The Mallik 2L-38 test samples were kept frozen prior to placement in GHASTLI. They were removed from the transportation vessels, jacketed, and placed between end caps within a walk-in freezer maintained at about -30°C before being brought into the lab. The presence of ice helped to stabilize the hydrate at atmospheric pressure during the test setup procedures. Although the specimens were still partially frozen at the beginning of testing, they were allowed to warm to a temperature where the ice melted, but the gas hydrate remained solid.
Each GHASTLI laboratory test consists of different steps designed to address different physical-property measurements (Fig. 4). Initial acoustic measurements on gas hydrate and partially-ice-bonded samples (Fig. 5) were followed by converting the ice to water. Temperature was raised to approximately 4°C for at least 24 hours until all ice had melted and acoustic velocity stabilized. After all of the ice (which was not present in situ) melted, temperature was slowly raised in 1 to 2°C increments until dissociation began. The dissociated gas, specimen pore water, and water released from hydrate entered the back pressure collector where water and gas were separated and their volumes measured.
In all cases, the acoustic signal previously established was lost during initial dissociation of gas hydrate in the test samples but was recovered using a "rebuilding" procedure. One strength test was performed on a sample that contained gas hydrate; the rest were sheared after dissociation.
Was this article helpful?