TABLE OF CONTENTS In the last few years, many horizontal wells have been drilled around the world. [1] [27] The major purpose of a horizontal well is to enhance reservoir contact and thereby enhance well productivity. As an injection well, a long horizontal well provides a large contact area, and therefore enhances well injectivity, which is highly desirable for enhanced oil recovery (EOR) applications.
In general, a horizontal well is drilled parallel to the reservoir bedding plane. Strictly speaking, a vertical well is a well which intersects the reservoir bedding plane at 90 . In other words, a vertical well is drilled perpendicular to the bedding plane (see Fig. 1-1). If the reservoir bedding plane is vertical, then a conventional vertical well will be drilled parallel to the bedding plane and in the theoretical sense it would be a horizontal well. As shown in Figure 1-2, even in the reservoirs with vertical bedding plane, it is still possible to drill down vertically and then drill sideways. The objective here is to intersect multiple pay zones. (In some instances, from the drilling standpoint, it may be easier to stay in one zone to have effective control on well trajectory.) In the mid-continental region and in the Gulf Coast region of the United States, some reservoir bedding planes are almost vertical. Similarly, in California some reservoirs are steeply deepening. Thus, while analyzing horizontal well performance, geometric configuration of the reservoir bedding planes should be considered.
