Directional drilling refers to the process of drilling along a prescribed well path to a target located at a given depth and some lateral distance from a vertical axis through the drill site. To a large extent, directional drilling is like flying an airplane. A flight plan is established based on prevailing winds and weather conditions between point of departure and destination. Power is essential. The crew navigates and makes course changes when necessary. Directional drilling also requires a plan, which defines the road map or well path from surface location and target.