A 3D hydrogeological and geomechanical model of an Enhanced Geothermal System at The Geysers, California
A 3D hydrogeological and geomechanical model of an Enhanced Geothermal System at The Geysers, California
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DOI：
10.1016/j.geothermics.2014.01.013
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发表时间：
2014-07
期刊：
影响因子：
3.9
通讯作者：
P. Jeanne;J. Rutqvist;D. Vasco;Julio Garcia;P. Dobson;M. Walters;C. Hartline;A. Borgia
中科院分区：
文献类型：
--
作者：
P. Jeanne;J. Rutqvist;D. Vasco;Julio Garcia;P. Dobson;M. Walters;C. Hartline;A. Borgia
本文采用耦合过程模拟和现场观测相结合的方法，建立了美国加州the Geysers地热田西北部增强型地热系统（EGS）的三维水文地质和地质力学模型。建立了相关地质层的水力力学特性模型，并对多个相交剪切带体系进行了表征。通过对为期一年的注入增产进行详细的耦合过程建模，同时对油藏压力、微震活动和地表变形进行现场监测，得出了这一特征。研究人员发现，地表变形的分析尤其具有挑战性，因为在3公里以下的深度，由注入引起的细微地表变形与构造效应和与降雨相关的季节性地表效应造成的变形混合在一起。然而，通过对现场数据的详细分析，我们确定了与注入相关的变形。利用三维水文地质和地质力学模型确定了相关岩层和剪切带的水力和力学特性。通过拟合注入井周围监测井的压力变化，采用反分析方法确定了注入井的水力特性。通过将预测的微震活动性电位与观测到的微震活动性电位进行比较，并将预测的垂直位移与卫星测量的地表变形拟合，估算了其力学性质。结果表明，考虑区域断裂系统，特别是储层断层和剪切带对注入水量和蒸汽压力扩散的影响至关重要。在EGS示范项目附近，流体流动路径和压力扩散锋沿N130向剪切带最大，沿N50向剪切带最小。证据来自微地震事件震源，这些震源从注入井向水平方向延伸数公里，并深入到高温储层下方的花岗岩侵入体中。
In this study, integrated coupled process modeling and field observations are used to build a three-dimensional hydrogeological and geomechanical model of an Enhanced Geothermal System (EGS) in the northwestern part of The Geysers geothermal field, California. We constructed a model and characterized hydraulic and mechanical properties of relevant geological layers and a system of multiple intersecting shear zones. This characterization was conducted through detailed coupled process modeling of a one-year injection stimulation with simultaneous field monitoring of reservoir pressure, microseismicity, and surface deformations. The analysis of surface deformations was found to be particularly challenging as the subtle surface deformations caused by the injection taking place below 3 km depth are intermingled with deformations caused by both tectonic effects and seasonal surface effects associated with rainfall. However, through a detailed analysis of the field data we identified deformations associated with injection. Hydraulic and mechanical properties of relevant rock layers and shear zones were determined using a 3D hydrogeological and geomechanical model. Hydraulic properties were determined using inverse analysis by fitting the pressure evolution in monitoring wells surrounding the injection well. Mechanical properties were estimated by comparison of the predicted microseismicity potential with the observed microseismicity and by fitting the predicted vertical displacement with the surface deformations measured by satellite. The results show the critical importance of considering the regional fault system, especially reservoir-level faults and shear zones that modify injection water flow and steam pressure diffusion. In the vicinity of the EGS Demonstration Project, fluid flow pathways and pressure diffusion fronts appears to be at a maximum along N130 oriented shear zones and at a minimum along N50 oriented shear zones. Evidence for this comes from microseismic event hypocenters which extend several kilometers horizontally from the injection well and deep into a recent granitic intrusion that underlies the high temperature reservoir.