Can cyclopentane hydrate formation be used to screen the performance of surfactants as LDHI anti-agglomerants at atmospheric pressure?

Abstract

Anti-agglomerants (AAs) are a class of low dosage hydrate inhibitors (LDHIs) that have been used commercially in oilfield operations for almost two decades to prevent the plugging of flow lines with gas hydrates. AAs are surfactants and the ranking of their AA performance usually requires high pressure equipment with the ability to collect visual data to determine the plugging tendency. A simple but crude screening method for determining the AA performance of a chemical has been developed using cyclopentane hydrate at atmospheric pressure. The method requires is limited by the maximum subcooling allowable, which for our system was found to be 5.3°C from hydrate dissociation experiments if ice formation is to be avoided. The reproducibility of the screening method was found to be good although no hydrate formation occurred for some chemicals with significant kinetic inhibition activity due to the low subcooling. These chemicals were usually the commercial AAs which have good crystal growth inhibition properties. Therefore, the method was not able to distinguish good AA performance between the best AAs. In general, the AA performance results with cyclopentane hydrate correlated well with those obtained in high pressure natural gas hydrate equipment. Those surfactants with poor results with the cyclopentane hydrate method gave also poor performance using the gas hydrate method. However, some discrepancies between the results for the two test methods were found, which is sufficient to conclude that the cyclopentane hydrate test method is only a simple, crude method for first time screening of a surfactant to determine if it has any potential for further testing in high pressure gas hydrate systems.