Downhole cement evalution using pulsed neutron measurements
AssigneeBaker Hughes Incorporated
InventorDavid M. Chace
Life of this patent
Estimating the term…
Abstract
Estimating cement voids in between a casing and a borehole wall of a borehole penetrating the earth formation includes forming with a computing device an actual ratio of radiation induced by a neutron source and measured by a first detector and a second detector when the tool is at two or more different locations in the borehole. A relationship between the actual ratio and the porosity at each of the two or more different locations is used and compared to two different cases of estimates of the ratio. Based on the comparison, an estimate of the cement voids at the two or more locations.
Claims13
A method for estimating cement voids in between a casing and a borehole wall of a borehole, the method comprising:
- conveying a tool through a borehole penetrating the earth formation;
- irradiating an earth formation external to the borehole wall with neutrons from a neutron source disposed at the tool;
- forming measurements of radiation emitted from the earth formation resulting from the irradiating using a first detector and a second detector in the tool, when the tool is in two or more different locations in the borehole;
- forming an actual ratio of radiation measured the by first detector and the second detector at two or more of the different locations;
- determining a porosity of the earth formation at the two or more locations;
- forming a relationship between the actual ratio and the porosity at each of the two or more different locations in the borehole;
- forming an estimate, via numerical techniques, of the ratio versus porosity, the estimate including at least a first case and second case;
- comparing the relationship at the two more locations to both the first and second cases at corresponding locations;
- and
- determining an estimate of the cement voids at the two or more locations based on the comparing.
A method of estimating cement voids in between a casing and a borehole wall of a borehole penetrating the earth formation, the method comprising:
- forming with a computing device an actual ratio of radiation measured by a first detector and a second detector when the tool is two or more different locations in the borehole, the first and second detector being contained in a tool conveying a tool through the borehole penetrating the earth formation;
- determining a porosity of the earth formation at the two or more locations;
- forming a relationship between the actual ratio and the porosity at each of the two or more different locations;
- forming an estimate, via numerical techniques, of the ratio versus porosity, the estimate including at least a first case and second case;
- comparing with the computing device the relationship at the two more locations to both the first and second cases at corresponding locations;
- and
- determining an estimate of the cement voids at the two or more locations based on the comparing.
An apparatus for estimating cement voids in between a casing and a borehole wall of a borehole penetrating the earth formation, the apparatus comprising:
- a tool adapted for conveyance though the borehole, the tool including a neutron source for irradiating an earth formation external to the borehole wall with and a first and second detector for forming measurements of radiation emitted from the earth formation resulting from the irradiating at different locations in the borehole;
- and
- one or more processors for:
- forming an actual ratio of radiation measured the by first detector and the second detector when the tool is in two or more of the different locations;
- determining a porosity of the earth formation at the two or more locations;
- forming a relationship between the actual ratio and the porosity at each of the two or more different locations;
- forming an estimate, via numerical techniques, of the ratio versus porosity, the estimate including at least a first case and second case;
- comparing the relationship at the two more locations to both the first and second cases at corresponding locations;
- and
- determining an estimate of the cement voids at the two or more locations based on the comparing.
Dependencies are inferred from the claim text.