Constraint of thermal breakthrough on rational well spacing of karst thermal reservoir:A case study of Heze geothermal field
Geothermal energy presents a compelling alternative to traditional fossil fuels,offering substantial advantages in terms of resource abundance,widespread distribution,renewability,and favorable exploitation conditions.The Heze subuplift geothermal field,located in Shandong Province,exemplifies this potential,representing one of the region's major large-scale carbonate karst thermal storage geothermal fields.To ensure the sustainable development and utilization of these resources,this study focuses on the Heze subuplift field.Based on long-term dynamic monitoring of the geo-temperature field across the entire well section of geothermal production and reinjection wells in Wuan Fuqian and Wenchangyuan communities in Yuncheng County,this paper describes the change patterns and evolution trends of the geo-temperature field.A numerical model of coupled water-thermal production and reinjection is established to calculate the optimal well spacing and production/reinjection rates for the recharge project.This model aims to prevent thermal breakthrough during production well operation.Results show that as recharge years increase,the heat storage temperature around recharge wells decreases annually,and the influence range of injected cold water expands gradually.A 1℃ reduction in the thermal reservoir temperature of the production well is considered a thermal breakthrough.The numerical model predicts that the low-temperature cold water recharge influence zone will gradually expand with the operation of the production and reinjection project,eventually reaching the vicinity of the production well.Furthermore,increasing production and reinjection rates or decreasing the spacing between production and reinjection wells leads to a gradual increase in the low-temperature zone around the production well and a shortened time to thermal breakthrough.This relation between thermal breakthrough time(t)and recharge quantity(Q)follows a power function,whereas the relationship between t and well spacing(R)is exponential.The study concludes that with a production and reinjection volume of 50 m3/h and a well spacing greater than 350 m,no thermal breakthrough will occur in the well system for 100 years.For production and reinjection rates of 70,90,120,150,and 180 m3/h,the corresponding well spacing required to prevent thermal breakthrough within 100 years is 400,425,475,500,and 550 m,respectively.These findings provide a scientific basis for the rational layout of production and reinjection wells,ultimately contributing to the sustainable cycle development of geothermal resources.
geothermal tailwater reinjectionkarstic geothermal reservoirgeo-temperature fieldheat breakthroughreasonable well spacing
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