鄂尔多斯盆地南部延长组油气成藏期次研究

为了研究鄂尔多斯盆地南部延长组油气成藏期次和成藏模式,采取镜下观察、激光拉曼、显微测温等方法对盆地南部地区延长组储层成岩作用和包裹体的特征进行了研究,并结合烃源岩生烃史、盆地热演化史,综合分析研究区延长组成藏期次。研究结果表明:鄂尔多斯盆地南部地区延长组存在两期油气包裹体:第一期油气包裹体在荧光显微镜下呈蓝绿色或深绿色的液烃包裹体,丰度较低,伴生的盐水包裹体均一温度主峰为100~110 ℃;第二期油气包裹体以气液烃包裹体为主,包裹体在单偏光下为无色或淡黄色,荧光显微镜下为亮蓝色,丰度较高,伴生的盐水包裹体均一温度主峰为130~140 ℃。通过对油气包裹体的均一温度、盐度、密度研究明确了研究区为“一期两幕”成藏,结合盆地热演化史认为鄂尔多斯盆地南部地区延长组存在两次油气充注:第一次油气充注在早白垩世中期(距今115~125 Ma),第二次油气充注主要在早白垩世晚期(距今97~105 Ma)。两次油气充注表明鄂尔多斯盆地南部地区延长组油气成藏时期为早白垩世(距今97~125 Ma)。

Classification of Hydrocarbon Accumulation Phases of Yanchang Formation in Southern Ordos Basin

The timing of hydrocarbon accumulation of Yanchang Formation in the southern Ordos Basin is determined, according to the fluid inclusion characteristics and hydrocarbon generation history of source rock and oil maturity. Characteristics of fluid inclusions (under microscope and UV fluorescence) suggest two generations of hydrocarbon inclusions. The first generation comprises yellow or aquamarine liquid hydrocarbon inclusion under fluorescence microscope. These fluid inclusions are low in abundance, and the accompanied saline inclusions homogenized at 100~110 ℃. The second generation includes mainly gas and liquid hydrocarbon inclusions, the former is colorless or light-yellow under polarized light and bright blue under fluorescence. Its abundance is high, and the accompanied saline inclusions homogenized mainly at 130~140 ℃. Integrated with salinity and density analyses, we suggested a one-phase and two-stage model for the major accumulation of hydrocarbons in the Yanchang Formation. Considering the basin thermal evolution history of southern Ordos basin: the first hydrocarbon charging stage occurred in the middle of Early Cretaceous (ca. 125 ~ 115 Ma), whilst the second stage occurred in the late of Early Cretaceous (ca. 97 ~ 105 Ma). These two oil and gas filling stages indicate that the oil and gas accumulation occurred in the Early Cretaceous.