Caliper-Behind-Casing from Pulsed Neutron Apparatus
AssigneeWeatherford Technology Holdings, LLC
InventorsPaul Pavlakos, Gregory J. Schmid
Life of this patent
Estimating the term…
Abstract
A caliper-behind casing apparatus and method determines a location and size of a washout (i.e., a void) behind casing in a borehole for a salt cavern used for storing hydrocarbons. The cavern and tubing in the casing are filled with brine. Gaseous nitrogen is used to fill an annulus between the tubing and the casing above and below a casing shoe to obtain image responses from operating a pulsed neutron logging tool in the tubing along the borehole. Analysis of burst ratios of near and far detectors on the pulsed neutron logging tool from these passes is used to detect and estimate a void or washout in the formation behind the casing.
Claims20
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;
- and
- detecting a void in the formation behind the casing based on the comparison.
A method of testing integrity of a salt cavern in a salt formation, the salt cavern having a borehole lined with casing to a casing shoe, the borehole having tubing installed in the casing and extending beyond the casing shoe into the salt cavern, the method comprising:
- filling the tubing and an annulus between the tubing and the casing with brine;
- 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 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;
- monitoring pressure of the injected gas for a predetermined time interval and calculating a leak rate of the injected gas as a function of the monitored pressure relative to the predetermined time interval;
- predicting a washout in the formation behind the casing based on the calculated leak rate;
- obtaining a second image response of the portion of the borehole with the annulus filled with the injected gas below the shoe by operating the logging tool in the tubing along the borehole;
- and
- estimating a volume of the washout in the formation behind the casing by comparing the second image response to the first image response.
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;
- 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 system 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 extending beyond the casing shoe, the system comprising:
- injection equipment in fluid communication with an annulus between the casing and the tubing, the injection equipment operable to inject gas in a first stage into the annulus between the tubing and the casing to a first point above the casing shoe of the casing in the borehole and operable to inject gas in a second stage into the annulus between the tubing and the casing to a second point below the casing shoe of the casing in the borehole;
- a logging tool configured to deploy in the tubing, the logging tool operable to obtain a first image response of a portion of the borehole in the first stage and operable to obtain a second image response of the portion of the borehole in the second stage;
- and
- processing equipment in operable communication with the logging tool, the processing equipment configured to:
- compare the second image response to the first image response;
- and
- detect a void in the formation behind the casing based on the comparison.
Dependencies are inferred from the claim text.