Verification of the carbonate double-porosity conductivity model based on digital cores

Abstract

Carbonate reservoirs have complicated pore structure and reserving space, and the pore size distribution ranges are very large. Pore structure distributions represent a bimodal or trimodal state, which is also accompanied with an obviously non-Archie phenomenon. Double- and triple-porosity conductivity models based on the classification of pore dimensions were of a good coincidence with the non-Archie behavior. We have adopted digital core technology to verify the carbonate double-porosity conductivity model. Also, many rock-physical experiments and numerical simulations were performed. Through CT scanning under appropriate resolutions, macro- and micropore digital cores, which could respectively characterize the different pores, were constructed for the carbonate samples. Then the superposition method was further applied to construct the superposition digital cores, which can characterize different pores simultaneously. To quantitatively analyze and compare the effect of basic structural parameters to different digital cores, the pore network model was extracted using the Lee-Kashyap-Chu algorithm to furtherly verify the differences between scanning resolutions and pore selection characterization. In terms of qualitative validation of the double-pore conductivity model, the electrical characteristics and resistivity index (RI) under different saturations were simulated using the finite-element method and the lattice Boltzmann method. The RI curves indicated that the calculation results from the double-pore conductivity model based on a digital core are coincident with the numerical simulation results. In other words, the digital core technology can verify the double-porosity conductivity model effectively.