摘要
鄂尔多斯盆地奥陶系上统乌拉力克组发育一套分布稳定的黑色页岩,为盆地奥陶系的优质烃源岩层,近期多口探井获得工业油气流,证实了具有较好的勘探潜力.勘探研究证实,优质烃源岩分布为页岩气富集的基础,因此,系统开展乌拉力克期沉积特征及对优质烃源岩的控制作用研究,对于寻找优质页岩及指导下一步勘探方向意义重大.通过系统开展沉积特征及地球化学特征研究,建立了乌拉力克期沉积模式,明确了优质烃源岩分布规律.①乌拉力克组平面上稳定分布,整体具有"西厚东薄"的特征,主要发育盆地相、广海陆棚相、斜坡相三类大相,斜坡相可细分为上斜坡亚相和下斜坡亚相两类亚相.②建立了乌拉力克期沉积模式:盆地西部乌拉力克期属祁连海域,为台地边缘型沉积,水体整体具有"西深东浅,南深北浅"的沉积格局,斜坡坡度较大,相变快.③乌拉力克组发育一套低有机质丰度页岩,有机质含量的变化主要受页岩纹层矿物成分、沉积相带、沉积层序控制.结论认为,鄂尔多斯盆地西部地区乌拉力克期发育一套台地边缘沉积,广海陆棚相、下斜坡亚相黑色页岩发育,有机质丰度高,为有利相带,优质页岩主要分布在底部20～30 m范围内.
Abstract
It developes thick shale with stable distribution and it is the best source rock in Wulalike Formation of Ordovician in Ordos Basin.Many exploration wells have obtained high production of industrial oil and gas re-cently,it shows a good exploration situation.It has significance to study sedimentary characteristics and con-trolling effect on high-quality source rocks'distribution.Based on the study of sedimentary characteristics and geochemical characteristics,it shows that:① Wulalike Formation distribute extensively and characterd by"thick in the west and thin in the east",it developes basin facies,open shelf facies and slope facies,slope fa-cies includes upper slope subfacies and lower slope subfacies.②It belongs to the Qilian Sea in Wulalike peri-od,seawater is deep in the west and shallow in the east,deep in the south and shallow in the north,the slope grade is large and the facies transition is fast.③It developes low-abundance shales in the Wulalike Formation and the spatial distribution of high-quality shales is mainly controlled by the mineral composition,sedimentary facies and sedimentary sequence.The conclusion is that open shelf facies and lower slope subfacies are favora-ble facies,high-quality shales are mainly distributed in the bottom 20～30 m range.
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