下切谷的特征及油气地质意义

下切谷的形成是构造运动和海（或湖）平面共同作用的结果。下切谷具有典型的几何特征，因此它既可以作为低水位体系域时期沉积物运移的主要通道，又可以作为低水位体系域晚期碎屑沉积物堆积的主要场所。通常，下切谷内沉积物具有两种充填机制：当海（或湖）平面影响超过构造运动影响时，谷内沉积物堆积方式为“溯源堆积”，反之为“顺源堆积”。下切谷中极易形成四类隐蔽油气藏：透镜型岩性油气藏，侧向尖灭型岩性油气藏，地层超覆型岩性油气藏和断层-岩性复合型油气藏。因此，下切谷的研究具有非常重要的实际意义。

Characteristics of Entrenched Valley and Its Geologic Meanings

The formation of entrenched valley is the mutual effect of tectonic movement and sea (lake) level. The entrenched valley has typical geometry characteristics. Therefore, it can be not only the main migration channel for sediments during lowstand, but also the main place to accumulate clastic sediments at late period during low-stand. Generally, there are 2 filling mechanisms for the sediments in the entrenched valley: when the effect of sea (lake) level exceeds that of tectonic movement, the accumulation of sediments in the valley is headward accumulation; on the contrary, it is head-downward accumulation. In the entrenched valley 4 kinds of subtle reservoirs areeasy to be formed; lens type lithologic reservoir, strati-graphic overlap lithologic reservoir, lateral pinchout lithologic reservoir, and fault-lithology complex reservoir. So, it is significant to study the entrenched velley.