Addressing sand production in oil and gas wells is a major challenge, and various methods have been devised to tackle it. However, many of these methods have drawbacks like high costs, slower production rates, or potential damage to the wellbore. Recently, researchers have been exploring enzyme-induced carbonate precipitation (EICP) solutions as a solution to consolidate loose sand around the wellbore. Typically, urease is used in EICP solutions to catalyze the hydrolysis of urea. However, due to its costliness, there's a need for alternatives. Alpha amylase has emerged as a potential substitute for urease in EICP solutions. Previous studies have investigated its effectiveness but haven't determined the optimal concentration for complete urease replacement or focused on sand consolidation. Our research successfully identified the optimal concentration of alpha-amylase to entirely replace urease in EICP solutions while achieving effective sand consolidation and maintaining permeability. We comprehensively studied the microstructure and crystal of the precipitates formed SEM. Additionally, sand pack flooding tests were conducted to assess the permeability of the consolidated sand samples.
To understand how alpha amylase affects EICP solutions, we prepared a total of 10 solutions for our investigation, among them solutions 1 through 9 are cured at a temperature of 70°C and solution 10 is cured at a temperature 120°C. The first solution served as our baseline, containing 3 g/l of urease enzyme. Solutions 2 through 5 were prepared with both urease enzyme (at a fixed concentration of 1.5 g/l) and varying concentrations of alpha amylase (1.5, 5, 10, and 15 g/l, respectively). Solutions 6 through 9 consisted solely of alpha amylase (without urease enzyme), with concentrations of 3, 5, 10, and 15 g/l. For solution 10, we added 3 g/l of AN 125 (copolymers of AM-AMPS) to solution 7. The solution prepared with 15 g/l of alpha amylase along with 3 g/l urease, showed the highest strength at 1,419 psi. Solution containing 5 g/l of alpha amylase only, exhibited the highest strength at 1,645 psi. Comparatively, the strength of the consolidated sample prepared from the baseline EICP solution was measured at 370 psi. Thus, it's clear that adding 5 g/l of alpha amylase provided the highest strength among all the solutions tested. EICP solution with AN 125 copolymer was cured at high temperature, the consolidated sample showed a strength of 450 psi. The solution with 5 g/l alpha amylase demonstrated the highest strength, further tests were conducted to assess its permeability. It was found that there was only a 20% reduction in permeability after consolidating a sand pack using this solution. This research delivers a novel finding by successfully identifying the optimal concentration of alpha amylase to entirely replace urease enzyme in EICP solutions, enabling effective sand consolidation while maintaining high permeability.
