ABSTRACT

As an important green energy source, the presence of gas hydrates very demanding. They are only found on the seabed at a depth of kilometer. Large-scale exploitation of natural gas hydrates is likely to cause dramatic changes in the seabed topography, resulting in certain risks. Therefore, it is necessary to carry out in-situ on-line monitoring of the terrain while mining. Based on the above considerations, this paper designs a device for terrain monitoring of gas hydrate test mining area. Taking into account the complexity of the marine environment and the difficulty of submarine operations, the design uses a winch as the underwater control center, the MEMS accelerometer is placed in a cylindrical pressure chamber, and multiple sensors in the same direction form a sensor array with a coil wound on the winch. The ROV robot is used for stretching and is distributed by the motor to drive the drum to rotate. In order to ensure the reliability of long-distance data transmission and simplify the circuit, the design uses RS-485 (RS-485 is a serial bus standard that uses balanced transmit and differential receive.) for communication, and the data is transmitted to the upper computer for reconstruction to obtain the terrain of the test mining area. In the end, two experiments were designed to simulate the operation of the device on the seabed, which proved that the device can work normally under the complicated conditions of the seabed.

INTRODUCTION

Natural gas hydrate is a new type of green energy, but it is quite unstable, which makes it generally found in high pressure (≥3.8Mpa) and low temperature (≤10°C) environment (deep-sea). Gasification is easy to occur once the environment changes (E. Dendy, 2003). Natural gas hydrates are widely distributed in the world's oceans. How to rationally and efficiently mine on a large scale has become an urgent problem to be solved. Considering the harsh condition of natural gas hydrates, once the pressure changes during the mining process, a large amount of gas will be released, causing its volume to decrease, leading to settlement of the seabed topography (Paull, 2007), and the surface position of the mining area is offset, causing drilling equipment position and work affected. Therefore, in order to prevent accidents, accurately locate the surface location of the test mining area and improve the efficiency of mining operations, it is necessary to carry out terrain monitoring of the gas hydrate test mining area.

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