Percussion method and apparatus for the investigation of a casing cement in a borehole
AssigneeSchlumberger Technology Corporation
InventorDennis Rader
Life of this patent
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Abstract
A percussion technique is described with which an impulse is applied to an element to bounce it off the inner surface of a casing cemented in a borehole. The movement of the element is automatically measured to produce information from which the bond between the casing and cement behind the point of impact of the element can be evaluated. In accordance with one embodiment, the cement bond evaluation is automatically derived by comparing impact and rebound velocities of the element such as by generating a coefficient of restitution of the bouncing element. In another embodiment, the contact time of the element with the casing is measured to derive an indication of the quality of the cement bond.
Claims19
A method for evaluating the cement bond behind a casing cemented in a borehole, comprising the steps of
- applying an impulse to an element disposed to impact on a segment of an inner surface of the casing to bounce the element off said surface, said impulse terminating prior to contact of the element with the inner casing surface so that said element is moving freely prior to contact with the casing;
- and
- measuring the motion of the element for a time period including the element's motion prior to and after the bouncing of said element off said inner wall to enable measurement of the rebound of said element by said casing.
An apparatus for evaluating the cement bond behind a casing cemented in a borehole, comprising
- an element positioned to bounce off an inner surface of the casing;
- means for applying to said element an impulse advancing said element to one segment of said inner casing surface with said impulse being of a duration less than the time needed for the element to contact said inner casing surface;
- and
- means for producing a motion signal representative of the motion of the element prior to and after rebounding off said inner casing surface.
Dependencies are inferred from the claim text.