaviour consists in the injection of artificial tracer tests at loss points and in careful analysis of the recovery tracer fluxes at one or several outlets of the systems. These injections are also an efficient way of providing hypotheses on characteristic time of contaminant transfer in these type of aquifers. Here, we propose a Laplace-transform transfer function of the Residence Time Distribution function that allows to discriminate between a quick-flow advection-dominated component and a slow-flow advection–dispersion/dominated component in the artificial tracer transfer in the system. We apply this transfer function on five high resolution sampling rate artificial tracer tests operated on the Baget system in the Pyrenees (France) in order to illustrate the advantages and limitations of this approach. We provide then an interpretation of the relationship between tracer test recovery shape and karstic system organisation between inlet and outlet site.

Using Multiple-Point Geostatistics for Tracer Test Modeling in a Clay-Drape Environment with Spatially Variable Conductivity and Sorption Coefficient

This study investigates the effect of fine-scale clay drapes on tracer transport. A tracer test was performed in a sandbar deposit consisting of cross-bedded sandy units intercalated with many fine-scale clay drapes. The heterogeneous spatial distribution of the clay drapes causes a spatially variable hydraulic conductivity and sorption coefficient. A fluorescent tracer (sodium naphthionate) was injected in two injection wells and ground water was sampled and analyzed from five pumping wells. To determine (1) whether the fine-scale clay drapes have a significant effect on the measured concentrations and (2) whether application of multiple-point geostatistics can improve interpretation of tracer tests in media with complex geological heterogeneity, this tracer test is analyzed with a local three-dimensional ground-water flow and transport model in which fine-scale sedimentary heterogeneity is modeled using multiple-point geostatistics. To reduce memory needs and calculation time for the multiple-point geostatistical simulation step, this study uses the technique of direct multiple-point geostatistical simulation of edge properties. Instead of simulating pixel values, model cell edge properties indicating the presence of irregularly shaped surfaces are simulated using multiple-point geostatistical simulations. Results of a sensitivity analysis show under which conditions clay drapes have a significant effect on the concentration distribution. Calibration of the model against measured concentrations from the tracer tests reduces the uncertainty on the clay-drape parameters. The calibrated model shows which features of the breakthrough curves can be attributed to the geological heterogeneity of the aquifer and which features are caused by other processes.

The Viscoelastic Effect of Polymer on Tracer Dispersion

Polymer flooding works as the main enhance oil recovery method in China, but tracer test interpretation during and after polymer flooding still uses the technology of water flooding. And a lot of problems exposed in the application Experimental study of tracer dispersion in viscoelastic fluid through porous media isreported. We use different viscoelastic non-Newtonian fluid with the same shear shinning properties as the carrier fluid. It is evident that viscoelastic property is also the key factor influences the velocity field and the dispersivity in non-Newtonian fluid. High Peclet number yields the enhancement of the viscoelastic effect on the dispersivity of the tracer. Compared to pure viscous fluid, polymer viscoelasticity may lead to a larger vortex and, thus, a larger sweeping volume and speed field difference which leads to a higher dispersivity.

Tracer tests in geothermal resource management

Geothermal reinjection involves injecting energy-depleted fluid back into geothermal systems, providing an effective mode of waste-water disposal as well as supplementary fluid recharge. Cooling of production boreholes is one of the main disadvantages associated with reinjection, however. Tracer testing is an important tool for reinjection studies because tracer tests actually have a predictive power since tracer transport is orders of magnitude faster than cold-front advancement around reinjection boreholes. A simple and efficient method of tracer test interpretation, assuming specific flow channels connecting reinjection and production boreholes, is available. It simulates tracer return profiles and estimates properties of the flow channels, which are consequently used for predicting the production borehole cooling. Numerous examples are available worldwide on the successful application of tracer tests in geothermal management, many involving the application of this interpretation technique. Tracer tests are also used for general subsurface hydrological studies in geothermal systems and for flow rate measurements in two-phase geothermal pipelines. The tracers most commonly used in geothermal applications are fluorescent dyes, chemical substances and radioactive isotopes. New temperature-resistant tracers have also been introduced and high-tech tracers are being considered.

