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“Natural Gas Hydrates: Experimental Techniques and Their Applications” attempts to broadly integrate the most recent knowledge in the fields of hydrate experimental techniques in the laboratory. The book examines various experimental techniques in order to provide useful parameters for gas hydrate exploration and exploitation. It provides experimental techniques for gas hydrates, including the detection techniques, the thermo-physical properties, permeability and mechanical properties, geochemical abnormalities, stability and dissociation kinetics, exploitation conditions, as well as modern measurement technologies etc.

This book will be of interest to experimental scientists who engage in gas hydrate experiments in the laboratory, and is also intended as a reference work for students concerned with gas hydrate research.

Yuguang Ye is a distinguished professor of Experimental Geology at Qingdao Institute of Marine Geology, China Geological Survey, China. Professor Changling Liu works at the Qingdao Institute of Marine Geology, China Geological Survey, China.



Chapter 1. Introduction

Natural gas hydrate, or clathrate, sometimes called “flammable ice” or “combustible ice,” is a nonstoichiometric ice-like crystalline compound that is formed by water and gas molecules under high pressure and low temperature. In this chapter, we firstly summarize the properties of natural gas hydrate (i.e., compositions, structures, and the chemical and physical properties) and then give a brief history of gas hydrate researches from 1810 to present. It is found that great progress has been made in basic gas hydrate researches over the last two decades. Here, we discuss the formation conditions (e.g., gas origin, P-T conditions) of marine gas hydrate, summarize and predict the distribution and amount of gas hydrates in the world, and describe four prospecting techniques (i.e., seismic technique, drilling, logging, and geochemical exploration) for marine gas hydrate. In a word, gas hydrate researches involve multidiscipline, including geology, geochemistry, geophysics, regional engineering geology in the hydrate zone, and the related global climate.

Yuguang Ye

Chapter 2. Development of the Experiment Detection Technique

Three detection techniques, namely, acoustic, resistivity, and time domain reflectometry (TDR) methods, are available here to measure the physical properties of gas hydrate-bearing sediments. These techniques have been developed from repeated experiments and prove suitable for tests of gas hydrate. The acoustic detection technique contains a traditional acoustic detection and a new kind of bender element technique, which is used to measure acoustic velocities of hydrated consolidated sediments and hydrated unconsolidated sediments, respectively. A precision resistance testing system is developed to monitor chemical reactions and also study dynamic equilibrium according to the frequency response characteristics of the system. TDR is successfully introduced in detecting hydrate saturations in real time during hydrate formation and dissociation in sediments. Such technical innovation can guarantee smooth experimental research. In particular, the TDR technique, combined with other methods, provides a very promising approach to these experiments. It can detect, in real time, hydrate saturation in sediments and lets us know the quantitative relationships between the various physical parameters and hydrate saturation.

Yuguang Ye

Chapter 3. Relationship Between Acoustic Properties and Hydrate Saturation

Geophysical prospecting method still plays an important role in gas hydrate explorations and quantifications. Many velocity models have been constructed to relate elastic velocities with hydrate saturations in the hydrate-bearing sediments. Unfortunately, it is found that the results predicted by these models are quite different. Observations on relationship between gas hydrate saturation and elastic velocities are needed to validate these models. Since the data of hydrate saturation in field exploration is insufficient, experimental methods to obtain the relationship between hydrate saturation and acoustic properties are thought to be economically and effectively. In this chapter, gas hydrate has been formed and subsequently dissociated in both consolidated sediments and unconsolidated sediments, respectively. The acoustic properties of gas hydrate-bearing sediments are investigated by an acoustic detection. Simultaneously, hydrate saturations of the host sediments are measured by time domain reflectometry (TDR). With the experimental data, we verified seven velocity models (e.g., BGTL, Biot-Gassmann theory by Lee) that can predict velocities of both hydrate-bearing consolidated and unconsolidated sediments.

