论等效深度法预测地层压力存在的问题

On the problems of predicting pore pressure by equivalent depth method

等效深度法是一种基于泥页岩欠压实理论预测地层压力的方法,认为同一口井中声波速度或体积密度相等的岩石有效应力相等,由泥页岩正常压实趋势线与地层声波时差或速度偏离来判断地层是否超压,并且根据偏离程度估算地层压力。在石油勘探开发实践中,等效深度法预测地层压力存在疑问和不确定性。从石油地质学和岩石物理学的角度剖析等效深度法预测地层压力的理论依据,认为等效深度法预测地层压力受地层岩性的影响,并且指出了等效深度法预测地层压力的不确定因素和适用条件,为声波速度和地震波速度预测地层压力提供进一步的理论依据。

The equivalent depth method is a method to predict the formation pressure based on undercompaction the- ory of shale or mud, It is thought that the effective stress of the porous rock which have same sonic velocity or bulk density are same in borehole, the overpressure or not is determined by the deviation of between the normal compac- tion trend line of shale or mud and the interval transit time or velocity of the rock, and the formation pressure is es- timated by using the degree of deviation. The prediction of formation pressure by the equivalent depth method is doubtful and uncertain in the oil exploration and development.In this paper, we dissect the basis of the equivalent depth method for predicting pore pressure from the point of view of petroleum geology and petrophysics, and find that the equivalent depth method is affected by the lithology, and also point out the uncertain factors and applicable conditions for predicting pore pressure by the equivalent depth method, which provides a theoretical basis for pre- dicting pore pressure by acoustic velocity and seismic velocity further.