自然伽马反演模型重构方法研究

油气储层往往分布于多个不同沉积时期的地层中。由于不同沉积时期的砂泥岩地层在埋藏深度、岩性及矿物含量等方面均不相同，导致相同或相近岩性的测井响应值存在差异。在有些地区因受沉积作用等因素的影响，相同岩性的自然伽马测井值随埋藏深度的增加呈增大或减小的趋势，若利用其计算储层的泥质含量或进行储层参数反演，均无法采用统一的标准（公式）来进行评价。为此，在分析自然伽马测井曲线在不同沉积时期的测井响应差异及其随地层埋藏深度和地层岩性变化特征的基础上，利用测井资料综合解释中泥质含量计算方法的逆运算，对自然伽马测井曲线进行了重构处理。结果表明，重构后的自然伽马曲线可不受不同地层沉积时期等因素的影响，对多个不同地质时期的目的层可以采用统一的标准来进行岩性解释。该重构方法可适用于不同类型砂泥岩地层的储层反演及泥质含量计算。

Study on natural gamma-ray model reconstruction method

Oil and gas reservoirs are often distributed in several strata in different sedimentary periods. Due to the differences of buried depth, lithology and mineral content in sand shale formation during different sedimentary periods, the logging responses of the same lithology are different. Natural gamma?ray logging curve is affected by sedimentation in some regions, so its log value increases or decreases with buried depth change. If use the log value to calculate the shale content of reservoirs or carry out reservoir parameter inversion, it is unable to use a unified standard（formula）to evaluate the shale content of target zone. Based on the analyses of logging response differences of natural gamma-ray logging curve during different sedimentary periods, as well as its change characteristics with buried depth and formation lithology, the inverse operation of shale content calculation method in the comprehensive interpretation of log data was used to reconstruct natural gamma ?ray logging curve. The result shows that the reconstructed natural gamma -ray logging curve is not affected by factors such as strata of different sedimentary periods, and a unified standard can be used to carry out lithology interpretation for the target zone during different geological periods. This reconstruction method can be applied for reservoir inversion and shale content calculation for different types of sand shale formation.