渤海湾盆地乐亭凹陷下第三系含油气系统

LOWER TERTIARY PETROLEUM SYSTEM IN LETING SAG,BOHAI BAY BASIN

为深入分析渤海湾盆地乐亭凹陷油气生成条件及成藏规律,对其下第三系含油气系统进行了综合研究,结果表明:区内存在丰富而成熟的烃源岩,暗色泥岩分布范围广且具备生烃能力,沙三中、下段泥质岩以及沙一下段泥质岩均具有良好的封盖性;发育有下生上储、自生自储2种生储盖组合形式;存在有断块(鼻)圈闭、岩性圈闭、地层圈闭、复合圈闭等多种圈闭类型;油气以砂岩疏导层供油、断层供油和不整合面供油3种方式进行运移和聚集;下第三系含油气系统经历了隆升褶皱变动、断陷、沉降3个主要阶段。以源岩潜量指数(SPI)为参数对含油气系统进行了评价,指出以侧向运移为主的自生自储式成油组合具备有利的成油条件,以垂向运移为主的下生上储式成油组合成藏条件次之。

To analyze the petroleum condition and hydrocarbon accumulation in the Leting sag of Bohai Bay basin, the Lower Tertiary petroleum system is studied. It is shown that there is plenty of mature source rock and large scale distribution of dark mudstone which has the ability of hydrocarbon-generation. Both the middle-lower Es^3 and lower Es^1 argillaceous rocks have excellent seal ability. There are two reservoir patterns： source below and reservoir above, self source-reservoir. In this sag, four traps are found： fault block or fault nose trap, lithologic trap, stratigraphic trap and complex trap. Channels for oil migration are as follows： sandstone, fault and unconformity surface. The formation of the Lower Tertiary petroleum system experienced three main stages, including uplifting and folding, faulting, and sedimentation. The Lower Tertiary petroleum system is evaluated based on the parameter of source rock potential. It suggests that the ＂self source-reservoir＂ by lateral migration has better oil accumulation conditions than the ＂source below and reservoir above＂ by vertical migration.