Testing system and experimental study of pressure parameters of natural gas hydrate core samples

Abstract

The analysis of the performance parameters of natural gas hydrates through pressure testing is extremely important for explaining the growth mechanism of hydrates existing in the formation and predicting changes in the physical and mechanical properties of the formation during hydrate decomposition. It is also the key to constructing a prediction model for the occurrence behavior of gas hydrates in the complex situations just mentioned, which is of great significance for evaluating the mode of occurrence and resource quantity of natural gas hydrates in the reservoir. Estimating the various parameters of hydrate cores using seismic or logging data often results in significant errors from actual values, and it is difficult to conduct in situ formation parameter testing under existing technical conditions. Therefore, obtaining hydrate formation cores through drilling and testing and analyzing their physical, chemical, and mechanical properties is the most reliable method. This study introduces a system that can interface with hydrate pressure to maintain core drilling tool parameters and perform on-site pressure transfer and parameter testing on hydrate cores. The system is mainly composed of core capture and cutting units, sampler pressure-maintaining units, core sample parameter testing units, core sample storage units, and temperature and pressure-maintaining units. The structure and working principle of each unit are introduced in detail. To verify the performance of the parameter testing system and the influence of the different pressure environments on the parameter testing, the system tested the longitudinal wave velocity, resistivity, and shear strength of three different hydrate simulation cores under different pressures. Research has shown that the pressure parameter testing system for natural gas hydrate core samples can work stably and reliably at a high pressure of 30 MPa. Our results show that the influence of pressure on the resistivity testing of hydrate core samples is not significant. Pressure impacts the wave velocity testing of hydrate core samples, and the higher the pressure, the greater the longitudinal wave velocity. Pressure has a great influence on the test of core shear strength.