桂东南地区干热型地热资源潜力分析

Analysis of hot-dry geothermal resource potential in southeastern Guangxi

干热岩作为地热资源的重要组成部分,被视为未来的清洁能源,极具开发前景和研究价值。文章以桂东南潜在的干热岩为研究对象,通过基础地质、地球物理和地球化学资料的二次开发和实地考察,对区域构造-岩浆-沉积建造系统、岩石圈结构、现今地热场特征和地震、温泉分布规律等进行综合分析,旨在初步探讨桂东南地区干热型地热资源的潜力。结果表明:桂东南地区岩石圈较薄,分别在25km之上和6~8km处存在厚约6km和2km的双层低速层/带,指示滑脱型韧性剪切和高温地质体的存在;印支期花岗岩提供稳定的放射性生热物质基础(U含量均值5.41×10^-6,Th含量均值18.38×10^-6,K2O含量均值4.43%),新生代火山活动(OIB)在补给大量地热能的同时,为深部热物质上涌提供通道;桂东南地区现今地热存在明显异常,大地热流值介于80~100mW/m^2,北海-南宁地温梯度值高于30℃/km,钦州、合浦中-新生代断陷盆地因沉积盖层裂隙度、孔隙度和导热率低且圈闭性好而属于干热岩地热资源丰富区。对桂东南干热型地热资源潜力的研究,将为广西能源结构调整、生态环境优化和产业转型升级助力。

As an important part of geothermal resource,hot dry rock(HDR)is regarded as future clean energy with great developmental prospect and research value.Here,we studied southeastern Guangxi by reexamining the basic geological,geophysical and geochemical data.We carried out field investigations of tectonic-magmatic-sedimentary formation system,lithospheric structure,characteristics of present-day geothermal field and distribution of earthquakes and hot springs to explore the potential of dry-heat geothermal resources in southeastern Guangxi.The results show that the lithosphere is relatively thin with two low-velocity layers about 6 and 2 km thick at above 25 and 6-8 km,respectively,indicating presence of slippage type ductile shears and high temperature geological bodies.In this area,Indosinian granites can provide stable supply of radiogenic heat materials(mean U concentration 5.41×10^-6;Th 18.38×10^-6;K2 O4.43%),whilst Cenozoic volcanic activities(OIB)provide a channel for the upwelling of deep thermal material while replenishing large amounts of geothermal energy.Indeed,we observed obvious geothermal anomalies in southeastern Guangxi:in Beihai-Nanning,terrestrial heat flow was at 80-100 mW/m^2 with geothermal gradient above 30℃/km;in Qinzhou and Hepu,Mesozoic-Cenozoic fault basins possess rich HDR geothermal resources that the sedimentary cap was of low cracking,porosity and thermal conductivity.Our research of dry heat geothermal potential will assist energy structural adjustment,ecological environmental optimization and industrial transformation and upgrading in Guangxi.