VERTICAL DIRECTION ADJUSTMENT TOOL FOR DOWNHOLE DRILLING APPARATUS

摘要

A direction adjustment tool (2) for a downhole drilling apparatus is disclosed. The tool has a tubular housing (8) adapted to be incorporated into a downhole drilling apparatus, and steering blades (10) mounted to the housing. A drive shaft (16) 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 (32) 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 (54) is pivotably mounted to extend in a vertical orientation when the shaft is not rotating relative to the housing, and pistons (60) 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.