塔里木盆地顺北地区奥陶系碳酸盐岩层序模式及其意义

Sequence Model of Ordovician Carbonate Strata in Shunbei Area,Tarim Basin,and Its Significance

近年来塔里木盆地顺北地区深层碳酸盐岩油气勘探取得了丰硕成果。依据全球海平面变化,结合钻井及地震资料,将顺北地区奥陶系下统—中统碳酸盐岩划分为1个二级层序,8个三级层序,总结了每个层序界面及层序内部特征,提出顺北地区奥陶系碳酸盐岩发育三种层序模式——海侵、高位与低位模式,并分析其控制因素。顺北地区奥陶系碳酸盐岩主要储集空间显示为大型岩溶洞穴,位于三级层序界面之下的蓬莱坝组岩心与薄片具明显的溶蚀孔洞特征,反映了低位期岩溶与高位期岩溶对顺北地区奥陶系碳酸盐岩储层发育的控制作用。顺北地区地表水无法通过断裂从上穿过约800 m的奥陶系上统泥岩段,进入中下统碳酸盐岩储层,因此塔河地区“断溶体”理论并不适用于顺北地区,三级层序界面控制的岩溶作用是顺北地区奥陶系碳酸盐岩储层形成的主要控制因素。

Recent exploration for hydrocarbons in the deep carbonate rocks of the Shunbei area of the Tarim Basin has been fruitful.Drilling and seismic data indicate that global sea-level change during the Lower to Middle Ordovician divided the carbonate rocks into a second-order sequence containing eight third-order sequences.Three sequence development models are proposedtransgressive,highstand and lowstandand their influencing factors are analyzed.Cores and rock slices of Penglaiba strata below the sequence boundary clearly show dissolution pores,indicating lowstand and highstand karsts in the reservoir.Analysis of the actual geological conditions concludes that the fault/karst theory of the Tahe area is not applicable to the Shunbei area.Karstification below the sequence boundary is the main factor in the formation of the Shunbei reservoirs.