裂隙分布及井间距对增强型地热系统采热性能的影响

Effect of fracture distribution and well spacing on heat recovery performance of enhanced geothermal system

中高温岩热型储层开采属于增强型地热系统,开采方式主要通过回注井、生产井、裂隙储层来实现,井间距的布设和裂隙参数将直接影响到流体的流动路径,进而影响着回灌量和换热效率,由此我们考虑通过对裂隙参数与井间距的组合变化对采热性能影响的研究,优选出对生产最有利的裂隙分布与井间距组合参数,为人工造储提供裂隙网络目标,为布井设计提供井间距参考.本次研究采用TOUGH2软件在建立水热力多场耦合模型的基础上,在储层设置了16组不同的裂隙参数组合,进行了48组试验模拟,分析了200 m、300 m、500 m井间距条件下运行30年不同裂隙参数组合对采热性能的影响,结果显示储层和采热温度受井间距影响较大,储层压力受裂隙参数影响较大.不同裂隙参数组合条件下,200 m井间距开采30年生产井温度由初始的81℃下降到47℃左右,300 m井间距开采30年生产井温度下降到55℃左右,500 m井间距开采30年生产井温度下降到67℃左右.不同裂隙参数条件下储层压力相差较大,最大由初始的24 MPa上升到98 MPa,最小上升到28 MPa.根据模拟结果我们得到80 m厚储层最佳压裂开采参数组合为井间距500 m、裂隙开度0.8e^(-4)~0.9e^(-4)m、裂隙条数在10~15条之间、裂隙间距10 m时为最佳开采方案.该研究结果可应用于增强型地热系统(EGS-Enhanced Geothermal Systems)开发中,为高效压裂开采中高温低渗储层提供指导,提高采热效率的同时延长系统使用寿命.

The mining of medium-high temperature rockheat reservoirs belongs to the enhanced geothermal system.The mining method is mainly realized by reinjection wells,production wells and fractured reservoirs.The layout of well spacing and fracture parameters will directly affect the flow path of fluid,and then affect the recharge amount and heat exchange efficiency.Therefore,we consider the study of the influence of the combination of fracture parameters and well spacing on the heat recovery performance,and select the most favorable combination parameters of fracture distribution and well spacing for production,so as to provide fracture network target for artificial storage and well spacing reference for well layout design.In this study,TOUGH2 software was used to establish a multifield coupling model of water and heat.Sixteen sets of different fracture parameter combinations were set up in the reservoir,and 48 sets of experimental simulations were carried out.The influence of different fracture parameter combinations on heat recovery performance under the condition of 200 m,300 m and 500 m well spacing for30 years is analyzed.The results show that the reservoir and heat recovery temperature are greatly affected by well spacing,and the reservoir pressure is greatly affected by fracture parameters.Under the condition of different fracture parameter combinations,the temperature of production wells with 200 m well spacing for 30 years decreased from 81℃to 47℃,the temperature of production wells with 300 m well spacing for 30 years decreased to 55℃,and the temperature of production wells with 500 m well spacing for 30 years decreased to67℃.The reservoir pressure varies greatly under different fracture parameters.The maximum increases from the initial 24 MPa to 98 MPa,and the minimum increases to28 MPa.According to the simulation results,we get the best combination of fracturing parameters for 80 m thick reservoir:well spacing 500 m,fracture opening 0.8e^(-4)~0.9e^(-4)m,fracture number between 10~15,fracture spacing 10 m.The results of this study can be applied to the development of EGS,which can provide guidance for the efficient fracturing of medium-high temperature and low permeability reservoirs,improve the heat recovery efficiency and prolong the service life of the system.