来凤地区龙马溪组含气页岩测井识别--以WY1井为例

    Log-based identification of gas-bearing shales in the Longmaxi Formation of the Laifeng area: A case study of well WY1

    • 摘要: 湖北龙马溪组海相页岩是除四川盆地外可能实现页岩气勘探突破点之一, 测井技术是一种十分成熟的油气勘探开发研究手段, 本文以来凤地区WY1井的测井为基础, 对龙马溪组含气页岩层段测井响应特征进行系统研究。结果表明, WY1井龙马溪组含气页岩层段具有高自然伽马、高铀、高钍、高补偿中子、高声波时差及低密度的测井响应特征, 深、浅侧向电阻率低于下伏宝塔组碳酸盐岩, 高于砂质页岩, 且正差异反映岩层中发育高角度裂缝的层段。通过测井曲线叠合以及交会图版分析发现, 含气页岩层自然伽马—岩性密度测井叠合曲线及声波时差—岩性密度测井叠合曲线具有明显的正差异, 而自然伽马—补偿中子和声波时差—补偿中子呈现明显的负差异, 且声波时差—岩性密度叠合测井曲线对于含气层段的指示作用最为准确; 声波时差—补偿中子测井交会图、补偿中子—自然伽马测井交会图以及深侧向电阻率—补偿中子测井交会图对于富有机质含气页岩的识别作用最明显。

       

      Abstract: Except for the Sichuan Basin, the marine shales in the Longmaxi Formation in Hubei show great potential for shale gas exploration. Logging technology is highly mature in the exploration and development of hydrocarbons. This study systematically analyzed the log response characteristics of gas-bearing shales in the Longmaxi Formation based on logs obtained from well WY1 in the Laifeng area. As indicated by the analysis results, the gas-bearing shales of the Longmaxi Formation in well WY1 are characterized by high natural-gamma-ray values, high contents of uranium, thorium, and compensated neutrons, high interval transit time, and low density. Their deep and shallow lateral resistivity is lower than that of the underlying Baota Formation carbonate rocks but is higher than that of the sandy shales. Moreover, the positive differences indicate that high-angle fractures occur in the shales. The superimposition of log curves and the analysis of cross plots for gas-bearing shales reveal that ① the superimposed log curves of both natural gamma ray-lithologic density and interval transit time-lithologic density show significant positive differences, while those of both natural gamma ray-compensated neutrons and interval transit time-compensated neutrons show significant negative differences; ② the superimposed log curves of interval transit time-lithologic density indicate the gas-bearing intervals the most accurately; ③ the organic-rich gas-bearing shales can be identified the most effectively using the log cross plots of interval transit time-compensated neutrons, compensated neutrons-natural gamma ray, and deep lateral resistivity-compensated neutrons.

       

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