冀中坳陷束鹿凹陷地热系统成因模式

Genetic Mechanism of the Geothermal System in Shulu Sag,Jizhong Depression

地热系统内部地质要素特征分析是建立其成因模式的基础,也是后期研究地热资源赋存特征和资源量评价的依据。结合前人研究成果和区内地热钻井资料,通过对冀中坳陷束鹿凹陷地热系统“源、储、通、盖”主要地质要素分析,建立了其概念模型,并开展了地热资源量评价。束鹿凹陷为一新生代发育在渤海湾盆地冀中坳陷内的典型的箕状凹陷,接受可能来自于其下深部地壳结构约20 km处低阻体的热源供给。新近系馆陶组砂岩热储和奥陶系碳酸盐岩热储分别构成了两套独立的地热系统。其中,馆陶组砂岩热储全区稳定分布,底板埋深介于1100~2000 m,储层厚度约为200~320 m,孔隙度约在15%~35%之间,渗透率最高可达1200 mD,热储底板温度在57~78℃;奥陶系碳酸盐岩热储受箕状凹陷边界断裂的控制呈单斜状倾伏,埋深1800~6000 m,储层厚度100~550 m,孔隙度2%~18%,渗透率0.5~50 mD,地热水井口温度在75~92℃。两套地热系统由西边太行山的大气降水沿着地层不整合面和断裂运移通道进行补给,通过深部热传导和局部热对流增温后,在储层中富集形成地热水。上覆松散的第四系沉积和明化镇组河流相碎屑岩沉积厚300~1400 m,热导率0.9~1.8 W/(m·K),构成了良好的区域盖层。束鹿凹陷地热资源量评价结果表明,馆陶组砂岩地热系统含244.430×10^(8)GJ,奥陶系岩溶地热系统含203.752×10^(8)GJ,总量合计448.182×10^(8)GJ,折合标煤15.296×10^(8)t。年开采地热资源量满足的供暖面积可达1.106×10^(8)m^(2),开发潜力巨大。

Analyzing the characteristics of geological factors in a geothermal system is the basis to establish its genetic model and to evaluate the geothermal resource.Combined with previous research and regional geothermal well data,we analyze the main geological factors including“source,reservoir,migration,and cap”of the geothermal system in the Shulu Sag,Jizhong Depression with an aim to establish the genetic model of the geothermal system and to evaluate geothermal resources.The Shulu Sag is a typical Cenozoic half graben,where heat may be supplied by a low-resistance body about 20 km in the deep crust.The Guantao Formation(Fm)sandstone thermal reservoir and Ordovician karst thermal reservoir make up two sets of geothermal systems,respectively.The sandstone thermal reservoir in the Guantao Fm is stably distributed in the whole area with itsbottom boundary at depth between 1100-2000 m.The reservoir is about 200-320 m thick with 15%-35%porosity.The permeability can reach up to 1200 mD.The temperatures at its bottom boundary are mostly 57-78℃;The distribution of the Ordovician carbonate reservoir is controlled by the half-graben and the reservoir shows a monoclinal dip with its top boundary at depth of 1800 to 6000 m.The reservoir is about 100 to 550 m thick with the porosity of mostly 2 to 18%and permeability of mostly 0.5 to 50 mD.The wellhead temperatures of the thermal reservoir are about 75-92℃.The two geothermal systems are replenished by atmospheric precipitation from the Taihang Mountains to the west of the study area.Water migrated along the unconformity of the layers and the faults,then warmed by deep heat conduction and local heat convection,and finally enriched in the reservoir.The overlying loose Quaternary sediments and Minghuazhen formations fluvial clastic sediments are 300-1400 m thick with thermal conductivity of 0.9-1.8 W/(m·K),and thus can be a good cap layer.Evaluation of the geothermal resources in the Shulu Sag shows that the sandstone geothermal system of the Guantao Fm contains 244.430×10^(8)GJ and the Ordovician karst geothermal system contains 203.752×10^(8)GJ.The total amounts to 448.182×10^(8)GJ,which is equivalent to 15.296×10^(8)t standard coal.The annual geothermal resources can meet the heating area of 1.106×10^(8)m^(2).Therefore,the development potential is huge.