Reliability experiment on the calculation of natural gas hydrate saturation using acoustic wave data

Abstract

In this paper, compression wave velocity, shear wave velocity and their change during the formation of natural gas hydrate in unconsolidated sand and mud sediments were measured through petrophysical experiments to discuss the reliability of calculating natural gas hydrate saturation by using acoustic velocity data. Then, a computation model of natural gas hydrate saturation during the experiments was established based on the material balance equation, combined with the PVT (pressure, volume, temperature) state equation and its test conditions. On this basis, the changing law of the acoustic velocity of the unconsolidated sediments with the increase of natural gas hydrate saturation was analyzed. Finally, natural gas hydrate saturation was calculated by using the modified Lee's weight sonic formula, and was compared with that measured in the experiments. And the following research results were obtained. First, the acoustic data can be used to calculate the natural gas hydrate saturation when the content of natural gas hydrate reaches a certain extent. Second, the compression and shear wave velocities of unconsolidated sand and mud sediments increase with the rise of their natural gas hydrate content, and they are in a good relationship of linear correlation. And third, the natural gas hydrate saturation calculated based on the acoustic data is close to that measured in the laboratory with much smaller errors. It is concluded that the research results provide a basis for the calculation of natural gas hydrate saturation using the actual acoustic logging data. Keywords: Natural gas hydrate, Porous media, Unconsolidated sediment, Petrophysical experiment, Saturation, Computation model, Acoustic velocity, PVT state equation