The Impact of Concentration and Size of Oil Droplets Accompanied by Water on the Reduction of Injectivity in the Produced Water Re-Injection Process

Document Type : Research Paper

Authors

1 Department of Petroleum Engineering , School of Chemical and Petroleum Engineering, Shiraz University,Iran

2 National Iranian South Oilfields Company (NIOC), Ahwaz , Iran

Abstract

Produced water, along with oil, constitutes one of the largest wastewater outputs from various industries. One method of managing this water is by reinjecting it into oil reservoirs to enhance pressure. However, the presence of multiple pollutants risks damaging the formation. Notably, oil droplets within this water significantly contribute to structural damage by clogging the porous medium, reducing injectability, and increasing injection pressure. In this research, we created synthetically produced water containing oil droplets emulsified in water. Through microscopic investigations and micromodel tests, we examined the impact of oil concentration on the size of the emulsion droplets and the resultant reduction in porosity. The microscopic tests analyzed oil concentrations and salinities ranging from 30 to 100 drops and 4 ppm to 32 ppm, respectively, with oil concentrations of 70 and 150 drops injected up to a pore volume (PV) of 35. The microscopic observations revealed that an increase in oil concentration correlates with a rise in the size of oil droplets. Specifically, increasing the oil concentration from 30 to 100 drops resulted in the average droplet size growing from 1.56 to 1.98 micrometers. In the micromodel tests, we calculated the occupied porosity due to trapped oil droplets and found that the ratio of final occupied porosity to initial porosity decreases with increasing injection volume and oil concentration. For instance, with an oil-in-water emulsion containing 150 drops of oil, as the injection volume increased from 7 PV to 35 PV, this ratio decreased from 0.875 to 0.642. Moreover, injecting 35 PV of synthetically produced water with two concentrations of 70 and 150 drops of oil resulted in a reduction in the porosity ratio from 0.914 to 0.642, further confirming the potential for formation damage. These findings quantitatively underscore the necessity of removing oil droplets from produced water before injection into wells to prevent decreased injectivity.

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References

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Journal of Petroleum Research
Volume 34, 1403-3 - Serial Number 136
September and October 2024
Pages 16-28

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