Fundamentals of coaxial and coplanar coil arrays in induction tools

Carvalho, Paulo Roberto de; Santos, Walleson Gomes dos; Régis, Cícero Roberto Teixeira

doi:10.1590/s0102-261x2010000100002

Cited by 7 publications

(7 citation statements)

References 10 publications

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“…This is true for the fields generated by vertical (VMD) and horizontal (HMD) Magnetic Dipoles within a laminated formation Carvalho et al, 2010) as well as for the magnetic field components generated by an HMD in an anisotropic bed bordered by two half-spaces (Kaufman & Dashevsky, 2003). Kaufman & Dashevsky (2003) deduced through current density distribution and Anderson et al (2008) show through circuit theory (parallel and series resistors) an identical relation between the horizontal and vertical conductivities of the homogeneous anisotropic media and the conductivities of the thinly laminated medium formed by two alternating and distinct laminae (σ 1 and σ 2 ) when their thicknesses are less than the tool's vertical resolution:…”

Section: Laminated Formation and Anisotropic Bedmentioning

confidence: 99%

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Revisiting Some Old Unexplained Effects in Induction Logs Within Laminated Formations With the Triaxial Induction Tool

Carvalho¹,

Régis²

2016

Rev. Bras. Geof.

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ABSTRACT. Modern induction triaxial or multicomponent well logging tools provide resistivity anisotropy logs, and estimates of the electrical resistivity of sand laminae in thinly laminated formations. In this paper, coaxial and coplanar vertical logs were modeled in one-dimensional (1D) laminated packages and in their equivalent anisotropic beds, neglecting the presence of the borehole and the invasion zones, to simulate geological environments of hydrocarbon reservoirs with resistivity anisotropy. The objective of this paper is twofold: to perform a quantitative analysis of the anisotropy level of a thinly laminated reservoir as compared to an equivalent anisotropic bed, and, in doing so, to revisit some old and unexplained effects that appear on the triaxial induction logs. These subtle effects may have only a faint influence on the logs themselves, but their study contribute to our understanding of the electromagnetic phenomena involved in the induction logging. The results show that the coaxial logs in the laminated formation converge to the equivalent anisotropic bed response much sooner than the coplanar logs. They also show that there is a considerable difference between the anisotropy index obtained by the triaxial induction tool within laminated formations and the anisotropy coefficient of its equivalent anisotropic bed, even for extremely thin laminae thicknesses.Keywords: well logging, multicomponent induction tools, laminated reservoirs, electrical anisotropy. RESUMO.As atuais ferramentas de perfilagem em poço por indução eletromagnética, denominadas triaxias ou multicomponentes, fornecem perfis de anisotropia elétrica e permitem estimar a resistividade de lâminas de areia em ambientes finamente laminados. Neste artigo, os perfis dos arranjos coaxial e coplanar de bobinas foram simulados em modelos unidimensionais (1D) de sequências laminadas e de suas respectivas camadas anisotrópicas equivalentes, negligenciando o poço e as zonas de invasão, visando simular ambientes de reservatório de hidrocarbonetos com anisotropia elétrica. Os objetivos deste trabalho são basicamente dois: fazer uma análise comparativa do grau de anisotropia de reservatórios laminados com relação a uma camada anisotrópica equivalente e, no desenrolar deste estudo, reavaliar alguns antigos e ainda não explicados efeitos presentes nos perfis de indução. Estes efeitos têm apenas uma sutil influência nos perfis, embora sejam importantes para uma clara compreensão dos fenômenos eletromagnéticos envolvidos na perfilagem. Pelos resultados pode-se verificar que ao reduzir progressivamente as espessuras das lâminas, os perfis do arranjo coaxial convergem para os da camada anisotrópica equivalente bem mais rápido do que os perfis do arranjo coplanar. Pode-se verificar também que, mesmo para lâminas extremamente finas, existe uma considerável diferença entre oíndice de anisotropia, obtido com as ferrramentas triaxiais, com relação aoíndice de anisotropia da camada equivalente.Palavras-chave: perfilagem de poço, ferramentas multicomponente...

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Section: Laminated Formation and Anisotropic Bedmentioning

confidence: 99%

“…(5) by the coaxial array constant K/4. Analogously, Carvalho & Verma (1999) presented a "coplanar complex conductivity" by dividing Eq. (6) by the coplanar array constant K/8:…”

Section: Homogeneous Isotropic Mediamentioning

confidence: 99%

Revisiting Some Old Unexplained Effects in Induction Logs Within Laminated Formations With the Triaxial Induction Tool

Carvalho¹,

Régis²

2016

Rev. Bras. Geof.

