Quantitative ranking and development of hydrate anti-agglomerants

During the production of offshore oil and gas, production fluids will cool toward seafloor temperatures which will place the flowline into the natural gas hydrate stability region. Small particles of hydrate can form, which can aggregate and result in blockage of the flowline. The most common hydrate management strategy involves using large volumes of thermodynamic inhibitor (THI) to operate outside the hydrate stability region. The THI hydrate management strategy represents a significant CAPEX and OPEX investment, rendering some deepwater fields economically unviable to develop. Low dosage hydrate inhibitors (LDHIs), in the form of kinetic hydrate inhibitors (KHIs) and anti-agglomerants (AAs), present an alternative to THIs. AAs allow hydrates to form, but limit hydrate agglomeration and enable the transport of a stable hydrate-in-oil slurry. AAs have traditionally been qualified for field deployment on black oils using high-pressure rocking cells and autoclaves. These tools provide qualitative assessments of AA performance, but are unable to resolve structure-function relationships at the interfacial length scale. In this study, a quantitative micromechanical force (MMF) has been deployed to study the performance of seven industry AAs. Four of these AAs are current generation AAs being deployed today and the remainder represent successive generations of AA products. The results illustrate that an effective AA must be one that lowers the cohesive forces between hydrate particles. For the four generations of AA chemistry an improvement in the maximum hydrate cohesive force reduction for the current generation chemistry (80%> force reduction) relative to the previous ones (40-50% force reduction) we observed. All current generation AA chemistries lower hydrate cohesive force by more than >80% indicating a high likelihood of successfully dispersing hydrates. To assess this likelihood each chemistry was then validated in high pressure sapphire autoclave under high shear; in this technique, which is analogous to more traditional qualification methods, performance may be quantified in terms of the maximum relative torque, defined as the ratio of the maximum torque required to maintain a set shear rate in the presence of hydrates to the torque required before hydrate formation. Consistent with the observations in the MMF, all current generation AAs kept the relative torque < 2, while systems with no AA experienced a maximum relative torque of ∼20. The MMF results are consistent with the more traditional autoclave qualification but provides a more quantitative insight into hydrate cohesion which is a key aspect of AA performance.