基于伽马能谱测井信息的古水深恢复方法——以塔河油田4区巴楚组为例

Palaeobathymetric Reconstruction Based on Natural Gamma Ray Spectrometry Logging Data——By Taking Bachu Formation in Region 4 of Tahe Oilfield for Example

古水深恢复是盆地分析、层序地层学研究、古地貌恢复的重要基础内容之一。根据U、Th、K的地球化学特征及迁移规律,提出了通过数据检验、沉积背景分析、氧化-还原环境评价和古水深计算的古水深半定量恢复技术。结合塔里木盆地塔河油田4区测井数据研究表明,巴楚组沉积时期以还原环境为主,其"双峰灰岩"之下泥岩段还原程度最强,对应于该沉积层序的凝缩段沉积。利用提出的预测水深计算公式,对灰岩层之下的泥岩层进行古水深恢复结果表明,上部泥岩层(Ⅱ号)水深范围在1～10m之间,平均仅3m;下部泥岩层(Ⅳ号)水深范围在1～20m之间,平均为5m。该方法的提出有助于含油气盆地中古生物资料缺乏条件下的古水深恢复的开展,也有利于改进基于沉积学方法和古生物方法进行的古水深恢复的精度,实现垂向上连续的古水深恢复,深化层序地层划分和盆地分析。

Palebathymetric reconstruction was one of the important foundations of basin analysis,sequence stratigraphic study as well as paleogeomorphy recovery.Based on geochemical characteristics and rules of migration and accumulation of Th,U,K,a semi-quantitative method with 4 steps was introduced to restore paleo-depth of water and checking.The method was used in Block 4 of Tahe Oilfield for example.Log analysis shows that there is hardly any oxygen of water in the second and third members of Bachu Formation,and the latter one corresponds to the condensend section which has the strongest reductibility.The upper mudstone(Ⅱ) is deposited on the ocean floor between 1 to 10 m and the average depth of water is 4 m.The lower mudstone(Ⅳ) is deposited in between 1 to 20 m and the average depth of water is 5 m.This method is beneficial for rebuilding the palebathymetry of sedimentary basin which is in short of paleontological data,also beneficial for improving the accuracy of restoring palebathymetry,recovering the continuous curve of water depth,and deepening sequence stratigraphic subdivision and basin analysis.