Downhole gravity tool

摘要

A tool for conducting gravimetry survey downhole in an earth formation includes a pressure vessel which houses a gravity sensor (65) that is supported by a gimbal (64). The gravity sensor (65) is aligned with vertical before taking gravity measurements by a first stepper motor and a second stepper motor. The first stepper motor incrementally rotates the gimbal about the pivot axis (68) of the gimbal (64) while the second stepper motor incrementally rotates the gimbal (64) about the longitudinal axis (26) of the pressure vessel (18). The stepper motors are controlled by an electronic processor that responds to signals from an accelerometer assembly (110) that measures the inclination of the pressure vessel (18) with respect to vertical. An elevator mechanism translates the gravity sensor from one station to the next inside the pressure vessel to make gravity measurements and an optical encoder monitors the position of the gravity sensor inside the pressure vessel. <IMAGE>