ABSTRACT

The rapid sampling technology for marine gas hydrate (RSTGH) is proposed to improve the efficiency of hydrate resource evaluation. RSTGH mainly consists of hydraulic reverse circulation sampling (HRCS) apparatus and mud cooling system. By Lab tests of mud cooling system, it is verified that 800 L/min mud circulation of 24°C could be cooled to −6.1°C within 45 min. Furthermore, the experiment of HRCS was carried out in offshore, and average core recovery rate is 86% in unconsolidated formation. Through simulation of mud circulation, the temperature of mud outlet is stable at −1.21°C after circulating 9 h in 1200 m hole, with the temperature of mud inlet −5°C and flow rate 800 L/min. Finally, the feasibility of RSTGH is verified. It provides a new method for rapid evaluation of marine hydrate resources.

INTRODUCTION

Natural gas hydrate is a solid ice-like crystalline substance formed from natural gas and water under high pressure and low temperature conditions (Sloan et al., 2007; Makogon et al., 2007). It is estimated that the global geological resources of gas hydrates are roughly twice as much as total global resources of fossil fuels such as coal, oil and natural gas (Milkov, 2004; Boswell et al., 2011). And approximately 97% of the world's gas hydrate is found in the oceans, only 3% are found in the terrestrial permafrost area (Klauda et al., 2005; Timothy et al., 2011). Until now, hydrate reservoirs have been found in South China Sea, Nanki Trough of Japan, eastern coast of India, Gulf of Mexico of United States, and Ulleung Sea of South Korea.

At present, the pressure and temperature sampling tools are often used in the process of marine gas hydrate exploration to obtain in-situ samples from hydrate formation, avoiding hydrates decomposition in sampling. The famous pressure core tools have been used successfully including pressure core barrels (PCB) developed by Deep Sea Drilling Project (DSDP) (Peterson, 1984), Pressure Core Sampler (PCS) used in Ocean Drilling Project (ODP) (Pettigrew, 1992), Fugro Pressure Corer (FPC) and HYACE Rotary Pressure Corer (HRC) developed by EU funded HYACE/HYACINTH programs (Schultheiss et al., 2009), Pressure Temperature Core Sampler (PTCS) and hybrid PCS developed by Japan (Kawasaki et al., 2006; Kubo et al., 2014).

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