Research on the Influence of Injection–Production Parameters on Challenging Natural Gas Hydrate Exploitation Using Depressurization Combined with Thermal Injection Stimulated by Hydraulic Fracturing

Abstract

The development of low-permeability hydrate reservoirs is facing serious problems. Our previous studies determined that depressurization combined with hot water injection stimulated by hydraulic fracturing (D + Tiw + HF) development mode has an excellent production potential in low-permeability hydrate reservoirs. Based on these, this study further explored the influences of injection–production parameters including injection temperature (Ti), injection pressure (Pi), and production pressure (Pp) on D + Tiw + HF through single-factor and multivariate sensitivity analysis. Results show that the influence of Ti, Pi, and Pp on D + Tiw + HF was divided into two opposite stages by the water breakthrough of production wells (twb). The hydrate decomposition rate and CH4 production rate increase linearly with the increase in Ti and Pi and decrease in Pp before twb; however, they decrease gradually with the increase in Ti and Pi and decrease in Pp after twb. The sensitivity ranges of cumulative CH4 production (VP) to Pp, Ti, and Pi are (3, 4.5), (0, 1.5), and (0, 1) in the first year and (1, 5), (0.5, 3), and (1, 2) in the fifth year, respectively. The sensitivity ranges of the energy ratio (ER) to Pp, Ti, and Pi are (−2, −1), (−6, 0), and (−2.5, −1.5) in the first year and (−1.5, −1), (−7, 0), and (−2, 1) in the fifth year, respectively. This determines that VP is most sensitive to Pp, and the ER is most sensitive to Ti. Furthermore, the ER is more sensitive to smaller Ti. The VP is more sensitive to smaller Pp in the early development stage (1 year, before twb), while it is more sensitive to lager Pp in the later development stage (5 years, after twb). As a result, an as low as possible Pp, low Ti, and higher Pi is suggested in the early development stage, while low Ti and higher Pi are suggested in the later development stage, and too small Pp is unnecessary.