Pressure-retaining sampler for sediment and overlying seawater based on heavy duty ROV-Jellyfish

Abstract

Methane leakage at sediment seawater interface is an important basis for gas hydrate exploration. Therefore, a low disturbance in-situ encapsulation and pressure-retaining sampler for sediment and overlying water with a working depth of 3000 m is developed recently to provide support for evaluating regional methane flux. This sampler can also separate and transfer the sediment and overlying water with retaining pressure. By using the coupled Eulerian-Lagrangian (CEL) approach in the finite element software ABAQUS, which provides a variety of soil constitutive models, the tube-soil interaction during penetration is numerically investigated. The use of a 60 mm diameter sampling tube can achieve a higher sampling rate under low penetration resistance. Through the laboratory pressure test (30 MPa), it is verified that the pressure-retaining capacity of sampler can ensure that the pressure drop does not exceed 3.9% within 2 h. Furthermore, the pressure-retaining samples of more than 700 ml were obtained each time in sea trials at three stations, which verifies the feasibility of the device application. The analysis of gas composition shows that the dissolved gas is mainly methane (> 99.1%), and all the sampling points fall in the thermogenic gas area.