The aims of ERD are: a) to reach a larger area from one surface drilling location, and b) to keep a well in a reservoir for a longer distance in order to maximize its productivity and drainage capability.
Today's challenges in ERD are hole cleaning, managing the mechanical loads on the drill string and downhole pressure, and cost.
ERD wells then can be described conveniently as shallow, intermediate, deep, and ultradeep.
What exactly determines a well to be "extended reach" varies over time and location with the development of technologies and of experiences.
[2] New technologies have emerged that claim to be pushing the existing boundaries of ERD.