Underground GPR measurements for spatial investigations in a salt dome
Ground penetrating radar (GPR) is an efficient non destructive tool for the exploration of underground salt deposits. The complex geological structures (bent, folded, sometimes faulted layering of salt, potassium, clay, and anhydrite) in low-conductive salt can be mapped if distance and direction of reflecting objects are known. In boreholes the information is given by direction sensitive borehole radar. In shafts rotation symmetry helps to detect the direction. In drifts direction finding antennae provide the reflection angle. Various antenna types help to enhance the resolution or the penetration depth. Measurements with different polarizations offer additional information about the reflecting structures. Within the last two decades unique results from a salt dome in Northern Germany with various GPR systems were achieved. With this information and some geological knowledge a three dimensional model of the structures has been created.
Salt dome exploration by directional borehole radar wireline service
3 D borehole radar, a standard logging method? This was the title of the paper, DMT contributed to the GPR conference 2000. Now this question can be answered. Since more than seven years DMT is applying directional borehole wireline services for salt dome exploration up to depths of 2000 m. The salt dome investigations can be carried out in boreholes or caverns.
Three-dimensional borehole radar measurements: a standard logging method?
A lot of different logging methods are established for many exploration purposes. The borehole radar or Electro Magnetic Reflection (EMR) method is not that popular. There are two main reasons for this situation: Borehole radar measurements are not applicable in situations where drilling mud or other conductive materials are in the borehole and the available borehole radar equipment need special logging cables like optical or coaxial cables. The first aspect limits the application of borehole radar to stable drillholes where no hydrostatic pressure is necessary or where only pure water may replace the drilling mud. Especially a dry salt environment is suitable for borehole radar. The second aspect is related to the equipment. A very ruggedised borehole tool with easy assembling and fitting to standard cableheads and standard logging cables is desirable. This paper describes the development and the outline of a directional borehole radar system which may be integrated in standard logging programs. This system makes it easier for companies to carry out borehole radar measurements at their drilling locations.