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Texto completo:acesso restrito. p. 94–99 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-01-24T15:39:54Z No. of bitstreams: 1 Olivar A.L de Lima.pdf: 523482 bytes, checksum: 298172efc2f8f5defeff8ae76eb5e614 (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2015-10-09T18:51:20Z (GMT) No. of bitstreams: 1 Olivar A.L de Lima.pdf: 523482 bytes, checksum: 298172efc2f8f5defeff8ae76eb5e614 (MD5) Made available in DSpace on 2015-10-09T18:51:20Z (GMT). No. of bitstreams: 1 Olivar A.L de Lima.pdf: 523482 bytes, checksum: 298172efc2f8f5defeff8ae76eb5e614 (MD5) Previous issue date: 2003 This paper is devoted to the additional use, other than ground water exploration, of surface geoelectrical sounding data for aquifer hydraulic parameter estimation. In a mesoscopic framework, approximated analytical equations are developed separately for saline and for fresh water saturations. A few existing useful aquifer models, both for clean and shaley sandstones, are discussed in terms of their electrical and hydraulic effects, along with the linkage between the two. These equations are derived for insight and physical understanding of the phenomenon. In a macroscopic scale, a general aquifer model is proposed and analytical relations are derived for meaningful estimation, with a higher level of confidence, of hydraulic parameter from electrical parameters. The physical reasons for two different equations at the macroscopic level are explicitly explained to avoid confusion. Numerical examples from existing literature are reproduced to buttress our viewpoint.

Texto completo: acesso restrito. p. 255–264 Submitted by Suelen Reis (suelen_suzane@hotmail.com) on 2013-01-04T14:41:58Z No. of bitstreams: 1 Porsani.pdf: 221906 bytes, checksum: 27b510f66932c527f1c661f17e23f114 (MD5) Made available in DSpace on 2013-01-04T14:41:58Z (GMT). No. of bitstreams: 1 Porsani.pdf: 221906 bytes, checksum: 27b510f66932c527f1c661f17e23f114 (MD5) Previous issue date: 2001 The root cause of the instability problem of the least-squares (LS) solution of the resistivity inverse problem is the ill-conditioning of the sensitivity matrix. To circumvent this problem a new LS approach has been investigated in this paper. At each iteration, the sensitivity matrix is weighted in multiple ways generating a set of systems of linear equations. By solving each system, several candidate models are obtained. As a consequence, the space of models is explored in a more extensive and effective way resulting in a more robust and stable LS approach to solving the resistivity inverse problem. This new approach is called the multiple reweighted LS method (MRLS). The problems encountered when using the L1- or L2-norm are discussed and the advantages of working with the MRLS method are highlighted. A five-layer earth model which generates an ill-conditioned matrix due to equivalence is used to generate a synthetic data set for the Schlumberger configuration. The data are randomly corrupted by noise and then inverted by using L2, L1 and the MRLS algorithm. The stabilized solutions, even though blurred, could only be obtained by using a heavy ridge regression parameter in L2- and L1-norms. On the other hand, the MRLS solution is stable without regression factors and is superior and clearer. For a better appraisal the same initial model was used in all cases. The MRLS algorithm is also demonstrated for a field data set: a stable solution is obtained.

Texto completo. Acesso restrito. p. 12–26 Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-07-24T17:54:50Z No. of bitstreams: 1 4444444444444.pdf: 557354 bytes, checksum: 6b65b2885712b1ec57459fec0a37b36f (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2013-11-26T13:19:32Z (GMT) No. of bitstreams: 1 4444444444444.pdf: 557354 bytes, checksum: 6b65b2885712b1ec57459fec0a37b36f (MD5) Made available in DSpace on 2013-11-26T13:19:32Z (GMT). No. of bitstreams: 1 4444444444444.pdf: 557354 bytes, checksum: 6b65b2885712b1ec57459fec0a37b36f (MD5) Previous issue date: 2000 Electrical and hydraulic conductivities of shaly sandstones are described using a capillary approach for a granular, clay bearing material. The clays are assumed to occur as shale shells uniformly coating the insulated sand grains. The real and imaginary components of the complex electrical conductivity for this material model are written in terms of a unique solid matrix conductivity, treated as a volumetric property. Above a critical salt concentration the conductive contribution of the shells is independent of the electrolyte salinity. Under this condition the equation for the bulk conductivity of the sandstone can be expressed in a simplified form. However, below the critical concentration the matrix conductivity is dependent on the conductivity of the water saturating the shaly component and can be expressed only by the complete equation. The hydraulic conductivity for this model is expressed by a modified Kozeny–Carman equation. A new semi-empirical equation relates the hydraulic conductivity for such rocks, to their porosity, formation resistivity factor and the electrical conductivity of its solid matrix. These combined properties are described as the lithoporosity factor. In this new formulation the petrophysical parameters involved are easily determined from the electrical geophysical measurements. The performance of this equation is firmly tested with experimental laboratory data available in the literature. Its application is then extended to estimate the hydraulic parameters of a shaly sandstone aquifer in Bahia-Brazil, using either the borehole or the surface geoelectrical data. Examples are given to emphasize the combined use of electrical resistivity and induced polarization measurements in computing hydraulic properties. Salvador