Vertical direction adjustment tool for downhole drilling apparatus

Abstract

A direction adjustment tool for a downhole drilling apparatus is disclosed. The tool has a tubular housing adapted to be incorporated into a downhole drilling apparatus, and steering blades mounted to the housing. A drive shaft transmits drive to a drill bit of a drilling apparatus, wherein the shaft defines a passage for transmitting drilling fluid to the drill bit. A first pressure chamber is defined between the housing and the shaft and communicates with the passage, wherein the steering blades are moved from retracted positions to extended positions thereof as a result of increase of fluid pressure the first pressure chamber. A pendulum member is pivotably mounted to extend in a vertical orientation when the shaft is not rotating relative to the housing, and pistons prevent movement of at least one steering blade to the extended position thereof as a result of the angle between a longitudinal axis of the shaft and the longitudinal axis of the pendulum member exceeding a predetermined amount. This causes at least one steering blade to adjust the direction of drilling of the drilling apparatus towards a vertical direction and/or to resist movement of the direction of drilling away from a vertical direction.