Experimental research on the breaking effect of natural gas hydrate sediment for water jet and engineering applications

Abstract

Experimental studies on the influence of traverse speed, jet flow rate, and reciprocating times of jet flushing on natural gas hydrate sediment breaking effect under water jet were carried out. The breaking effect was evaluated from four aspects: shape regularity of broken hole, variation of broken hole diameter, breaking efficiency, and solid phase concentration of slurry formed by the jet. Results show that a uniform arrangement of 18 nozzles in radial direction of the water jet mining head can ensure that broken hole shape is regular and circular. To reach a 0.5 m hole diameter, the reciprocating times of flushing increases with the increase of the traverse speed and decreases with the increase of the jet flow rate. The breaking efficiency which is very low at small borehole diameter increased first and then decreased with the increase of the hole diameter. The increase of the jet flow rate and traverse speed is conducive to improve breaking efficiency. However, that leads to extremely high solid phase concentration of slurry, which will increase the risk of pipeline transportation. In order to achieve well breaking effect of natural gas hydrate sediment by water jet, the recommended technological parameters are jet flow rate of 450 L/min, traverse speed of 5 m/min and 5 reciprocating times of flushing when the initial hole diameter is 0.1 m. This study provides a reference for the formulation of the technological parameters for the first solid fluidization well testing and production operation in the world.