Intensification of Acid-Induced Sludge Formation During Stimulation of Asphaltenic Oil Reservoirs: an Experimental Study

Document Type : Research Paper

Authors

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

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

Abstract

Acidizing process increases the productivity of oil and gas wells, but its improper design can cause the formation of acid-induced sludge as a serious formation damage. There is a main question that is it possible to control the sludge through regulating operational parameters instead of using additives. In this research, the effect of main parameters such as crude oil-acid mixing speed (as a representative of acid injection rate), acid-crude oil mixture ratio (as a representative of acid injection volume), temperature, and crude oil specification (colloidal instability index and asphaltene content) were examined on sludge formation. Standard compatibility test RP-42 with some modification was utilized for this purpose. In addition, in order to study the effect of viscosity, some experiments were done using synthetic oil prepared by diluting the crude oil with toluene and heptane. Moreover, the results showed the noticeable effect of mixing speed, increasing it from 500 to 1500 rpm was led to increase the amount of sludge in three crude oil samples A, B and C by 2.1, 1.58 and 1.49 times, respectively. In addition, it can be attributed to create more interface area of acid and crude oil droplets for higher shears. Also, by changing the acid mixture ratio from 0.2 to 0.8 in crude oil samples A, B and C, caused to intense the sludge deposition by 1.27, 2.37 and 3 times, respectively. Furthermore, increasing the temperature from 30 to 85 °C produced similar behavior for sludge formation by increasing 2.7, 1.57 and 1.84 times, respectively. The crude oils have been shown different tendencies for sludge formation. The sample A has formed the sludge 6.1 and 37.7 times higher than B and C oils, respectively. Ultimately, the composition of sample A with higher colloidal instability index and asphaltene content leads to higher tendency for sludging. In addition, in order to investigate the effect of oil viscosity exclusively, the results of crude oil B and its synthetic oil showed the sludge reduction due to 1.68-fold decrease of viscosity in the prepared synthetic oil.

Keywords

Main Subjects

References

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Journal of Petroleum Research
Volume 34, 1403-6 - Serial Number 139
January and February 2025
Pages 128-140

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