The effects of hydrate reformation in production wells on gas recovery from sandy hydrate bearing sediments

doi:10.13745/j.esf.sf.2024.11.21

Abstract

Abstract:

The depressurization method is widely regarded as one of the most economical and efficient methods for recovery from natural gas hydrate reservoirs. Hydrate reformation usually occurs around and inside the wellbore, hindering fluid flow, which may cause damage to engineering equipment and significantly affect the efficiency and sustainability of gas production. Based on the hydrate exploitation modeling apparatus developed by Zhejiang University, the hydrate reformation effect under different depressurizing rates and its impact on the pressure, temperature, gas production, and deformation of the hydrate bearing sediment are investigated. Results indicate that the reformation of hydrate in the wellbore causes the cyclic production of hydrate dissociation gas, significantly affecting the temperature and pressure of the reservoir. The dissociation rate decreased due to mass transfer obstruction when the wellbore flow was obstructed. The higher the depressurizing rate, the higher the peak of gas production rate; however, the higher average gas production rate can not be achieved due to the more significant hydrate reformation in the wellbore. During field multiwell exploitation, an appropriate depressurizing rate should be selected based on reservoir permeability, temperature, pressure, and other conditions, and each well can be opened and closed alternately so that the effective gas production rate can be increased by utilizing the ambient supplemental sensible heat during the well closure period.

Key words: hydrate, sediments, wellbore, hydrate reformation, depressurizing rate

CLC Number:

WANG Peng, WANG Lujun, ZHU Bin, WANG Xinbo, CHEN Yunmin. The effects of hydrate reformation in production wells on gas recovery from sandy hydrate bearing sediments[J]. Earth Science Frontiers, 2025, 32(2): 206-215.

Figures/Tables 11

Fig.1 Apparatus schematic

Fig.2 Boundary conditions and measurement point distribution

Table 1 Test conditions

工况	降压速率/ (MPa·min^-1)	初始压力/ MPa	降压目标压力/MPa	初始温度/℃	初始水合物饱和度
Case 1	0.2	3.5	1.5	5	0.165
Case 2	0.1
Case 3	0.05

Fig.3 (a)Solid liquid gas composition at initial state, (b)during hydrate dissociation, and (c)after hydrate dissociation.

Fig.4 Change of sediment pore pressure during hydrate dissociation by depressurization

Fig.5 Changes in the gas production volumes during the whole test (a) and the first 100 minutes (b)

Fig.6 Evolution of temperature during hydrate dissociation in Case 1 (a), Case 2 (b), and Case 3 (c).

Fig.7 Gas recovery rate during hydrate dissociation

Fig.8 Duration of pipeline blockage caused by hydrate reformation

Fig.9 Average and peak gas production rates of hydrate-bearing sediment

Fig.10 Displacement of sediment surface after hydrate dissociation in Case 1 (a), Case 2 (b), and Case 3 (c).

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