歧口凹陷异常压力对古近系烃源岩热演化的抑制作用及其意义

Overpressure Retardation of the Thermal Evolution of Paleogene Source Rocks and Its Significance for Petroleum Geology in Qikou Sag

沉积盆地流体动力学特征是盆地分析的主要内容,对烃源岩热演化及油气成藏具有重要的影响。以歧口凹陷为例,通过大量实测数据和分析化验资料综合分析,探讨了古近系中深层流体压力特征及对成烃演化的抑制作用,建立了超压背景下的烃源岩成烃演化模式,指出了超压存在的石油地质意义。研究表明,歧口凹陷中深层普遍发育异常高压,压力系数为1.2~1.6,属于＂正常地温梯度、异常高压＂环境,这种环境对古近系中深层烃源岩热演化具有明显的控制作用。超压的普遍发育对歧口凹陷中深层的液态烃下限、有效储层下限、油气保存及有效勘探深度都有十分重要的影响。

Fluid dynamic characteristics in the sedimentary basin are the main content of basin analysis,which has great significance on source rock thermal evolution and hydrocarbon accumulation.Taking Qikou Sag as an example,based on the analyses of measured data and experimental results,this paper discusses the fluid pressure characteristics and retardation of the thermal evolution of Paleogene source rock,and points out the significance for petroleum geology.An evolution model is established with over pressure background.Obvious overpressure retardation of deep source rock thermal evolution was found through the ＂normal geothermal gradient range but abnormal formation pressure＂geological terms,whose overpressure develops commonly in the main sag and slop zone,with the coefficients of the pressure range from 1.2 to 1.6.The overpressure commonly existing in Qikou Sag is significant for the cutoff value of liquid hydrocarbons,the lower limit of effective reservoir,oil and gas preservation and exploration depth.