六盘山盆地南部白垩系油气成藏条件分析

Hydrocarbon accumulation conditions analysis of Cretaceous reservoirs in southern Liupanshan basin

六盘山盆地白垩系为主要勘探层系之一,在南部下白垩统中见较多油气显示,展示较好的勘探潜力。通过对烃源岩、储盖特征、圈闭以及油气运聚史等各种地质要素进行梳理和评价,明确其对油气成藏的控制作用。结果表明,盆地南部下白垩统李洼峡组中段和马东山组两套烃源岩具有一定的生烃能力,白垩系发育两套储盖组合,其中储集层具有低孔低渗、与烃源岩相互叠置且累计厚度大的特点;受构造活动的影响,油气在晚白垩世和渐新世晚期发生过两个期次充注;盆地南部各成藏要素间时空匹配关系较为合理,弱改造区的古油藏以及强改造区的完整构造圈闭为下一步勘探的有利方向。

Liupanshan Cretaceous basin is one of the most important exploration strata and there are more hydrocarbon shows in lower Cretaceous in the south,which shows a good exploration potential in this area.Through analysis and evaluation of hydrocarbon accumulation elements such as hydrocarbon source rocks,reservoir-cover features,trap,hydrocarbon migration and accumulation history,the controlling effect of these geological elements on hydrocarbon accumulation has been clarified.The results indicate two sets of source rocks,namely the middle member of Liwaxia formation and Madongshan formation from lower Cretaceous in southern Liupanshan basin,are considered to be capable of generating hydrocarbon.Two sets of reservoir-cap assemblages have been developed,among which the reservoir is characterized by low porosity and low permeability,superimposing with source rocks and large gross thickness.Influenced by the tectonic activities,two phase of hydrocarbon filling have occurred in late Cretaceous and late Oligocene.The matching relationship among different accumulation elements is reasonable,the paleo-oil reservoir in weakly reworked area and complete structural traps in intensely reworked area are the most favorable targets for further exploration.