岩溶热储合理采灌井距的热突破约束——以菏泽地热田为例

Constraint of thermal breakthrough on rational well spacing of karst thermal reservoir:A case study of Heze geothermal field

与煤炭、石油、天然气等传统化石能源相比,地热能具有资源储量大、分布广、可再生、开采条件好等优点。菏泽潜凸起地热田是山东省主要大型碳酸盐岩岩溶热储地热田之一,地热资源储量丰富。为保证地热资源可持续开发利用,本文基于郓城县武安府前小区、文昌苑社区岩溶热储地热采灌井全井段地温场长期动态监测,阐述了地温场变化规律及演化趋势,建立水-热耦合采灌对井数值模型,计算回灌工程合理采灌井距、合理采灌量,防止开采井运行期内发生热突破。结果表明,随着回灌年限的延长,回灌井周围热储温度逐年降低,回灌冷水影响范围逐渐扩大。将开采井热储温度降低1℃视为热突破,利用数值模型模拟预测,回灌低温冷水影响范围随采灌工程运行逐渐扩展并到达开采井附近。随着采灌量的增加或采灌井间距的减小,开采井周边的低温范围逐渐增大,产生热突破的时间逐渐缩短。热突破时间t与回灌量Q呈幂函数减小、与采灌井间距R呈指数函数增长。采灌量50 m^(3)/h,采灌井距大于350 m可保证对井系统运行100年不发生热突破;采灌量70 m^(3)/h、90 m^(3)/h、120 m^(3)/h、150 m^(3)/h、180 m^(3)/h时,100年不发生热突破的合理采灌井距分别为400 m、425 m、475 m、500 m、550 m。该结论为采灌井合理布局、地热资源可持续循环开发提供科学依据。

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 regions 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 m^(3)/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 m^(3)/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.