Enhancement of gas production from natural gas hydrate reservoir by reservoir stimulation with the stratification split grouting foam mortar method

The stratification split grouting foam mortar method (SSGFM) was first proposed to stimulate the low-permeability gas hydrate reservoir through constructing the fast flow channel for enhancing gas production. Based on the low-permeability hydrate-bearing sediments (HBS) at SH2 site in the Shenhu area of South China Sea, the foam mortar layer (FML) reservoir model was constructed. The numerical simulation that coupled thermal-hydraulic-mechanical processes was employed to evaluate the efficiency and feasibility of this method. Results show that the FML could effectively promote the expansion of the low-pressure zone into the hydrate reservoir, and enhance gas hydrate dissociation rate, cumulative gas production and energy efficiency. The foam mortar layers (FMLs) have significant influence on the spatial distribution and the evolution characteristics of reservoir thermophysical and geomechanical parameters during gas production. The sensitivity analysis of FML shows the number of FMLs, thickness and permeability of FML exist the critical values for meeting the demand of promoting hydrate dissociation and gas production. Although the cumulative gas production and gas production rate will greatly increase with enlarging the radius, the gas-to-water ratio increase slightly. In view of the hydrate reservoir at SH2 site, the recommended number of FMLs is 4-6, and the distance between the FML and overburden/underburden should be more than 7.5 m. In addition, the optimal values of thickness, radius and permeability of FML are 5 cm, 40 m and 1 x 10(-10) m(2), respectively. The geomechanical response indicates that the FMLs are beneficial for reservoir stability while improving gas production.