On Conductivity Model with Continuous Clay Distribution in Low Porosity and Low Permeability Shaly Sand Reservoirs

Research on conductance law in low porosity and low permeability shaly sand reservoirs is one of the key methods to improve the accuracy to calculate saturation.In this paper,based on symmetrical effective medium conductance theory,a new conductivity model is proposed for low porosity and low permeability shaly sand reservoirs with continuous clay distribution and high capillary bound water in pores.In the model the effect of continuity of clay distribution on shaly sand conductivity is considered.By theoretical analysis,it is found that the conductivity of formation increases and resistivity index reduces as clay distribution in pores occurs from discontinuity to continuity.Clay content cutoffs can be estimated for cubic clay-covered grain arrangement model and rhomboidal clay-covered grain arrangement model while the single-layer clay or doublelayer clay occurs around the grains.Also,validation of experimental data of Group 2from Waxman and Smits shows that the continuity of clay distribution changes with the clay content.The interpretation result for log data proves that the proposed model can describe the conductance law in low porosity and low permeability shaly sand reservoirs.