利用自然伽马能谱测井识别碳酸盐岩高频层序——以塔里木盆地塔中地区T1井良里塔格组为例

碳酸盐岩系地层中普遍发育高频层序，且与四级、五级层序界面伴生的早期岩溶作用对油气储层的改善十分关键，然而基于测井资料如何客观的识别和划分高频层序是学界不断探索的难点问题。论文选取塔里木盆地塔中地区的T1井，利用自然伽马能谱测井中Th/U （钍/铀）比值曲线，使用滑动平均滤波和小波变换等方法，对上奥陶统良里塔格组开展了高频层序研究。结果表明，Th/U比值曲线滑动平均滤波处理后，能清晰、客观地反映沉积旋回，其比值的增加指示沉积水体加深、泥质增多，比值减少指示沉积水体变浅、泥质减少；该井良里塔格组可划分为3个三级层序、8个四级层序和32个五级层序，三～五级层序分别与小波变换得出一维离散曲线的振荡趋势非常吻合，四级和五级层序极有可能分别反映了米兰科维奇旋回中地球偏心率长周期旋回（0.4 Ma）和短周期旋回（0.1 Ma）；连井对比表明塔中地良里塔格组下部的三级和四级层序发育具有明显差异，这种差异受控于良里塔格组沉积前古地貌形态；储层发育段均与四级、五级层序界面有关，塔中地区东部更易发育有利的储层。研究结果对于依据测井资料开展碳酸盐岩高频层序研究具有理论意义，对于建立区内的高精度层序地层格架进而预测礁滩相储层分布具有实际意义。

Using Spectral Gamma Ray Log to Recognize High-frequency Sequences in Carbonate Strata: A case study from the Lianglitage Formation from Well T1 in Tazhong area,Tarim Basin

High-frequency sequences are commonly developed in carbonate strata, and eogenetic karst related to fourth- to fifth- order sequence boundaries are of great importance to the improvement of carbonate reservoir quality. However, how to identify high-frequency sequences objectively is a generally acknowledged issue which has been long been explored. In this study, we analyze the high-frequency sequences of the Lianglitage Formation in the Tazhong area of Tarim Basin, by using the natural gamma ray logging data and utilizing moving average flitering and wavelet transformation methods. Th/U ratio log, after moving average filtering process, can clearly and objectively reflect the depositional cycles, with its increase indicating the deepening of depositional environment and the concentration of clay, and its decrease indicating the shallowing of depositional environment and purer limestone deposits. The Lianglitage Formation in this well can be divided into three third-order sequences, eight fourth-order sequences, and 32 fifth-order sequences, the sea-level change reflected by various rank sequences are well coincided with the three one-dimensional discrete curves derived from wavelet transform analysis. Correlation between wells indicates the third- and fourth-order sequences of the lower part of the Lianglitage Formation vary between different areas in the Tazhong Uplift, and the differences attribute to the distinct paleogeomorphology of the Tazhong Uplift before Late Ordovician. The fourth- and fifth-order sequences are believed to reflect the eccentricity long periods and short periods, respectively, in Milankovitch cycles. The reservoir units in the well are all related to the fourth- and fifth-sequence boundaries. The results of this study are of great significance of analyzing high-frequency sequences in carbonate strata based on well-logging data, as well as forecasting favorable reservoirs in a high-resolution sequence framework in this area.