古油势和低序次断层与砂岩透镜体圈闭含油性的关系——以东营凹陷牛庄洼陷沙三段中亚段为例

Relationship between paleo-fluid potential and sub-seismic faults and hydrocarbon saturation in lenticular sand body traps:case of lithological reservoirs in Niuzhuang sag,Dongying depression

对于岩性油气藏,除了相和生烃强度之外,古油势和低序次断层也是极为重要的控藏因素。运用流体包裹体测试方法,通过东营凹陷牛庄洼陷沙三段中亚段三角洲前缘滑塌浊积砂岩岩样分析,确定了砂岩透镜体圈闭的3期油气充注时间,分别为34～24,13.8～8和8～0 Ma,其间24～13.8 Ma为成藏间歇期。结合对低序次断层的解释,由样品流体包裹体古压力恢复和古油势计算结果可知,古油势和隐蔽输导体系对砂岩透镜体圈闭含油性具有耦合控制作用;第3期古油势相对低势区及低序次断层的相对发育,提高了牛庄洼陷沙三段中亚段砂岩透镜体油藏的含油饱和度,表明断层不是岩性圈闭成藏的充要条件,其既有利于圈闭成藏,也可破坏圈闭成藏。

The lithological reservoirs are the most realistic and potential exploring domain for a considerably long time in China. Except microfacies and intensity of hydrocarbon generation,paleo- fluid potential and sub-seismic faults are able to control the hydrocarbon saturation in lithological traps as well.The systematic analysis tools,such as homogenization temperature,microbeam fluorescent spectrum analysis and thermodynamic modeling of paleo-fluid pressure,of fluid inclusion have been employed in this study.The measurements of 187 fluid inclusion samples from the collapsing turbidites of delta frontiers of the middle section of Sha 3 member of Niuzhuang sag in Dongying depression allow us to figure out three orders of oil charging:034-24 Ma,(2)13.8- 8.0 Ma,?8.0-0 Ma.There is a dormant period for hydrocarbon migration and accumulation between 24 and 13.8 Ma.The results of fluid pressure coefficients and potential by fluid inclusion thermodynamic modeling,integrated with sub-seismic fault interpretation in 3D seismic profiles,indicate the coupling control of fluid potentials and sub-seismic faults on the hydrocarbon saturations of the lenticular sand bodies.For example,the third order of oil charging,the hydrocarbon saturations increase at the relatively lower potential and sub-seismic faults developed traps in Niuzhuang sag.This phenomena tells us that sub-seismic faults are not essential for lithological reservoirs,and the relatively lower fluid potential lithological traps are always favorable for hydrocarbon migration and accumulation.