Research On Truth-Preserving Sampling Techniques For Gas Hydrates

Now, most organizations collect sediments in deep sea to analyse whether gas hydrates(GH) exist or not. Due to GH's special property, it can decompose in normal temperature and normal atmosphere when to offing. Thus, scientists begin to develop Pressure Core Sampler(PCS) to maintain GH in situ pressure .In this thesis, through the study of character of seabed sediments, character of pressure container, method of insulation and transfer of sample, puts forward high sampling-rate technique and low-disturbing sampling technique, truth-preserving sampling technique and safety sampling technique. Based on these theories, designs a new type of corer - pressure piston corer(PPC). It can meet our requirement of exploring GH through experiment.The thesis includes senven chapers.Chapter 1 introduces the background of gas hydrates and development of the sediment corer. Analyzes the advantages and disadvantages of present sampling technique, and its developing trend. Then puts forward the purpose, significance and main content of this project.In chapter 2, through the geological characteristics study of the bottom sediments, finds out the influence of the sediments' physical and mechanical characteristics to sampling. On this base, doing research on sampling rate and disturbing to sample, puts forward piston sampling, impulse sampling and optimum of the structure of sampling barrel, which increases sampling rate and reduces influence on sample.Chapter 3 analyzes the pressure theory of PPC during sampling. Puts forward the rule of auto pressure tight and insulation technique.Chapter 4 mainly illuminates safety sampling technique, including theory of corer tube stability, qualitative analysis of parameters of corer releasing and a new type connection of plug pin.Chapter 5 introduces the structure of PPC, its principle and key technique.Chapter 6 analyzes the experiment of PPC.The last chapter looks back to the whole thesis and puts forward the fruits of the study. At last, the further study direction is brought out.