Characterisation of the fracture- and karst-controlled geothermal reservoir below Munich from geophysical wireline and well information

IF 2.9 2区 地球科学 Q3 ENERGY & FUELS Geothermal Energy Pub Date : 2024-03-27 DOI:10.1186/s40517-024-00286-6
J. F. Krumbholz, M. Krumbholz, S. H. Wadas, D. C. Tanner
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Abstract

The Upper Jurassic carbonate aquifer in the German Molasse Basin (S Germany) below Munich is the focus of exploitation of geothermal energy. To implement geothermal wells, meaningful prediction of reservoir quality (e.g., volume, temperature, location of aquifers, porosity, permeability) is required. However, permeability of this aquifer is often highly heterogeneous and anisotropic, as in other karst- and fracture systems. Based on geophysical well logs from six wells, a 3D porosity model, and side-wall cores, we provide a comprehensive characterisation of the reservoir. We investigate the correlation between rock porosity and matrix permeability, and the impact of hyper-facies on fractures and karstification. We locate and analyse hydraulic active zones and compare them with hydraulic inactive zones within equivalent depth ranges, to characterise promising exploration targets. We show that fracture system parameters vary strongly between wells and within a single well. However, we observe local trends between the fracture systems and rock properties. For instance, fracture intensities and compressional wave velocity increase, while porosity decreases, in dolomitic reefal build-ups (massive facies). We observed substantial karstification dominantly within the massive facies. The main indicators for hydraulic active zones in the reservoir seem to be karstification, fractures, and fault zones. Although matrix porosity has neglectable impact on permeability, the identified hydraulic active zones appear more frequently in sections with higher porosity. We conclude, similar to previous studies, that the massive facies is a suitable exploitation target. Despite the favourable conditions within the massive facies, the strongest hydraulic active zones are nevertheless in the bedded facies, often considered as aquitard, directly below the top of the reservoir within the lithostratigraphic group of the Purbeck, at the transition between the Jurassic and the Cretaceous.

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根据地球物理有线和油井信息确定慕尼黑地下断裂和岩溶控制地热储层的特征
慕尼黑以下德国莫拉斯盆地(德国南部)的上侏罗统碳酸盐含水层是地热能源开发的重点。要开采地热井,必须对储层质量(如体积、温度、含水层位置、孔隙度、渗透性)进行有意义的预测。然而,与其他岩溶和断裂系统一样,这种含水层的渗透性通常具有高度异质性和各向异性。根据六口井的地球物理测井记录、三维孔隙度模型和侧壁岩心,我们提供了储层的综合特征。我们研究了岩石孔隙度与基质渗透率之间的相关性,以及超岩层对裂缝和岩溶化的影响。我们对水力活跃区进行定位和分析,并将其与同等深度范围内的水力不活跃区进行比较,以确定有潜力的勘探目标。我们发现,不同油井之间以及同一油井内部的裂缝系统参数差异很大。不过,我们观察到了裂缝系统与岩石属性之间的局部趋势。例如,在白云质岩礁堆积层(块状面)中,裂缝强度和压缩波速度增加,而孔隙度降低。我们观察到大量岩溶化主要发生在块状岩层中。储层中水力活动带的主要指标似乎是岩溶化、裂缝和断层带。虽然基质孔隙度对渗透率的影响可忽略不计,但在孔隙度较高的地段,水力活动带出现的频率更高。与之前的研究类似,我们得出结论,块状层是一个合适的开采目标。尽管块状层内条件有利,但最强的水力活动带仍位于普贝克岩层组中储层顶部正下方的层状层内,通常被视为含水层,处于侏罗纪与白垩纪的过渡时期。
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来源期刊
Geothermal Energy
Geothermal Energy Earth and Planetary Sciences-Geotechnical Engineering and Engineering Geology
CiteScore
5.90
自引率
7.10%
发文量
25
审稿时长
8 weeks
期刊介绍: Geothermal Energy is a peer-reviewed fully open access journal published under the SpringerOpen brand. It focuses on fundamental and applied research needed to deploy technologies for developing and integrating geothermal energy as one key element in the future energy portfolio. Contributions include geological, geophysical, and geochemical studies; exploration of geothermal fields; reservoir characterization and modeling; development of productivity-enhancing methods; and approaches to achieve robust and economic plant operation. Geothermal Energy serves to examine the interaction of individual system components while taking the whole process into account, from the development of the reservoir to the economic provision of geothermal energy.
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