Heat transfer characteristics of coaxial tubes type deep borehole heat exchanger in water-rich geothermal reservoir

doi:10.11949/0438-1157.20201651

Abstract

Abstract:

According to the operation principle of the coaxial tubes type deep borehole heat exchanger (DBHE), a three-dimensional unsteady state heat transfer model coupled inside and outside of the borehole was established, based upon hydrogeological conditions of water-rich hot reservoirs with the buried depth of 1000—3000 m in Bohai Basin. The transient analytical solutions were obtained by applying Laplace and Fourier transform methods to calculate the vertical temperature profiles in the inlet (outlet) pipe and the grout of the DBHE and the excess temperature in aquifers. The mathematical model and the analytical solutions were validated by the experimental data determined from a demonstration project and the numerical simulation of the finite volume method (FVM). Based on the dual-continuum spatial coupling approach, the influence was performed to examine the seepage process of underground water on the heat transfer performance of the DBHE in water-rich hot reservoirs. The simulated calculation indicates that the average heat exchange capacity increment of the DBHE is up to 55 kW, when the quantity of the circulating water is stable at 30 m³/h and the Darcy velocity of underground water increases from 0 to 5×10^-6 m/s in water-rich hot reservoirs. However, the average heat exchange capacity increases 34 kW meanwhile the circulating pump power consumption increases 20.6 kW, ignoring the seepage process, when the quantity of the circulating water is enhanced from 30 m³/h to 60 m³/h. Studies have shown that as the seepage velocity increases, the heat transfer mechanism in the thermal reservoir changes, thereby enhancing the heat transfer process of the deep well heat exchanger; at the same time, it reduces the influence of the circulating water flow on the heat transfer performance of the deep well heat exchanger.

Key words: deep borehole heat exchanger, water-rich geothermal reservoir, heat transfer, numerical analysis, computer simulation, seepage process

摘要：

基于所建立的深井套管式换热器井孔内、外非稳态传热模型，推导得到富水型热储层地下水渗流作用下深井换热器进（出）水管、固井水泥温度以及热储层过余温度的瞬态解析解。以示范工程现场监测数据与有限体积法数值计算结果为验证依据，探究热储层中渗流过程对于深井换热器传热特性的影响。计算得到，当深井换热器循环水量稳定在30 m³/h时，热储层中达西流速由0提高到5×10^-6 m/s时，平均换热量增大55 kW。然而在忽略热储层中渗流过程时，循环水量由30 m³/h提高到60 m³/h，平均换热量增大34 kW，循环水泵耗功提高20.6 kW。研究表明：随着渗流速度的增大，热储层中的传热机制发生改变，从而强化深井换热器的传热过程；同时降低了循环水流量对于深井换热器换热性能的影响程度。

关键词: 深井换热器, 富水型热储层, 传热, 数值分析, 计算机模拟, 渗流过程

CLC Number:

TK 529

Jiuchen MA, Feiyu YI, Qiuli ZHANG, Yu WANG. Heat transfer characteristics of coaxial tubes type deep borehole heat exchanger in water-rich geothermal reservoir[J]. CIESC Journal, 2021, 72(8): 4134-4145.

马玖辰, 易飞羽, 张秋丽, 王宇. 富水型热储层深井套管式换热器传热特性研究[J]. 化工学报, 2021, 72(8): 4134-4145.

Figures/Tables 11

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典型参数	数值
地埋管长度 H	2000 m
井孔直径D	350 mm
出液管外径 d_o	140 mm
出液管壁厚 b_o	14 mm
进液管外径 d_i	245 mm
进液管壁厚 b_i	18 mm
进液管壁热导率 λ_pi	41 W/(m·K)
出液管壁热导率 λ_po	0.42 W/(m·K)
固井水泥热导率 λ_g	2.8 W/(m·K)
固井水泥体积比热容 ρ_gc_g	2.19×10⁶ J/(m³·K)
循环液热导率 λ_r	0.65 W/(m·K)
循环液体积比热容 c_rρ_r	4.2×10⁶ J/(m³·K)

典型参数	数值
地埋管长度 H	2000 m
井孔直径D	350 mm
出液管外径 d_o	140 mm
出液管壁厚 b_o	14 mm
进液管外径 d_i	245 mm
进液管壁厚 b_i	18 mm
进液管壁热导率 λ_pi	41 W/(m·K)
出液管壁热导率 λ_po	0.42 W/(m·K)
固井水泥热导率 λ_g	2.8 W/(m·K)
固井水泥体积比热容 ρ_gc_g	2.19×10⁶ J/(m³·K)
循环液热导率 λ_r	0.65 W/(m·K)
循环液体积比热容 c_rρ_r	4.2×10⁶ J/(m³·K)

地层类型	岩性构成	埋深 H/m	水平渗透系数 K_XY/(m/s)	孔隙率 ε_s	体积比热容 c_sρ_s/(J/(m³·K))	热导率λ_s/ (W/(m·K))	纵向热弥散度 α_L/m	横向热弥散度α_T/m
第四系	黏土层	0~40	5.0×10^-9	0.41	3.2×10⁶	1.4	0.3	0.03
第四系	粉砂	40~200	4.2×10^-9	0.38	2.4×10⁶	1.9	1.0	0.1
新近系	泥岩	200~660	4.2×10^-8	0.31	2.0×10⁶	2. 7	2.0	0.2
新近系	泥岩/砂岩互层	660~1060	3.0×10^-6	0.29	3.1×10⁶	2.9	2.0	0.2
奥陶系	石灰岩	1060~1780	2.0×10^-5	0.28	3.0×10⁶	2.8	5.0	0.5
寒武系	泥岩	1780~2000	4.2×10^-8	0.31	2.0×10⁶	2. 7	2.0	0.2

地层类型	岩性构成	埋深 H/m	水平渗透系数 K_XY/(m/s)	孔隙率 ε_s	体积比热容 c_sρ_s/(J/(m³·K))	热导率λ_s/ (W/(m·K))	纵向热弥散度 α_L/m	横向热弥散度α_T/m
第四系	黏土层	0~40	5.0×10^-9	0.41	3.2×10⁶	1.4	0.3	0.03
第四系	粉砂	40~200	4.2×10^-9	0.38	2.4×10⁶	1.9	1.0	0.1
新近系	泥岩	200~660	4.2×10^-8	0.31	2.0×10⁶	2. 7	2.0	0.2
新近系	泥岩/砂岩互层	660~1060	3.0×10^-6	0.29	3.1×10⁶	2.9	2.0	0.2
奥陶系	石灰岩	1060~1780	2.0×10^-5	0.28	3.0×10⁶	2.8	5.0	0.5
寒武系	泥岩	1780~2000	4.2×10^-8	0.31	2.0×10⁶	2. 7	2.0	0.2

达西流速u_f/ (m/s)	进水管垂向温升/ (℃/100 m)		出水管垂向温降/ (℃/100 m)
达西流速u_f/ (m/s)	10 d	120 d	10 d	120 d
0	0.73	0.61	0.41	0.37
1×10^-6	0.84	0.73	0.43	0.38
5×10^-6	0.92	0.82	0.44	0.40