Petroleum Engineering 405 Drilling Engineering * Well Drilling Engineering Prediction of Abnormal Pore Pressure Dr DO QUANG KHANH * Prediction of Abnormal Pore Pressure Resistivity of Shale Temperatur[.]
Well Drilling Engineering Prediction of Abnormal Pore Pressure Dr DO QUANG KHANH Prediction of Abnormal Pore Pressure Resistivity of Shale Temperature in the Return Mud Drilling Rate Increase dc - Exponent Sonic Travel Time Conductivity of Shale Read: Applied Drilling Engineering, Ch HW # Shale Resistivity vs Depth Establish trend line in normally pressured shale Look for deviations from this trend line (semi-log) EXAMPLE Shale Resistivity vs Depth Establish normal trend line Look for deviations (semi-log) Shale Resistivity vs Depth Pore Pressure (lb/gal equivalent) 16 14 12 10 Establish normal trend line Look for deviations ppg (normal) Use OVERLAY to quantify pore pressure (use with caution) Depth, ft Shale Density , g/cc Depth, ft Mud Temperature in flowline, deg F Example 8.2 X Why? Example 8.8 X Thermal conductivity, heat capacity, pore pressure 10 Typical Drilling Rate Profiles Transition Zone Shale As the pressure p becomes very small, the gas in the pores has a tendency to expand which causes the shale particles to pop from the wall This is called sloughing shale The transition zone generally has a higher porosity, making drilling rates higher In a clean shale the ROP will increase in a smooth manner 17 Typical Drilling Rate Profiles Note: If you are drilling overbalanced in a transition it will be very difficult to pick up the transition zone initially This will allow you to move well into the transition zone before detecting the problem 18 Typical Drilling Rate Profiles This could cause you to move into a permeable zone which would probably result in a kick The conditions you create with overbalanced hydrostatic head will so disguise the pending danger that you may not notice the small effect of the drilling rate curve change This will allow you to move well into that transition zone without realizing it 19 Determination of Abnormal Pore Pressure Using the dc - exponent From Ben Eaton: P S D D S P dc D D n d cn 20