Abstract
This work focuses on the assessment of the effect of well completion types on gas productivity in subsea gas hydrate reservoirs of class 1G type where the gas hydrates have decomposed into gas and water. Three types of vertical well completions are considered: frac-packed well with vertical hydraulic fracture; frac-packed well with horizontal hydraulic fracture, and a cased-hole gravel-packed well. Sensitivity analysis was conducted with analytical well inflow models to determine factors that affect the gas well productivity. The results of the analyses indicated that proppant mass pumped during fracture treatment slightly improves well productivity for frac-packed natural gas hydrate wells. Well productivity increases nonlinearly with fracture productivity up to a threshold value of 50,000 md for frac-packed well with horizontal fracture, above which further increase in fracture conductivity would create no benefit. With a proppant mass of 50,000 Ibm and a corresponding proppant volume of 504 ft3, commercial gas production rates of 14.9 MMscf/d, 5.621 MMscf/d, and 11.35 MMscf/d are possible for frac-packed well with vertical fracture, frac-packed well with horizontal fracture, and cased-hole gravel-packed well, respectively. Because hydraulic fracture orientation depends on the in-situ formation stress, whether a well should be hydraulic-fractured or not depends on in-situ formation stress.
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