A small sample with a great deal of meaning: Deutsche Erdoel specialists take rock samples during the drilling operations to obtain more detailed information about the characteristics of a reservoir. A sample is taken from the rock in much the same way as the core is removed from an apple. And this little sample from hundreds or thousands or metres underground is then used to analyse the reservoir in greater detail.
Core samples are drilled out by means of a special bit and, among other things, provide information about the formation, mineralogy, chemical composition and physical properties of the rock as well as its permeability, pore space and pore content.
An analysis of the five senses
In the first step of this process, our geologists rely entirely on their five senses and a few simple tools like a foot rule and a magnifying glass. In this way they can draw up a macroscopic record of the core sample and also carry out facies analyses – investigating all the characteristics of a rock that are derived from its genesis and the conditions under which it was deposited.
The next step involves removing tiny cylinder-shaped plugs from the sample at regular intervals. It is from these plugs that our lab specialists make the wafer-thin sections. These thin sections are no more than 0.03 mm thick and are placed under a microscope to create the micro-facies images that help to show us the mineralogical composition of the rock. If a scanning electron microscope is used, our geoscientists can even look into the pore space of the rock.
Indication of production opportunities
These plugs are then put to further investigative use. When pressure is exerted on the plugs by means of helium and mercury, the amount of gas or liquid that flows through the rock can be measured to discover more about the permeability of the rock and how easy it will be to produce oil or gas.
Zoom Thin sections tell us a great deal about the structure of reservoir rocks Last but not least, the so-called diagenesis is of particular interest to geologists. How did pressure and temperature affect the rock those millions of years ago? Did the porosity decrease and were new minerals formed in the pore spaces? What kinds of cement material (e.g. calcite) are to be found?
All in all, the results of such an extensive core analysis deliver decisive pointers to the way a reservoir functions and how high the chances of success will be for possible exploration activities.