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Vaz A.,North Fluminense State University | Bedrikovetsky P.,University of Adelaide | Fernandes P.D.,Petrobras | Badalyan A.,University of Adelaide | Carageorgos T.,University of Adelaide
Journal of Petroleum Science and Engineering | Year: 2017

Particle capture in porous media and the consequent permeability reduction occur in oilfields during water injection or produced water re-injection, migration of mobilized reservoir fines, and invasion of drilling and completion fluids into formations. Reliable modelling-based prediction of particle propagation in natural reservoirs is an essential step in the planning and design of waterflooding. The mathematical model for suspension-colloidal transport in natural reservoirs contains two empirical functions of retained particle concentration. The filtration function expresses the particle capture rate. The formation-damage function determines the permeability decline due to particle capture and retention. Previous works developed an inverse-problem solution to recover both functions from breakthrough concentration and the pressure drop. The present paper develops a new method that determines the filtration and formation-damage functions from pressure measurements only. The method uses pressure data at an intermediate point of the porous column (core), which supplements pressure measurements at the core inlet and outlet. The proposed method furnishes two retained-concentration functions for filtration and formation-damage. The method is validated by comparison with laboratory experiments. A high fit with the pressure data at three core points was observed. Moreover, the fitted model predicts the pressure measured at other core points with high precision. © 2017 Elsevier B.V.

Bedrikovetsky R.,University of Adelaide | Vaz Jr. A.S.L.,North Fluminense State University | Furtado C.,Petrobras | De Souza A.L.S.,Petrobras
SPE Reservoir Evaluation and Engineering | Year: 2011

Injcctivity decline of oilfield injection wells is a widespread phenomenon during seawaler/produced-waler injection. The decline may result in significant cost increase of the waterflooding project. Reliable modeling-based prediction of injectivity-index decrease is important for waterflood design as well as for the planning of preventive injected-water treatment. One of the reasons for well injectivity decline is permeability decrease caused by rock plugging by solid/liquid particles suspended in the injected water. The mathematical model for deep-bed filtration contains two empirical functions: the filtration coefficient and the formation-damage coefficient. These empirical coefficients must be determined from laboratory coreflood tests by forcing water with particles to flow through the core samples. A routine laboratory method determines the filtration coefficient from expensive and difficult particle-concentration measurements at the core effluent; then, the formation-damage coefficient is determined from inexpensive and simple pressure-drop measurements. An alternative three-point-pressure method uses pressure data at an intermediate point of the core, supplementing pressure measurements at the core inlet and outlet. The method provides unique and stable values for constant-filtration and formation-damage coefficients. In the current work, we consider a more complex case in which both coefficients are linear functions of retained-particle concentration. In this case, the model is fully determined by four constants. The three-point-pressure method furnishes unique values for the four model parameters. A new semianalytical model for axisymmetric suspension filtration was developed to predict well-injectivity decline from the linear coreflood data with pressure measurements in three core points. Copyright © 2011 Society of Petroleum Engineers.

Moco M.K.S.,North Fluminense State University | Gama-Rodrigues E.F.,North Fluminense State University | Gama-Rodrigues A.C.,North Fluminense State University | Baligar V.C.,U.S. Department of Agriculture
Applied Soil Ecology | Year: 2010

This study was undertaken to investigate the relationship between soil and litter attributes to soil and litter fauna, and further to determine which of these attributes would be most significant in explaining the distribution of faunal communities in cacao agroforestry systems in the south of Bahia, Brazil. Soil and litter samples were collected in five cacao agroforestry systems: a cacao system renewed under Erythrina sp. (CRE); a cacao system renewed under natural forest (Cabruca-CRF); a cacao system under Erythrina sp. (CE); a cacao system under a natural forest system (Cabruca-CNF) and a cacao germplasm collection area (CGC). Soil and litter samples were also collected from natural forest (NF) near the agroforestry systems. The path analysis was used to evaluate the interdependencies among a set of variables including direct and indirect test effects that can be mediated by an intermediary variable. An average of 1367 (±126.5) individualsm -2 and 10 (±0.3) taxa per sample were found under these areas. Soil attributes and litter quality under different cacao agroforestry systems affected the diversity of the soil and litter fauna, and these attributes are potential regulators of the fauna functional groups. The chemical components related to acidity, nutrition, and palatability are most decisive for abundant and diverse soil and litter fauna. Attributes which affected soil fauna in cacao agroforestry systems included mainly pH and bulk density in soil and polyphenols and lignin content in the litter. The faunal communities were more sensitive to litter quality than soil quality. Litter management could be a good practice to maintain healthy activities of the faunal community and to maintain improved ecosystem functioning in cacao agroforestry systems. © 2010 Elsevier B.V.

