Study on Connectivity Model for Low Porosity and Permeability Sand Reservoirs in Daqing Placanticline

Studied are the reservoir characters in F formation of Daqing placanticline,where the reservoir is characterized by low porosity,low permeability,high shale content,more microscopic capillary pore,complex pore structure and high irreducible water saturation.Based on three conducting components of shale,irreducible water and free water in F formation,and the features of connectivity theory,the reservoirs in F formation are divided into matrix phase,free fluid phase and clay phase.After analyzing the effect of the conductance paths of clay water,free water and irreducible water on rock conductivity,it is found that the three conducting phases have different conductivity exponents,and the conductivity of each phase may be calculated using connectivity equation.Finally,total rock conductivity can be related with the conductivities of three phases by mixing conductivity law,and the connectivity model in F formation of Daqing placanticline is established.After that,the influence of water connectivity correction index on the conductivity of the rock is discussed,and the relationship of conductivity exponent of each phase is analyzed theoretically.Therefore,it is concluded that the conductivity exponents of matrix phase and clay phase are either less than or equal to that of the free fluid phase.Also,the conductivity exponent of each phase is determined from core experimental data with an optimization technology.Comparison of core-analyzed water saturation in sealed coring well with well test results shows that the connectivity model can be used in quantitative evaluation of low porosity and permeability shaly sand reservoirs in F formation.