水流损失和热补偿共同作用对增强型地热系统(EGS)产能影响的研究

基于青海共和盆地-3705m地热田实测数据,结合流固耦合传热理论并运用Comsol软件,建立了离散型裂隙岩体流体传热模型。考虑水流损失和热补偿共同作用,模拟得到了开采过程中上、下岩层(盖层和垫层)为绝热不渗透、传热不渗透、渗透传热时,储层(上、下岩层和压裂层)温度场的变化特征,分析了产出流量、水流损失、产出温度、产热速率的变化规律。研究结果表明:采热过程中产出流量始终小于注入流量;产出流量增幅速率先增大后减小,最后趋于稳定,前3a产出流量增幅超过总增幅量的3/4;忽略水流损失,将高估产热速率,采热初期甚至达到考虑水流损失时产热速率的3倍以上;考虑水流损失,产热速率呈先快速上升再趋于稳定后逐渐下降的趋势,最优开采时间为3a^11a;研究上、下岩层对产出温度的影响,仅考虑传热,采热寿命延长5.43%,同时考虑渗流传热时,采热寿命延长2.71%;采热前9a,水流损失占主导作用,即流入上、下岩层水流损失对产热速率的影响高于热补偿效应,开采10a后,热补偿效应占主导作用;同时考虑水流损失和热补偿效应得到的产热速率变化规律与实际工程更为符合,建议选择低渗透能力的上、下岩层延长增强型地热系统(EGS)运行时间。

Influence of water flow loss and thermal compensation on enhanced geothermal system(EGS) production capacity

Based on the measured parameters of the geothermal field-3705m in the Gonghe Basin,Qinghai,combined with the theory of fluid-structure coupled heat transfer,using COMSOL software,a fluid heat transfer model for discrete fractured rock masses is established.Considering the combination of water flow loss and thermal compensation,the simulation shows that the upper and lower rock layers(cover and cushion)are adiabatic,non-permeable,and permeable to heat transfer during the mining process,temperature field variation characteristics of reservoirs(upper and lower rock layers and fracturing layers),the variation of output flow,water flow loss,output temperature and heat production rate are analyzed.The results indicate that:the output flow rate during the heat recovery process is always less than the injection flow rate;the rate of increase in output flow increases first and then decreases and finally stabilizes.The increase in output flow in the first 3 years exceeds the total increase by 3/4;ignoring the loss of water flow,the heat production rate will be overestimated,and the heat production rate will be more than 3 times in the initial stage of heat recovery even when considering the loss of water flow;considering the loss of water flow,the rate of heat production rises rapidly and then tends to stabilize and then gradually decline,the optimal mining time is 3a^11a;study the effect of the upper and lower rock layers on the output temperature,only considering the heat transfer effect,the heating life is extended by 5.43%,and the heat recovery life is extended by 2.71%when considering the heat transfer effect of the seepage;before 9a heating,the water flow loss dominates,that is,the water flow loss into the upper and lower rock layers has a higher effect on the heat production rate than the heat compensation effect.After 10a of mining,the thermal compensation effect plays a dominant role;at the same time,considering the water flow loss and thermal compensation effect,the heat generation rate change law is more consistent with the actual project.It is recommended to select the upper and lower rock layers with low permeability to extend the EGS running time.The conclusions obtained have important reference significance for accurately predicting EGS production capacity.