Seepage and heat transfer characteristics of sandstone thermal reservoir under aquitard damage: Fid-Bau Portal

Seepage and heat transfer characteristics of sandstone thermal reservoir under aquitard damage

Song, Wei / Bai, Ze / Wang, Zihan / Wang, Jing / Li, Ziteng / Zhang, Qian

Highlights • Effect of aquitard damage on the flow breakthrough was described. • Temperature distribution and flow-rate variation in the aquifer were analyzed. • Main factors affecting thermal breakthrough strength were explored. • Factors affecting flow breakthrough strength and efficient operation time were identified using orthogonal analysis.

Abstract Flow and thermal breakthroughs are the main reasons for the reduction in the operational efficiency of a single-well groundwater heat pump (SWGWHP) system. Furthermore, a large initial pumping flow rate, attributed to the large initial heating/cooling load of the building, can consolidate and damage the aquifer. In this study, an aquitard damage test bench was constructed to investigate the formation and development of flow and thermal breakthroughs during the operation of the SWGWHP system by varying the initial recharge rate (Q), aquifer thickness (H), and the time difference between pumping and recharge ( $Δ t$ ); and to investigate the aquifer damage, seepage, and heat transfer patterns. The results indicated that pressure was the main factor that damaged the aquitard. Aquitard damage can cause or aggravate the flow breakthrough phenomenon. The flow breakthrough strength is the main factor affecting the thermal breakthrough strength. The results of the orthogonal test analysis indicate that the order of the primary and secondary influencing factors of the flow breakthrough strength and operating time efficiency is aquitard thickness (H) > initial recharge rate (Q) > pumping and recharging time difference ( $Δ t$ ). The existence of the aquitard reduced the flow breakthrough strength by 15.2–33.2% and prolonged the efficient operation time of the system by 2.5–5 times. Based on quantitative analyses of the flow and thermal breakthrough strengths, and the variation in the system coefficient of performance, this study reveals the reasons for the formation of thermal breakthrough and provides theoretical suggestions to ensure a safe and stable operation of the SWGWHP system. The results of the study can guide practical installations as well as future research on SWGWHP systems.