Experimental Determinations of the Complete Inhibition, the Slow Growth, and the Rapid Failure Regions of Methane Hydrate Formation in the Presence of Polyvinylpyrrolidone and Polyvinylcaprolactam Aqueous Solutions

Gas hydrate formation in gas transmission pipelines is one of the most critical troubles in the petroleum industry. One of the most convenient techniques to intercept gas hydrate formation is using inhibitors: e.g., thermodynamic hydrate inhibitors and kinetic hydrate inhibitors (KHIs). KHIs postpone the hydrate nucleation and slow down the hydrate growth rates by increasing the induction time. Because hydrate nucleation is probabilistic, the measurement of the induction time is difficult, and the measured data are normally nonrepeatable. It was observed that KHIs have repeatable behaviors by evaluating the KHIs based on the crystal growth inhibition approach in which the regions of inhibited hydrate growth can be considered as a function of subcooling: by increasing the subcooling from the complete inhibition region (CIR), reaching the slow growth rate region (SGR), and finally reaching the rapid failure region (RFR). In this study, the CIR, the SGR, and the RFR of methane hydrate formation in the attendance of polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap) aqueous solutions were experimentally measured. Also, in the pressure range of 35-80 bar, the effects of KHIs concentrations, i.e., 0.0025, 0.0050, and 0.0100 mass fractions for PVP and 0.0010 and 0.0025 mass fractions for PVCap, were investigated in these regions. It was concluded that the optimum concentration of PVP was 0.0050 for CIR and SGR. Also, by comparing the CIR, SGR, and RFR of PVP and PVCap aqueous solutions, it was observed that PVCap has a stronger inhibition impact with respect to PVP.

Automated summary

The formation of gas hydrates in gas transmission pipelines is a critical issue in the petroleum industry, and inhibitors have been proven to be an effective method to intercept hydrate formation. By experimentally measuring the CIR, SGR, and RFR, it was found that PVCap has a stronger inhibition impact compared to PVP.