开平凹陷文昌组沉积特征及半深湖空间分布

Sedimentary characteristics and semi-deep lacustrine facies spatial distribution of Wenchang Formation in Kaiping sag

始新统文昌组半深湖相烃源岩分布及规模是开平凹陷油气勘探面临的主要问题。以区域沉积背景为基础,利用孢粉组合与地球化学指标判断文昌组沉积环境;利用岩心、薄片、测井和地震资料,类比陆丰凹陷文昌组沉积相,分析开平凹陷文昌组沉积特征;基于地质认识,利用多属性神经网络方法,预测文昌组半深湖相空间分布。研究认为,开平凹陷文昌组为河流-湖泊沉积环境,气候温暖略干,识别出辫状河三角洲平原和前缘亚相,滨湖、浅湖和半深湖亚相,建立起扇三角洲-辫状河三角洲-湖泊沉积相模式;利用有监督的多属性神经网络深度学习方法,预测半深湖相从文六段沉积时期开始发育,文五段持续扩张,文四段规模达到最大,到文三段时期半深湖相萎缩,文一—二段则不发育半深湖相。其中开平凹陷主洼在文四段半深湖面积达166 km^(2),体积达98.6 km^(3),推测主洼东部及东洼也有半深湖相发育。

The distribution and scale of semi-deep lacustrine facies source rocks of Eocene Wenchang Formation are the main problems of oil and gas exploration in Kaiping sag.Based on the regional sedimentary background,the sedimentary environment of Wenchang Formation is determined by palynological assemblage and geochemical indicators;compared with the sedimentary facies of Wenchang Formation in Lufeng sag,the sedimentary characteristics of Wenchang Formation in Kaiping sag are analyzed by using core,thin section,logging and seismic data;and based on geological knowledge,the spatial distribution of semi-deep lacustrine facies of Wenchang Formation is predicted by using multi-attribute neural network method.The study shows that Wenchang Formation in Kaiping sag was deposited in a warm and dry river-lake facies environment,with braided river delta plain,braided river delta front,shore lacustrine,shallow lacustrine,and semi-deep lacustrine subfacies developed,forming a sedimentary model of fan delta-braided river delta-lacustrine facies.The deep learning method of multi-attribute neural network was used to predict that the semi-deep lacustrine facies began to develop in the sedimentary period of the sixth member of Wenchang Formation,continued to expand in the fifth member of Wenchang Formation,reached the largest scale in the fourth member of Wenchang Formation,and shrunk in the third member of Wenchang Formation,but it did not develop in the first and second members of Wenchang Formation.The area and volume of the semi-deep lacustrine facies in the fourth member of Wenchang Formation of the main depression in Kaiping sag are 166 km^(2)and 98.6 km^(3),respectively,and it is inferred that the semi-deep lacustrine facies was also developed in the eastern part of the main depression and the east depression.