A Lithology Identification Method for Buried Hills in the Lishui-Jiaojiang Sag Based on Correspondence Analysis

As oil and gas exploration in the Lishui-Jiaojiang Sag moves towards buried hills, drilling has encountered many lithology formations such as granite, gneiss, and limestone. In addition, with the application of new drilling technology, the cuttings for logging are fine and usually mixed together, and it is difficult to identify the lithology accurately on the well site. In order to solve this problem, based on X-ray diffraction (XRD) and X-ray fluorescence (XRF) element logging data, firstly, the ReliefF algorithm was used to identify eight elements and four minerals sensitive to buried hills and overlying strata, and then the selected elements and minerals were used as the characteristic parameters of the original data set for corresponding analysis. The H₁and H₂ functions of granite, gneiss, limestone, and other complex lithologies were established, and the complex lithology identification chart was drawn. Specifically, the H₁and H₂ of granite were −3.0～1.0 and 1.0～3.0, and those of gneiss were −4.0～0 and −2.5～1.0. The H₁and H₂ of limestone were 0.5～2.5 and −9.0～−3.0, and those of sandstone were 2.5～10.0 and −1.0～2.5. In addition, the H₁and H₂ of mudstone were −1.0～3.5 and −1.0～0.5. The lithology identification method based on corresponding analysis was applied to six wells in the oil and gas area of the Lishui-Jiaojiang Sag, and the identification accuracy of complex lithology reached 90.7%, which can provide technical support for drilling operation safety and comprehensive evaluation of buried hill reservoirs.