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Multiscale short-circuiting mechanisms in multiple fracture enhanced geothermal systems
Geothermics ( IF 3.5 ) Pub Date : 2021-03-26 , DOI: 10.1016/j.geothermics.2021.102094
Bruce Gee , Robert Gracie , Maurice B. Dusseault

Heat extraction from an enhanced geothermal system (EGS) is a complex coupled thermo-hydro-mechanical process. The viability of an EGS is compromised by short-circuiting, a phenomenon resulting from positive thermo-hydro-mechanical feedback loops within the reservoir. In this article, the mechanisms by which short-circuiting occurs in EGSs are studied and described. EGS well doublets are modelled using a fully-coupled thermo-hydro-mechanical finite element model. Flow through the reservoir is restricted to discrete fracture planes, which are hydraulically linked via the injection and production wells. The general behaviour of the system is modelled, starting from the initially distributed flow through the fractures, through to the dominance of flow along a single flow pathway. Both single and multi-fracture EGSs are studied. Short-circuiting is demonstrated to be a multiscale phenomenon, as both in-plane and inter-plane short-circuiting mechanisms are observed. In-plane short-circuiting manifests through flow channeling and, in the studied systems, is the dominant mechanism that controls the production temperature of the system. The behaviour of flow channeling is characterized with four production regimes. It is demonstrated that the effects of flow channeling are more severe in multi-fracture EGSs. Two new inter-plane short-circuiting mechanisms are observed for the first time: plane channeling, and bifurcation of the short-circuiting pathway. The inter-plane mechanisms are demonstrated to have large impacts on the distribution of flow through the reservoir, but are observed to have little effect on the production temperature.



中文翻译:

多裂隙增强地热系统中的多尺度短路机制

从增强的地热系统(EGS)提取热量是一个复杂的热-水-机械耦合过程。EGS的生存能力因短路而受损,短路是由储层内的正热-水力-机械反馈回路造成的。在本文中,研究和描述了EGS中发生短路的机制。使用完全耦合的热-水-机械有限元模型对EGS井双峰进行建模。通过储层的流量被限制在离散的裂缝平面上,这些裂缝平面通过注入井和生产井以液压方式连接在一起。对系统的总体行为进行建模,从最初分布在裂缝中的流动开始,一直到沿着单个流动路径的流动占主导地位。研究了单断裂和多断裂EGS。事实证明,短路是一种多尺度现象,因为同时观察到平面内和平面间短路机制。平面内短路通过流动通道表现出来,并且在所研究的系统中,是控制系统生产温度的主要机制。流道的行为以四种生产方式为特征。结果表明,在多裂隙EGS中,流道效应更为严重。首次观察到两个新的平面间短路机制:平面通道化和短路路径的分叉。平面间机制对通过储层的流量分布有很大影响,但对生产温度几乎没有影响。因为观察到了平面内和平面间的短路机制。平面内短路通过流动通道表现出来,并且在所研究的系统中,是控制系统生产温度的主要机制。流道的行为以四种生产方式为特征。结果表明,在多裂隙EGS中,流道效应更为严重。首次观察到两个新的平面间短路机制:平面通道化和短路路径的分叉。平面间机制对通过储层的流量分布有很大影响,但对生产温度几乎没有影响。因为观察到了平面内和平面间的短路机制。平面内短路通过流动通道表现出来,并且在所研究的系统中,是控制系统生产温度的主要机制。流道的行为以四种生产方式为特征。结果表明,在多裂隙EGS中,流道效应更为严重。首次观察到两个新的平面间短路机制:平面通道化和短路路径的分叉。平面间机制对通过储层的流量分布有很大影响,但对生产温度几乎没有影响。平面内短路通过流动通道表现出来,并且在所研究的系统中,是控制系统生产温度的主要机制。流道的行为以四种生产方式为特征。结果表明,在多裂隙EGS中,流道效应更为严重。首次观察到两个新的平面间短路机制:平面通道化和短路路径的分叉。平面间机制对通过储层的流量分布有很大影响,但对生产温度几乎没有影响。平面内短路通过流动通道表现出来,并且在所研究的系统中,是控制系统生产温度的主要机制。流道的行为以四种生产方式为特征。结果表明,在多裂隙EGS中,流道效应更为严重。首次观察到两个新的平面间短路机制:平面通道化和短路路径的分叉。平面间机制对通过储层的流量分布有很大影响,但对生产温度几乎没有影响。流道的行为以四种生产方式为特征。结果表明,在多裂隙EGS中,流道效应更为严重。首次观察到两个新的平面间短路机制:平面通道化和短路路径的分叉。平面间机制对通过储层的流量分布有很大影响,但对生产温度几乎没有影响。流道的行为以四种生产方式为特征。结果表明,在多裂隙EGS中,流道效应更为严重。首次观察到两个新的平面间短路机制:平面通道化和短路路径的分叉。平面间机制对通过储层的流量分布有很大影响,但对生产温度几乎没有影响。

更新日期:2021-03-27
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