annual 2010/2011 of the croatian academy of engineering - HATZ

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38 Annual 2010/2011 of the Croatian Academy of Engineering THE WAY TO REDUCE PIPE WEARING WHILE DRILLING Matanović Davorin, Moslavac Bojan, Nediljka Gaurina-Međimurec University of Zagreb Faculty of Mining, Geology and Petroleum Engineering Pierottijeva 6, 10000 Zagreb, Republic of Croatia Tel. +385 1 5535 835; fax: +385 1 48 36 074 E-mail: dmatan@rgn.hr Abstract While drilling there is an additional load on the coiled tubing due to friction with the well walls/rocks regardless the drilling mode; rotating or sliding. According to recent investigations fatigue is the major factor controlling the service life of coiled tubing. The rate of fatigue damage accumulation is affected by a number of operating factors: mechanical damage, corrosion damage, damage incurred by exceeding the ultimate capacity of the string, and damage due to cycling plastic strain or fatigue. Determination of the actual friction coefcient is essential in dening the project technical feasibility. As the part of drilling system, drilling uid can impact on the reduction of friction coefcient by implementation of lubricants. Selection of lubricants, their compatibility with drilling uid and rocks was determined through laboratory testing. The results are shown and elaborated in the paper. Key words: drilling, pipe wearing, lubricants Introduction Horizontal wells are more expensive to drill than vertical wells so increased production must offset increased drilling costs. In drilling horizontal or highly deviated wells, more serious problems appear than in drilling vertical wells. These problems are: poor hole cleaning, excessive torque and drag, hole lling, pipe sticking, well bore instability, loss of circulation, formation damage, poor cement job, and difculties at logging jobs. From that reason, the principle factors that require extra consideration for choosing a uid for drilling a horizontal well are: formation damages, hole cleaning, hole stability and lubricity. Good lubricating properties of the drilling uid can improve greatly drilling operation efciency. When drilling long sections of highly deviated wells, there is considerable contact between the drill string and the borehole wall, generating frictional resistance to movement. The friction between the drill pipe and the wall will increase torque and power required to rotate the drill pipe and the stress on the drill pipe. It could also interfere with running the pipe in and out of the hole. The frictional resistance to movement can be large enough to be the limiting factor in horizontal and extended-reach drilling. Since there are many factors that affect torque and drag, it is sometimes difcult to detect what is causing increased down hole friction. Regardless of the drilling uid or lubricant used, down hole friction can be reduced by
Annual 2010/2011 of the Croatian Academy of Engineering 39 conditioning the uid to achieve a thin, slick, compressible lter cake, and by practicing good hole-cleaning techniques to minimize the cuttings bed. In order to design the best suitable drill-in uid for horizontal well, drilling problems generally encountered in each eld should be studied and laboratory tests planned and conducted. Systematic approach to drilling optimization To optimize a drilling process there is a need to develop methods and processes that will improve drilling efciency. The method must be systematic, logical and must have quantiable approach. The applicable method is one that denes and quanties two sets of parameters for the drilling operation: performance objectives and requirements, as shown in Fig. 1. The gure is taken from reference [1] but is slightly changed to apply for coiled tubing drilling with down hole positive displacement motor. Fig. 1 Systematic approach inuence diagram To achieve minimal interval cost we have to maximize on-bottom time and effective rate of penetration. First branch determines parameters that are not direct drilling parameters, but depend on well path and used equipment. Second branch determines parameters that are of greatest inuence in drilling process. Bit design and used down hole motor combination efciency according to observed formation characteristics are essential. To obtain optimal performance of bit-motor combination optimal ow rate must be obtained and proper uid used. In deviated or horizontal wells proper determination of weight on bit in any moment or point of the well trajectory is essential. The determination of compressive load in vertical section, build section or horizontal section depends on well trajectory and coiled tubing dimensions. Buckling of coiled tubing and lock-up condition is the next limitation that must be considered. Because of different possible well paths and segment length and slope (Fig. 2) it is necessary to determine forces and stresses in coiled tubing.
Page 1: ANNUAL 2010/2011 OF THE CROATIAN AC
Page 4 and 5: Published by Croatian Academy of En
Page 6 and 7: Mario Žagar, Ivica Crnkovi, Darko
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Page 20 and 21: 20 CONCLUSION Annual 2010/2011 of t
Page 42 and 43: 42 LUBRICANTS Annual 2010/2011 of t
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122 5.0 Conclusion 6.0 References A
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124 2 The Community of Raša Annual
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206 4 Results and discussion Annual
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Podupirajui lanovi: Arhitektonski f
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