分地层法构建声波测井曲线
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摘要
速度参数是波阻抗反演必不可少的条件,人们通常使用Gardner或Faust公式根据不同岩性选择不同参数进行声波测井曲线的合成,但由于不同地区、不同地层及不同岩性,其计算参数值也不尽相同,因此合成的声波测井曲线难免会产生较大误差,特别是遇到第四系、新近系、古近系及煤层等松软地层时,Gardner公式转换的速度表现为偏低,Faust公式转换的速度往往又较高,严重影响速度参数的正确性。采用密度转换速度和电阻率转换速度分别乘以一个加权系数,再求和的办法可有效减少误差,其加权速度曲线可较好的反映岩性变化,其解释结果更符合钻孔实际地质特征。根据内蒙古鄂尔多斯某区测井资料,在拟合Gardner和Faust公式参数的基础上,使用加权法构建了声波测井曲线,结果表明:加权校正后的速度与实际速度值的平均绝对误差为208.43m/s,平均相对误差为7.76%;加权后修正的地震记录与井旁地震道的拟合度为0.509,远远高于Gardner公式、Faust公式的合成地震记录拟合度。
Velocity parameters are indispensable in elastic impedance inversion.The Gardner or Faust formulae are commonly used in synthesis of sonic logging traces based on different lithology and parameters.Because of computing parameters are different in different area,strata and lithologic characters,larger errors will come into being in synthesized sonic logging traces.Especially in loose strata of Quaternary,Neogene,Paleogene systems and coal seams,the velocity conversed from Gardner formula will be on the low side,while from Faust formula on the high side,and thus impact velocity parameter correctness seriously.Multiply by a weighting coefficient respectively on density conversed and resistivity conversed velocities then find the sum can reduce errors effectively.The weighted velocity traces can reflect lithologic variation better,and interpreted results tally with actual geological characters in a greater degree.Based on logging information of an area in Ordos,Inner Mongolia,on the basis of Gardner and Faust formulae parameter fitting,build sonic logging traces by weighting method.The results demonstrated that: mean absolute error of weighted and practical velocities is 208.43m/s,and mean relative error 7.76%;fitting degree of weighted seismic record and well side seismic channel is 0,509,far higher than that of Gardner and Faust formulae synthesized seismic record.
Velocity parameters are indispensable in elastic impedance inversion.The Gardner or Faust formulae are commonly used in synthesis of sonic logging traces based on different lithology and parameters.Because of computing parameters are different in different area,strata and lithologic characters,larger errors will come into being in synthesized sonic logging traces.Especially in loose strata of Quaternary,Neogene,Paleogene systems and coal seams,the velocity conversed from Gardner formula will be on the low side,while from Faust formula on the high side,and thus impact velocity parameter correctness seriously.Multiply by a weighting coefficient respectively on density conversed and resistivity conversed velocities then find the sum can reduce errors effectively.The weighted velocity traces can reflect lithologic variation better,and interpreted results tally with actual geological characters in a greater degree.Based on logging information of an area in Ordos,Inner Mongolia,on the basis of Gardner and Faust formulae parameter fitting,build sonic logging traces by weighting method.The results demonstrated that: mean absolute error of weighted and practical velocities is 208.43m/s,and mean relative error 7.76%;fitting degree of weighted seismic record and well side seismic channel is 0,509,far higher than that of Gardner and Faust formulae synthesized seismic record.
引文
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