辽河盆地大民屯凹陷流体压力特征

大民屯凹陷是辽河断陷内4个下第三系凹陷之一。在综合利用钻井、试井及地震等资料的基础上，系统研究并论述了大民屯凹陷流体压力特征。基于57口井的声波测井资料，凹陷内泥岩压力特征可区分为正常压力、异常压力或强超压等类型；根据152口井391个点的压力测试数据，凹陷内产油层段的压力梯度多接近于1；利用公式法模拟计算了47条地震剖面的流体压力、剩余压力及压力系数的分布特征，凹陷内剖面压力系统自上而下一般由正常压力、弱超压和强超压3部分组成。此外，还根据流体压力演化的基本原理及钻井、岩性与试井等实际资料，模拟恢复了大民屯凹陷的压力演化史，其可划分为超压原始积累、超压部分释放及超压再积聚3个阶段。总体上，大民屯凹陷的超压强度低于渤海湾盆地其他地区的超压强度。

CHARACTERISTICS OF FLUID PRESSURE IN THE TERTIARY DAMINTUN SUB-BASIN OF LIAOHE BASIN IN NORTH CHINA

The Damintun sub-basin is one of the four sub-basins in the Liaohe basin in North China, and regarded as a rift basin initiated in the Paleogene. Synthesizing the data from boreholes, well tests and seismic surveys, the characteristics of pressure of the Damintun sub-basin are discussed in detail.From the data of sonic logs in 57 wells, shale in the Damintun sub-basin could be of normally pressured, overpressured or highly overpressured characteristics. From 391 pressure measurements from 152 wells, pressure-depth gradient in oil-producing intervals is near to unity in general. The fluid-pressures, excess pressures and pressure coefficients in 47 representative seismic profiles were predicted using seismic methods. The resultant pressure profiles showed normal pressure, slight overpressure and intense overpressure increasing with depth. Using the basic principles of fluid pressure evolution and data from drilling, lithology and well tests,the pressure evolution in profiles was restored. It showed that the pressure evolution can be divided into three stages of initial overpressure accumulation,partly overpressure dissipation and overpressure re-accumulation. The intensities of abnormal pressures in the Damintun sub-basin were less than those in other areas in the Bohai Bay basin.