CH4/C2H6 gas hydrate interparticle interactions in the presence of anti-agglomerants and salinity

Abstract

Gas hydrate interparticle cohesive forces are essential to evaluate hydrate interfacial properties and determine the hydrate particle agglomeration behavior. In this study, a technique was developed in a modified high-pressure micromechanical force (HP-MMF) apparatus that enables hydrate anti-agglomerants (AAs) to be evaluated at an interfacial level under deepwater petroleum flowline conditions of high pressure and low temperature in a liquid hydrocarbon-dominated system. The hydrate cohesive force was found to decrease from the baseline (23.5 ± 2.5 mN m−1) to a non-measurable force value (<0.05 mN m−1) with increasing concentration of a high-performance AA (0.25 vol% to 2 vol% of AA1). To mimic the shut-in scenario in subsea flowlines that may be required in an emergency response, cohesive force was measured with shut-in times varying from 10 sec to 18 hr. It was observed that long contact times can lead to higher cohesive forces and eventually resulting in a system failure, i.e. irreversible interparticle interactions, if the system is under-dosed. Utilizing these results, under-dosed scenarios were identified for AA1 in the model liquid hydrocarbon. In addition, salt ions were found to promote the performance of AA1, but salt only slightly reduced the force with AA2 at the same subcooling. The results demonstrate that this modified HP-MMF method can capture the differences between high and low performance AAs. These data/tests can be used to help improve our understanding on the gas hydrate interfacial properties and determine the minimum effective dosage of AA additives for hydrate mitigation treatments in subsea flowlines.