Investigation into gas production from natural gas hydrate: A review

This paper aims at exploring the tectonic characteristics of the South China Continent (SCC) and extracting the universal tectonic rules from these characteristics,to help enrich the plate tectonic theory and better understand the continental dynamic system. For this purpose, here we conduct a multi-disciplinary investigation and combine it with the previous studies to reassess the tectonics and evolution of SCC and propose that the tectonic framework of the continent comprises two blocks, three types of tectonic units, four deformation systems, and four evolutionary stages with distinctive mechanism and tectonic characteristics since the Neoproterozoic. The four evolutionary stages are: (1) The amalgamation and break-up of the Neoproterozoic plates, typically the intracontinental rifting. (2) The early Paleozoic and Mesozoic intracontinental orogeny confined by plate tectonics, forming two composite tectonic domains. (3) The parallel operation of the Yangtze cratonization and intracontinental orogeny, and multi-phase reactivation of the Yangtze craton. (4) The association and differentiation evolution of plate tectonics and intracontinental tectonics, and the dynamic characteristics under the Meso-Cenozoic modern global plate tectonic regime.

Tectonics of South China continent and its implications

Over the past century, fossil fuels have provided the majority of China's energy. However, their extensive utilization leads to a shortage and environmental pollution. Recently, submarine and permafrost gas hydrate deposits have been investigated as a possible clean and sustainable energy source by governmental institutions, research organizations, and energy industries in China. The primary objective of this paper is to review the potential studies pertaining to gas hydrate exploration and resource assessment, the safe and efficient exploitation of gas hydrates and the basic properties of gas hydrates. To date, there are over 20 institutions and organizations in China committed to gas hydrate investigation, among which the Guangzhou Marine Geological Survey (GMGS) and the Chinese Academy of Geological Sciences (CAGS) etc. primarily focus on gas hydrate exploration research, while the China National Offshore Oil Corporation (CNOOC) Research Center, Guangzhou Institute of Energy Conversion (GIEC) and China University of Petroleum-Beijing (CUPB) etc. concentrate on gas hydrate mining technologies. In this paper, the occurrence and exploration of gas hydrates in both permafrost regions and the continental slope of China have been determined from numerous research contributions and are presented. Moreover, the latest progress in gas hydrate fundamental studies, including hydrate phase equilibria, hydrate formation mechanisms, hydrate thermal physical properties and the acoustics and resistivity characteristics of gas hydrates are briefly reviewed, and relevant data are gathered and compared. Emphasis is also placed on gas hydrate mining technologies and gas production using depressurization methods, thermal stimulation methods or other methods. Furthermore, the security of natural gas hydrate-bearing sediments during gas production and the environmental impacts of gas hydrate are identified. With additional financial and political support and advanced research facilities, research on gas hydrates in China is progressing rapidly but is still in its early developing stage, thus, future work should be undertaken with greater diligence.

The status of natural gas hydrate research in China: A review

State of the art: Natural gas hydrates as a natural resource

Methane hydrates: A future clean energy resource

Qilian Mountain permafrost,with an area of about 10×104km2,is located in the north of Qinghai-Tibet plateau. It has of perfect conditions and great prospecting potential for gas hydrate. The Scientific Drilling Project of Gas Hydrate in the Qilian Mountain permafrost,which locates at the Jugenghu Mining Area in the Muli Coalfield,Tianjun County,Qinghai Province,has been implemented by China Geological Survey in 2008~2009. Four scientific drilling wells have been completed with a total footage of 2059.13m. Samples of gas hydrate were collected separately in the holes of DK-1,DK-2 and DK-3. Gas hydrate is hosted under permafrost zone at the 133~396m interval. The samples are white or ivory crystal and easily burning. Distinct low temperature anomaly has been identified by infrared camera. The gas hydrate-bearing cores strongly bubble in water. Gas-bubble and water-drop emit from the samples and then retain characteristic honeycombed structure. The typical spectrum curve of gas hydrate is detected using Raman spectrometry. Furthermore,the logging profile also indicates high electrical resistivity and sonic velocity. Gas hydrate in Qilian Mountain is found within a thinner permafrost zone with a shallower buried depth and characterized by more complex gas component and coalbed methane origin,suggesting a new type of hydrate.

Gas Hydrates in the Qilian Mountain Permafrost, Qinghai, Northwest China

Gas hydrate occurrences in the Qilian Mountain permafrost, Qinghai Province, China

Based on gas composition and temperature measurements in the course of field drilling, the upper and lower depths of gas hydrate stability zone are calculated by modeling in the Muli permafrost, Qinghai, then the modeling results are compared with the drilling results. The modeling results show that the upper depth of gas hydrate stability zone is 148.8~122.7 m and the lower depth of gas hydrate stability zone is 324.6~354.8 m, with the thickness of gas hydrate stability zone of 175.8~232.2 m; the drilling results indicate that gas hydrate and its related indications occur at the interval of 133~396 m. These two types of results are comparable and thus are basically accordant, suggesting that the modeling can serve as a prediction of the upper and lower depths of gas hydrate stability zone. Gas composition, depth of permafrost, thermal gradients above and below the base of permafrost are sensitive factors affecting the upper and lower depths of gas hydrate stability zone in the Muli permafrost.

Characteristics of Gas Hydrate Stability Zone in The Muli Permafrost, Qinghai: Results Compared Between Modeling and Drilling

Gas hydrate was obtained in the Qilian Mountain permafrost in Qinghai, China. It occurs in fissures of mudstone, oily shale, siltstone, fine sandstone, and in the pore space of fine to middle grained sandstone between 133 to 396 mbs. Gas hydrate is composed of CH4, C2H6, C3H8 and CO2 indicated by Raman spectrometry. Gas composition and isotope geochemistry show that gases from gas hydrate mainly originate from thermo-genesis. Furthermore, a practical formula is put forward for estimation of gas hydrate resources and the total amount is estimated to be 446.5 × 104 m3 methane within the drilling area.

Huaijun Wen

Papers

Gas Hydrates in the Qilian Mountain Permafrost, Qinghai, Northwest China

Gas hydrate occurrences in the Qilian Mountain permafrost, Qinghai Province, China

Characteristics of Gas Hydrate Stability Zone in The Muli Permafrost, Qinghai: Results Compared Between Modeling and Drilling

Geological And Geochemical Characteristics of Gas Hydrate In the Qilian Mountain Permafrost, Qinghai Province, China