Oliveira M.A.,North Fluminense State University | Vaz A.S.L.,University of Adelaide | Siqueira F.D.,North Fluminense State University | Yang Y.,University of Adelaide | And 2 more authors.
Journal of Petroleum Science and Engineering | Year: 2014

Permeability decline during high rate flows has been widely reported for corefloods and for production wells. The phenomenon is attributed to mobilisation of fine particles at elevated velocities, their migration in porous space with the following straining in thin pores and attachment to pore walls. Sixteen sets of corefloods with piecewise constant rate have been performed under increasing flow rate. The particularities of this study are long injection periods, allowing estimating permeability stabilisation times, and pressure measurements in intermediate core points, permitting for evaluation of the permeability profile variation along the core. It was found out that the mobilised particles drift with speeds significantly lower than the carrier fluid velocity, resulting in long permeability stabilisation periods. © 2014 Elsevier B.V.

Gama-Rodrigues E.F.,North Fluminense State University | Nair P.K.R.,University of Florida | Nair V.D.,University of Florida | Gama-Rodrigues A.C.,North Fluminense State University | Baligar V.C.,U.S. Department of Agriculture
Environmental Management | Year: 2010

Shaded perennial agroforestry systems contain relatively high quantities of soil carbon (C) resulting from continuous deposition of plant residues; however, the extent to which the C is sequestered in soil will depend on the extent of physical protection of soil organic C (SOC). The main objective of this study was to characterize SOC storage in relation to soil fraction-size classes in cacao (Theobroma cacao L.) agroforestry systems (AFSs). Two shaded cacao systems and an adjacent natural forest in reddish-yellow Oxisols in Bahia, Brazil were selected. Soil samples were collected from four depth classes to 1 m depth and separated by wet-sieving into three fraction-size classes (>250 μm, 250-53 μm, and<53 μm)-corresponding to macroaggregate, microaggregate, and silt-and-clay size fractions-and analyzed for C content. The total SOC stock did not vary among systems (mean: 302 Mg/ha). On average, 72&percent; of SOC was in macroaggregate-size, 20&percent; in microaggregate-size, and 8&percent; in silt-and-clay size fractions in soil. Sonication of aggregates showed that occlusion of C in soil aggregates could be a major mechanism of C protection in these soils. Considering the low level of soil disturbances in cacao AFSs, the C contained in the macroaggregate fraction might become stabilized in the soil. The study shows the role of cacao AFSs in mitigating greenhouse gas (GHG) emission through accumulation and retention of high amounts of organic C in the soils and suggests the potential benefit of this environmental service to the nearly 6 million cacao farmers worldwide. © Springer Science+Business Media, LLC 2010.

Machado M.V.B.,Petrobras | Dias C.A.,North Fluminense State University
Geophysical Prospecting | Year: 2012

The electric and magnetic fields generated by an individual horizontal current ring induced inside a homogeneous conductive half-space, originating from an external large circular loop source of current in the presence of a flat half-space, are deduced. A check of self-consistency for these expressions led to the known general functions for these fields due to the same external source in the presence of that medium. The current rings' mutual coupling related to the magnetic field's radial component is thoroughly analysed and its specific members are presented. The existence of a relatively small zone inside the half-space responsible for the main contribution for the signal measured at the observation point, with the source and receiver on the ground surface, is made evident. For increasing values of frequency, at a given transmitter-receiver (T-R) configuration, this zone shrinks and its central point moves away from a maximum depth of about 30% and horizontal distance of nearly 85%, of the T-R separation, to a point very close to the receiver position. The coordinates of the central point of this zone of main contribution are provided as approximated functions in terms of the induction number. © 2012 European Association of Geoscientists & Engineers.

