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Wireline distributed acoustic sensing allows 4.2 km deep vertical seismic profiling of the Rotliegend 150 °C geothermal reservoir in the North German Basin
Solid Earth ( IF 3.4 ) Pub Date : 2021-02-25 , DOI: 10.5194/se-12-521-2021
Jan Henninges , Evgeniia Martuganova , Manfred Stiller , Ben Norden , Charlotte M. Krawczyk

We performed so-far-unprecedented deep wireline vertical seismic profiling at the Groß Schönebeck site with the novel method of distributed acoustic sensing (DAS) to gain more detailed information on the structural setting and geometry of the geothermal reservoir, which is comprised of volcanic rocks and sediments of Lower Permian age. During the survey of 4 d only, we acquired data for 61 source positions using hybrid wireline fiber-optic sensor cables deployed in two 4.3 km deep, already existing wells. While most of the recorded data have a very good signal-to-noise ratio, individual sections of the profiles are affected by characteristic coherent noise patterns. This ringing noise results from incomplete coupling of the sensor cable to the borehole wall, and it can be suppressed to a large extent using suitable filtering methods. After conversion to strain rate, the DAS data exhibit a high similarity to the vertical component data of a conventional borehole geophone. We derived accurate time–depth relationships, interval velocities, and corridor stacks from the recorded data. Based on integration with other well data and geological information, we show that the top of a porous and permeable sandstone interval of the geothermal reservoir can be identified by a positive reflection event. Overall, the sequence of reflection events shows a different character for both wells explained by lateral changes in lithology. The top of the volcanic rocks has a somewhat different seismic response in both wells, and no clear reflection event is obvious at the postulated base of the volcanic rocks, so that their thickness cannot be inferred from individual reflection events in the seismic data alone. The DAS method enabled measurements at elevated temperatures up to 150 C over extended periods and led to significant time and cost savings compared to deployment of a conventional borehole geophone string. This wireline approach finally suggests significant implications for observation options in old wells for a variety of purposes.

中文翻译:

有线分布式声波传感技术可以对德国北部盆地Rotliegend 150°C地热储层进行4.2 km深的垂直地震剖面分析

我们使用新颖的分布式声波传感(DAS)方法在GroßSchönebeck站点进行了前所未有的深层电缆垂直地震剖面分析,以获取有关由火山岩组成的地热储层结构设置和几何形状的更多详细信息和下二叠纪的沉积物。仅在4 d的调查期间,我们使用部署在两个4.3 km深的现有井中的混合有线光纤传感器电缆获取了61个震源位置的数据。尽管大多数记录的数据都具有非常好的信噪比,但配置文件的各个部分都会受到特征性相干噪声模式的影响。这种振铃噪声是由于传感器电缆与井眼壁的耦合不完全引起的,可以使用适当的过滤方法在很大程度上将其抑制。转换为应变率后,DAS数据与常规钻孔地震检波器的垂直分量数据具有高度相似性。我们从记录的数据中得出了准确的时深关系,区间速度和走廊堆栈。基于与其他井数据和地质信息的整合,我们表明,地热储层的多孔且可渗透的砂岩层段的顶部可以通过正反射事件来识别。总体而言,两个井的反射事件序列显示出不同的特征,这可以通过岩性的横向变化来解释。火山岩的顶部在两个井中的地震响应都略有不同,并且在假定的火山岩底部没有明显的反射事件,因此,仅从地震数据中的单个反射事件就无法推断出它们的厚度。DAS方法可在高达150的高温下进行测量 deployment C延长了使用时间,与部署常规钻孔地震检波器弦相比,可节省大量时间和成本。最终,这种有线方法表明,出于各种目的,对旧井中的观测方案具有重要意义。
更新日期:2021-02-25
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