The Molasse Basin is one of the most promising areas for deep geothermal exploitation in Germany and the target horizon is the aquifer in the Upper Jurassic carbonates. Carbonate deposits can be very heterogeneous even over a small area due to diagenetic processes and varying depositional environments. The preferential targets for geothermal exploitation in carbonate deposits are fault zones, reef facies and karstified areas, since they are expected to act as hydraulically permeable zones due to high porosity and high permeability. Therefore, identifying these structures and characterizing, e.g., their internal porosity distribution are of high importance. This can be accomplished using 3D reflection seismic data. Besides structural information, 3D seismic surveys provide important reservoir properties, such as acoustic impedance, from which a porosity model can be derived. In our study area in Munich we carried out a seismic amplitude inversion to get an acoustic impedance model of the Upper Jurassic carbonate reservoir using a 3D seismic data set, a corresponding structural geological model, and logging data from six wells at the ‘Schäftlarnstraße’ geothermal site. The impedance model and porosity logs were than used to calculate a porosity model. The model shows a wide porosity range from 0 to 20% for the entire reservoir zone and the lithology along the wells reveals that dolomitic limestone has the highest porosities and calcareous dolomite has the lowest porosities. The study area is cut by a large W–E striking fault, the Munich Fault, and the footwall north of it shows higher porosities and more intense karstification than the hanging wall to the south. Considering the entire study area, an increase in porosity from east to west is observed. Furthermore, we identified a complex porosity distribution in reef buildups and pinnacle reefs. The reef cores have mostly low porosities of, e.g., < 3% and the highest porosities of up to 7 to 14% are observed at the reef caps and on the reef slopes. The reef slopes show a characteristic interfingering of the reef facies with the surrounding bedded facies, which indicates a syn-sedimentary reef development with slightly varying build up growth rates. We also assessed the reservoir quality with regard to porosity distribution and determined areas with moderate to good quality for geothermal exploitation by defining porosity evaluation levels. The porosity evaluation maps show that the carbonate rocks of Berriasian to Malm $$\zeta$$ 1 are preferential targets for exploitation, especially in the footwall of the Munich Fault and to the west of the hanging wall, because these areas are characterized by high porosities due to intense karstification of bedded and massive facies, although the latter is mainly restricted to reef caps and reef slopes.

中文翻译：

---

基于地震振幅反演的德国莫拉塞盆地地热碳酸盐岩储层孔隙度估算

Molasse盆地是德国深部地热开发最有希望的地区之一，目标层位是上侏罗统碳酸盐岩中的含水层。由于成岩过程和不同的沉积环境，即使在小范围内，碳酸盐沉积物也可能非常不均匀。碳酸盐矿床地热开发的优先目标是断裂带、礁相和岩溶区，因为它们具有高孔隙度和高渗透率的特点，有望成为水力渗透区。因此，识别这些结构和表征，例如，它们的内部孔隙度分布是非常重要的。这可以使用 3D 反射地震数据来完成。除了结构信息外，3D 地震勘测还提供了重要的储层特性，例如声阻抗、从中可以推导出孔隙度模型。在我们位于慕尼黑的研究区，我们使用 3D 地震数据集、相应的结构地质模型和来自 'Schäftlarnstraße' 地热的六口井的测井数据进行了地震振幅反演，以获得上侏罗统碳酸盐岩储层的声阻抗模型地点。然后使用阻抗模型和孔隙度测井来计算孔隙度模型。该模型显示整个储层的孔隙度范围很广，从 0% 到 20%，沿井的岩性表明白云质灰岩的孔隙度最高，钙质白云岩的孔隙度最低。研究区被一条大的 W-E 走向断层——慕尼黑断层切割，其北部的下盘显示出比南部的上盘更高的孔隙度和更强烈的岩溶作用。考虑到整个研究区，观察到孔隙度从东向西增加。此外，我们确定了珊瑚礁堆积和尖峰珊瑚礁中的复杂孔隙度分布。礁岩芯的孔隙度大多较低，例如< 3%，在礁盖和礁坡上观察到的最高孔隙度可达 7% 至 14%。礁坡表现出礁相与周围层状相的特征性交错，表明同沉积的礁体发育，堆积生长速率略有不同。我们还评估了孔隙度分布方面的储层质量，并通过定义孔隙度评估水平确定了用于地热开采的质量中等至良好的区域。