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“…According to Anderson et al (1992) these "horns" may be good quality interface indicators. Carvalho et al (2010) show that as the dip angle increases the coplanar polarization horns are reduced progressively, and the logs tend to become straight lines at the horizontal limit.…”

Section: Resultsmentioning

confidence: 92%

“…In the theoretical treatment, the coils are represented as point magnetic dipoles, as illustrated in Figure 1-b. The magnetic field components from the vertical (VMD) and horizontal (HMD) magnetic dipoles are calculated as described in Carvalho et al (2010) for an isotropic multilayered medium without the borehole and invasion zones. The magnetic field components from the HMD within an anisotropic medium are calculated as described in Kaufman & Itskovich (2017).…”

Section: Theory and Analysis Methodsmentioning

confidence: 99%

Effects of the Deviation Angle of the Borehole in the Induction Anisotropy Logs

Carvalho¹,

Régis²,

Silva³

2018

Braz J Geophys

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ABSTRACT. This paper performs an analysis of the effects of the well’s deviated angle on the tensor triaxial induction tool signals within a thinly sand-shale laminated reservoirs and their equivalent intrinsic anisotropic models. The responses from coaxial and coplanar coil arrays in inclined wells are studied in detail, including the analysis of their apparent anisotropy logs, as well as their estimation of sand conductivity in the environments with a structural anisotropy.The dip angle effects are modeled in simple geometries as one-dimensional (1D) models, neglecting the presence of the borehole and the invasion zones, since they provide basic insight for understanding tool responses in more complex models. The results show a strong sensitivity of both the coaxial and coplanar signals to the deviated angle. It is verified that the anisotropy values are significantly reduced when the well is inclined as compared to what is found for the true vertical case, even for inclinations small enough for the wells to be classified as technically vertical (30 degrees or less). Therefore, the angle effects must be carefully considered, even for technically vertical wells. Otherwise, potential finely laminated reservoirs can be underestimated or even ignored.Keywords: deviated well logging, tensor induction tool, laminated reservoirs, electrical anisotropy.RESUMO. Neste trabalho é apresentado como as incertezas na interpretação sísmica impactam na cons-trução do modelo de velocidades e na conversão tempo-profundidade resultante. A área de estudo de estudo está localizada na Bacia de Campos, Brasil. O principal objetivo deste trabalho é mostrar como os dados de entrada e parâmetros afetam na modelagem de velocidade e conversão tempo x profundidade. A metodologia é comparar três diferentes cenários para calibração da velocidade de processamento e imageamento com as interpretações sísmicas e de poços: o cenário 1 utiliza ajuste por horizonte com marcador geológico e raio de influência 5 km; no cenário 2 é utilizada as tabelas tempo-profundidade, raio de influência 5 km por krigagem com derivada externa; e o cenário 3 utilizou-se tabelas tempo-profundidade, raio de influência 2 km por krigagem com deriva externa. O controle de qualidade dos três modelos de velocidade são avaliados pela conversão dos horizontes, seções sísmicas e perfis de pseudo-impedância. No cenário 1, os horizontes convertidos apresentam menores diferenças de profundidade em relação aos marcadores comparados aos demais cenários. Por outro lado, os cenários 2 e 3 apresentam maiores correlações entre o sismograma sintético e a seção sísmica convertida para o cenário 1. Palavras-chave: poços desviados, ferramentas triaxiais, reservatórios laminados, anisotropia elétrica.

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“…The magnetic fields components from the vertical (VMD) and horizontal (HMD) magnetic dipoles are calculated using Schelkunoff potentials as described in Carvalho et al (2010).…”

Section: Methodsmentioning

confidence: 99%

Effects of the dip angle in the induction anisotropy logs

Carvalho¹,

Régis²,

Silva³

2018

Proceedings of the VIII Simpósio Brasileiro E Geofísica

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Some of the most modern induction well logging tools provide resistivity anisotropy logs and estimates of the electrical resistivity of sand laminae in thinly laminated formations.In this work, coaxial and coplanar logs were modeled in one-dimensional (1D) laminated packages, neglecting the presence of the borehole and the invasion zones, to simulate geological environments of hydrocarbon reservoirs with electrical anisotropy.The objective of this paper is to perform an analysis of the effects of the well's inclination angle on the induction tool response in a thinly laminated reservoir. Thus, it's shown only the responses from coaxial and coplanar coil array, which are used to produce anisotropy logs as well as to estimate the sand conductivity of the formation.The results show the strong sensitivity of the coaxial and coplanar signals to the deviated angle and, consequently, these angle's effects on the anisotropy logs.

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Fundamentals of coaxial and coplanar coil arrays in induction tools

Cited by 7 publications

References 10 publications

Revisiting Some Old Unexplained Effects in Induction Logs Within Laminated Formations With the Triaxial Induction Tool

Revisiting Some Old Unexplained Effects in Induction Logs Within Laminated Formations With the Triaxial Induction Tool

Effects of the Deviation Angle of the Borehole in the Induction Anisotropy Logs

Effects of the dip angle in the induction anisotropy logs

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