Petrophysical Properties of Icelandic Rocks
Petrophysical Properties of Icelandic Rocks
复制标题
冰岛岩石的岩石物理性质
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
G. Ó. Friðleifsson
中科院分区：
文献类型：
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作者：
H. Franzson;Steinar Þór Guðlaugsson;G. Ó. Friðleifsson
在冰岛目前活跃的热液区的侵蚀等价物中进行了系统的岩石取样，以研究地热系统的储层特征。该数据库共有约500个岩石样本。该项目正在进行中，在本文中，我们集中在两个方面的数据收集：首先，岩石学数据显示，热液蚀变严重改变了岩石的原生孔隙度，并进一步表明，岩石蚀变玄武熔岩是有关的原生孔隙度的岩石。据认为，观察到的系统性差异之间的孔隙度测定的气体膨胀和岩石学分析的薄片是由于微孔隙度（<30 μm），这是低于检测限的薄片分析。对于玄武岩侵入体和大多数熔岩，这种差异大多在5%以内。在高蚀变较大的差异，观察到一些熔岩。凝灰质岩石和沉积物显示出更大的差异，表明微孔隙的比例更高。在蚀变程度高于混层粘土带时，孔隙被充填85%以上。原生孔隙度高于14%的岩石似乎比孔隙度较低的岩石更容易充填，这可能表明前者的渗透性更好。颗粒密度随着蚀变的增加而降低，并且当岩石经历逐渐更高的温度蚀变时，颗粒密度再次增加是合理的，其中更高密度的蚀变矿物优先形成。雷克雅未克一个年轻的未蚀变的橄榄石拉斑玄武岩熔岩流的渗透率显示出不寻常的岩石物理性质：高孔隙的流动边缘的渗透率比孔隙较少的内部低一个数量级。高渗低孔样品还具有低地震速度和高颗粒密度的特征。渗透率异常的首选解释是，晶界微裂纹的广泛连接网络是导致流动的较粗部分和内部部分具有高渗透率的特征。另一个但显然不太可能的解释是，熔岩流边缘部分的囊泡周围的隔离玻璃涂层抑制了孔隙之间的渗透性连接。
A systematic rock sampling has been carried out in the eroded equivalents of the presently active hydrothermal areas in Iceland in order to study the reservoir characteristics of geothermal systems. A total of about 500 rock samples form the database. The project is ongoing and in this paper we focus on two aspects of the data collection: Firstly, petrographic data is presented to show that hydrothermal alteration severely alters the primary porosity of the rock and furthermore show that the rock alteration in basaltic lavas is related to the primary porosity of the rock. It is suggested that the observed systematic difference between the porosity determined with gas expansion and petrographical analysis of thin sections is due to microporosity (<30 μm) which is below the detection limit in the thin section analysis. This difference is mostly within 5% for basaltic intrusions and for most lavas. At high alteration larger differences are observed for some of the lavas. Tuffaceous rocks and sediments show a much greater difference indicating higher proportion of microporosity . The pores are more than 85% filled at higher alteration than mixed layer clay zone. Rocks with primary porosities higher than about 14% seem to fill more readily than those with lower porosities, probably indicating better permeability of the former. Grain density is shown to decrease with increasing alteration, and it is plausible that grain density increases again as the rocks go through progressively higher temperature alteration where higher density alteration minerals are preferentially formed. The permeability of a young unaltered olivine tholeiite lava flow in Reykjavik shows unusual petrophysical properties: The highly porous margin of the flow has an order of magnitude lower permeability than the less porous inner part. The high permeability – low porosity samples are also characterised by low seismic velocity and high grain density. The preferred explanation of the permeability anomaly is that an extensive connected network of grain boundary microcracks is the feature that causes high permeability in the coarser and inner part of the flow. Another but apparently less likely explanation is that an isolating glass coating around the vesicles in the marginal part of the lava flow inhibits permeable connections between the pores.