Abstract: Based on the consistency of pressure system within the same reservoir,the theoretical linear relationship between formation pressure and depth is currently used as an important criterion to determine the connectivity of sand bodies within the same sequence stratigraphic framework under normal pressure.However,the linear rule for determining sandbodies connectivity has its limitations due to the influences of high permeability and fluid heterogeneity of reservoir.A new method for connectivity analysis of sand bodies is proposed based on mathematical induction,established the inverse proportional function between pressure coefficient and depth of reservoir.The properties of inverse proportional function such as intersection,monotonicity,boundedness and symmetries provide us a way to explore the relationship between inverse proportional function and reservoir pressure system,and to further determine the connectivity of two or more sand bodies.With hydrostatic pressure data from more than 50 normal pressure reservoirs out of 7 oilfields in Bohai Sea whose connectivity have been confirmed by wells,we verified the relationship between the connectivity of sand bodies and the properties of inverse proportional function of pressure coefficient and depth.The following conclusions were made.① The function image being continuous and overlapping,monotonicity and asymptote being consistent,and symmetry axis being unique are the critical criteria for determining the connectivity of sand bodies within the same sequence stratigraphic framework;② The pressure coefficient is more sensitive and reliable than the linear function;③ The curvature of inverse proportional function is affected by reservoir permeability and fluid properties,thus overcomes the limitations of linear rule.

Key words: pressure coefficient, inverse proportional function, fluid heterogeneity, permeability, normal pressure reservoir, Bohai Sea