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 (T i), injection pressure (P i), and production pressure (P p) on D + Tiw + HF through single-factor and multivariate sensitivity analysis. Results show that the influence of T i, P i, and P p on D + Tiw + HF was divided into two opposite stages by the water breakthrough of production wells (t wb). The hydrate decomposition rate and CH4 production rate increase linearly with the increase in T i and P i and decrease in P p before t wb; however, they decrease gradually with the increase in T i and P i and decrease in P p after t wb. The sensitivity ranges of cumulative CH4 production (V P) to P p, T i, and P i 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 P p, T i, and P i 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 V P is most sensitive to Pp , and the ER is most sensitive to T i. Furthermore, the ER is more sensitive to smaller T i. The V P is more sensitive to smaller P p in the early development stage (1 year, before t wb), while it is more sensitive to lager P p in the later development stage (5 years, after t wb). As a result, an as low as possible P p, low T i, and higher P i is suggested in the early development stage, while low T i and higher P i are suggested in the later development stage, and too small P p is unnecessary.

Numerical Evaluation of Long-Term Depressurization Production of a Multilayer Gas Hydrate Reservoir and Its Hydraulic Fracturing Applications

“…The initial conditions of the hydrate reservoir are determined according to the process described by Moridis et al , The top and bottom boundaries of the simulated domain (corresponding to the uppermost and lowermost grid block layers, respectively) are set as a constant pressure and temperature. , The geothermal gradient at this site is 0.0443 °C/m with a seabed temperature of 3.7 °C, and the pressure in the sediments is considered to follow a hydrostatic distribution. Then, the temperature and pressure of the boundary layers can be determined, where the pressure is calculated using the pressure, temperature, and salinity-adjusted water density .…”

Numerical Evaluation of Commingled Production Potential of Marine Multilayered Gas Hydrate Reservoirs Using Fractured Horizontal Wells and Thermal Fluid Injection

“…The co-production performances of four development modes were compared, that is, depressurization without stimulation (D), stimulation using fracturing (D+F) or thermal fluid injection (D+T), or both (D+T+F). Additionally, referring to the existing research, the fracture conductivity was set to 10-100 D•cm [21]. Ultimately, the factors examined include stimulation methods, fractured sublayers, fracture spacing, and fracture conductivity, with simulation scenarios presented in Table 2.…”

“…injecting gases (mainly CO 2 ) that are more likely to form hydrates to replace CH 4 molecules in NGH cages [19]; v. injecting chemical inhibitors like brine to promote NGH dissociation [20]; vi. integrating multiple methods, such as combining fracturing and multi-well systems [21], and using thermal stimulation and chemical inhibitors [22]. Nevertheless, these studies mainly focus on the production dynamics of reservoirs with a single HBL, with few simulations exploring the commingled production of multilayers.…”

Reservoir Stimulation Technologies for Natural Gas Hydrate: Research Progress, Challenges, and Perspectives

“…Chen et al explored the influence of different heat injection pressures, temperatures, and production pressures on mining using the above scheme. They found that the hydrate dissociation and gas production rates increased linearly with an increase in the heat injection temperature pressure and a decrease in the production pressure before t wb but showed the opposite trend after t wb .…”

“…Furthermore, horizontal fracture conductivity is the main influencing factor for improving gas production, whereas the influence of vertical fracture conductivity is negligible. An optimal fracture spacing exists and the hydrate decomposition performance is significantly improved when the fracture spacing is less than 2 m. Chen et al 105 explored the influence of different heat injection pressures, temperatures, and production pressures on mining using the above scheme. They found that the hydrate dissociation and gas production rates increased linearly with an increase in the heat injection temperature pressure and a decrease in the production pressure before t wb but showed the opposite trend after t wb .…”