Gaowei Hu, Yuguang Ye, Jian Zhang, Shaobo Diao

Chapter 4. Detecting Hydrate in Porous Media Using Electrical Resistance

Natural gas hydrate synthesized in the porous medium is hardly observed by naked eyes, so indirect technique has to be employed to research the characteristics of hydrate and the relevant reactions. Electrical resistance detection is one of the most important methods to investigate the hydrates formation and dissociation processes. A lot of experiments have been done to clarify the relationship between the electrical resistance variation and hydrates thermodynamic or kinetics properties. In this chapter, three main aspects of electrical resistance application in hydrate experiments are discussed, including dividing different stages of hydrate formation or dissociation process reflected by electrical resistance variation, establishing hydrate nucleation theoretical model based on electrical resistance data, and the determination of hydrate saturation in porous-medium system.

Qiang Chen, Shaobo Diao, Yuguang Ye

Chapter 5. Thermophysical Properties of Gas Hydrate in Porous Media

Gas hydrates are very important compounds due to their capacity to store large volumes of gases. From the viewpoint of maintenance process of gas hydrates in the sediments, thermophysical properties such as thermal conductivity, dissociation heat, and heat capacity play important roles. The thermal-time-domain reflection (TDR) method is a relatively new technique to acquire thermophysical properties of sediments with different hydrates saturation. In this chapter, a detailed introduction of thermal-TDR method is clarified, especially on hydrates research field. Experimental data such as thermal conductivity and volumetric heat capacity of different measurement conditions are listed. Besides, an experiment technique to investigate thermal-stimulating dissociation of gas hydrates is introduced, which can provide some fundamental data used for the hydrates resource exploitation program.

Qiang Chen, Shaobo Diao, Yuguang Ye

Chapter 6. Experimental Techniques for Permeability and Mechanical Properties of Hydrate-Bearing Sediments

The permeability and mechanical properties of hydrate-bearing sediments are important basic parameters for natural gas hydrate drilling and exploitation. It is difficult to obtain and preserve the actual gas hydrate specimens for measurements of these characteristics. Experimental techniques are considered to be essential and unique methods to obtain the parameters of the permeability and mechanical of gas hydrate-bearing sediments. Here, we summarize the principle, experimental apparatus, and methods for determinations of permeability and mechanical properties of hydrate-bearing sediments. We have also developed two experimental equipments for researches of the relationship between the permeability, mechanical properties, and gas hydrate saturation in different sediments, respectively. The combination, configuration, and advantages of the two equipments, as well as some preliminary experimental results, were introduced in this chapter.

Jian Zhang, Yuguang Ye, Gaowei Hu, Shaobo Diao

Chapter 7. Experimental Studies of Marine Gas Hydrate Geochemical Anomalies

Geochemical exploration of marine gas hydrate based on the geochemical anomalies (e.g., ion concentrations in pore water and isotope in water and gas) caused by the formation/dissociation processes of marine gas hydrate. Geochemists are very interested in determining whether the ion concentration change seen in seawater as a result of hydrate formation can be observed at laboratory timescales. To solve this problem, we have designed a simple but efficient experimental device and developed the experimental techniques and methods for measuring gas hydrate geochemical anomalies. The concentrations of ions and isotopes are measured before and after an experiment so that the variations of ion and isotope in water can be estimated in a sediment-seawater-methane system. The fractionation coefficients of H and O isotopes have been also calculated in this system. Thus, a qualitative and quantitative understanding of how ion concentrations change under different formation conditions has been preliminarily established.

Changling Liu, Min Chen, Yuguang Ye, Qiang Chen

Chapter 8. Experimental Simulation of Hydrate Accumulation and Dispersion in Pore Fluids

Dynamic accumulation and dispersion of gas hydrate in the stability zone are actually controlled by the transformations of methane between hydrate and pore fluid. In this study, hydrate formation and dissociation in sediment column was simulated, and the experiment shows that hydrate can nucleate either at the free gas-fluid interface or in the aqueous phase oversaturated with methane, in both fine and coarse sediments, but nucleates easier in the coarse sediments. The processes that methane dissolved from free gas and transported in aqueous solution to precipitate at the surface of hydrate crystal were monitored. Methane concentrations in saline water in equilibrium with hydrate in the absence of a vapor phase was studied by in situ Raman spectroscopy. Hydrate growth and dissolution induced by temperature changes was observed. The rate of growth and dissolution of methane hydrate is controlled by mass transportation in aqueous solution.

