鄂尔多斯盆地中东部上古生界三角洲沉积特征

上古生界是鄂尔多斯盆地重要的含气层系，天然气的聚集受相带的控制，其主产层均为三角洲沉积体系。通过对盆地中东部上古生界野外露头、岩心及测井曲线等的综合分析，将区内上古生界三角洲沉积体系划分为辫状河三角洲及曲流河三角洲。分析表明，研究区两类三角洲沉积在岩性、沉积构造、沉积序列、测井曲线等方面存在差异。辫状河三角洲主要发育在中二叠世下石盒子组下部盒₈、盒₉段气层组，主体为辫状河三角洲前缘亚相；曲流河三角洲主要发育在早二叠世山西组山₂段气层组，以曲流河三角洲前缘沉积为主。勘探实践表明，曲流河三角洲沉积体系对于研究区天然气的富集有着更为重要的作用。今后应重点加强对山₂段气层组曲流河三角洲沉积体系中有利储集相的寻找，同时兼顾盒₈、盒₉段气层组的辫状河三角洲沉积体系。

CHARACTERISTICS OF UPPER PALEOZOIC DELTA DEPOSITS IN EAST-CENTRAL ORDOS BASIN

The Upper Paleozoic is the major gas-bearing series of strata in Ordos basin, where gas accumulation is controlled by facies belts and all the major pay zones are of delta sedimentary systems. Based on comprehensive analysis of the field outcrops, coring and well logging data of the Upper Paleozoic in the east-central Ordos basin, the Upper Paleozoic delta sedimentary systems in the study area is divided into braided river delta and meandering river delta deposits, which are different in respects of lithology, sedimentary structure, sedimentary sequence and borehole log, etc. The braided river delta deposits are mainly developed in He-8 and He-9 gas-bearing units in the lower interval of the Middle Permian Lower Shihezi Fm, with the braided river delta front subfacies in predominance. While the meandering river delta deposits are mainly developed in Shan-2 gas-bearing unit in the Upper Permian Shanxi Fm, with the meandering river delta front subfacies in predominance. Exploration practices show that the meandering river delta sedimentary system would have played a more important role in gas accumulation in the study area. Priority should be given to searching for the favorable reservoir facies in the meandering river delta sedimentary system of Shan-2 gas-bearing unit, while the braided river delta sedimentary systems in He-8 and He-9 gas-bearing units should be taken as exploration targets at the same time.