Enhanced CH4-CO2 Hydrate Swapping in the Presence of Low Dosage Methanol

Jyoti Shanker Pandey,Charilaos Karantonidis,Adam Paul Karcz,Nicolas Von Solms

doi:10.3390/en13205238

Abstract

CO2-rich gas injection into natural gas hydrate reservoirs is proposed as a carbon-neutral, novel technique to store CO2 while simultaneously producing CH4 gas from methane hydrate deposits without disturbing geological settings. This method is limited by the mass transport barrier created by hydrate film formation at the liquid–gas interface. The very low gas diffusivity through hydrate film formed at this interface causes low CO2 availability at the gas–hydrate interface, thus lowering the recovery and replacement efficiency during CH4-CO2 exchange. In a first-of-its-kind study, we have demonstrate the successful application of low dosage methanol to enhance gas storage and recovery and compare it with water and other surface-active kinetic promoters including SDS and L-methionine. Our study shows 40–80% CH4 recovery, 83–93% CO2 storage and 3–10% CH4-CO2 replacement efficiency in the presence of 5 wt% methanol, and further improvement in the swapping process due to a change in temperature from 1–4 °C is observed. We also discuss the influence of initial water saturation (30–66%), hydrate morphology (grain-coating and pore-filling) and hydrate surface area on the CH4-CO2 hydrate swapping. Very distinctive behavior in methane recovery caused by initial water saturation (above and below Swi = 0.35) and hydrate morphology is also discussed. Improved CO2 storage and methane recovery in the presence of methanol is attributed to its dual role as anti-agglomerate and thermodynamic driving force enhancer between CH4-CO2 hydrate phase boundaries when methanol is used at a low concentration (5 wt%). The findings of this study can be useful in exploring the usage of low dosage, bio-friendly, anti-agglomerate and hydrate inhibition compounds in improving CH4 recovery and storing CO2 in hydrate reservoirs without disturbing geological formation. To the best of the authors’ knowledge, this is the first experimental study to explore the novel application of an anti-agglomerate and hydrate inhibitor in low dosage to address the CO2 hydrate mass transfer barrier created at the gas–liquid interface to enhance CH4-CO2 hydrate exchange. Our study also highlights the importance of prior information about methane hydrate reservoirs, such as residual water saturation, degree of hydrate saturation and hydrate morphology, before applying the CH4-CO2 hydrate swapping technique.

Highlights

Natural gas hydrates (NGHs) are cage-like crystalline compounds formed by the van derWaals-forced inclusion of natural gas molecules in hydrogen-bonded water molecules under high pressure and low temperature conditions [1,2]
low dosage hydrate inhibitors (LDHI) are further divided into kinetic hydrate inhibitors (KHI) and anti-agglomeration compounds (AA) [59]
AA chemicals are different than Thermodynamics hydrate inhibitors (THI) and KHI as AA disperse the hydrate into the condensate phase [60]

Summary

Introduction

Natural gas hydrates (NGHs) are cage-like crystalline compounds formed by the van derWaals-forced inclusion of natural gas molecules in hydrogen-bonded water molecules under high pressure and low temperature conditions [1,2]. These deposits remain untouched and hold a reserve estimated to be twice the amount of known fossil fuels available [3,4,5]. To produce methane from a gas hydrate reservoir, several techniques have been suggested, including depressurization [6], thermal stimulation [7] and chemical inhibitor injection [8]. There are many depressurization techniques that are suggested to optimize gas production, including constant rate depressurization [9], multistage depressurization [10], cyclic depressurization [11,12], slow stepwise depressurization [13,14] and depressurization combined with gas injection [15,16]. As all the above production techniques are based on the decomposition of methane hydrate, catastrophic sediment failures can be triggered with an additional risk of methane release to the atmosphere, accelerating the greenhouse effect due to rapid hydrate decomposition

Methods

Results

Conclusion