# US 8,788,208 B2 · Method to estimate pore pressure uncertainty from trendline variations > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,788,208 B2 - Document ID: US8788208B2 - Status: Granted - Kind: B2 - Application number: 13/229,212 - Filed: 2011-09-09 - Published: 2013-03-14 - Granted: 2014-07-22 - Earliest claimed: 2011-09-09 - Assignees: Baker Hughes Incorporated - Applicants: Stefan Wessling; Jianyong Pei - Inventors: Stefan Wessling; Jianyong Pei - Web page: https://patentgrep.com/patent/US8788208B2 ## CPC - E21B 49/00: Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells - G01V 1/40: specially adapted for well-logging - G01V 9/00: Prospecting or detecting by methods not provided for in groups G01V1/00 - G01V8/00 - G01V 11/00: Prospecting or detecting by methods combining techniques covered by two or more of main groups G01V1/00 - G01V9/00 - E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS - G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02) ## Abstract Disclosed is a method for estimating a pore pressure of an earth formation penetrated by a borehole and an associated uncertainty. The method includes: conveying a carrier through the borehole; performing formation measurements relating to porosity at a plurality of depths in the borehole using a downhole tool coupled to the carrier; 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; and calculating a pore pressure line and associated uncertainty using the plurality of trendlines. ## Claims ### Claim 1 A method for estimating a pore pressure of an earth formation penetrated by a borehole and an associated uncertainty, the method comprising: conveying a carrier through the borehole; performing formation measurements relating to porosity at a plurality of depths in the borehole using a downhole tool coupled to the carrier; 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; and calculating a pore pressure line and associated uncertainty using the plurality of trendlines. ### Claim 2 (depends on 1) The method according to claim 1, wherein calculating comprises calculating a representative trendline. ### Claim 3 (depends on 2) The method according to claim 2, wherein the representative trendline is an average of the plurality of trendlines. ### Claim 4 (depends on 2) The method according to claim 2, wherein the plurality of trendlines comprises a first trendline defined by a measurement point in the first depth interval and a measurement point in the second depth interval that provide a minimum of all slopes of trendlines resulting from all combinations of measurement points in the first and second depth intervals. ### Claim 5 (depends on 4) The method according to claim 4, wherein the first trendline has a minimum intercept of a Y-depth axis compared to all trendlines resulting from all combinations of measurement points in the first and second intervals second depth interval. ### Claim 6 (depends on 4) The method according to claim 4, wherein the plurality of trendlines comprises a second trendline defined by a measurement point in the first depth interval and a measurement point in the second depth interval that provide a maximum of all slopes of trendlines resulting from all combinations of measurement points in the first and second depth intervals. ### Claim 7 (depends on 6) The method according to claim 6, wherein the second trendline has a maximum intercept of the Y-depth axis compared to all trendlines resulting from all combinations of measurement points in the first and second intervals second depth interval. ### Claim 8 (depends on 6) The method according to claim 6, wherein the pore pressure line is calculated from converting the representative trendline to pore pressure as a function of depth using a mathematical relation relating formation measurements to pore pressure. ### Claim 9 (depends on 8) The method according to claim 8, wherein the first trendline is converted to a first pore pressure line and the second trendline is converted to a second pore pressure line using the mathematical relation and the uncertainty at a selected depth is the width between the first and second pore pressure lines at the selected depth. ### Claim 10 (depends on 1) The method according to claim 1, wherein the plurality of trendlines comprises a trendline for every combination of a first measurement point in the first depth interval and a second measurement point in the second depth interval. ### Claim 11 (depends on 10) The method according to claim 10, wherein calculating comprises converting the plurality of trendlines to a plurality of corresponding pore pressure lines using a mathematical relation relating formation measurements to pore pressure and determining a standard deviation of the plurality of corresponding pore pressure lines from the calculated pore pressure line. ### Claim 12 (depends on 10) The method according to claim 10, further comprising randomly varying an exponent of a mathematical relation relating formation measurements to pore pressure for converting the plurality of trendlines to a plurality of corresponding pore pressure lines and determining a standard deviation of the plurality of corresponding pore pressure lines from the calculated pore pressure line. ### Claim 13 (depends on 1) The method according to claim 1, further comprising shifting the second depth interval deeper into the borehole and iterating the steps of claim 1 until the second interval reaches an end of a normal compaction zone. ### Claim 14 (depends on 13) The method according to claim 13, further comprising shifting the first depth interval deeper into the borehole. ### Claim 15 (depends on 14) The method according to claim 14, wherein a distance between the first depth interval and the second depth interval remains constant. ### Claim 16 (depends on 14) The method according to claim 14, wherein a distance between the first depth interval and the second depth interval is a proportion of a total distance of a drill string drilling the borehole. ### Claim 17 (depends on 1) The method according to claim 1, further comprising moving a deepest end point of the second depth interval to be at a depth where formation measurements are being performed by the downhole tool and iterating the steps of claim 1 until the second interval reaches an end of a normal compaction zone. ### Claim 18 (depends on 1) The method according to claim 1, wherein each trendline in the plurality of trendlines is linear with the porosity-related measurements being plotted along a logarithmic scale. ### Claim 19 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. ### Claim 20 (depends on 19) The apparatus according to claim 19, wherein the downhole tool comprises at least one of a resistivity tool, a density tool, and an acoustic tool. ### Claim 21 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.