磁井径测井方法的研究

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1、中文摘要本文针对油井套管最常见的井径异常和裂缝缺陷，利用涡流无损检测技术，将一个载有交变电流的检测线圈探入套管，套管的井径异常和裂缝直接表现为与检测线圈距离的变化。在测量系统参数固定的条件下，线圈阻抗与这个距离呈单值对应关系，在满足场论向路论转换的条件下，推导出了引起线圈交流阻抗变化的理论公式。通过理论计算曲线可以得出:井径的变化与线圈输出阻抗在一定范围内呈线性关系，并且对裂缝的检测有较高的灵敏度;测量时应注意选取发射线圈尺寸，发射线圈尺寸大，线性范围增加，但灵敏度降低，灵敏度与线性范围相互矛盾;发射线圈尺寸

2、相同时，井径越小，测量裂缝越灵敏。利用发射线圈与电容并联的谐振调幅电路，将线圈阻抗变化转换成电压的输出。文中对井径、裂缝长度与厚度、发射探头激励频率、套管磁导率、探头偏心等因素对测量结果的影响作了理论分析，为套管缺陷检测提供了定量解释理论依据。关键词:套管缺陷电磁检测涡流探头线性度灵敏度AbstractThispapergivesaneddycurrentinspectionmethodforthemostcommondefectsoccurringinoilpipecasing,whichareknowna

3、sdiameterabnormityandcrack.Thedetectioncoilcaryingalternatingcurrentwereloweredintopipeandthediameterabnormityandcrackweredirectlyrepresentedbythechangesindistancebetweenthedefectandthedetectioncoil.Underconditionthatthemeasurementsystemparameterswerefixed,

4、thealternatingcurrentcoilimpedanceiscorrespondingtosuchdistanceinmonotropy.Basedontheassumptionthatthefieldtheorycanbeconvertedtocircuittheory,atheoreticformularepresentingthechangeinalternatingcurrentimpedanceofthecoilwasderived.Itisshownthatthereisalinear

5、relationshipbetweenthechangeinpipediameterandcoilimpedancewithinacertainrangebythetheoreticcalculation,inaddition,thecoilimpedanceissensitivetothecrackofcasingWhenmeasuring,thesizeofemitingcoilshallbecarefullyselectedinordertomatchthepipediameter.Thelinearr

6、angeisincreasedwiththeincreaseofemittingcoilsize,butthesensitivitywillbedecreased,exhibitingacontradictionbetweenthesensitivityandthelinearrange;Ifthesizeofemitingcoilkeepsunchanged,thesensitivityofcasingcrackmeasurementisincreasedwiththedecreaseinpipediame

7、ter.Theemitingcoilandcapacitanceareconnectedinparallelandformaresonantamplitude-modulationcircuit,whichconvertstheimpedanceintooutputvoltage.Theinfluencefactorsareanalyzedonthemeasurementsuchaspipediameter,lengthofcasingcrackandthickness,excitationfrequency

8、ofemitingcoil,casingmagneticconductivityandemittingcoileccentricity，etc.itprovidsatheoreticfoundationforthequantitativeinterpretationofcasinginspection.Keywords:Thecasingdefects,Electromagneticinspecti