Fabrication and testing of apparatus for laboratory simulation of Alaska frozen rock encountered during hydrate gas reservoir coring

Gas hydrates are inclusion compounds in which gas is trapped in ice. They are widely found in nature in permafrost and deep-sea sediments and hold huge potential as a methane gas resource. As a result, a National Methane Hydrate R&D program was launched in 2000 by the United States Department of Energy. One of the projects under the program, run by the National Energy Technology Laboratory (NETL/DOE DE-FC26-01NT41331), is to drill, core, and test one gas hydrate well in the Prudhoe Bay/Kuparuk River area of northern Alaska. In this project, cores are studied to gather field data on a hydrate reservoir in permafrost regions. Tests were required to develop coring techniques and handling procedures on frozen rocks prior to actual coring in Alaska. These tests were performed at a Houston research facility where frozen rocks were prepared using an apparatus fabricated to simulate hydrate reservoir in permafrost. The permafrost formation was simulated with a water-saturated sand pack, which was frozen using liquid nitrogen. Frozen rocks of up to 3.6 m (12 ft) high and 0.254 m (10 in.) diameter were prepared with the apparatus. The setup was designed and evaluated in several stages. First, a computer model was developed to understand the rock-freezing process. Then a prototype setup was constructed to have similar radial dimensions as the full-scale apparatus, but with a smaller height. Several experiments were performed to test the prototype and the full-scale apparatus. The apparatus has been successfully employed to prepare frozen rock, thereby assisting in development of improved coring methodology for Alaskan permafrost hydrates exploration.