Using ultrasonic as a new approach for elimination of inorganic scales (NaCl): an experimental study

Abstract

Because inorganic scales reduce permeability near wellbores, they cause an additional pressure drop in this region (skin damage) and reduce production. NaCl precipitation, particularly in gas-producing wells, is one of the formation damage problems which impair the permeability. The use of backwashing water not only requires a large quantity of water, but is also inefficient. This study examined the effect of the ultrasonic waves in NaCl scale removal. Twenty core samples with different permeabilities were saturated with NaCl. After precipitation of NaCl within the cores, the samples were first subjected to water injection and then to water injection with ultrasonic wave radiation. At each stage, the permeability of cores was measured and recorded. Experimental results reveal that applying ultrasonic waves restores the permeability of cores more than water injection alone. In samples with permeability lower than 20, 30-100, 100-700 md and cores with permeabilities higher than 1000 md, ultrasonic waves recover permeability to 80, 42, 87 and 81%, respectively. In contrast, water injection alone improves permeability to 29, 18.5, 62 and 77%, respectively. The effect of these waves is much more obvious than water injection alone in low-permeability cores. SEM images from cores show that ultrasonic waves destroy the structure of deposits of sodium chloride. This phenomenon is due to propagation of these waves and the resulting temperature increase in the surroundings, which leads to the increased solubility of these scales. After exposure to ultrasonic waves, sodium chloride deposits inside the induced fractures of cores could be removed from the fracture, whereas water injection alone could not wash and remove the deposits from the fracture. According to the results of this paper, ultrasonic waves can be used as a novel and efficient technology in gas wells to remove inorganic scales in the near-wellbore region.

Recent applications of ultrasonic waves in improved oil recovery: A review of techniques and results

“…Results showed that while increasing the ultrasound frequency, only transducer 1-3 produced better cleaning effect as shown in Figure 5b, implying that higher frequency may have a minor impact on the deposited scales. Some of their findings were in agreement with the experimental results of Taheri-Shakib et al [27]. Taheri-Shakib et al [27] used ultrasound to treat NaCl scales and restore the near wellbore permeability damaged by the inorganic scales, while demonstrating the influence of core permeabilities.…”

“…Some of their findings were in agreement with the experimental results of Taheri-Shakib et al [27]. Taheri-Shakib et al [27] used ultrasound to treat NaCl scales and restore the near wellbore permeability damaged by the inorganic scales, while demonstrating the influence of core permeabilities. Some core samples from Iranian reservoirs with permeability ranges of less than 20, 30-100, 100-700md, and higher than 1000md were used to carry out the experiments.…”

Recent developments, challenges, and prospects of ultrasound-assisted oil technologies

“…Furthermore, combined water flooding and US treatment created wormholes in the KCl crystals which improved the scale withdrawal. Similar behavior of integrated water injection and US for the treatment of NaCl scales was reported by Taheri-Shakib et al [74] in a different study. They showed that the water flooding with US increased the permeability recovery as compared to water injection, with the enhancement reaching 51% in some cases.…”

“…There are several studies that have attempted to improve the permeability and pore structure of porous media which have been damaged, and hence, improve the oil recovery of the reservoir [71] , [72] , [73] , [74] , [75] , [76] , [77] . Some of these studies have focused on the removal of inorganic salts causing formation damage in the near wellbore region ( Fig.…”

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Fig. 10 Removal of inorganic scales in near wellbore region with US: a Ultrasonic flooding set-up (f = 22 kHz, Power = 1000 W) [74] b I Unplugging of sodium chloride deposit within a core sample through the injection of water with and without US treatment [74] II Unplugging of potassium chloride deposit within a core sample through the injection of water with and without US treatment [73] III Saturated Core Sample with Potassium Chloride Before Treatment [73] .

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