雄安新区地热井同轴套管闭式循环取热技术研究

Performance Study of the Downhole Coaxial Closed-Loop Heat Exchange Technology in Xiong’an New Area

地热能是一种含量丰富、成本相对低廉且分布广泛的可再生能源.雄安新区地热储量丰富,亟需高效取热的技术.地热井同轴套管闭式循环取热技术是一种适用于中深层地热、兼具换热效率高和“取热不取水”等优点的新型地热开发模式.单井同轴套管闭式换热系统由钻入地热地层中的垂直井以及井筒中呈同轴位置关系的中心管组成.在此系统中,循环工质从地面通过高压泵被注入环空,通过热对流和热传导从井壁提取热量,然后通过中心管返回地面流经热交换器被利用.本文针对雄安新区地热储层,首先完成同轴套管保温结构、高导热水泥的设计与研发;然后根据设计结果,对地热储层最大产能、井下换热系统取热效率及关键参数的影响规律进行了数值模拟研究;最后在研究基础上,开展同轴套管闭式循环取热技术的现场试验,完成针对中低温地热资源的同轴套管闭式循环取热技术研究及分析,并基于现场情况对不同热储条件和保温结构进行了经济性分析.研究结果表明,地热井同轴套管闭式循环取热技术可以满足对中深层地热能的开发需求,设计的保温结构和高导热水泥对取热供热有积极作用,形成了包括井身结构设计、保温结构设计、井下高效取热装置开发等在内的地热井高效取热完整技术体系.

Geothermal energy is a resource-rich,low-cost and widely distributed energy.Xiong’an New Area is rich in geothermal resources and urgently needs efficient heat extraction technology.The downhole coaxial heat exchange technology is suitable for the development of medium-deep geothermal resources with advantages of high heat extraction efficiency and“heat extraction without water extraction”.The downhole coaxial heat exchange system consists of a vertical well drilled into the geothermal formation and a central tube in the wellbore in a coaxial position.In this system,the working fluid is injected into the annulus and extracted through the insulated inner tubing,forming a reverse circulation.The working fluid inside the annulus extracts heat via heat convection and heat conduction from the hot wellbore.This paper aims at the geothermal reservoir in Xiong’an New Area and has done the following work.First,the design and development of thermal insulation structure and high thermal conductivity cement was completed.Then,based on the design results,numerical simulations were carried out to study the maximum capacity of the geothermal reservoir,the heat extraction efficiency of the downhole heat exchange system and the influence of key parameters.Finally,a field trial of downhole coaxial heat exchange technology was conducted on the basis of the previous numerical simulation,and a performance study of the downhole coaxial closed-loop heat exchange technology was completed.And a related commercial analysis of different geothermal reservoir conditions and insulation structures was carried out based on the field condition.The research results show that the downhole coaxial heat extraction technology can meet the development needs of mid-deep geothermal energy resources.The designed insulation structure and high thermal conductivity cement have a positive effect on heat extraction.And a set of efficient heat extraction technology system for geothermal well have been formed,which include well structure design,insulation structure design,and development of high-efficiency downhole heat exchangers.