BASE GEOPHYSICS

Resistivity survey measures the electrical conductivity of the various geological materials in subsurface by simply applying the direct current into the ground through current electrodes and recording the potential difference between potential electrodes to give the electrical resistivity of the subsurface. However the survey design depends on the geology of the site and the expected end goal of the survey. Electrical Resistivity gained attention especially in searching for groundwater resources, due to promising direct relationship between electrical conductivity of groundwater and electrical Resistivity. Groundwater exploration is the systematic process of searching for groundwater resources (aquifers) by applying geologic, geochemical and geophysical techniques. Groundwater refers to the water that occupies the subsurface spaces and interacted with subsurface geologic environment. There are three (3) common methods of conducting electrical resistivity surveys for groundwater explo...

Electrode array configuration defines how much distance should put either current electrodes or potential electrodes so that to obtain the expected resistivity information about the given geological terrain. So this is a task that you need to consider when you set up your geophysical survey design. There are many types of array configuration that you can use depending on your survey objective, however this post will only provide to you the basics of three (3) commonly used array configurations in most electrical surveys.  First of all we have to consider the concept laid behind the electrode array configuration as simple as possible. When we consider the figure in a homogeneous and isotropic half-space, when the current is passed into the ground by current electrodes, it will behave to spread out at radial distance r, so the Potential gradient between electrodes can be given as, ∆V/∆r = -pJ Since, J = current density ( I/a), Also A = 2πr 2 since radial assume hemispherical shape T...

It is obvious sometimes when we carry out electrical resistivity surveys in the field especially in complex and dry geological terrain to be faced with this problem. You can detect this issue when resistance reading in your measuring device becomes very high. Unfortunately if the issue is too serious sometimes it may cause the survey to stop for a while. It is the electrode contact resistance problem that I want you to know about. I want to share my experience with you through this post regarding the basic causes, how it affects electrical resistivity results and how we can overcome this problem in the field. Without wasting time Let's move straight to the main point. What is Contact resistance? Electrode Contact resistance can be defined as the situation at which there is significant increase in measured electrical resistance at electrodes due to presence of poor conductive materials in the subsurface during electrical resistivity surveys. As explained above, electrical surveys ...

Electrical Resistivity is the one of the most commonly used methods for measuring earth resistivity at which current is injected into the ground by using galvanic metal electrodes. For almost all electrical geophysical methods, the true and the specific resistivity of the rock is of interest. Let us look through this post for brief principles on how this technique works. basic principles Electrical Resistivity (ρ): Is the measure of the tendency of a material to resist a flow of electric current. The inverse is electrical conductivity. Conductivity (σ) : is the relative ability of material to conduct electricity when a voltage is applied. It has units of Siemens/meter (S/m) which are equivalent to mhos/meter (Ω -1 m -1 ). Mathematically, σ = 1/ρ  Conversely, the resistance offered by a material to current flow is expressed in terms of resistivity. The true resistivity of a rock unit is defined as being equal to the resistance of a unit cube of the rock. It is well known that: The ...

Carrying out Electrical resistivity data collection is the one step among others that you should pass through when conducting your resistivity project. The process is procedural and systematic, involving field set up of resistivity equipment such as resistivity meters. And the best and unique fact of resistivity surveying is that metal electrodes should be directly plugged into the ground. As the basic rule of thumb is that if you want to win your geophysical project your data should be quality collected and checked. Also the same rule applies in resistivity surveying that we should qualify that rule so as to increase our chances to win the project. However one among the challenges for poor quality resistivity data you may be faced are contributed by sensitivity of resistivity  instruments and tools themselves utilized during resistivity data acquisition. This is why I have presented to you through this post  these equipment that are at least the basics for any resistivity dat...