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首页> 外文期刊>Journal of Environment and Earth Science >Correlation Between Geological Logs and Geophysical Logs to Estimate Aquifer Positions in the Crystalline Basement Rocks of the Birimian System, Ghana
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Correlation Between Geological Logs and Geophysical Logs to Estimate Aquifer Positions in the Crystalline Basement Rocks of the Birimian System, Ghana

机译：地质测井和地球物理测井之间的相关性，以估计加纳Birimian系统的结晶基底岩石中的含水层位置

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This study has enabled the lithological units intersected by a well, locate contacts of adjacent beds, locate depth to groundwater and determine the thickness of the units. Records of three geophysical logs parameters; resistivity, gamma ray and self-potential (SP) measured in five boreholes which were drilled as part of a Rural Water Supply Project Phase II in the Juabeso –Bia District were correlated with the geological logs on site from the drill cuttings of the bore hole. The boreholes depths were between 45-52m and were drilled over hornblende, phyllites and granites which constitute part of the various rock types of the Birimian system. Deflections of the SP logs established the presence of permeable rock formations. Alternatively, the long-short- normal logs distinguished between permeable and impermeable beds by recording lower or higher apparent resistivity signals respectively on the log sheet. These anomalies are identified mostly in the weathered zones and also within the fresh rocks. In almost all the boreholes the gamma ray logs indicated low clay content which may be due to the absence of intensely weathered rocks or low concentration of radioactive rocks within the survey area. The application of gamma ray logs rely on the fact that the concentrations of radioactive isotopes varies from one rock type to another and that acidic rocks are more radioactive than the basaltic rocks hence most of the rocks in the project area is more basaltic. Though the SP deflection was able to indicate permeable formations there was no guarantee that the rock formation could contain water. However, the combined interpretation of the three other logs shows that deflections of SP close to the basement rocks and lower resistivity values on the long-short-normal logs generally indicated the presence of water bearing formations. Three lithological units were identified over the various rock types: a top layer predominantly clay of thickness between 0-25m overlying a weathered zone about 16-45m thick above the fresh rocks of the various types.
机译：这项研究使岩性单元可以与一口井相交，定位相邻床层的接触面，定位地下水深度并确定单元的厚度。记录三个地球物理测井参数;在Juabeso –Bia地区的农村供水项目第二阶段中钻探的五个钻孔中测得的电阻率，伽马射线和自电势（SP）与钻孔钻屑现场的地质测井相关。钻孔深度在45-52m之间，并钻在构成Birimian系统各种岩石类型的一部分的角闪石，千枚岩和花岗岩上。 SP原木的挠曲确定了渗透性岩层的存在。可替代地，通过在测井纸上分别记录较低或较高的视在电阻率信号，长-短法线测井在可渗透床和不可渗透床之间进行区分。这些异常大多在风化带和新鲜岩石中被识别。在几乎所有的井眼中，伽马射线测井表明粘土含量低，这可能是由于在调查区域内没有强烈风化的岩石或放射性岩石的浓度低。伽马射线测井的应用是基于这样的事实，即放射性同位素的浓度随一种岩石类型而变化，并且酸性岩石比玄武岩具有更高的放射性，因此项目区域中的大多数岩石都是玄武岩。尽管SP挠度能够指示可渗透的地层，但不能保证岩石地层可以含水。但是，对其他三个测井的综合解释表明，SP靠近基底岩石的挠度和长短法线测井中较低的电阻率值通常表明存在含水层。在各种岩石类型上确定了三个岩性单元：顶层，主要是厚度在0-25m之间的粘土，覆盖在各种类型的新鲜岩石上方约16-45m厚的风化带上。

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