Influence of wettability upon IP characteristics of rocks in low porosity and low permeability reservoirs

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The induced polarization characteristics of oil-bearing rocks in reservoirs can play a key role in reservoir evaluation in the stage of oil and gas exploration and development. With the continuous advancement of oil and gas exploration, low porosity and low permeability reservoirs have become important objects of exploration and development, but the research on the response mechanism of complex resistivity of reservoir rocks is still not deep enough. In this study, the reservoir rocks with low porosity and low permeability were taken as the research object. By measuring the complex resistivity of oil-bearing rock samples under two different wetting conditions, the amplitude and phase of complex resistivity of reservoir rocks under different oil saturation were obtained. The MGEMTIP model was used to invert the low-frequency data and calculate IP parameters such as DC resistivity and polarizability to study the induced polarization characteristics of reservoir rocks under different oil saturation conditions. The results showed that the DC resistivity of reservoir rocks increased with the increase of oil saturation, and the trend was influenced by the conductivity of oil-water mixture and rock surface. When the oil saturation was about 45%, for the same rock, with the increase of contact angle before and after aging, the DC resistivity had a certain downward trend. Under low oil saturation, the polarizability of relatively hydrophilic rocks tended to increase with the increase of oil saturation. After the wettability was changed, the reservoir rocks were relatively hydrophobic, and the polarizability first decreased with the increase of oil saturation, and then under the influence of Maxwell-Wagner polarization, the polarizability of the rocks increased with the increase of oil saturation. Therefore, the characteristics of induced polarization of reservoirs with different wettability can provide physical basis for oil reservoir exploration, development and evaluation.