自然伽马能谱录井技术在川南地区威远构造页岩气勘探中的应用

Application of natural gamma spectrometry in shale gas logging of Weiyuan structure in southern Sichuan

在川南地区威远构造页岩气录井作业过程中,受钻井工艺改进和提升的影响,非常规储层岩屑细碎,常规录井技术在岩性识别、地层对比、储层评价等方面存在困难。为此,现场录井过程中引入了自然伽马能谱录井技术,利用该技术中铀(U)、钍(Th)、钾(K)参数来指示沉积环境和储层有机质变化,通过研究铀(U)、钍(Th)、钾(K)、伽马、无U伽马等参数的变化趋势,建立了数值法、趋势法、Th与K交会图板法,可有效识别沉积环境和储层有机质、准确鉴别岩性、及时对比地层并实时评价储层。通过在川南地区威远构造页岩气层岩性识别、小层划分、储层评价中的应用表明,该技术能够有效克服常规录井技术的不足,满足非常规油气勘探现场快速实时解释评价的需求。

In the shale gas logging of Weiyuan structure in southern Sichuan,due to the improvement of drilling technology,the fine cuttings from unconventional reservoir rock,it is difficult in lithology identification,stratigraphic correlation and reservoir evaluation by conventional mud logging.Therefore,the natural gamma spectrometry has been introduced into field mud logging.The uranium(U),thorium(Th),potassium(K)can be used to indicate the change of sedimentary environment and reservoir organic matter,and by studying the trends of U,Th,K,gamma,uranium⁃free gamma and other parameters,the numerical method,trend method and Th⁃K cross⁃over method can be established to effectively identify sedimentary environment and organic matter,accurately identify lithology,compare strata and evaluate reservoirs in real⁃time.The application results of lithology discrimination,subzone division and reservoir evaluation of shale gas in Weiyuan structure in southern Sichuan show that this method can effectively solve the shortages of conventional mud logging technology and meet the rapid and real⁃time interpretation and evaluation of unconventional oil and gas exploration demands.