Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Design of MEMS Sensor Network for Submarine Hydrate Mounds Deformation Monitoring
Yongqiang Gea,b, Jiawang Chena,b,c*, Xiaoling Lea, Jingkun Aia,b, Chen Caoa, Peng Zhoua, Tao Lianga

Ocean college, Zhejiang University, Zhoushan, ChinabHainan Institute, Zhejiang University, Sanya, China
cThe Engineering Research Center of Oceanic Sensing Technology and Equipment, Ministry of Education, Zhoushan, China*Corresponding author: Jiawang ChenaThe MEMS (Micro-Electro-Mechanical System) Sensor Network usedon submarine hydrate mounds deformation monitoring is proposed,
which consists of horizontal array (up to 21 m) and vertical array (up to3 m) and can realize synchronous monitoring of the seabed and shallow
strata deformation. The deployment mechanism of the verticalmonitoring array is analyzed. The self-capacitive monitoring network
has low power consumption and is easy to achieve long-term in-situ
monitoring.

pressure (Liu et al., 2015) and topography changes (Saito andYokoyama, 2008; Yokoyama et al., 2012), but the single monitoringnode and limited monitoring range make. The submarine cabled
observatory can achieve long-term, in-situ and real-time monitoring,but in fact, the monitoring location of which is relatively fixed and poor
mobility, the cost is high, and the placement technique is difficult,making it not suitable for submarine hydrate mound monitoring.
Therefore, in order to deeply study the evolution processes and its
mechanism of hydrate mounds and carry out long-term in-situ
monitoring, long-term in-situ device based on MEMS sensor network isdeveloped in this paper.

KEY WORDS: Gas hydrate; Submarine hydrate mound; MEMS
sensor network; Long-term monitoring; In-situ deployment.

IN-SITU MONITORING DEVICE BASED ON MEMSSENSOR NETWORKINTRODUCTION

The MEMS sensor monitoring network consists of horizontal arrays
and vertical arrays, respectively deployed on the surface and inside thehydrate mound, as shown in Fig. 1. The horizontal array is mainlycomposed of MEMS nine-axis sensors (accelerometers, gyroscopes andmagnetometers), which are used to monitoring the vertical changes ofterrain (including terrain subsidence and uplift). The vertical one iscomposed of more types of MEMS sensors (including
temperature/pressure/methane sensors, accelerometers and gyroscopes),to monitor the deformation, temperature, pressure and the concentrationof methane at different depths. The three-dimension sensor network canobtain the vertical and horizontal deformation of the hydrate mound atdifferent moment. Finally, the evolution process of hydrate moundswith the changes of temperature, pressure and methane flux can beobtained through three-dimension terrain deformation reconstruction
and data synchronization.

ABSTRACTGas hydrate is a solid phase comprised of water and low-molecularweight gases, usually methane, that forms within sediments underconditions of low temperature, high pressure and adequate gas
concentration (Ruppel and Waite, 2020). The submarine hydrate moundis a common micro-topography in the submarine gas hydrate
occurrence area or the natural gas seepage region (Mackay, 1998), theshape of which is similar to the pingo-like feature in the permafrostregion, therefore, also called submarine hydrate pingo (Paull et al.,2007). Studying on the seafloor hydrate mounds is crucial since they
are important indicators of submarine methane seepages, shallow gas
hydrate, hydrocarbon reservoirs and seabed instability. The exposed
hydrates above and inside hydrate mounds is in a critical equilibrium
state. Once the seabed temperature increases, pressure or the gas flux
decreases, the near-seabed gas hydrate will decompose, reducing thestrength of sediments, causing the collapse and instability of the seabed,and even large-scale disasters in landslide areas (Loher et al., 2018).

Horizontal sensor array

The horizontal array is composed of MEMS nine-axis sensors, and theoutside is a flexible oil-filled tube (PVC tube), as shown in Fig. 2. The
length of the array is 21m, with 21 nodes, and the interval between
adjacent nodes is 1m. In order to ensure the good coupling between thehorizontal array and the seabed sediments, lead blocks are placed
between the sensor nodes to improve the overall density of the sensor
array to resist the buoyancy of seawater. The MEMS sensors are placedin the pressure chamber, and each sensor is connected by watertightconnectors to ensure its ability to work at a depth of 3000 meters. TheThe geophysical instrument and vessel-based equipment enables in-situ
observation the morphology of submarine hydrate mounds. However,these instruments need to be equipped with scientific ships, having along observation period, preventing long-term continuous in-situ
monitoring from being realized. The existing self-capacitive sensor
systems can realize in-situ continuous monitoring of seabedtemperature (Macdonald et al., 1994; Vardaro et al., 2006), pore water579