By China Geological Survey(CGS)

New types of high-concentration gas hydrate samples were found in the sea to the east of Pearl River Mouth Basin in offshore of Guangdong Province by Chinese scientists through drilling for first time during June to September, 2013. The probable reserves of gas hydrates are very considerable. Gas hydrate samples discovered this time are characterized by shallow burying, large thickness, multiple types, high concentration. The gas hydrates exist in two layers within 220 meters below seafloor with 600~1100m water depth. The thickness of upper layer is about 15m and the lower one is about 30m. The natural occurrences of gas hydrates have several types, including bed, bulk, nodule and vein, which can be visible. The average concentrations of gas hydrates in cores are 45%~55%, and methane makes up 99% of the sample. Through the 23 drilled wells, gas hydrates are estimated to be distributed in 55km² areas. The probable reserves of newly discovered gas hydrates are equivalent to natural gas reserves of 100b-150b cubic meters, which reaches to the scale of super-large conventional natural gas field. These data are helpful for determining the target of trial production in the next step, and creating the stable foundation for Chinese to produce the gas from hydrate deposits.

The investigation and evaluation of gas hydrates in China started late. In 1995, the former Ministry of Geology and Mineral Resources started the research work. And in 1999, with the great supports from the National Development and Reform Commission and the Ministry of Finance, the Ministry of Land and Resources formally initiated the gas hydrates investigation. Up till now, China Geological Survey of the Ministry of Land and Resources has carried out 40 cruises of gas hydrates investigation in northern South China Sea and have accomplished 45800km of high-resolution multi-channel seismic survey, 36800km of multi-beam bathymetric survey, 7100km of sub-bottom profile survey, 1480 sites of submarine geological sampling and 222 sites of submarine heat flow survey. Besides, China-Germany co-operation cruise of SO-177 conducted in 2004 has made significant contribution on the study of distribution and formation of gas hydrates and its impact on environment in the northern South China Sea.

After more than ten years, China gradually finds out a comprehensive technology system for gas hydrates investigation which adapts to the China seas. China has developed key technologies by itself, such as target exploration by combination of high-resolution multi-channel seismic survey and submarine seismic, submarine micro-geomorphology, heat flow exploration, submarine in-situ pore water sampling, and so on. China has systematically summarized the controlling factors and enrichment models of gas hydrates, and has built a multiple-enrichment theory of gas hydrates in the passive continental margin.

On the basis of comprehensive research, China has been finding out plenty of abnormal features about geology, geophysics, geochemistry and biology of gas hydrates occurrences. China has delineated the perspective areas and favorable areas of gas hydrates resources, and has determined the drilling target for gas hydrates. All of these provide powerful theoretical guidance and technological guarantee to the investigation and evaluation for gas hydrates resources in China seas.

In 2013, Guangzhou Marine Geological Survey, which belongs to Chines Geological Survey, has carried out three legs of drilling works for 102 days in the sea to the east of the Pearl River Mouth Basin for the first time. 26 scientists from 5 institutions participated gas hydrate drilling expedition including the field deploying, coring planning, samples analyzing and other works. During the period, they overcame the harsh oceanic conditions such as typhoons, and utilized technologies including advanced deep diving submersible, logging while drilling, pressure coring, doing field experiments, and accomplished accurate positioning of drilling hole, monitoring while drilling, target locking and sampling under the condition of 600~1100m water depth.

In the first leg, logging while drilling of 10 pilot holes of 10 sites was carried out and the logging footage is 2198m. Logging data including temperature and resistivity data were obtained. Obvious abnormal features for gas hydrates in 4 pilot holes were found out, which are helpful for the determination of target sites and beds in the next step of drilling.

In the second leg, 8 wells drilling in 4 sites were carried out. Multiple types of gas hydrates samples were obtained. Distribution ranges of gas hydrates were determined, and the probable reserves of gas hydrates converted to natural gas were also calculated. The most significant discovery in this leg is that there are multiple types and multiple layers of gas hydrates. Furthermore, the new discovered gas hydrates with characteristics of large thickness of hydrate-bearing layers, high concentration of gas hydrates and high purity of methanes.

In the third leg, wire line logging in 3 sites and 2 drilling wells were carried out, which provides abundant materials for further study of accumulation mechanism and evaluation of gas hydrates.

In the future, according to the requirement of national planning and deploying, the Ministry of Land and Resources will implement investigation and evaluation of gas hydrates in sea and land areas in comprehensive organization and operation. There are following works still need to be done well: (1) Speed up investigation and evaluation of gas hydrates and core drilling of key target areas; (2) Conduct theoretical studies such as accumulation mechanism and enrichment pattern of gas hydrate; (3) Enhance the work in key technologies including gas production from hydrate deposits and their environment assessment, to accomplish the aims of developing and utilizing of gas hydrates as soon as possible and try to make efforts to guarantee of national clean energy reserves.