鄂尔多斯盆地西缘下古生界奥陶系包裹体特征及油气充注史

Characteristics of Lower Paleozoic Ordovician inclusions and oil and gas filling history in the western margin of Ordos Basin

鄂尔多斯盆地西缘下古生界奥陶系碳酸盐岩储层油气成藏期次尚不明确。选取研究区内5口典型井8块下古生界储层碳酸盐岩样品,进行流体包裹体岩相学分析、显微测温及激光拉曼光谱分析,结合典型井埋藏史—热史恢复,确定了鄂尔多斯盆地西缘下古生界奥陶系油气成藏期次。结果表明,鄂尔多斯盆地西缘下古生界奥陶系碳酸盐岩储层中流体包裹体可分为2期:第Ⅰ期包裹体主要以液态烃类包裹体及其伴生的大量盐水包裹体为主,荧光显示为黄色,主要呈串珠状分布在溶孔填充方解石和早期裂缝填充方解石中,其伴生盐水包裹体均一温度的峰值介于120~130℃之间;第Ⅱ期包裹体主要发育气态烃类包裹体及其伴生的大量盐水包裹体和少量沥青包裹体,呈带状分布在晚期裂缝填充方解石中,无明显荧光显示,其伴生盐水包裹体均一温度的峰值介于150~170℃之间。研究区下古生界奥陶系储层经历了2期烃类充注过程:第一期发生在早侏罗世晚期,为大量油气充注时期;第二期充注发生在早白垩世早期、中期,为大量天然气充注时期。

The hydrocarbon accumulation period of the Lower Paleozoic Ordovician carbonate reservoirs in the western margin of Ordos Basin is not clear.Carbonate rock samples from eight Lower Paleozoic reservoirs in five typical wells in the study area were selected for petrographic analysis of fluid inclusions,microthermometry and laser Raman spectroscopy.Combined with the burial-thermal history recovery of typical wells,the hydrocarbon accumulation periods of the Lower Paleozoic Ordovician in the western margin of Ordos Basin were determined.The results show that the fluid inclusions in the Lower Paleozoic Ordovician carbonate reservoirs in the western margin of the Ordos Basin can be divided into two stages.The first stage of inclusions is mainly com‐posed of liquid hydrocarbon inclusions and a large number of associated aqueous inclusions.The fluorescence is yellow,mainly in the form of beads distributed in the cave-filled calcite and the early fracture-filled calcite.The peak value of the homogenization temperature of the associated aqueous inclusions is between 120℃and 130℃.The inclusions in the second stage mainly develop gaseous hydrocarbon inclusions and their associated large amount of aqueous inclusions and a small amount of asphalt inclusions,which are distributed in the late fracturefilled calcite in bands,with no obvious fluorescence,and the peak value of the homogenization temperature of the associated brine inclusions is between 150℃and 170℃.The Lower Paleozoic Ordovician reservoir in the study area has undergone two hydrocarbon filling processes.The first stage occurred in the late stage of Early Jurassic,which was a period of large oil and gas filling.The second stage occurred in the early and middle stage of Early Cretaceous,which was a period of large gas filling.