地热储层热传导和渗透率评价中渗透率各向异性的影响分析

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地热储层热传导和渗透率评价中渗透率各向异性的影响分析

Advances in Geo-Energy Research, 2019, 3(1): 43-51

原文网址:  http://www.astp-agr.com/index.php/Index/Index/detail?id=92

       地热储层中的开发主要依赖于冷水在裂缝之中的循环导热过程，储层中的渗透率会直接影响流体传播的路径，以及由于液体与岩石导热产生的降温反应。因此流体，固体，热三个物理场需要耦合考虑它们每一个对于岩石物理特性以及渗透率改变的影响。

基于开发的全耦合流固热模拟软件TFREACT-FLAC3D， 本文通过改变在三个主方向的裂缝间距（保持相同的初始裂缝宽度），定义了深层地热（EGS）储层中五个不同的初始渗透率各向异性值，从而能够探索渗透率的各项异性引起的热传导模式的不同，导致的裂缝渗透率演化规律。在该模拟实验中，分析从注水井到开采井之间的热前缘推进的结果表明：各向异性值低的情况下，热前缘推进速度较慢，且岩石受冷水驱替面积更大。各向同性情况下表现出更低的温度梯度，同时随着时间的热产能也是最低。相同时间内各向异性值为0.01情况产生了最大的地热产能。衍生出的热应力能够起到降低应力载荷作用，通过降低挤压法向应力。所以热应力效应能够起到增大裂缝宽度和渗透率效果。经历同样时间的注采周期循环，各向异性值0.01的情况下降低了0.35倍，高各向异性值100情况下增加了2.5倍。

Influence of permeability anisotropy on heat transfer and permeability evolution in geothermal reservoir

Janim Joshua Ijeje, Quan Gan, Jianchao Cai

(Published: 2018-09-12)

CorrespondingAuthor and Email: Quan Gan, gan.quan@abdn.ac.uk; ORCID: https://orcid.org/0000-0001-5201-8817

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Citation: Ijeje, J.J., Gan, Q., Cai, J. Influence of permeability anisotropy on heat transfer and permeability evolution in geothermal reservoir. Advances in Geo-Energy Research, 2019, 3(1): 43-51, doi: 10.26804/ager.2019.01.03.

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ArticleType: Original article

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Abstract：

  Extracting heat energy from geothermal reservoirs essentially relies on circulating cold fluid within fractured hot rocks. The intrinsic anisotropic permeability in the reservoir directly affects the path of flow and the associated thermal drawdown from cooling procedure. Consequently, each individual component including thermal, hydraulic, and mechanical field needs to be considered, to evaluate the influence of permeability anisotropy on the thermal production and evolution of rock properties. In this work, the fully implicit coupled simulator TFReact was successfully implemented to generate results prototypical of an enhanced geothermal system. Anisotropic permeability values were generated from the variation of fracture spacing at three orthogonal principal directions, with identical initial fracture aperture. Five case scenarios of permeability anisotropy were simulated to evaluate the influence of anisotropic thermal drawdown in triggering permeability evolution. Analysis of the propagation of the thermal front from injector to producer indicated that low anisotropic permeability values will lead to late cold water breakthrough at producer, slower migration rate and wider sweep area than high anisotropic permeability values. Isotropic permeability scenario showed a lower thermal gradient profile, comparing against the scenarios of anisotropic permeability. The anisotropic value of 0.01 produced the highest power output, while isotropic permeability generated the least power output. Induced thermal stress resulted an unloading response by reducing compressive normal stress in sub-horizontal direction, and thereby increase fracture aperture in sub-horizontal direction. Invariably, the induced thermal expansion stress increased the compressive stress and reduced fracture aperture and permeability. After the same timing of injection-production cycle, the highest anisotropic permeability scenario resulted a factor of 2.5 increment in evolving fracture permeability, while lowest anisotropic permeability scenario lead to a factor of 0.35 decrease in changing fracture permeability. The generated thermal output suggested the most favorable strategy in maximizing thermal sweep across the reservoir, by prompting thermal transfer normal to direction of injector-producer.

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Keywords: Permeability anisotropy, fracture aperture, thermal drawdown, geothermal reservoir.

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