Overpressure zone detection

Another important feature of mud logging and MWD/LWD, is the capability of overpressure zone detection. As was discussed previously in this section, overpressure estimates can be done during drilling with many techniques and accuracy increases with the number of parameters available. 

The -sonic log can also be used to detect overpressured zones. The sonic measurements until recently were available only on wireline. Now, MWD sonic tools have been developed adding one more parameter for overpressure detection while drilling. Two equations relating the formation porosity to the transit time are used ... 

Abnormal Formation Pressure Detection from Kicks. The kicks, or flow of formation fluids into the borehole, are the ultimate indication that the well has encountered an overpressured zone. Kick detection during drilling usually is achieved by use of a pit-volume indicator and/or a flow indicator. The usual pit-volume alert is 10 barrels drilling fluid volume increase. A differential mud flow indicator can also be used to detect kicks more quickly. 

The equipment required to develop this type of sensor is very simple and resembles closely that used to implement ordinary liquid-solid separations in FI manifolds. The only difference lies in the replacement of the packed reactor located in the transport-reaction zone with a packed (usually photometric or fluorimetric) flow-cell accommodated in the detector. Whether the packing material is inert or active, it should meet the following requirements (a) its particle diameter should be large enough (< 80-100 fim) to avoid overpressure (b) it should be made of a material compatible with the nature of the integrated detection system e.g. almost transparent for absorbance measurements) and, (c) the retention/elution process should be fast enough to avoid kinetic problems. 

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