Oliveira S.A.M.,North Fluminense State University | Oliveira S.A.M.,INVISION | Lupinacci W.M.,North Fluminense State University
Geophysical Prospecting | Year: 2013

In order to perform a good pulse compression, the conventional spike deconvolution method requires that the wavelet is stationary. However, this requirement is never reached since the seismic wave always suffers high-frequency attenuation and dispersion as it propagates in real materials. Due to this issue, the data need to pass through some kind of inverse-Q filter. Most methods attempt to correct the attenuation effect by applying greater gains for high-frequency components of the signal. The problem with this procedure is that it generally boosts high-frequency noise. In order to deal with this problem, we present a new inversion method designed to estimate the reflectivity function in attenuating media. The key feature of the proposed method is the use of the least absolute error (L1 norm) to define both the data and model error in the objective functional. The L1 norm is more immune to noise when compared to the usual L2 one, especially when the data are contaminated by discrepant sample values. It also favours sparse reflectivity when used to define the model error in regularization of the inverse problem and also increases the resolution, since an efficient pulse compression is attained. Tests on synthetic and real data demonstrate the efficacy of the method in raising the resolution of the seismic signal without boosting its noise component. © 2013 European Association of Geoscientists & Engineers.

Lupinacci W.M.,North Fluminense State University | Oliveira S.A.M.,North Fluminense State University | Oliveira S.A.M.,INVISION | Oliveira S.A.M.,Brazilian National Council for Scientific and Technological Development
Journal of Applied Geophysics | Year: 2015

Attenuation is one factor that degrades the quality of reflection seismic subsurface imaging. It causes a progressive decrease in the seismic pulse energy and is also responsible for limiting seismic resolution. Currently, many methods exist for inverse Q filtering, which can be used to correct these effects to some extent; however, but all of these methods require the value of the Q factor to be known, and this information is rarely available. In this paper we present and evaluate three different strategies to derive the Q factor from the time-frequency amplitude spectrum of the seismic trace. They are based in the analyses of the amplitude decay trend curves that can be measured along time, along frequency or along a compound variable obtained from the time-frequency product. Some difficulties are highlighted, such as the impossibility to use short time window intervals that prevents the method from providing a precise map of the Q factor value of the subsurface layers. However, the Q factor estimation made in this way can be used to guide the parameterization of attenuation correction by means of inverse Q filtering applied to a stacked seismic section; this is demonstrated in a real data example. © 2015 Elsevier B.V.

de Souza Jr. D.I.,Federal University of Fluminense | Rocha R.,North Fluminense State University
International Journal of Performability Engineering | Year: 2012

In this paper the test purpose will have two objectives: First will be to verify if times to breakdown of insulating fluid between electrodes recorded at three different voltages have an exponential distribution as predicted by theory. Second will be to assess whether or not the accelerated model proposed by Eyring will be able to translate results for the shape and scale parameters of an underlying Inverse Weibull model, obtained under two accelerating using conditions, to expected normal using condition results for these two parameters. The product being analyzed is a new type of insulate fluid, and the accelerating factor is the voltage stresses applied to the fluid at two different levels (30KV and 40KV). The normal operating voltage is 25KV and it was possible to test the fluid at normal voltage using condition. Both results for the two parameters of the Inverse Weibull model, obtained under normal using condition and translated from accelerated using conditions to normal conditions, will be compared to each other to assess the accuracy of the Eyring model when the accelerating factor is only the voltage stress. © RAMS Consultants.

de Ceia M.A.R.,North Fluminense State University | Missagia R.M.,North Fluminense State University | Neto I.L.,North Fluminense State University | Archilha N.,North Fluminense State University
Journal of Applied Geophysics | Year: 2015

The estimation of dry bulk modulus is required for the successful application of the Biot-Gassmann theory to forecast fluid changes within a reservoir. The Pride model is one of the several models described in the literature for predicting the dry elastic moduli of rocks. However, the accuracy of the Pride model depends on the estimation of the consolidation parameter. In this paper, the consolidation parameter was estimated using the pore stiffness, mineral bulk modulus and porosity. That approach allowed calculating the dry bulk modulus of a set of microporous carbonate rocks according to the Pride model and compare those estimates to the results obtained using the elastic velocities. The change in the consolidation parameter over a range of pressures suggests that the relationship between this parameter and the unconfined porosity increases at high effective pressure. Statistical analyses of the distribution of those consolidation parameter values were performed to verify how the effective pressure influences the mean value and variance. Mean pore aspect ratios were estimated using Kuster-Toksoz methodology to establish a relationship with the consolidation parameter and the unconfined porosity. Such relationship also accounts for pressure-dependence within the studied pressure range. Although only 20 samples were analyzed, those studies can contribute to advise the estimation of the consolidation parameter in this type of carbonate rocks. © 2015 Elsevier B.V.

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