牛驼镇地热田深部蓟县系岩溶热储特征及构造演化控制作用

Control of tectonic evolution on karst geothermal reservoirs of Jixian system in Niutuozhen geothermal field

  • 摘要: 牛驼镇地热田以得天独厚的地热资源禀赋和开发条件成为雄安新区的地热田之一,以往地热勘探开发以2 000 m以浅热储为主,对4 000 m深度蓟县系雾迷山组和高于庄组2套碳酸盐岩热储系统的分异规律、构造演化控制机理及地热富集机制认识不足。基于深部地球物理勘查、地热钻探、测井、产能试验等实测数据的综合研究,揭示了蓟县系碳酸盐岩热储的空间分布、岩溶发育及产能特征:现今蓟县系碳酸盐岩潜山构造总体呈南高北低,东高西低,高点位于凸起南端,向东北部逐渐倾没,在雄县县城南部雾迷山组局部缺失,高于庄组不整合于新生界之下;地热井储层解释显示,雾迷山组整体上以靠近顶部风化壳200 m范围内岩溶裂隙、溶蚀孔洞最为发育,孔渗性最好,成为热储最发育部位,地热产能优良;高于庄组井间差异大,少部分井靠近风化壳不整合面150 m附近岩溶发育,大部分井整体岩溶欠发育。纵向上,随地层深度增加,岩溶发育程度变差,出水量下降,产能较差。以区域构造演化阶段为背景,通过分析廊固凹陷—牛驼镇凸起—霸县凹陷的典型剖面演化历程,阐述了地热田经历了新元古代—中生代储层发育形成→古近纪凸起构造发育→新近纪—第四纪储层埋藏3个沉积和构造演化阶段,以及对2套热储空间分布、岩溶发育及物性的控制作用,最终造就了现今热储形态和物性特征。通过典型地热井稳态测温与大地热流数据分析,认为热折射聚热效应叠加深大断裂–高渗透性岩溶通道内的流体对流作用,共同控制了研究区现今地温场空间格局。

     

    Abstract: Possessing exceptional geothermal resource endowments and superior development conditions, the Niutuozhen geothermal field is one of the leading geothermal fields in Xiong’an New Area. Geothermal exploitation historically concentrated on reservoirs above 2 000 m, yet the differentiation rules, tectonic evolution control mechanisms, and geothermal enrichment patterns above 4 000 m carbonate reservoirs of the Wumishan and Gaoyuzhuang formations of are still poorly understood. There was a lack of understanding of deep carbonate rock thermal reservoirs. Spatial distribution, karst development and productivity characteristics of Jixian system carbonate thermal reservoirs are revealed in this study through comprehensive research based on authentic data acquired from deep geophysical exploration, geothermal drilling, well logging and productivity tests: the Jixian system carbonate buried hill internal structure is generally characterized by high in the south and low in the north, high in the east and low in the west, and the high point is located in the south of the uplift and gradually sinks to the northeast. The highest point is located at the southern end of the uplift, gradually dipping towards the northeast. The Wumishan formation in the south of Xiongxian County is partially missing, and the Gaoyuzhuang formation is unconformably overlaid on the Mesozoic strata. The interpretation of geothermal well reservoirs shows that the Wumishan formation is characterized by developed karst fractures and dissolution pores within a range of 200 m near the top weathering crust. These intervals are the development sites of geothermal reservoirs, characterized by good porosity and permeability and excellent geothermal productivity. In contrast, the Gaoyuzhuang formation shows significant inter-well variability, with only a few wells near the 150-meter vicinity of the weathering crust unconformity displaying developed karst features, while most wells exhibit overall underdeveloped karst conditions. As the depth of the strata increases, the degree of karst development deteriorates, the water output decreases, and the geothermal production capacity is poor. Against the backdrop of regional tectonic evolution, analysis on the typical section evolution of the Langgu depression-Niutuozhen uplift-Baxian depression reveals three evolutionary phases of sedimentation and tectonism for the geothermal field: Neoproterozoic-Mesozoic reservoir formation, Paleogene uplift construction, and Neogene-Quaternary reservoir burial. Such evolution controls the spatial distribution, karst growth and physical properties of the two thermal reservoir sequences, determining their modern geometry and petrophysical features. Analyses of steady borehole temperature and terrestrial heat flow data demonstrate that the superposition of heat accumulation by thermal refraction and fluid convection along deep major faults and high-permeability karst conduits jointly governs the spatial distribution of present-day subsurface temperature in the research area.

     

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