Wanjun Lu, Feifei Wang, Menghan Wang

Chapter 9. Stable Conditions of Marine Gas Hydrate

Marine gas hydrate exists below the phase equilibrium boundary which is very sensitive to temperature and pressure. Investigations of the stable conditions can provide important information for gas hydrate development and utilization. In this chapter, we summarize the apparatus and the test methods used for gas hydrate stability condition experiments and discuss the experimental data and influencing factors in different systems (including pure water, seawater, artificial porous media, marine sediment). Meanwhile, the formation and dissociation behavior of gas hydrate in sediments is also investigated. Here, our research achievements of hydrate stable conditions combined with others can provide the basic theory and experimental testing technology of hydrate stability conditions for the safety development of natural gas hydrate resources.

Shicai Sun, Yuguang Ye, Changling Liu, Jian Zhang

Chapter 10. Natural Gas Hydrate Dissociation

Experimental study of natural gas hydrate dissociation can provide a theoretical basis and technical reserves for future hydrate exploitation. Hydrate dissociation includes the thermodynamic and dynamic processes. Once thermodynamic conditions of the dissociation are satisfied, the dynamics plays a significant role for hydrate dissociation. Here, we establish and describe the techniques and methods for hydrate dissociation research from both the macroscopic and microscopic views. Macroscopic dissociation experiments mainly focus on the reaction devices, detection methods, and technical approach, including methane hydrate and different natural gas hydrates dissociation in vacuum. Microscopic dissociation experiment introduces an experimental technique to observe the microprocess of THF hydrate dissociation in situ using nuclear magnetic resonance imaging, intending to investigate the micro-mechanism of hydrate dissociation.

Qingguo Meng, Changling Liu, Qiang Chen, Yuguang Ye

Chapter 11. Experimental Studies on Techniques to Extract Natural Gas Hydrate

Extraction techniques are the key to the utilization of natural gas hydrate resources and have attracted attention worldwide. At present, no reliable methods for marine gas hydrate extraction are available although four extraction methods have been proposed for several decades. The methods are still in the exploratory stage. In this chapter, four methods (i.e., the thermal excitation method, depressurization method, chemical reagent method, and gas displacement method) are discussed for their advantages and disadvantages. Several experiment systems for gas hydrate extraction are summarized and commented. We have also developed the techniques and methods for simulated extraction of gas hydrate based on a specially designed device, which can be used to extract gas from gas hydrate with these four methods. Finally, the depressurization method has been successfully used for gas hydrate extraction in marine sediment from South China Sea.

Changling Liu, Jianye Sun, Yuguang Ye

Chapter 12. Measurement of Gas Hydrate by Laser Raman Spectrometry

Raman spectrometry is a powerful tool for gas hydrate researches to provide vital information regarding the structure of the hydrate, hydrate composition, and cage occupancy. This chapter begins with discussing the basic knowledge and application of laser Raman spectrometry and then, giving the techniques and methods which have been developed in our laboratory for different experiments of gas hydrate with Raman. The techniques and methods are used for measuring hydration number of methane hydrate prepared under different conditions; investigating the Raman spectra characteristics of air, nitrogen, and oxygen hydrates; and observing methane hydrate dissociation in sediments with different particle sizes. Observation of the microprocesses of hydrate formation and dissociation is also carried out based on a low-temperature high-pressure device for in situ Raman detection. The methods are also successfully used to determinate the natural gas hydrate samples collected from Shenhu area of the South China Sea and from Qilian Mountain permafrost area, respectively, providing microscopic evidences for gas hydrate existence in the sediments.

Changling Liu, Qingguo Meng, Yuguang Ye

Chapter 13. Application of Modern Instruments Measurement Techniques for Hydrate Research

The characterization of natural gas hydrate samples is significant for us to know the property, distribution, and dynamic process of gas hydrate formation in sediments. Various advanced modern instrument test techniques can provide technical support for hydrate researches. However, these advanced techniques have many exclusive features because hydrates cannot exist in a stable form at normal temperatures and pressures. This chapter is concerned with the application of X-ray computerized tomography (X-CT), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), high-pressure differential scanning calorimeter (high-pressure DSC), atomic force microscopes (AFM), and neutron diffraction (ND) to hydrate measurement and identify its potential prospects.

Gaowei Hu, Qiang Chen, Qingguo Meng, Yugang Ye


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