Quantification of CH4 Hydrate Film Growth Rates in Micromodel Pores

Stian Almenningen,Geir Ersland,Maksim Lysyy

doi:10.1021/acs.cgd.1c00396

Abstract

In this paper, we report the growth pattern and the rate of CH4 hydrate in sandstone pores. A high-pressure, water-wet, transparent micromodel with pores resembling a sandstone rock was used to visualize CH4 hydrate formation at reservoir conditions (P = 35–115 bar and T = 0.1–4.9 °C). The CH4 hydrate preferably formed and grew along the gas–water interface until the gas phase was completely encapsulated by a hydrate film. Two different growth rates were identified on the gas–water interface: CH4 hydrate film growth along the vertical pore walls (∼1200 μm/s) was more than 100 times faster than the film growth toward the pore center (∼8 μm/s). CH4 hydrate crystal growth directly in the water phase was slow and the rate was less than 0.5 μm/s. The film growth rate along the gas–water interface was independent of the pore size, gas saturation, and gas distribution, but the pore wall growth rate displayed a power law dependency on the applied subcooling temperature, ΔT, with a power law exponent equal to 2. The results of this study can be used as input to numerical models aiming to simulate pore-scale CH4 hydrate growth behavior.

Highlights

Natural gas hydrates are solid inclusion compounds consisting of crystalline water and one or more guest molecules
Hydrate nucleation typically occurred on the gas−water interface and was followed by a hydrate film spreading along the gas−water interface
Hydrate film growth along the vertical gas−water interface is labeled as the pore wall hydrate growth rate, vw, throughout the manuscript

Summary

Introduction

Natural gas hydrates are solid inclusion compounds consisting of crystalline water and one or more guest molecules. The fundamental nature of CH4 hydrate growth in a porous medium is not clear. The rate at which the hydrate grows, both on the gas−water interface and in liquid water containing dissolved CH4, is an important parameter that is needed to accurately model the formation of hydrate accumulations in natural geological settings. The rate at which the hydrate dissociates is closely linked to how the hydrate was formed and how the hydrate and related fluids are distributed in a porous medium.[2] Understanding the pore-scale growth pattern of gas hydrates is vital for assessing and predicting CH4 gas production from natural sediments and the stability of hydrates in the context of climate change

Methods

Results

Conclusion