Method and Apparatus for Detecting Gamma Radiation Downhole

摘要

The embodiments described herein generally relate to a method for detecting gamma radiation downhole using a downhole probe assembly. The method includes rotating the downhole probe assembly and measuring gamma radiation passing through a window of a gamma sensor module and hitting a gamma sensor therebelow. A gyroscope output is sampled at predetermined time intervals to indicate the speed of rotation of the downhole probe assembly. The angle of rotation of the window is calculated based on the speed of rotation of the downhole probe assembly. Each revolution of the downhole probe assembly is conceptually divided up into a plurality of bins. Measured gamma radiation is allocated to one of the plurality of bins based on the calculated angle of rotation of the window to provide a real time indication of the direction and strength of gamma radiation emitted by the formation surrounding the borehole. This information can be used for real time geosteering of the drill bit during downhole drilling.

主权项

1. A method for detecting gamma radiation downhole using a downhole probe assembly comprising:
a gamma sensor module comprising a shield housing and a gamma sensor enclosed within the shield housing, the shield housing including a window exposing the gamma sensor therebelow; a gyroscope fixedly mounted in a plane perpendicular to an axis of rotation of the downhole probe assembly; and a controller in electrical communication with the gamma sensor module and the gyroscope;the method comprising:
(a) rotating the downhole probe assembly; (b) measuring gamma radiation passing through the window and hitting the gamma sensor therebelow; (c) sampling gyroscope output at predetermined time intervals and determining speed of rotation of the downhole probe assembly for each sampled gyroscope output; (d) calculating a gyro angle for each sampled gyroscope output by multiplying the determined speed of rotation of the downhole probe assembly by the predetermined time interval; (e) calculating an angle of rotation of the window as an aggregate of the calculated gyro angles; and (f) based on the calculated angle of rotation of the window allocating measured gamma radiation to one of a plurality of conceptual bins dividing each revolution of the downhole probe assembly.