鄂尔多斯盆地三叠系延长组长7段浊积扇对油气聚集的控制

摘要

The sedimentary environment of the Chang 7 Member of Triassic Yanchang Formation in Ordos Basin is lacustrine facies with the background of large area mudstone deposition in the deep lake. The turbidity current deposits are widespread, and are char⁃acterized by extensive sedimentary range, large thickness, and proximal hydrocarbon source rocks. With these favorable factors, the Chang 7 Member has become the advantageous reservoir of oil. It is therefore necessary to find out the characteristics of sedimentary facies of the turbidite fan and sand bodies formed from different microfacies which affected the oil accumulation. Based on the analysis of the field outcrop and the core statistics, the authors divided turbidite fan microfacies in detail, which helps to study the turbidite for⁃mation, distribution, and sedimentary characteristics. According to previous research results, the channel turbidite fan with fixed sup⁃ ply and the channel turbidite fan with no fixed feeder were named respectively slope moving turbidite fan and slumping turbidite fan. On the basis of differences in thickness of single sand, turbidite types and formation locations, the authors divided the slope moving turbidite fan into three subfacies, i.e., upper fan, middle fan and the edge of the fan. The three subfacies contain six microfacies, such as the main channel and the overflow deposits. The slumping turbidite fan facies was divided into two subfacies, i.e., central fan and marginal fan. The recognition of microfacies of the turbidite fan and the study of their formation can help the log work to identify fa⁃vorable sand body, distinguish different oil and gas reservoirs, and control the distribution of oil and gas. Massive texture sand body⁃and layers sand body help to find the favorable oil and gas reservoir.%鄂尔多斯盆地三叠系延长组长7段为湖盆环境，盆地深湖区以深湖泥岩沉积为背景，普遍发育浊流沉积，沉积范围广、厚度大，近源的先天优势使其成为油气充注的最先储集单元。弄清浊积扇的沉积特征及不同微相形成的砂体对油气聚集具有重要意义。通过野外剖面分析与岩心观察统计，对浊积扇微相进行精细划分，明确浊积岩的形状、展布与沉积特征。根据前人研究成果，将有固定补给水道的浊积扇和无固定补给水道的浊积扇划分为坡移浊积扇和滑塌浊积扇。通过单砂体厚度、浊积岩类型与发育位置的不同，将坡移浊积扇划分为内扇、中扇、外扇3个亚相和主沟道、溢岸沉积等6个微相；滑塌浊积扇相划分出中心扇和边缘扇2个亚相。浊积扇微相的划分及其成因的讨论能够指导测井对有利砂体的解释，区分不同的油气储集体，为寻找有利油气储层的分布提供依据。