TRAC, a collaborative computer tool for tracer-test interpretation

Artificial tracer tests are widely used by consulting engineers for demonstrating water circulation, proving the existence of leakage, or estimating groundwater velocity. However, the interpretation of such tests is often very basic, with the result that decision makers and professionals commonly face unreliable results through hasty and empirical interpretation. There is thus an increasing need for a reliable interpretation tool, compatible with the latest operating systems and available in several languages. BRGM, the French Geological Survey, has developed a project together with hydrogeologists from various other organizations to build software assembling several analytical solutions in order to comply with various field contexts. This computer program, called TRAC, is very light and simple, allowing the user to add his own analytical solution if the formula is not yet included. It aims at collaborative improvement by sharing the tool and the solutions. TRAC can be used for interpreting data recovered from a tracer test as well as for simulating the transport of a tracer in the saturated zone (for the time being). Calibration of a site operation is based on considering the hydrodynamic and hydrodispersive features of groundwater flow as well as the amount, nature and injection mode of the artificial tracer. The software is available in French, English and Spanish, and the latest version can be downloaded from the web site http://trac.brgm.fr.

Study on the Assemble Interpretation Method of Inter Well Tracer Test

At present, test interpretation technology is still based on the rule and theory during 1960s-1980s, which wasn’t be developed and improved further in view of the new problems in field. The field practice and theory comparison have shown that these basic theory and interpretation model diverges obviously appropriate category, and have the singlet, unilateral problem of considered element, which can’t adapt to the quantification description of complex filtrate in porous medium. The basic theory and mathematic model of tracer test interpretation need to develop further, and interpretation means needs to improve corroboratively. From the point of numerical mathematics, the independent variables in reservoirs were found out and the objective function was constructed. Making use of improved real-number-style inheritance-arithmetic, the unitary parameters inversion and interpretation were accomplished in inter well tracer test.

Interpreting tracer tests in the enhanced geothermal system (EGS) of Soultz-sous-Forêts using the equivalent stratified medium approach

A new interpretation of tracer tests performed in 2005 in the French EGS located at Soultz-sous-Forêts is presented. A previous analysis of fluorescein tests revealed significant differences in terms of connectivity between the injection well (GPK3) and the two production wells (GPK2 and GPK4). The results suggested the existence of at least three fluid circulation loops. Two of them (loops 1 and 2) connecting GPK3 to GPK2, and the third one (loop 3) connecting GPK3 to GPK4. The present analysis is based on the equivalent stratified porous medium model, in which each circulation loop corresponds to a flow path through the rock formation and is regarded as a stratified porous medium having a log-normal permeability distribution. The heterogeneity of this equivalent porous medium is quantified by the stratification factor defined as the standard deviation to the mean permeability ratio. A very accurate fit of the concentration curves for both production wells was obtained. The stratification factors show that the three circulation loops have different levels of heterogeneity. The wellhead pressure recorded during the tests was used to calculate the mean permeability of the loops. Loop 1 appears to be very permeable and narrow while loops 2 and 3 are less permeable and wider. This tracer test model is compared to a new deterministic 3D model of the fracture zones observed in the Soultz granitic reservoir. A well-known major fault in the Soultz Graben intersecting GPK2 and GPK3 could explain the rapid tracer circulation in loop 1.

Assessment of local hydraulic properties from electrical resistivity tomography monitoring of a three‐dimensional synthetic tracer test experiment

In recent years geophysical methods have become increasingly popular for hydrological applications. Time‐lapse electrical resistivity tomography (ERT) represents a potentially powerful tool for subsurface solute transport characterization since a full picture of the spatiotemporal evolution of the process can be obtained. However, the quantitative interpretation of tracer tests is difficult because of the uncertainty related to the geoelectrical inversion, the constitutive models linking geophysical and hydrological quantities, and the a priori unknown heterogeneous properties of natural formations. Here an approach based on the Lagrangian formulation of transport and the ensemble Kalman filter (EnKF) data assimilation technique is applied to assess the spatial distribution of hydraulic conductivity K by incorporating time‐lapse cross‐hole ERT data. Electrical data consist of three‐dimensional cross‐hole ERT images generated for a synthetic tracer test in a heterogeneous aquifer. Under the assumption that the solute spreads as a passive tracer, for high Peclet numbers the spatial moments of the evolving plume are dominated by the spatial distribution of the hydraulic conductivity. The assimilation of the electrical conductivity 4D images allows updating of the hydrological state as well as the spatial distribution of K. Thus, delineation of the tracer plume and estimation of the local aquifer heterogeneity can be achieved at the same time by means of this interpretation of time‐lapse electrical images from tracer tests. We assess the impact on the performance of the hydrological inversion of (i) the uncertainty inherently affecting ERT inversions in terms of tracer concentration and (ii) the choice of the prior statistics of K. Our findings show that realistic ERT images can be integrated into a hydrological model even within an uncoupled inverse modeling framework. The reconstruction of the hydraulic conductivity spatial distribution is satisfactory in the portion of the domain directly covered by the passage of the tracer. Aside from the issues commonly affecting inverse models, the proposed approach is subject to the problem of the filter inbreeding and the retrieval performance is sensitive to the choice of K prior geostatistical parameters.

