Numerical experiments for the conductive properties of saturated rock

Abstract

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 equation. 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.electrical transport property, non-Archie phenomenon, fluid saturation, porous media, Lattice Boltzmann methodThe main purpose of reserves evaluation is to quantify the content of oil and gas in reservoir. And the comprehensive interpretation of well logs has been an important approach for the reserves evaluation. The Archie's equation [1] , as a basic formula for calculation of fluid saturation, has played a critical role in the interpretation of well logs since 1942.With the development of oil production, most reservoirs of oil field in China are complex with low porosity and permeability, which are difficult to develop. A lot of non-Archie phenomena, the relationship of resistivity index to water saturation (I-S w ) being a curve in log-log scale instead of a straight line as described in Archie's equation, have been observed in rock experiments of those complex reservoirs. The non-Archie phenomenon is important for its critical effects on quantifying the reservoir content of oil and gas preciously. For the non-Archie reservoir, the error of the water saturation calculated with Archie's equation for evaluating fluid content would be high to increase the difficulty in reducing the risk of oil exploration. Therefore, the key point for improving the reservoir evaluation and the saturation calculation is to study the nature of nonArchie phenomenon and construct a new model for I-S w .Many researches have been done for revealing the nature of non-Archie and constructing the appropriate model. Li [2] developed a mixture conductive model of parallel and series through the research of mineral and fluids in rock slice to construct the model of I-S w based on the theoretical analysis. Jing's [3] research indicated that the conductive mechanism of rock is extremely complex, and the non-Archie phenomenon had been observed in both the oil-wetted rock and the formation of low resistivity with complicated pore ...