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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Structural model and slip-dilation tendency analysis at the Copahue geothermal system: Inferences on the reservoir geometry
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Structural model and slip-dilation tendency analysis at the Copahue geothermal system: Inferences on the reservoir geometry

机译：科纳苏地热系统结构模型及防滑趋势分析：储层几何的推论

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摘要

The Copahue volcano host one of the most attractive geothermal resources of Argentina. Several studies focused on both the volcanic activity and the related geothermal manifestations, including a feasibility report during the '90s. However, limited, unclear and usually contradictory structural interpretations are found in the literature, and the role of the main faults over the geothermal system remains thus unsolved. This paper provides the first structural characterization and role assessment of the faults over the fluid flow and the reservoir geometry. A 3D structural model has been constructed to achieve this goal, and a fault-plane striations survey has been carried out at Anfiteatro, Termas and Maquinitas hydrothermal zones. Using this dataset, a slip and dilation tendency analysis over the main structures have been performed. The 3D structural model indicates that the Copahue geothermal field is bounded by an N60 degrees-trending fault set and constrained to the north by the Trolope fault and to the south by the Chancho-Co fault, both with WNW-ESE trend. The collected fault-plain striations data was inverted to obtain the paleostress tensor related to the formation of the Copahue village fault system (CVFS), the structure that controls the hydrothermal areas. The subvertical maximum principal stress axis obtained defines a well constrained tensional regime, with a subhorizontal NW-SE minimum principal stress, consistent in all the surveyed locations. Both the 3D model and the inverted paleostress tensor indicate that the geothermal field, and probably the entire northeastern slope of the volcano, is subjected to an extensional faulting regime. Our analysis shows that the N degrees 60-trending fault set is critically stressed for dilation and probably behaves as an active hydrological fault system, whereas the N105 degrees and N135 degrees fault sets have intermediate and low dilation tendency, respectively. These tendencies might lead to a northeast-trend fluid path between the Chancho-co and the N135 degrees faults and might define the extension of the steam cap. We propose a compartmentalized reservoir model made up by three fault segmented blocks. While a steam cap over a deeper reservoir controlled by the CVFS characterizes the central segment, a pressurized liquid-dominated reservoir could prevail to the west of Termas and the east of Maquinas hydrothermal zones. This model explains the differences between the fumaroles inside the CVFS (i.e., Termas to Maquinas fumaroles) and outside this structural system (i.e., Anfiteatro), is consistent with the steam cap identified by the exploration boreholes and is consistent with the 3D structural framework proposed. Also, the model suggests that the collapse of the eastern slope of the Chancho-co hill might constitute the initial state of the current configuration of the geothermal system. Additional studies are needed to verify the proposed reservoir model before defining deep exploration targets, including magnetotellurics, discrete fracture network analysis, and preliminary thermodynamical models. (C) 2019 Elsevier B.V. All rights reserved.
机译：科普苏火山举办阿根廷最具吸引力地热资源之一。一些研究专注于火山活动和相关地热表现，包括在90年代期间的可行性报告。然而，有限，不清楚，并且通常在文献中发现矛盾的结构解释，并且主要断层对地热系统的作用仍未得到解决。本文提供了流体流量和储层几何故障的第一种结构表征和作用评估。建立了3D结构模型来实现这一目标，并且在ANFITEATRO，TERMAS和MAQUINITAS水热带区域进行了故障平面策略调查。使用该数据集，已经进行了对主结构的滑移和扩张趋势分析。 3D结构模型表明，切割地热场被N60度趋势故障集合，并通过沿脚趾故障和南方受到南部的北部的朝南，与WNW-ESE的趋势。收集的故障普通条纹数据被反转，以获得与Copahue Village故障系统（CVFS）的形成相关的古青铜张量，该结构控制水热区域。获得的增强最大主应力轴定义了一个受影响的张力制度，具有脱色的NW-SE最小主应力，在所有调查的位置一致。 3D模型和倒立的古聚四大浪琴都表明地热场，以及火山的整个东北坡，受到了一个延伸的断线状态。我们的分析表明，N度60-趋势故障集被批判性地强调扩张，并且可能表现为有源水文故障系统，而N105度和N135度故障集别分别具有中间和低扩张趋势。这些趋势可能导致Chancho-Co和N135度断层之间的东北趋势流体路径，并且可以定义蒸汽帽的延伸。我们提出了一个由三个故障分段块组成的分区化水库模型。虽然由CVFS控制的深层水库的蒸汽帽表征中央部门，但加压的液体主导的水库可以在Tommars和Maquinas热水区以东普遍存在。该模型解释了CVFS内部（即，Tomminas Fumaroles）内部的umaroles之间的差异，并且在该结构系统（即AnfiteAtro）之外，与勘探钻孔识别的蒸汽帽一致，并且与所提出的3D结构框架一致。此外，该模型表明，南丘山的东部坡的崩溃可能构成地热系统的当前配置的初始状态。在定义深度勘探目标之前，需要进行额外的研究来验证所提出的储层模型，包括磁仪，离散的断裂网络分析和初步热力学模型。 （c）2019 Elsevier B.v.保留所有权利。

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