二连盆地异常低压成因机理探讨

二连盆地主要凹陷的压力场基本上都呈现为异常低压特征,地层压力系数大多小于1.0,但用现有的异常低压成因机理来解释二连盆地的异常低压却遇到了困难,为此将该区异常低压埋藏史曲线与异常高压盆地(渤海湾盆地和莺歌海盆地)的埋藏史曲线进行了对比。结果表明,二连盆地在晚白垩世具有长达50~60 Ma的沉积停滞期,长时期的沉积停滞可能是二连盆地异常低压的主要原因。沉积停滞条件下既不会出现欠压实现象,也无法产生异常高压,但却造成地层具有较高的压实程度,使得后来再次沉积深埋时,压实作用受阻,上覆负荷过多地加载在了岩石骨架上,流体压力相对变小,形成异常低压。

Investigation on genetic mechanism of subnormal pressure in Erlian Basin

The pressure field of the sags in Erlian Basin shows characters of basically subnormal pressure, and the pressure coefficients are most less than 1. And it is difficulty to interpret the genetic mechanisms of subnormal pressure of Erlian Basin with conventional genetic mechanisms. Compared with the burial history of the basins of Yinggehai Basin and Bohai Bay Basin which dominated with overpressure, it is found that Erlian Basin underwent a long depositional stagnancy stage that almost extends 50 - 60 Ma in later Cretaceous, and this may be the key factor that leads to presently subnormal pressure environment. Under depositional stagnancy stage, neither undercompaction nor overpressure can be generated, but the subsurface stratus experience .continuous compaction which prevents the subsequent compaction caused by the overloading process in the following sedimentary periods. In the following sedimentary process, because the overburden mainly exerts on the matrix of the rock and the pressure of the inner contained fluid is concealed out, the subnormal pressure is formed.