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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. Source


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. Source


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. Source


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. Source


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. Source

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