Cerâmica 54 (2008) [55][56][57][58][59][60][61][62] INTRODUÇÃOAs ferritas Ni-Zn são materiais cerâmicos ferrimagnéticos, também conhecidos como materiais magnéticos moles ou macios (soft), cuja estrutura cristalina é semelhante à do mineral espinélio. O desempenho das ferritas Ni-Zn não é determinado apenas pelos altos valores de resistividade e permeabilidade magnética inicial, mas também por outras características, tais como baixos valores de perdas por histerese e correntes parasitas (Foucault), altas densidades de fluxo de saturação, baixos campos coercitivos e alta permeabilidade magnética final em altas freqüências (10-500 MHz), dureza mecânica, estabilidade química e custo relativamente baixo [1][2][3][4][5].Atualmente, materiais com propriedades ferrimagnéticas vêm desempenhando papel de grande importância no campo científico devido às suas inúmeras aplicações tecnológicas, tais como transformadores de potência e de pulso, transformadores para distribuição de energia, transformadores de banda larga e baixa potência, geradores, fontes de potência, indutores e transdutores, filtros de freqüência variável e supressores de ruído [ ResumoA microestrutura e as propriedades magnéticas das ferritas Ni 0,5-x Cu x Zn 0,5 Fe 2 O 4 com x = 0,1/0,2/0,3/0,4 mol de cobre, preparadas a partir de pós obtidos por reação de combustão com tamanho de partícula na faixa de 23 a 29 nm, foram avaliadas. Os pós obtidos foram prensados uniaxialmente e sinterizadas a 1000 ºC/2 h. As amostras foram caracterizadas por medidas de densidade e porosidade aparente, difração de raios X, microscopia eletrônica de varredura e medidas magnéticas M-H. Os difratogramas de raios X mostram a presença da fase majoritária cristalina do espinélio inverso em todos os sistemas, e traços da fase secundária Fe 2 O 3 nas amostras com x = 0,1 e 0,4. O aumento do teor de cobre causou um pequeno aumento no tamanho médio de grão (0,65 para 0,68 μm), uma redução da porosidade aparente (33,7% para 6,6%) e redução da magnetização de saturação de 69 para 54 emu/g. Palavras-chave: ferrita Ni-Zn, propriedades magnéticas, microestrutura. Abstract

Impact of CO2 corrosion on well integrity is an issue in mature fields of Colombian foothill wells. Concerns in regard to corrosion of casing strings having access only through the existing 7" completion challenged the use of new technology to achieve both: log corrosion on outer strings and do not suspend the well to get a full column of fluid. Therefore, corrosion monitoring was performed through 7" chrome production tubing with a new Electromagnetic Scanning Tool (EMST), in a challenging scenario: shut-in well with 3 outer casing strings with a gas cap in the upper wellbore. The job objectives were first to test the technology to detect metal loss from the outer casing strings as well as loss both inside and outside of production tubing (without pulling the production tubing) and second to establish a base line for future corrosion analysis after the immediate drilling rig intervention for sidetracking. A careful candidate selection was performed based on criticality for CO2 corrosion, completion design, service years and operating status of the well including consequence analysis to get a pilot well for EM logging. In production since 1998, the BA Y16 well was selected to be logged before a thru tubing deepening to reach two other reservoirs and further service conversion from oil producer into a gas injector well; the EMST was run in Q1 2013 and measuring the cumulative thickness up to three strings determining that no external corrosion was present in particular in the section of interest, also the high resolution image showed no presence of internal corrosion. Therefore, a successful operation was achieved meeting the proposed objectives with no HSE incidents and within budget. This technology is proven and has become a solution for further wells where CO2 or bacteria damage has been evidenced including corrosion mapping through chromed and carbon steel in a single run avoiding the excessive costs related to pulling the completion to get access to the outer casing strings.

A Coiled Tubing Gas Lift (CTGL) pilot project was implemented in a reservoir with a compositional fluid system in the Casanare foothills area in the northeast of Colombia. This paper presents the life cycle of the project from design to operation including production test results after installation to "revive" wells with high water production and very low gas liquid ratio. High pressure gas was injected through conventional 1-3/4" and 2" 110 Kpsi coiled tubing, installed inside completion strings and hung to the Christmas tree to reduce cost of the project and avoiding recompletion of the well in a low-cost environment. A pilot project included three well was executed ending 2015, being a world first CTGL for 1-3/4" and 2" CT deployment beyond 12,000 feet. Challenges for deployment of CT string, well control aspects, barriers for control upon disabling of DHSV and master hydraulic valve among of moderate CO2 corrosion impact were some of the risks associated to this project. A pilot installation on three wells was successful and this paper compiles lessons learnt from this process including candidate selection, deployment, material selection, well intervention and risk assessment among of operational performance and pipe recovery after end of project life.

This work involved the synthesis and characterization of Cu0.5Zn0.5Fe2O4ferrite powders prepared by combustion reaction for use as soft magnetic materials. The powders were characterized by nitrogen adsorption (BET), XRD, Rietveld refinement, SEM, TEM and magnetic measures. The results indicate that the combustion reaction yielded crystalline powders containing spinel ferrite as the primary phase and traces of Fe2O3as secondary phase. The crystallite size and lattice microdeformation calculated from Rietveld refinements were 36 and 0.24 nm, respectively. The micrographic analysis revealed particles smaller than 100 nm and fine particle agglomerates. The particles were approximately spherical and their size, calculated by TEM, was 29 nm. The magnetic parameters indicated that the Cu-Zn ferrite powders presented closed hysteresis loops and soft magnetic properties.