Caliper-behind-casing from pulsed neutron apparatus

A method of logging a borehole in a formation, the borehole having casing installed therein to a casing shoe, the borehole having tubing installed in the casing and extending beyond the casing shoe, the method comprising:

• filling the tubing and an annulus between the tubing and the casing with a liquid;
• obtaining a first image response of a portion of the borehole with the annulus filled with the liquid by operating a logging tool in the tubing along the borehole;
• injecting a gas into the annulus between the tubing and the casing to a point below the casing shoe of the casing in the borehole by injecting the gas directly at an open hole portion of the borehole below the casing shoe, thereby allowing the gas to enter a potential void in the borehole behind the casing;
• removing any of the injected gas from the annulus while the gas is allowed to remain in the potential void;
• obtaining a second image response of the portion of the borehole while the annulus is filled with the fluid and the potential void is filled with the gas by operating the logging tool in the tubing along the borehole;
• comparing the second image response to the first image response;
• and
• detecting the potential void in the formation behind the casing based on the comparison.

A method of logging a borehole in a formation, the borehole having casing installed therein to a casing shoe, the borehole having tubing installed in the casing and extending beyond the casing shoe, the method comprising:

• filling the tubing and an annulus between the tubing and the casing with a liquid;
• injecting a gas into the annulus between the tubing and the casing to a first point above the casing shoe of the casing in the borehole;
• obtaining a first image response of a portion of the borehole with the annulus filled with the injected gas above the casing shoe by operating a logging tool in the tubing along the borehole;
• injecting the gas into the annulus between the tubing and the casing to a second point below the casing shoe of the casing in the borehole;
• obtaining a second image response of the portion of the borehole with the annulus filled with the injected gas below the casing shoe by operating the logging tool in the tubing along the borehole;
• comparing the second image response to the first image response;
• detecting a void in the formation behind the casing based on the comparison;
• estimating a volume of the detected void in the formation;
• and
• estimating an amount of resin to fill the estimated volume of the detected void.

A method of logging a borehole in a formation, the borehole having casing installed therein to a casing shoe, the borehole having tubing installed in the casing and extending beyond the casing shoe, the method comprising:

• filling the tubing and an annulus between the tubing and the casing with a liquid;
• obtaining a first image response of a portion of the borehole with the annulus filled with the liquid by operating a logging tool in the tubing along the borehole;
• injecting a gas into the annulus between the tubing and the casing to a point below the casing shoe of the casing in the borehole, thereby allowing the gas to enter a potential void in the borehole behind the casing;
• extracting the injected gas from the annulus by displacing the gas in the annulus with the liquid supplied through the tubing to remove any of the injected gas from the annulus while the gas is allowed to remain in the potential void;
• obtaining a second image response of the portion of the borehole while the annulus is filled with the fluid and the potential void is filled with the gas by operating the logging tool in the tubing along the borehole;
• comparing the second image response to the first image response;
• and
• detecting the potential void in the formation behind the casing based on the comparison.