It involves drilling a well through a formation at an angle of 90° from the vertical. Long laterals of the well increase the contact between the reservoir and the well, thus improving the productivity of the reservoir. It is usually applied to thin formations with good vertical permeability or formations with a high ratio of vertical to horizontal permeability. The horizontal well path starts with a VS, then a construction section starting at 0° from the vertical and gradually building up to 90°, then a horizontal or lateral section penetrating the formation of interest (Figure 3.8). Sometimes, a horizontal well can have a straight section between the two construction sections (Figure 3.9). The BUR of a horizontal well can vary depending on the objectives of the well. Hence, horizontal wells have been classified on the basis of construction radius into short radius, medium radius, long radius, and ultra-long radius. These classifications are summarized in Table 3.1.