Method and apparatus utilizing NMR measurements to gather information on a property of the earth formation surrounding a wellbore

A method of gathering information on the pore pressure in an earth formation surrounding a wellbore, the wellbore and the surrounding earth formation defining a drilling environment, said method comprising the steps of:

• (a) selecting at least one suitable property of the drilling environment, whereby variations in the suitable property over a wellbore depth interval can be correlated with variations in the pore pressure in the earth formation;
• (b) predicting a profile of the suitable property over a wellbore depth interval;
• (c) selecting at least one NMR parameter, such that values of the NMR parameter over the depth interval can be correlated with values of the suitable property over the depth interval;
• (d) providing an NMR measurement apparatus;
• (e) commencing a drilling operation so as to initiate forming of the wellbore;
• (f) during drilling, lowering the NMR measurement apparatus to a depth in the wellbore and operating the NMR measurement apparatus to generate an NMR response from the drilling environment;
• (g) accounting for the NMR parameter in the NMR response;
• (h) repeating steps (f) and (g) at a plurality of wellbore depths to provide values of the NMR parameter and establishing therefrom, an actual profile of the suitable property;
• and
• (i) correlating deviations of the actual profile from the predicted profile with variations in the pore pressure in the earth formation.

A method of drilling a wellbore in an earth formation, the wellbore and the surrounding earth formation defining a drilling environment, the method comprising the steps of:

• (a) commencing drilling of the wellbore in the earth formation, using drilling fluid having a fluid composition;
• and
• (b) while drilling, monitoring the pore pressure in the earth formation surrounding the wellbore, including
• selecting at least one suitable property of the drilling environment, such that variations in the suitable property over wellbore depths can be correlated with variations in pore pressure in the earth formation;
• obtaining NMR measurements at a plurality of wellbore depths, thereby obtaining an NMR response from the surrounding wellbore over the plurality of wellbore depths;
• from the NMR response, determining the behavior of the suitable property over the wellbore depths;
• and
• correlating the behavior of the suitable property over the wellbore depths with the behavior of the pore pressure in the earth formation.

A method of drilling a wellbore in an earth formation, the wellbore and the surrounding earth formation defining a drilling environment, the method comprising the steps of:

• (a) selecting at least one suitable property of the drilling environment, the suitable property being a property of drilling fluid provided in a near-wellbore region of the drilling environment during drilling, whereby variations in the suitable property over a wellbore depth interval can be correlated with variations in the pore pressure in the earth formation;
• (b) selecting at least one NMR parameter, whereby variations in the NMR parameter over the depth interval can be correlated with variations in the suitable property;
• (c) commencing a drilling operation so as to initiate forming of the wellbore;
• (d) during drilling, conducting NMR measurements at a plurality of wellbore depths to generate an NMR response from the near-wellbore region;
• (e) correlating values of the NMR parameter in the NMR response with values of the suitable property;
• and
• (f) determining the behavior of the pore pressure in the earth formation by comparing values of the suitable property over the depth interval.

A system for gathering information on the pore pressure in an earth formation surrounding a wellbore, the wellbore and the surrounding earth formation defining a drilling environment, the system comprising:

• an NMR measurement apparatus for conducting an NMR measurement at a plurality of wellbore depths and for receiving an NMR response from the drilling environment;
• a microprocessor disposed in communication with the NMR measurement apparatus so as to receive NMR response data therefrom, the microprocessor including an executable program configured for:
• selecting a suitable property of the drilling environment, such that values of the suitable property over a plurality of wellbore depths can be correlated with the characteristics of the pore pressure in the earth formation;
• accounting for at least one NMR parameter in the NMR response;
• and
• correlating values of the NMR parameter over a plurality of depths with the behavior of the suitable property over the plurality of depths, thereby correlating values of the NMR parameter with the behavior of the pore pressure over the plurality of depths;
• and
• a tangible medium for displaying the behavior of the suitable property over the plurality of wellbore depths.