Gas Production from Fractured Hydrate Reservoirs: Numerical Modeling and Evaluation

Fractured natural gas hydrate (NGH) reservoirs are widely tested all over the world. Existence of fractures will aggravate the basin-scale heterogeneity in both NGH distribution and seepage properties and, therefore, inevitably challenge some of our former understanding on gas production. However, gas productivities of the fractured NGH reservoirs have not been evaluated so far due to the rare accessible logging data for detailed characterization of fractures. Gas production from the fractured NGH reservoirs is modeled and the differences made by position, width, and length of the single conducive fracture and the single hydrate-filled fracture (HFF), respectively, are systematically analyzed. Sequentially, randomly distributed fracture networks are also considered in the gas productivity estimation. Results show that the conducive fractures in the overburden influence water production dramatically. When hydrate-bearing layers (HBLs) are characterized with HFFs, there will be obvious secondary formation near the HFFs, which together with its initial high NGH saturation hinders the pressure dissipation and the gas migration, generally shortening the production duration and reducing the accumulated gas. When the overburden and the HBLs are characterized with a randomly distributed fracture network, input fluid from upward could enhance gas production to some extent and lead to a fluctuated gas productive rate.

Automated summary

Fractured natural gas hydrate reservoirs can significantly impact gas production, with conducive fractures affecting water production dramatically and hydrate-filled fractures in HBLs hindering pressure dissipation and gas migration to shorten production duration and reduce gas accumulation. Additionally, randomly distributed fracture networks in the overburden may enhance gas production to some extent and lead to a fluctuated gas productive rate.