Mdt job planning and interpretation by: muhammad zahid

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MDT:- Modular Dynamic Formation Tester is the tool through which we can test the formation and measure the formation pressure, temperature and get the pure reservoir fluid and water samples. MAIN COMPONENTS OF AN MDT TOOL :- Formation Pressure Gauges Formation Resistivity Gauges Pump Out Live Fluid Analyzer Sample Chamber



  • MDT job is designed after evaluating the open hole logs. There are few main points which should be keep in mind before planning the job.

  • 1- Select the depth points for formation pressure.

  • 2- Select at least three (3) pressure points in one bed.

  • 3-Pressure points should fall in oil/gas zones and water bearing zone.

  • 4- Select the oil/gas sample point, which should be clean and try to get it from top of the reservoir.

  • 5-Also select a point for water sample in water bearing zone.

  • 6- MDT oil/gas sample is very suitable for PVT analysis.

MDT Operation:-

  • MDT Operation:-

  • If you have to QC or witness the MDT operation then you should consider the points which are given below:-

  • 1- MDT Gauges should be calibrated.

  • 2- Check the tool zero position.

  • 3-Tools probe should be against the desired depth.

  • 4- MDT packer should be set correctly.

  • 5-Formation pressure should be less than mud pressure.

  • 6- Don’t stay longer at any point.

  • 7- Take care before taking the formation sample. The representative sample should be formation fluid not the mud filtrate, for this check the resistivity gauge and Live Fluid Analyzer.



  • Interpretation of MDT data is very interesting. For interpretation you have to make a graph between the formation pressure and depth. When you plot the formation pressure against the depth you will get the density gradient, values of which are given as under:

  • Oil, Gas and Water has different gradients.

  • 1-Gas = 0.55 g/cc

  • 2-Oil = 0.88 g/cc

  • 3-Water = 1.0 g/cc

  • These are density gradients of different fluids. Where your gradient changes you can mark the Gas-Oil contact, Gas-Water contact, Oil-Water contact.

  • The deeper pressure points should have higher value of pressure. If this is not following then its means the data is not correctly recorded.

  • During plotting the data some points will fall away from normal behavior these points called “Super Charge” points due to low permeable formations like Shale.

  • In low permeable carbonates dual packer MDT is useful.

MDT gas/oil sample is very suitable for PVT analysis and other lab analysis. Through this sample we can calculate the compressibility factor and gas components.

  • MDT gas/oil sample is very suitable for PVT analysis and other lab analysis. Through this sample we can calculate the compressibility factor and gas components.

  • Calculate the salinity of formation water in laboratory through MDT water sample is very excellent use of formation water sample. Through this salinity we can calculate the formation water resistivity (Rw), which is the most essential parameter in log interpretation.

  • The formation water analysis is also very useful for well completion equipment.


  • THANKS!!!

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