Growth behavior and resource potential evaluation of gas hydrate in core fractures in Qilian Mountain permafrost area, Qinghai-Tibet Plateau

The Qilian Mountain permafrost area located in the northern of Qinghai-Tibet Plateau is a favorable place for natural gas hydrate formation and enrichment,due to its well-developed fractures and abundant gas sources.Understanding the formation and distribution of multi-component gas hydrates in fractures is crucial in accurately evaluating the hydrate reservoir resources in this area.The hydrate formation experiments were carried out using the core samples drilled from hydrate-bearing sediments in Qilian Mountain permafrost area and the multi-component gas with similar composition to natural gas hydrates in Qilian Mountain permafrost area.The formation and distribution characteristics of multi-component gas hydrates in core samples were observed in situ by X-ray Computed Tomography(X-CT)under high pressure and low temperature conditions.Results show that hydrates are mainly formed and distributed in the fractures with good connectivity.The ratios of volume of hydrates formed in fractures to the volume of fractures are about 96.8%and 60.67%in two different core samples.This indicates that the fracture surface may act as a favorable reaction site for hydrate formation in core samples.Based on the field geological data and the experimental results,it is preliminarily estimated that the inventory of methane stored in the fractured gas hydrate in Qilian Mountain permafrost area is about 8.67×1013 m3,with a resource abundance of 8.67×108 m3/km2.This study demonstrates the great resource potential of fractured gas hydrate and also provides a new way to further understand the prospect of natural gas hydrate and other oil and gas resources in Qilian Mountain permafrost area.

Evaluation of clayed silt properties on the behavior of hydrate production in South China Sea

Gas hydrate is one kind of potential energy resources that is buried under deep seafloor or frozen areas.The first trial offshore production from the silty reservoir was conducted in the South China Sea by the China Geological Survey(CGS).During this test,there were many unique characteristics different from the sand reservoir,which was believed to be related to the clayed silt physical properties.In this paper,simulation experiments,facilities analysis,and theoretical calculation were used to confirm the hydrate structure,reservoir thermo-physical property,and bond water movement rule.And the behavior of how they affected production efficiency was analyzed.The results showed that:It was reasonable to use the structure I rather than structure II methane hydrate phase equilibrium data to make the production plan;the dissociation heat absorbed by hydrate was large enough to cause hydrate self-protection or reformation depend on the reservoir thermal transfer and gas supply;clayed silt got better thermal conductivity compared to coarse grain,but poor thermal convection especially with hydrate;clayed silt sediment was easy to bond water,but the irreducible water can be exchanged to free water under high production pressure,and the most obvious pressure range of water increment was 1.9–4.9 MPa.

Formation mechanism,experimental method,and property characterization of graindisplacing methane hydrates in marine sediment:A review

Grain-displacing hydrate deposits exist at many marine sites,which constitute an important part of methane hydrate resources worldwide.Attributed to the difficulties in acquiring field data and synthesizing experimental samples,the formation and property characterization of grain-displacing hydrate remains less understood and characterized than the pore-filling hydrate in current literature.This study reviews the formation mechanisms of grain-displacing hydrate from the perspective of geological accumulation and microscale sedimentary property.The experimental methods of synthesizing grain-displacing hydrate in the laboratory and the current knowledge on the property of grain-displacing hydrate sediment are also introduced.Shortcomings in current theories and suggestions for future study are proposed.The work is hoped to provide valuable insights for the research into the hydrate accumulation,geophysics,and hydrate exploitation targeted at the grain-displacing hydrate in the marine sediments.

Introduction to Key Laboratory of Gas Hydrate,Ministry of Natural Resources

The Key Laboratory of Gas Hydrate, Ministry of Natural Resources, established in 2012 belongs to Qingdao Institute of Marine Geology, China Geological Survey. Prof. Neng-you Wu is the Director of Laboratory and Prof. Yu-guang Ye is the Director of Academic Committee (Fig. 1). Now, the laboratory has been recognized as one of the leading laboratories in the world in terms of gas hydrate experimental technology.