Cement evaluation with neutron-neutron measurement
AssigneeHalliburton Energy Services, Inc.
InventorsWeijun Guo, Daniel F. Dorffer
Life of this patent
Estimating the term…
Abstract
Various embodiments include apparatus and methods to conduct neutron-neutron measurements and to evaluate quality of cement between a casing and a formation. A tool can include a neutron source, a far detector, and a near detector, where the far detector and the near detector detect neutrons in response to activation of the neutron source. Measured counts of the detected neutrons can be compared with respect to expected counts of neutrons. From one or more comparisons, the quality of the cement can be evaluated. Additional apparatus, systems, and methods are disclosed.
Claims16
A method comprising:
- mixing neutron absorbing dopant material with cement flurry for an annular cement structure in a borehole;
- performing a neutron-neutron measurement in the borehole, the borehole surrounded by a casing, the annular cement structure, and a formation;
- generating a measured pattern from the neutron-neutron measurement, the measured pattern including measured near and far counts of neutrons and measured near count to far count ratio of neutrons;
- comparing the measured pattern to a corresponding expected pattern, the corresponding expected pattern including expected near and far counts of neutrons representing cement without voids and an expected near count to far count ratio of neutrons representing cement without voids;
- and
- evaluating quality of the cement from the comparison.
A system comprising:
- a neutron source positioned in a region in a borehole, the region of the borehole surrounded by a casing, a cement formed from a cement flurry mixed with a neutron absorbing material, and a formation;
- a first neutron detector spaced apart from the neutron source and configured to provide a near count of detected neutrons;
- a second neutron detector spaced apart from the neutron source, the second neutron detector configured to provide a far count of detected neutrons relative to the first neutron detector;
- and
- a processing unit configured to evaluate quality of the cement by comparing a measured pattern to an expected pattern, the measured pattern including a measured near count from the first neutron detector, a measured far count from the second neutron detector, and a measured near count to far count ratio, the expected pattern including expected near and far counts representing cement without voids and an expected near count to far count ratio representing cement without voids.
A method comprising:
- performing a neutron-neutron measurement in a borehole, the borehole surrounded by a casing, cement, and a formation, wherein the cement includes a mixture of cement flurry and a dopant having a high neutron capture cross-section;
- generating a measured pattern from the neutron-neutron measurement, the measured pattern including a measured near count of neutrons, a measured far count of neutrons, and a near count to far count ratio;
- comparing the measured pattern to a corresponding expected pattern of an expected near count of neutrons representing cement without voids, an expected far count of neutrons representing cement without voids, and an expected near count to far count ratio representing cement without voids;
- and
- evaluating quality of the cement from the comparison, wherein evaluating comprises detecting a defect in the cement based on the measured near and far counts being less than the expected near and far counts, and the measured near count to far count ratio being greater than the expected near count to far count ratio.
Dependencies are inferred from the claim text.