关键词: 油井前兆异常, 动力学成因, 东营凹陷, 地震, 陡坡带, 断裂体系

Abstract: The fault systems in the steep-slope zone of Dongying depression consist of NEE-and NWW-trending faults.The faults are deep and narrow,having dip angle of above45癮nd a throw of more than 3000m.The modern stress field in the steep-slope zone is currently very active.As the petroleum resources in this zone are very abundant,a great deal of oil wells have been drilled.All this specific geological conditions provide the foundation to seek for the relation of precursory anomaly in oil well to seismic activity and to discuss the dynamic genesis of this anomaly. This paper presents the analysis of the relationship between the precursory anomaly and earthquake observed in several tens of oil wells in steep-slope zone of Dongying depression in the past 3 decades.The results of analysis show that the precursory anomaly observed in oil well is very complex.Some wells may exhibit precursory anomaly,and the other may not.The type of anomaly is also very complicated.It might be a positive or negative anomaly,and a short-term or long-term anomaly,while the amplitude of anomaly is variable in different wells. Furthermore,the dynamical genesis of oil well precursory anomaly is discussed.It is generally accepted that the generation of earthquake is the process of transformation and adjustment of regional stress field.The concentration of stress under a specific geological condition is the main factor that causes the precursory anomaly in oil well.As a lot of faults and lateral discontinuity of strata occur in the steep-slope zone of Dongying depression,the zone becomes stress concentration zone during the development process of earthquake,so precursory anomaly of earthquake is easy to occur in oil well of this zone.The precondition of the occurrence of precursory anomaly depends on the facts that the stress change is translated into the change of pore pressure.If the oil well is located in compression area during the development process of earthquake,the positive anomaly will occur in the well,otherwise the negative anomaly will occur.The amplitude of anomaly depends on the variation amplitude of pore pressure.Precursory anomaly of earthquake in oil well is affected synchronously by various factors,such as the change of stress,tectonic setting,and the property of stratum etc,so the analysis of the dynamic genesis of precursory anomaly is critical to the understanding of the relationship between earthquake and oil well precursory anomaly.

Key words: oil-well precursory anomaly, dynamic genesis, Dongying depression, earthquake, steep-slope zone, fault system