Hydrate plugging problems in undersea natural gas pipelines under shutdown conditions

Jamaluddin, A.K.M., Kalogerakis, N. and Bishnoi, P.R., 1991. Hydrate plugging problems in undersea natural gas pipelines under shutdown conditions. J. Pet. Sci. Eng., 5: 323-335. Undersea oil and gas transportation pipelines in cold regions often have thermodynamically suitable conditions for the formation of gas hydrates. There is a widespread concern in the petroleum industry that the hydrate formation could result in a partial or complete plug. A shutdown offshore pipeline condition is emulated in the laboratory to obtain methane hydrate plug formation data. The experiments were conducted at a temperature of 274 K and at pressures of 4, 5 and 7 MPa. Furthermore, a mathematical model which couples intrinsic hydrate formation kinetics with heat and mass transfer phenomena is presented to describe the overall hydrate plug formation process. The effective diffusivities of methane gas through hydrate are estimated by matching the model predictions with the experimental data. The results indicate that the plugging problem is not severe for an unplanned pipeline shutdown for periods less than 48 h. However, caution in the restarting procedure is recommended.