The ability to drill horizontal wells is now firmly established, as is the ability to convey formation evaluation sensors into the horizontal hole environment However, the evaluation of these logging sensor measurements requires care in high angle wells. This is because most sensors and interpretation methods have been designed for lower angle holes, typically from 0° to 65° deviation. In near horizontal holes, there is a potential breakdown in radial symmetry around the wellbore, a symmetry that is normally taken for granted in conventional log interpretation. In a typical North Sea layered formation, a good understanding of the volume investigated by each logging sensor is essential to the complete interpretation of logs from near horizontal wells. Examples are provided that show how a layered formation model can be built up using logging data from such wells. This model can then be used to guide any further drilling, improve petrophysical evaluation or help design an optimum completion strategy.
Guide-lines are given to planning a logging job that should overcome some of the uncertainties of interpreting logging data from these high angle wells.