Study on the influence of reservoir permeability evolution around production wells on production capacity of natural gas hydrate

doi:10.13745/j.esf.sf.2024.11.25

Abstract

Abstract:

The use of fracturing technology to transform and increase production in hydrate reservoirs has been proven to have application prospects for hydrate production. The main purpose of this study is to analyze the gas production patterns of reservoirs under the interaction between two production wells, and to obtain the optimal distance between production wells. This article is based on the hydrate occurrence parameters of DK-2 station in the permafrost region of the Qilian Mountains. The reservoir outside the dual production wells were fractured by fracturing, and the production potential of this method for extracting hydrate sediments in the permafrost region was evaluated through numerical simulation. The simulation results show that the use of hydraulic fracturing method to enhance the permeability of the surrounding reservoirs of the mining well has broken through the technical bottleneck of using only depressurization method to extract hydrates. The gas production rate and cumulative gas release are higher than traditional depressurization methods, and the average gas water ratio has significantly increased. After the rock matrix around the horizontal well ruptures, it will increase the flow characteristics of the fracturing zone, thereby promoting the propagation distance of pressure drop. The infiltration of hydrate decomposition areas between horizontal production wells is conducive to promoting the decomposition of gas and water flow towards the production wells. In addition, hydraulic fracturing methods are very effective for hydrate reservoirs with intrinsic permeability below 1 mD, and the recommended optimal distance between production wells is 45-60 m.

Key words: gas hydrate, reservoir renovation, permeability, frozen soil areas, well spacing

CLC Number:

TE38

SHEN Pengfei, HOU Jiaxin, LÜ Tao, BI Haoyuan, HE Juan, LI Xiaosen, LI Gang. Study on the influence of reservoir permeability evolution around production wells on production capacity of natural gas hydrate[J]. Earth Science Frontiers, 2025, 32(2): 166-177.

Figures/Tables 13

Fig.1 DK-2 Simulation area model diagram

Table 1 Physical parameters of DK-2 in the permafrost region of Qilian Mountain

参数	数值
左右井间距	45.0 m
埋深	235.3 m
初始压力p_B	4.19 MPa
温度T_B	277.84 K
开采井初始压力p_W0	3.91 MPa
孔隙度、初始饱和度	Φ=0.3、S_H=0.40、S_A=0.60
气体组分	100% CH₄
地温梯度	0.013 K/m
本征渗透率(k_x=k_y=k_z)	1×10^-15 m² (1 mD)
开采井渗透率	5×10^-9 m² (5 000 D)
湿热导率、干热导率	3.1、1.0 W/(m·K^-1)
复合导热模型^[27]	k_ΘC=k_ΘRD+(S_A^0.5+S_H^0.5) (k_ΘRW-k_ΘRD)+ϕS_Ik_ΘI
毛细压力模型^[28]	P_cap=-P₀₁[(S^)^-1^/λ-1)] S^=(S_A-S_irA)/(S_mxA-S_irA)
相对渗透率模型^[28]	k_rA=( S_A^)ⁿ k_rG=(S_G^)^nG S_A^=(S_A-S_irA)/(1-S_irA) S_G^=(S_G-S_irG)/(1-S_irG)
(SirA & SirG)	0.30、0.05
(λ)	0.45
(P₀₁)	105 Pa
n和n_G^[29-30]	3.572

Fig.2 Accumulated gas production under different fracturing radius

Fig.3 Accumulated water production under different fracturing radius

Fig.4 Gas to water ratio and remaining resource percentage under different fracturing radius

Fig.5 Accumulated gas production under different permeability in the fracturing area

Fig.6 Accumulated water production under different permeability in the fracturing area

Fig.7 Gas to water ratio and remaining resource percentage under different permeability in the fracturing area

Fig.8 Comparison of Ori. and Ref. group for SH distribution

Fig.9 Comparison of Ori. and Ref. group for SG distribution

Fig.10 Comparison of Ori. and Ref. group for p distribution

Fig.11 Comparison of between origin and reference group for temperature T distribution

Fig.12 Comparison of origin and reference group for SIce distribution

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