Study On Conduction Mechanism And Conduction Model For Tight Sands

The tight sand reservoirs are characterized by low porosity,low permeability,high shale and calcite content,and complex pore structure.These characteristics make the conductance mechanism of tight sandstone reservoir more complicated than that of conventional reservoir.Few of existing saturation models can describe the influence of shale,calcium and pore structure on the conductivity law of tight sands,which increases the difficulty of saturation evaluation of the tight sandstone reservoir.Firstly fifteen tight sandstone cores have been selected in this paper.The rock electrical experiment,grain size analysis,carbonate analysis,mercury penetration experiment and nuclear magnetic resonance experiment are carried out for the fifteen cores.Based on the experimental data of fifteen cores,the conductivity law of tight sandstone is studied,and the three main factors that influence the conductivity law of the reservoir are analyzed.The three factors are shale cementation,calcareous cementation and pore structure.It is shows that the conductivity of rock increases as the shale content increases,calcite content decreases and the pore structure is better.Based on the characteristics of tight sandstone reservoir and the experimental research results of its conductivity law,considering the three main factors on tight sand conductivity,then two conductivity models of tight sandstone reservoir are established by combining the effective medium conduction theory with the pore geometric conduction theory and the connectivity conduction theory respectively.The pore geometric conduction theory and the connectivity conduction theory are used to describe the influence of pore structure on rock conductivity,and the effective medium conduction theory is used to describe the influence of shale and calcareous cementation on rock conductivity.The theoretical validation of two conduction models is carried out by changing single parameter,the result shows that the two models can correctly describe the influence of shale cementation,calcareous cementation and the variation of pore structure on the conductance mechanism of tight sandstone,and the theoretical law predicted by the proposed models are both consistent with the experimental rule.The experimental verification of two proposed models is also carried out with measured data in this paper and optimization method.It concludes that two conduction models for tight sands proposed in this paper can describe the conductivity law of tight sands.Compare the water saturation calculated by the two models with the analyzed saturation of the sealed coring well,the mean absolute error of the two proposed models is 5.8 percent and 5.7 percent respectively.The actual logging data of tight sandstone reservoir is processed and interpreted with the two proposed models,the interpretation results are in good agreement with the test oil results.The above results show that the two proposed conduction models can be well applied in the well logging interpretation and evaluation of tight sandstone reservoirs.