MILLING TOOL, WHIPSTOCK, MILLING SYSTEM AND METHOD OF FORMING A WINDOW IN THE WALL OF A TUBULAR

摘要

A milling tool (110) is provided with a valve member (122) which can be displaced to inhibit the flow of drilling fluid through the milling tool (110). A whipstock (150) is provided with a stop (155) which the valve member (122) engages as the milling tool (110) moves down the whipstock (150). Further downward movement of the milling tool (110) relative to the whipstock (150) displacing the valve member (122) relative to the milling tool (110) and inhibits the flow of drilling fluid therethrough. This results in a decrease in flow and increase in pressure at the mud pumps signifying that milling should cease. If the milling tool (110) is being driven by a mud motor (156) which exhausts through the milling tool (110) the mud motor (156) will stop when the flow through the milling tool is inhibited.