Avaliação de dano em meios porosos decorrentes da reinjeção de água produzida

Abstract

The rise in oil production has led to a growth in the generation of produced water, which can be reused as an injection fluid in oil reservoirs to enhance oil recovery. However, this water contains oil droplets, dispersed and dissolved solids, bacteria, and other contaminants that can negatively affect the formation permeability near the well. Many studies report a reduction in rock permeability due to the retention of emulsified oil droplets during the reinjection of produced water, but the formation damage mechanisms caused by each contaminant are still not completely known. For an accurate analysis of these processes, it is fundamental that the emulsions maintain their stability during the injection test in porous media. Therefore, this work aimed to investigate the stability of these emulsions and propose a new approach to evaluate the impact of each component in the reduction of rock permeability. The emulsions were prepared by varying the surfactant concentration (0.0025 to 0.0100 wt%), stirring speed (9.000 to 21.000 rpm) and oil concentration (0.0050 to 0.0500 wt%). Subsequently, coreflooding tests were conducted on Berea sandstone samples with different permeabilities and emulsions with varying volumetric oil concentrations ranging from 0.01 to 0.05 wt%, evaluating the permeability drop in three stages of injection: (I) brine; (II) brine + surfactant; (III) stage II + oil. Emulsions with interfacial tensions over 10.6 mN/m remained stable and unimodal throughout the analyzed period. Coreflooding tests showed that brine injection resulted in a permeability drop of 7% to 20% in rocks with permeabilities approximately ranging from 20mD and 120 mD, respectively. Following this, surfactant injection showed a permeability decrease ranging from 30% to 37% in the first section. Tests with emulsions containing oil concentrations of 0.05 wt% and 0.01 wt% caused a reduction to around 65% of the permeability in low-permeability rocks. Damage from the retention of oil droplets was more significant in all scenarios studied, especially in rocks with low permeability. The results indicated that emulsion components contributed to the reduction of the rock permeability, highlighting the importance of considering them to enhance experimental model and mathematical modeling of damage caused by different permeability reduction mechanisms.