The Mag Sus / Gamma tool is designed for the measurement of magnetic susceptibility and natural radioactivity of rocks in boreholes.
MAGNETICS
The magnetic susceptibility measurement is to distinguish the types of rocks in the borehole profile in a complex of sedimentary, igneous and metamorphic rocks up to the extent of magnetite.
This particular tool has been used effectively for ore mining / grade control applications. It has previously been demonstrated (Mutton 97) that the lithology can be predicted from natural gamma and magnetic susceptibility logs by using a known log as a template and matching the curve characteristics of the unknown logs.
GAMMA
Gamma Ray logs provide a clear indication of variations in lithology and also accurately define bed thickness. Shaly bands are obvious and can be readily identified because clay content results in a high gamma count.
The Gamma Ray log is used for identification of coal, as coal typically exhibits a low counting rate. In this application a high sensitivity Gamma tool generally provides best results. In petroleum applications the higher gamma activity of the clay size fraction is due to the potassium contained in clay minerals, fine mica and feldspars. This is not only useful information in its own right, but is a crucial parameter in the accurate interpretation of Density and Neutron logs.
Gamma ray tools are an obvious choice in uranium exploration and development. The relationship between uranium content and count rate may be employed to determine ore grades. Ground water and engineering applications utilize the gamma ray log for lithology indicators and strata thickness as well as clay content, to determine permeability and rock strength.
A680 High Sensitivity Range
10-5 - 0.5 SI unit
serves for measuring weakly magnetic rocks e.g. dolomites can be distinguished from limestone.
A680E Extended Range
10-4 - 2 SI unit
suitable for strongly magnetic rocks where the A680 would go out of range.
Specifications
Tool Parameters
Measuring Parameters
Diameter 38mm Length 135cm Weight 5 kg Max. Working Temperature 70° C Max. Working Pressure 10 MPa Min No. of Cable Conductor 1 Supply Voltage Range 20-45 VDC Maximum Current Consumption 110 mA Nominal Current Consumption 80 mA Voltage Polarity in tool Head + ve on pin 1
-ve on pin 2 or tool chassis
Sensor two coil system Gamma NaI Crystal (18.5 mm X 50 mm) Inter-coil Spacing 20 cm Range 10-5 - 0.5 SI unit Accuracy 3% Communication Digital RS232