Method to estimate pore pressure uncertainty from trendline variations

An apparatus for estimating a pore pressure of an earth formation penetrated by a borehole and an associated uncertainty, the apparatus comprising:

• a carrier configured to be conveyed through the borehole;
• a downhole tool coupled to the carrier and configured to perform formation measurements related to porosity at a plurality of depths in the borehole;
• and
• a processor coupled to the downhole tool and configured to implement a method comprising:
• receiving formation measurements from the downhole tool at a plurality of depths in the borehole;
• defining a first depth interval and a second depth interval deeper than the first depth interval, the first depth interval comprising a first set of formation measurement points and the second depth interval comprising a second set of formation measurement points;
• establishing a plurality of trendlines of depth versus porosity-related measurements with each trendline in the plurality of trendlines extending from a point in the first depth interval through a point in the second depth interval;
• and
• calculating a pore pressure line and associated uncertainty using the plurality of trendlines.

A non-transitory computer-readable medium comprising computer-executable instructions for estimating a pore pressure of an earth formation penetrated by a borehole and an associated uncertainty by implementing a method comprising:

• receiving formation measurements from a downhole tool configured to perform formation measurements related to porosity at a plurality of depths in the borehole;
• defining a first depth interval and a second depth interval deeper than the first depth interval, the first depth interval comprising a first set of formation measurement points and the second depth interval comprising a second set of formation measurement points;
• establishing a plurality of trendlines of depth versus porosity-related measurements using a processor with each trendline in the plurality of trendlines extending from a point in the first depth interval through a point in the second depth interval;
• calculating a pore pressure line and associated uncertainty using the plurality of trendlines.