Managing Global Warming

An Interface of Technology and Human Issues

Trevor Letcher, Trevor M. Letcher

• Éditeur: Academic Press
• Année: 2018
• ISBN:
  9780128141052
• Sujet: Economics
• Sous-sujet: Economic Theory

Managing Global Warming: An Interface of Technology and Human Issues discusses the causes of global warming, the options available to solve global warming problems, and how each option can be realistically implemented. It is the first book based on scientific content that presents an overall reference on both global warming and its solutions in one volume. Containing authoritative chapters written by scientists and engineers working in the field, each chapter includes the very latest research and references on the potential impact of wind, solar, hydro, geo-engineering and other energy technologies on climate change.

With this wide ranging set of topics and solutions, engineers, professors, leaders and policymakers will find this to be a valuable handbook for their research and work.

• Presents chapters that are accompanied by an easy reference summary
• Includes up-to-date options and technical solutions for global warming through color imagery
• Provides up-to-date information as presented by a collection of renowned global experts

Section C

Reducing Greenhouse Gases: Renewables and Zero Carbon/Carbon Neutral Forms of Energy and Electric Cars

7

Methane hydrate as a “new energy”

Liang Cui⁎; Azizul Moqsud^†; Masayuki Hyodo^†; Subhamoy Bhattacharya⁎^{,1 ⁎} University of Surrey, Guildford, United Kingdom
^† Yamaguchi University, Japan
¹ Corresponding author: [email protected]

Abstract

Methane hydrates could become a promising new energy source in countries such as China and Japan which have large reserves of the hydrate. The key mission is to find a safe and efficient exploitation method. The exploitation processes could cause stress changes, which may induce submarine landslides and failures of engineering projects. This chapter described some state-of-art exploitation methods reproduced in the laboratory and in numerical modeling procedures aimed at understanding the responses of soils during the exploitation process. These studies could provide valuable guidance for real life projects related to mining methane hydrates.

Keywords

Methane hydrate; Dissociation; Thermal recovery; Depressurization; Discrete element method; Micromechanics

Chapter Outline

• 7.1 Introduction
  • 7.1.1 What is methane hydrate?
  • 7.1.2 Where is the reserve and how much?
• 7.2 Production methods
  • 7.2.1 Thermal recovery method
  • 7.2.2 Depressurization method
• 7.3 Testing equipment and sample preparation
  • 7.3.1 Triaxial testing apparatus
  • 7.3.2 Specimen preparation
  • 7.3.3 Generation of MH and experimental procedure
  • 7.3.4 Triaxial compression tests
• 7.4 MH dissociation tests
  • 7.4.1 Initial stress before MH dissociation started
  • 7.4.2 Depressurization method
  • 7.4.3 Thermal recovery
  • 7.4.4 Experimental findings
• 7.5 DEM simulation of MH dissociation process
  • 7.5.1 Reproduction of MH dissociation process using DEM
  • 7.5.2 Micromechanism associated with MH dissociation
• 7.6 Conclusions
• References

7.1 Introduction

7.1.1 What is methane hydrate?

Methane hydrate (MH) is a solid compound in which a large amount of methane gas molecules (CH₄) are caged within a crystalline structure of water, as illustrated in Fig. 7.1, under low temperature and high pressure, forming a solid similar to ice [1]. It looks like ice, but starts burning when an open flame is brought close to it; methane hydrate is often called “fiery ice.” As found in previous investigations [2], a great amount of MH exists stably undersea. The natural methane hydrate may not be purely a white agglomeration like artificial methane hydrate. Since methane hydrate exists in between the sand particles of sandy sediments as shown in Fig. 7.2, the methane hydrate-bearing sediments do not appear white but rather look similar to soil.

Fig. 7.1 Crystal structure of methane hydrate.

Fig. 7.2 Methane hydrate-bearing sediment [3].

7.1.2 Where is the reserve and how much?

MH exploitation has attracted great attentions since the total carbon content in MH is twice as large as that in petroleum or coal [4]. One cubic meter of MH dissociates to approximately 160–170 m³ (at 0°C and 1 atm) of methane gas. MH is distributed almost all over the world (Figs. 7.3 and 7.4). The total worldwide estimated reserve is around (1 − 5) × 10¹⁵ m³ [7]. It is considered as a type of promising and hugely reserved energy which can alleviate the energy crisis to certain extent [8,9]. Therefore, how to exploit MH safely and efficiently has become a worldwide focus.

Fig. 7.3 Location of sampled and inferred gas hydrate occurrences worldwide [5].

Fig. 7.4 Reserve of methane hydrate in different parts of the world [6].

7.2 Production methods

The exploitation methods mainly include the chemical and physical methods. For chemical methods such as chemical injection method, the diffusion of chemicals is inhibited due to the low permeability of methane hydrate-bearing sand (MHBS) [10], leading to low gas production rate. Moreover, the costs of chemical method are high and not suitable for large-scale exploitation. These two defects make researchers seek other more efficient methods. Physical exploitation methods, which include thermal recovery and depressurization methods, have the advantage of low cost and high gas productivity [11]. The aim of these two methods is to change the environment of MH by either increasing the temperature or reducing the confining pressure until the temperature-confining pressure condition is such that MH dissociates into methane gas and water, as illustrated in Fig. 7.5[12,13].

Fig. 7.5 The base condition to form MH.

7.2.1 Thermal recovery method

In this method, a well is drilled into the methane hydrate-bearing layer, and the methane hydrate is dissociated by heating, using a fluid (hot water or steam) heated at the surface in a boiler or similar device and circulated down through the well, as illustrated in Fig. 7.6. This causes methane hydrate to dissociate and generate methane gas.

Fig. 7.6 Thermal recovery method for MH production.

7.2.2 Depressurization method

The depressurization method consists of lowering the pressure inside the well and encouraging the methane hydrate to dissociate into methane gas and water, as illustrated in Fig. 7.7. At the end of the production, the water is injected back and the water pressure recovered.

Fig. 7.7 Depressurization method for MH exploitation.

Promising progress has made in the MH gas production in both China and Japan [14]. Despite the obvious advantages of physical methods, there are potential problems associated with these exploitation processes: these include the stress changes caused by drilling, the settlement, landslide, and gas leakage. Due to these problems, some accidents have happened in these processes such as submarine landslides, platform foundation settlement, and failures of lifeline engineering projects [15,16]. Therefore, in order to safely extract the gas it is necessary to first understand the mechanical and dissociation properties of the methane hydrate deposits.

To study the dissociation process, previous in situ tests [17] have investigated the change of modulus by measuring the shear wave propagation velocities through the MHBS, while other mechanical properties, such as str...