Gas hydrate saturations estimated from pore-and fracture-filling gas hydrate reservoirs in the Qilian Mountain permafrost, China

Kun Xiao,Zhenquan Lu,Juzhi Deng,Changchun Zou

doi:10.1038/s41598-017-16531-x

Abstract

Accurate calculation of gas hydrate saturation is an important aspect of gas hydrate resource evaluation. The effective medium theory (EMT model), the velocity model based on two-phase medium theory (TPT model), and the two component laminated media model (TCLM model), are adopted to investigate the characteristics of acoustic velocity and gas hydrate saturation of pore- and fracture-filling reservoirs in the Qilian Mountain permafrost, China. The compressional wave (P-wave) velocity simulated by the EMT model is more consistent with actual log data than the TPT model in the pore-filling reservoir. The range of the gas hydrate saturation of the typical pore-filling reservoir in hole DKXX-13 is 13.0~85.0%, and the average value of the gas hydrate saturation is 61.9%, which is in accordance with the results by the standard Archie equation and actual core test. The P-wave phase velocity simulated by the TCLM model can be transformed directly into the P-wave transverse velocity in a fracture-filling reservoir. The range of the gas hydrate saturation of the typical fracture-filling reservoir in hole DKXX-19 is 14.1~89.9%, and the average value of the gas hydrate saturation is 69.4%, which is in accordance with actual core test results.

Highlights

Gas hydrate is a solid crystal with a cage structure consisting of water molecules and natural gas, which mainly exists in the terrestrial permafrost regions and beneath the sea along the outer continental margins of the world’s oceans[1]
The acoustic velocity characteristics of pore filling gas hydrate reservoir in the Qilian Mountain permafrost (QMP) are simulated using the forward modeling velocity model that is established by the effective medium theory (EMT) model, and the simulation results are compared with the elastic wave velocity model based on the two-phase medium theory (TPT) model
In the actual use of the model, the gas hydrate reservoir can be regarded as the equivalent homogeneous medium, where microscopic distribution patterns affect the elastic parameters, and we study the characteristics of the elastic wave

Summary

Introduction

Gas hydrate is a solid crystal with a cage structure consisting of water molecules and natural gas (mainly CH4), which mainly exists in the terrestrial permafrost regions and beneath the sea along the outer continental margins of the world’s oceans[1]. The acoustic velocities that are simulated by the pore- and fracture-filling reservoirs are used to estimate the gas hydrate saturation in the study area.

Results

Conclusion