A method for steering a downhole tool in a wellbore includes measuring a tool face when the drill bit is off-bottom, measuring an angular position of a drill string when the drill bit is off-bottom, and measuring a torque on the drill string when the drill bit is off-bottom. The method also includes measuring the tool face when the drill bit is on-bottom and measuring the torque on the drill string when the drill bit is on-bottom. The method also includes determining a transfer function comprising the angular position of the quill, the difference between the tool face when the drill bit is on-bottom and off-bottom, and the difference between the torque when the drill bit is on-bottom and off-bottom. The angular position of the drill string is varied at the surface, based upon the transfer function, to reduce an angle between the tool face when the drill bit is on-bottom and a target tool face.

The present disclosure provides a technique capable of increasing or decreasing the number of control devices in a control system for controlling a control target from a plurality of control devices. A control system of the present disclosure is a control system (300) including a plurality of control devices (301, 302), at least one control target (307) that is controlled by the plurality of control devices, and a computer (303) that is connected to the plurality of control devices and the control target via a control network, in which the computer is configured to execute processing of receiving an application to participate in the control system from an additional control device (311), processing of acquiring information related to states of the plurality of control devices and transmitting the information to the additional control device, and processing of managing transmission and reception in the control network.