An ice-valve-based pressure-coring system for sampling natural hydrate-bearing sediments: Proof-of-concept laboratory studies

Abstract

Less than 60% hydrate-bearing sediment pressure cores can be retrieved by current pressure corers because of sealing failures. This is attributed to the sensitivity of mechanical valves to solid particles and drilling cuttings. In order to improve the pressurized core recovery of natural gas hydrate-bearing sediment coring, a pressure corer based on an ice valve made out of in situ drilling fluid during coring is proposed. A series of preliminary laboratory experiments were conducted to characterize the ice valves proposed for the pressure corer. The ice valves made from the pure drilling fluid (used in the Scientific Drilling Project of Gas Hydrate in the Qilian Mountains) or the drilling fluid contains different mass concentrations and granularity of quartz and kaolin particles. Several ice valves with various lengths were tested for their sustained pressure. Results show that the sustained pressure of the ice valve increases almost linearly with the valve length. An ice valve formed at −30 °C with a nominal diameter of 58 mm and a length of 85 mm can retain a pressure greater than 25 MPa without leakage. The sustained pressure of the ice valve can be adjusted by changing the ice valve length to accommodate different drilling sites. Experiments verified that the ice valves were insensitive to both solid particles and rust. It indicates that the proposed ice-valve-based pressure corer can be a potential solution to increase the recovery of pressurized hydrate-bearing sediment core.