Bottle test and tube-blocking test are two major methods to estimate the minimum inhibitor concentration (MIC) for scale inhibitor applications, such as scale squeeze and continuous injection. However, they may not adequately represent the behaviors of scales and inhibitors in porous media. In this study, coreflood, bottle test and tube-blocking test were conducted, and the measured MIC values were compared to investigate the mechanism leading to the differences.
Bottle tests were conducted to determine the MIC of phosphino polycarboxylic acid (PPCA) by measuring the Ba2+ concentration in solution. Tube-blocking tests were carried out to determine the MIC of PPCA in stainless steel tubing by recording the increase of differential pressure. Finally, coreflood experiments were conducted to evaluate the performance of PPCA in porous media. Pressure changes were monitored along the core plug and were used to determine the location of BaSO4 deposition. Ba2+ concentrations in effluents were measured and compared with the bottle test results to investigate the performance of PPCA in porous media.
Results show that PPCA cannot stop scale deposition in porous media at the MIC determined by bottle tests and tube-blocking tests. Both bottle tests and tube blocking tests suggest an MIC of 6 ppm for PPCA. However, coreflood results show a noticeable increase of pressure in the first section of the core at 6 ppm. Moreover, the Ba2+ concentration in the effluent with 6 ppm PPCA of coreflood is just slightly higher that measured in the coreflood with no PPCA, which means that the MIC determined by bottle test and tube- blocking test cannot mitigate scale deposition in porous media. Sandpacks with higher permeability show higher permeability reduction after the same pore volume of water injection.
This study finds that the MICs determined by commonly used bottle tests and tube-blocking tests are not adequate to mitigate BaSO4 deposition in porous media. The mechanism of BaSO4 deposition and the behavior of inhibitors in porous media need to be further studied.