Effect Of Formation Dip Or Hole Deviation On Induction Logs

Computer-simulated deep induction logs show that the apparent resistivity at the center of a dipping bed is significantly affected by the dip angle. Generally speaking, the apparent resistivity decreases with the dip angle. It is not unusual to find that the apparent resistivity decreases by a factor of 2 or more when the dip angle is varied from 0to 60 degrees. It is also shown that the shape of the resistive log is also very much affected by the dip angle. As the dip angle increases, the resistivity measured by an induction sonde ate bed boundary also increases so that it is closer to the maximum resistivity than to the shoulder bed resistivity. This effect broadens the resistivity curve of a dipping bed. Two conclusions may be drawn. Firstly, unless a bed is thick, the apparent resistivity at the center of the bed is quite sensitive to the dip angle. To obtain the true resistivity, significant correction is usually needed. Such quantitative dipping bed correction has now been made available in the form of correction charts. Secondly, the shape of the induction log is sensitive to the dip angle. Additional care must be taken in order to estimate accurately the thickness of a dipping bed.