ZZ Resistivity Imaging Pty. Ltd.
1.3 What is a comprehensive array oriented resistivity system?
Firstly, we will provide an explanation of a 'Conventional arrays-oriented resistivity instrument.'
As we know, there are many different resistivity data collection arrays, namely, Wenner, Schlumberger, dipole-dipole, gradient arrays, and etc. The data collected with these arrays are normally plotted into pseudo-sections for the geological interpretation. In a majority of these data acquisition arrays, the quantity 'N' (related to electrode separation) is proportional to the explorable depth. Thus, when N=1 or 4 as the figure below shows, it represents the closest or furthest resistivity distribution to the surface, respectively.
Most resistivity instruments are designed to collect data through the use of these traditional data collection arrays, where N varies from 4 to 10. Therefore, the maximum number of channels for most multi-channel instruments is limited from 4 to 10.
It is to be noted that all these traditional data collection arrays were developed before the resistivity inversion technique, and they were designed to produce a pseudo-section for geological interpretation. Therefore, we categorise these kinds of resistivity equipments (based on conventional arrays) as conventional array-oriented resistivity instruments.
Comprehensive array-oriented resistivity instruments
With the development of the resistivity inversion technique, it isn't necessary to follow these arrays for the resistivity data collection. There are three main reasons for this. Firstly, the data amount collected with the conventional arrays is insufficient for the inversion technique (under-determined), which leads to a less optimal inversion result. Secondly, people have to follow an exact way of collecting data, which will limit some applications, such as surface-borehole survey. And thirdly, the conventional arrays are not capable of using all the electrodes at anytime to collect a more completed data set. Most resistivity manufacturers still follow the traditional methods in designing their resistivity instruments, and use the traditional arrays to collect data.
Recently, however, a new kind of multi-channel resistivity instrument can use all electrodes simultaneously (except two current electrodes used for current injection) to collect all potential data. This kind of instrument data is different from conventional array-oriented resistivity instruments. For this kind of resistivity instrument, we introduced a new name: comprehensive array-oriented resistivity instruments, which produce superior data collection speed and versatility. Please refer to the examples in the next section for more details.
Comprehensive array-oriented resistivity instruments have two basic requirements. They should be able to use all available electrodes (except two current electrodes) to collect all voltage data, and they must use the resistivity inversion technique to produce a resistivity distribution image for interpretation.
Read more about Comprehensive array-oriented resistivity instruments.