Numerical simulation of non-Archie electrophysical property of saturated rock with lattice Boltzmann method

The electrophysical property of saturated rocks is very important for reservoir identification and evaluation. In this paper, the lattice Boltzmann method （LBM） was used to study the electrophysical property of rock saturated with fluid because of its advantages over conventional numerical approaches in handling complex pore geometry and boundary conditions. The digital core model was constructed through the accumulation of matrix grains based on their radius distribution obtained by the measurements of core samples. The flow of electrical current through the core model saturated with oil and water was simulated on the mesoscopic scale to reveal the non-Archie relationship between resistivity index and water saturation （I-Sw）. The results from LBM simulation and laboratory measurements demonstrated that the I-Sw relation in the range of low water saturation was generally not a straight line in the log-log coordinates as described by the Archie equation. We thus developed a new equation based on numerical simulation and physical experiments. This new equation was used to fit the data from laboratory core measurements and previously published data. Determination of fluid saturation and reservoir evaluation could be significantly improved by using the new equation.

Investigation of effects of clay content on F-Ф relationship by Lattice gas automation using digital rock model

The Lattice Gas Automation （LGA） method, which is improved by introducing a reflection coefficient for the border between phases to show its effect on current path, is used in this paper to simulate the current flow in digital rock for investigating the effects of clay content and clay distribution types on the relationship between formation factor（F） and rock porosity（φ）. The digital rock model is constructed by simulating a natural deposit of matrix particles with different shapes and radius. Based on the simulation results, it was found that both dispersed clay and laminated clay can lead to a non-Archie relationship of F-φ. The non-Archie effect of laminated clay on the F-φ relationship was more significant than that of dispersed clay. Moreover, a realistic model is developed in this work for quantitatively describing the effect of clay content （Denoted as Vsh） on parameters a and m. These study results have further demonstrated the validity of LGA in study of electrical transport properties at a pore scale.

Numerical Experiments of Pore Scale for Electrical Properties of Saturated Digital Rock

The two dimensional Lattice Gas Automation (LGA) was applied to simulate the current flow in saturated digital rock for revealing the effects of micro structure and saturation on the electrical transport properties. The digital rock involved in this research can be constructed by the pile of matrix grain with radius obtained from the SEM images of rock sections. We further investigate the non-Archie phenomenon with the LGA and compare micro-scale numerical modeling with laboratory measurements. Based on results, a more general model has been developed for reservoir evaluation of saturation with higher accuracy in oilfield application. The calculations from the new equation show very good agreement with laboratory measurements and published data on sandstone samples.

Numerical experiments for the conductive properties of saturated rock

The reservoir evaluation as a key technology in oil exploration and production is based on the electrical transport property (ETP) of saturated rock that is described in a mathematical form with Arhcie’s equa-tion. But there have been increasing cases observed in many researches indicating that the ETP is non-Archie especially for the complex reservoir with low porosity and permeability. In this paper,the numerical experiments based on the Lattice Boltzmann method (LBM) have been employed to study the effect of porous structure and fluids on the ETP for revealing the nature of non-Archie phenomenon in micro-scale. The results of numerical experiments have proved that the saturation exponent n is a function of water saturation and porosity instead of being a constant in Archie’s equation. And then,a new formula has been developed for the EPT through combining the result of numerical simulation with that of laboratory measurements. The calculations from the new formula show very good agreement with laboratory measurements to demonstrate the efficiency of the new formula over the conventional methods in non-Archie rock.