Measured permeability and porosity of R11 (CCl3F) hydrate plugs

Two important parameters for the melting behaviour of a hydrate plug are the permeability and porosity. This paper presents permeability and porosity (volume phase fraction) measurements of R11 (CCl3F) hydrate plugs formed in glass pipe-sections. The plugs were formed without any circulation of fluids, i.e. under quiescent conditions. The hydrate solution was left to freeze in the pipe and when a satisfactory plug had formed, permeability measurements were performed with water. In order to determine the volume phase fractions and the porosity, the fresh water in the pore space was replaced with a 1 wt% NaCl solution. The plug volume and weight were measured and then the plug was melted. After melting, the volumes of water and R11 were measured. The water was a mixture of salt water from the pore space and fresh water from the melted hydrate. Based on the measured water conductivity, the plug porosity and the volume phase fractions were determined. The measured porosities varied from 0.34 to 0.60. The liquid water volume fractions ranged from 0.09 to 0.50 and the measured water permeabilities varied from 4.1 x 10(-15) to 3.7 x 10(-11) m(2), i.e. the permeabilities covered approximately four decades. The least porous plugs were very compact and hard while the most porous plugs were slush-like. The measured data support a correlation between permeability and porosity (more precisely the volume phase fraction) in good agreement with the phenomenological model of Rumpf and Gupte (1971, Chem. Ing. Technol. 43, 367-375). The porosity of a hydrate plug will decrease with time during hydrate formation. This is important to be aware of in a plug removal situation and procedures for plug removal should be initiated as soon as possible. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.