Modeling of changes in the permeability of the near-well zone of an oil reservoir during filtration of highly mineralized salt solution NaCl

UDK: 622.276.1/.4
DOI: 10.24887/0028-2448-2021-2-82-85
Key words: near-well zone, sodium chloride, pore space, mathematical model, permeability, colmatation
Authors: L.A. Gaydukov (Oil and Gas Research Institute of RAS, RF, Moscow)

When saline reservoirs are flooded with low-mineralized water in the near-well zone of producing wells, conditions may arise for intra-reservoir precipitation of solid salt sediment NaCl, which leads to colmatation of the pore space, reducing the permeability and productivity of wells. The effects of self-colmatation due to the precipitation of NaCl salt sediment in the pore space during flooding of salinized strata with low-salinity water is characteristic of a number reservoirs in Eastern Siberia. A mathematical model is proposed that allows us to calculate the technogenic change in reservoir permeability due to the deposition of solid NaCl particles, initiated by the effect of oversaturation of the filtered salt solution due to water evaporation at the border with the gas phase when the pressure decreases below the saturation pressure in the oil-gas system. It is shown that the intense precipitation of solid salt sediment and the corresponding damage of the reservoir permeability occur at a distance of ~ 1 m from the borehole wall. In the remote part of the near-wellbore zone and in the interwell space, the influence of this process on filtration flows in the formation can be neglected. Calculated model dependences of the dynamics of changes in the normalized permeability on the wellbore wall and the skin factor at different values of the reaction rate of the formation of solid sediment from a salt solution are obtained. The results of the assessment of the parameters of the technologically damage near-wellbore zone are basic information for the preparation of designs of effective geological and technological measures to restore the productivity of wells. In particular, they allow determining the optimal volume for flushing the near-wellbore zone with fresh water and correctly planning the timing of its implementation.


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