岩屑伽马能谱录井在川南地区龙马溪组小层卡取中的应用

Application of cuttings gamma spectrum logging in the determination of single layers of Longmaxi Formation in Southern Sichuan

川南地区龙马溪组页岩气开采过程中,由于钻井工艺的改进和提升,岩屑较细碎,常规录井技术对页岩的识别效果较差,很难判别龙马溪组小层情况。利用随钻伽马能谱录井中铀(U)、钍(Th)、钾(K)能够指示沉积环境的变化,通过研究铀(U)、钍(Th)、钾(K)、伽马、无铀伽马等参数或参数组合的变化趋势,建立Th/U比值法及伽马与无铀伽马交会法,可以有效识别沉积环境,划分地层。在川南地区志留系龙马溪组页岩气小层划分中的应用结果表明,该方法能够有效地解决现有录井技术的不足,满足了现场生产需求。

In the extraction of Longmaxi Formation shale gas in Southern Sichuan,the cuttings are relatively finely fragmented due to the improvement of drilling techniques,resulting in poor effect of shale recognition with conventional mud logging technologies and difficulties in distinguishing single layers of Longmaxi Formation.The uranium,thorium and kalium in gamma spectrum logging while drilling can be used to indicate changes in sedimentary environment.By studying variation trend of parameters such as uranium,thorium,kalium,gamma and uranium-free gamma and parameter combinations,thorium/uranium ratio method and gamma-uranium-free gamma intersection method are established to effectively identify sedimentary environment and divide strata.The application in single layer division of Silurian Longmaxi Formation shale gas in Southern Sichuan reveals that this method can effectively solve the shortcomings of existing mud logging technologies,meeting the needs on site.