Improving the Production Performance of Low-Permeability Natural Gas Hydrate Reservoirs by Radial Water Jet Slotting and Grouting in a Horizontal Well

Most natural gas hydrate (NGH) reservoirs have poor permeabilitycharacteristics, which is unfavorable to fluid flow and gas production.To enhance gas production, a new method of radial water jet slottingand grouting (RWJSG) was proposed to reconstruct the formation aroundhorizontal wellbores of a horizontal well. To evaluate the effectivenessof the proposed method, a three-dimensional (3D) gas production modelwas constructed with reference to the NGH reservoir at the SH2 sitein the South China Sea (SCS). The results show that RWJSG can effectivelyenhance the gas recovery of the horizontal well. Compared with anunreconstructed case, the hydrate dissociation efficiency, cumulativegas production, and average ratio of gas to water production in theRWJSG case are increased by 121.0, 116.3 and 46.1%, respectively,during the 720-day production period. RWJSG can enlarge reservoirexposed area, promote pressure drop transfer, and improve gas/waterflow near the wellbore. In addition, the effect of increasing productionmainly depends on the slot radius and number. Within a certain range,the decrease in slot spacing and increase in slot filler permeabilityhave positive effects. For the reservoir at SH2 site, the scheme witha radius of 5 m, a spacing of 5 m, a number of 5 and a permeabilityof 500 mD could achieve remarkable stimulation effect. This work providesideas and guidance for stimulation of horizontal wells in NGH reservoirsby RWJSG.