曲堤断鼻应力成因机制及对构造和油气的控制作用

Stress-Mechanism of Qudi Faulted Nose and Its Controlling on Tectonic Structure and Oil Distribution

曲堤断鼻是济阳坳陷一个大型中浅层富油断鼻构造,受张、扭、拱应力复合作用形成。古近纪以来NW向拉张应力和NE向右旋走滑扭应力持续作用使其在基底鼻形背景上形成NE走向的"两阶两垒夹一堑"构造格局,古近纪晚期以来叠加的基底块体差异性拱张又使其形成NW向地垒型"鼻脊带"。不同应力机制对油气有不同控制作用,张应力作用下断鼻主体区断层活动弱但油气丰度高,东西两翼断层活动强但油气丰度低;扭应力作用下断层压扭段附近油气富集,张扭段附近含油性变差;拱张应力作用使油气作垂向大幅疏导从而形成系列新断块圈闭并形成"鼻脊区"最有利聚油场所。断鼻内不同构造部位因应力作用不同从而形成不同构造单元并具有不同含油气丰度特征,约95%已探明储量赋存于张扭形成的"两垒夹一堑"断鼻主体区内,其中近60%已探明储量又富集于基底上拱"鼻脊区",显示构造高部位是控油的主要因素。

Qudi faulted nose is a big-faulted nose structure with rich oil in shallow layer of Jiyang sag, which was formed under the multi-stress functions including the tensional, torsional and arching. Qudi faulted nose was formed underground the continuous function of NW tensile stress and NE dextral slip tor- sional stress since Paleogene with a tectonic pattern of ＂one graben, two horsts and two fault steps＂, and finally the NW ＂ridge zone＂ was formed since the late Paleogene under the ＂base block differential arching movement＂. Different stress mechanism has different effects on oil and gas distribution. Under tension stress, the main area of the faulted nose has a weak faulting activity and an oil-enrichment and the east and west wings have a strong faulting activity with poor oil accumulation. Under torsional stress, the shearing- compressive part of the fault is favorable for oil accumulation and the shearing-tensional part is unfavor- able. The arching stress made oil migrate vertically on a large scale and lead to the formation of the ＂ridge zone＂ with series of new faulted traps, that is the most ideal accumulating area. The stress function differs with tectonic parts of fault and creating different tectonic units with different accumulation characters. Ac- cording to the statistic, 95% of known reserves is distributed in the two horsts and one graben units, and among which 60% is accumulated in the ＂ridge zone＂ unit, which indicates that the structural high is the most important factor for oil and gas accumulation in the Qudi faulted nose.