Development of Genetic Algorithm Models for Tracer Test Interpretation During Polymer Flood

Development of Genetic Algorithm Models for Tracer Test Interpretation During Polymer Flood

Modelling doublets and double porosity

Abstract A simple model has been developed as a scoping tool for transport between an injection well and an abstraction well pumping at the same rate (i.e. a doublet) in a fractured porous rock. This model is aimed primarily at the planning and preliminary interpretation of tracer tests and trial heat exchange using thermal doublets in the Chalk aquifer. The model is essentially a particular case of transport along multiple flow paths and relies on the invariance of double-porosity transport with respect to velocity variations along a flow path. Hypothetical simulations demonstrate that solute tracer tests need to be supplemented by information on fracture porosity in order to be able to predict thermal breakthrough.

Application of iterated Laplace transformation to tracer transients in heterogeneous porous media

The Laplace transformation technique has been widely applied to modeling of tracer transport in oil and geothermal reservoirs, and in groundwater aquifers. However, mathematical models of many flow and transport problems could only be obtained as Laplace space solutions, and hence, their computations had to involve a numerical inversion technique. In this work, we employ the iterated Laplace transformation technique to develop novel closed form solutions to the tracer transport models in heterogeneous media. Two types of configurations have been considered: tracer transport in single fracture located in low-permeability matrix and tracer transport in a double porosity medium consisting of flowing and dead-end pore systems. In addition, both linear and radial flow geometries have been considered for both configurations. Applications of iterated Laplace transform technique to these four types of models are presented as fundamental examples and their numerical results were used as benchmarking for the numerical inversion results from Stehfest and Dubner and Abate algorithms. As the technique is quite versatile, we expect that the method should gain widespread acceptance to develop solutions to a wide range of problems in flow and transport in porous media and improve the application of nonlinear regression technique to these solutions. This work has achieved four important objectives: first, two novel Laplace transform relations that are useful in tracer studies are presented. Second, the present work serves to verify/invalidate the results of numerical inversion algorithms. In addition, it provides better insight into tracer transport mechanisms. Finally, it serves as a powerful tool of design and interpretation of tracer tests. All four objectives are illustrated in this work.

Interpreting tracer breakthrough tailing in a conduit-dominated karstic aquifer

Abstract Breakthrough tailing has been observed during dye-tracing recovery tests in the Norville aquifer system (chalk), France. Karst-conduit flow and transport parameters were assessed using two different interpretative methods: the linear graphical method and the Chatwin method (implemented in the Qtracer2 program). The linear graphical method was used to model the observed tailing effects, which was explained by a second smaller delayed breakthrough curve. By comparing the results of tracertest interpretation for the two methods, it was possible to relate the area of this second curve to the importance of turbulent flow in spring discharge. The more turbulent the flow, the less important the contribution of the second breakthrough curve and the tailing effect. The observed tailing could possibly be controlled by hydrodynamics to a greater extent than usually expected, the tailing effectsbeing mostly attributed to diffusion phenomena. Tailing effects were expected to increase with discharge and the piezometric level, which would have resulted in overpressure in conduits, fissure flooding, etc. Instead, breakthrough tailing tended to disappear with increasing aquifer discharge, which would support the hypothesis of there being mostly hydrodynamic-controlled tailing effects instead of matrix- or fissure-diffusion.

Sensitivities of flow and transport parameters in fractured porous media using automatic differentiation

AbstractThe hydraulic complexity of hardrock aquifers with, for example, fast fluid flow in fractures, storage effects in the rock matrix, high contrasts in permeability, and a high spatial variability of structures requires a high standard of experimental and numerical techniques. This paper focuses on the interpretation of tracer tests. The sensitivity of tracer breakthrough curves with respect to flow and transport parameters is analysed for different model types in order to identify the relevant flow and transport processes. This leads to a better understanding of the system behaviour and facilitates the interpretation of experimental results. The technique of automatic differentiation is used to evaluate the sensitivities. The main advantage of this technique is that the sensitivities are calculated without truncation error. Copyright © 2005 John Wiley & Sons, Ltd.