Numerical simulation of gas hydrate production in shenhu area using depressurization: The effect of reservoir permeability heterogeneity

An accurate description of the reservoir characteristics is essential to the precise prediction of gas production from nature gas hydrate (NGH) deposits. In most numerical studies related to large-scale onshore or offshore NGH production cases, the reservoir permeability was usually assumed to be homogeneous. In this work, a multi-layered heterogeneous-permeability reservoir model (including a hydrate-bearing layer, a three-phase layer, and a free gas layer) was established, and the gas production behavior was analyzed by using the TOUGH + HYDRATE simulator. It is found that hydrate and free gas tend to be scatteredly distributed in this reservoir model. Reservoirs with heterogeneous permeability have better gas production performance than homogeneous ones. The 10-year cumulative gas production from the heterogeneous reservoir with the heterogeneity degree of 0.4μ (622 × 104 m3) is 15.19% higher than that from the homogeneous reservoir (540 × 104 m3). Moreover, the layered production results show that the free gas layer contributes the most to gas production among the three layers. The effect of heterogeneity on gas production in high-permeability reservoirs is more obvious than that in low-permeability reservoirs. Therefore, the permeability heterogeneity of the reservoir, especially the permeability heterogeneity of the free gas layer, should be considered in the long-term prediction of NGH production.