Scaling process simulation and anti-scaling measures in karst geothermal field in Baoding, Hebei

doi:10.13745/j.esf.sf.2021.11.4

Abstract

Abstract:

Scaling is a serious problem in geothermal power plants and certain geothermal projects in China hindering large-scale development and utilization of geothermal energy. At present, anti-scaling theory and technology is urgently needed in the geothermal market where calcium carbonate scaling is the most common problem. To solve this problem, the karst geothermal field in Baoding, northern China was selected to investigate the scale composition and the scaling mechanism, position and process as well as anti-scaling measures in a geothermal well. According to the study results, (1) the main cause of calcium carbonate scaling is flashing due to system pressure drop, caused primarily by carbon dioxide release from the liquid phase to the gas phase. (2) By combining the wellhead parameters with the laws of conservation of mass, momentum and energy and the theory of two-phase flow pressure drop, the scaling process can be simulated, and the scaling position as well as the pressure, temperature, steam quality and partial pressure of carbon dioxide at different depths can be calculated and determined. (3) Two anti-scaling measures could be implemented after identifying the flashing pressure and depth. One measure was to increase system pressure in order to prevent flashing thus inhibit carbon dioxide release. A minimum pressure was recommended via simulation. The other measure was to use chemical scaling inhibitor. An injection device was developed, anti-scaling experiment was carried out, and the chemical scaling inhibition effect was evaluated to show that chemical inhibitor could inhibit more than 90% of scaling, and thus the carbonate scaling problem could be effectively solved. From the above study, a set of valuable experiences—from scaling cause analysis, scaling position calculation, scaling process simulation, anti-scaling technology and equipment developments to field experiments and anti-scaling evaluation—were obtained. These experiences can be referenced in general for scaling control in geothermal wells.

Key words: karst reservoir, anti-scaling and scale removal, calcium carbonate scale formation, scaling simulation, flashing point, geothermal scaling, scale inhibitor

CLC Number:

P641

HE Yujiang, LIU Xiao, XING Linxiao, TAN Xianfeng, BU Xianbiao. Scaling process simulation and anti-scaling measures in karst geothermal field in Baoding, Hebei[J]. Earth Science Frontiers, 2022, 29(4): 430-437.

Figures/Tables 11

Fig.1 Tectonic divisions and sampling well locations in the study area

Table 1 Dimensions of the vertical wellbore for the Boye geothermal well

深度/m	套管直径/mm	套管长度/mm
0.00~550.00	406	550.00
513.66~1 950.00	273	1 436.34
1 909.86~3 275.00	177.8	1 365.14
3 275.00~3 860.00	裸眼152.00

Fig.2 Design of the geothermal heat-pump

Table 2 Concentrations of ions in geothermal water

离子名称	K⁺	Na⁺	Ca²⁺	Mg²⁺
浓度/(mg·L^-1)	149.3	1 691	88.56	20.08
离子名称	Cl^-	$SO 4 2 -$	$HCO 3 -$	$CO 3 2 -$
浓度/(mg·L^-1)	2 387	104.9	838.2	0.0

Table 2 Concentrations of ions in geothermal water

离子名称	K⁺	Na⁺	Ca²⁺	Mg²⁺
浓度/(mg·L^-1)	149.3	1 691	88.56	20.08
离子名称	Cl^-	$SO 4 2 -$	$HCO 3 -$	$CO 3 2 -$
浓度/(mg·L^-1)	2 387	104.9	838.2	0.0

Fig.3 Effect of scaling on a pipe

Fig.4 Effect of scaling on a valve

Fig.5 Variation of fluid temperature with depth

Fig.6 Variations of total fluid pressure and partial pressure of carbon dioxide with depth

Fig.7 Variation of fluid dryness with depth

Fig.8 Variation of flow regime with depth

Fig.9 Experimental setup for scale inhibitor filling

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