Numerical Simulation of Thermal Flow Coupling in Well-Rock Combined EGS

doi:10.12068/j.issn.1005-3026.2026.20240133

Abstract

Abstract:

Existing studies overlook the well-rock coupling process and deep wellbore heat transfer effects， making it difficult to accurately evaluate the heat extraction performance of enhanced geothermal system （EGS） in hot dry rock. To address this issue， a three-dimensional thermal flow coupling model for well-rock combination based on COMSOL was developed， and the impact of various factors on the heat extraction performance of the EGS was analyzed. The simulation results show that the heat extraction process of EGS primarily relies on heat transfer through fractures and wellbores， with heat exchange through fractures contributing 73% and that through wellbore accounting for 27%. In a single injection and production mode， the best heat extraction occurs at a 500 m spacing between wells， with an outlet temperature reaching 145.5 ℃. Increasing the injection flow rate raises the outlet temperature， but shortens the heat reservoir’s lifespan. Optimizing well layout and flow heat transfer paths reveals that the single injection and production layout has a longer lifespan and higher outlet temperature， while the single injection and four production mode achieves the highest heat extraction， 3.1 times that of the single injection and production.

Key words: hot dry rock, enhanced geothermal system, thermal flow coupling, heat extraction performance, outlet temperature

CLC Number:

TK 529

Ying-ying YU, Hui DONG, Liang ZHAO, Han-lu XU. Numerical Simulation of Thermal Flow Coupling in Well-Rock Combined EGS[J]. Journal of Northeastern University(Natural Science), 2026, 47(1): 145-152.

Figures/Tables 13

Fig.1 Geometric model of EGS

Table 1 List of symbols

符号	含义	单位	符号	含义	单位
$u s$	基质内达西速度	m/s	$ε s$	基质孔隙率
$u f$	裂隙内达西速度	m/s	$ε f$	裂隙孔隙率
$u h$	井内流动速度	m/s	$K s$	基质渗透率	m²
$ρ w$	采热工质密度	kg/m³	$K f$	裂隙渗透率	m²
$ρ s$	岩石基质密度	kg/m³	$d f$	裂隙开度	m
$μ w$	采热工质黏度	Pa·s	$A c$	井眼截面积	m²
$c w$	采热工质比热容	J/(kg·K)	$d h$	井直径	m
$c s$	岩石基质比热容	J/(kg·K)	$α$	地热扩散系数	m²/s
$ρ c p e f f$	有效体积热容	J/(kg·K)	$θ i n j$	注入温度	℃
$λ w$	采热工质导热系数	W/(m·K)	$θ h$	井筒温度	℃
$λ s$	岩石基质导热系数	W/(m·K)	$θ s$	基质温度	℃
$λ e f f$	有效体积导热系数	W/(m·K)	$θ f$	裂隙面温度	℃

Table 1 List of symbols

符号	含义	单位	符号	含义	单位
$u s$	基质内达西速度	m/s	$ε s$	基质孔隙率
$u f$	裂隙内达西速度	m/s	$ε f$	裂隙孔隙率
$u h$	井内流动速度	m/s	$K s$	基质渗透率	m²
$ρ w$	采热工质密度	kg/m³	$K f$	裂隙渗透率	m²
$ρ s$	岩石基质密度	kg/m³	$d f$	裂隙开度	m
$μ w$	采热工质黏度	Pa·s	$A c$	井眼截面积	m²
$c w$	采热工质比热容	J/(kg·K)	$d h$	井直径	m
$c s$	岩石基质比热容	J/(kg·K)	$α$	地热扩散系数	m²/s
$ρ c p e f f$	有效体积热容	J/(kg·K)	$θ i n j$	注入温度	℃
$λ w$	采热工质导热系数	W/(m·K)	$θ h$	井筒温度	℃
$λ s$	岩石基质导热系数	W/(m·K)	$θ s$	基质温度	℃
$λ e f f$	有效体积导热系数	W/(m·K)	$θ f$	裂隙面温度	℃

Fig.2 Relationship of well-rock thermal flow coupling

Table 2 Parameter setting

部件	参数	数值	单位	部件	参数	数值	单位
岩层	密度	2 700	kg/m³	地热井	注水流量	20	kg/s
	比热容	1 000	J/(kg·K)		井直径	0.3	m
	导热系数	3	W/(m·K)		注入温度	20	℃
	地表温度	20	℃		传热工质水
	孔隙度	0.05			井内壁面厚度	10	mm
	渗透率	2.9×10^-15	m²		注水井导热系数	40	W/(m·K)
裂隙	孔隙度	0.2			采出井导热系数	5	W/(m·K)
	渗透率^[17]	1×10^-10	m²
	裂隙开度	3	mm

Fig.3 Grid independence verification

Fig.4 Model verification

Fig.5 Temperature cloud map of well cross-section and fracture interface

Fig.6 Variation of temperature of main heat exchange channels with time

Fig.7 Variation of outlet temperature and heat extraction rate with well spacing

Fig.8 Variation of outlet temperature and heat extraction rate with injection flow rate

Fig.9 Well layout options

Fig.10 Temperature cloud map at 40 years for well cross-section and fracture interface

Fig.11 Variation of outlet temperature and heat extraction with well layout options

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