Abstract

—The potentialities of studying rock wettability by X-ray core tomography are considered using Visean terrigenous reservoirs of the Solikamsk depression as an example. The studies included comparison of the tomograms of core samples in a dry state and saturated of sodium iodide solution, which acts as a radiopaque analog of formation water. Differences in impregnation of the core samples, characterizing their wettability, have been established. According to the tomography data, in the hydrophilic samples the solution filled all pores, except for a small portion of the largest ones. In the hydrophobic samples, there was no impregnation of both small and large pores in the central zone. Based on the tomograms, the rocks were divided into groups by their wettability: absolutely hydrophobic, with strong signs of hydrophobicity, with signs of hydrophobicity, and hydrophilic. Comparison of the results of tomography with the standard approach showed that the Tulbovich method commonly used for the study area does not fully reflect the rock wettability.

Comparison of the results of core tomography and study of thin sections with the results of electrometric logging shows their good agreement. The rocks with absolute hydrophobicity established by tomography have an anomalously high electric resistivity, >1000 Ohm∙m, and the rocks with signs of hydrophobicity, >120 Ohm∙m. For the hydrophilic intervals, the electric resistivity values are significantly lower, from 17 to 100 Ohm∙m.

Thin sections of the core samples were studied. Their microscopic analysis has shown a higher content of organic matter in the hydrophobic rocks as compared with the hydrophilic ones. Few exceptions might be due to the study of only local thin sections of the samples.

Thus, rock wettability can be monitored by electrical methods, especially lateral logging. The results of the assessment of rock wettability by core study and well logging can be compiled for the exploration of Visean deposits of the Solikamsk depression. Geological models constructed with regard to the recognized zones of hydrophilic and hydrophobic reservoirs can be effectively used to optimize exploration of deposits, especially reservoir flooding.

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