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This chapter is from the book

Application of Directionally Drilled Wells

There are a number of reasons to drill a directional well. Some of the more common applications are shown in Figure 3-11. For many years, the most common application was the drilling of offshore wells from a single platform location (Fig. 3-11a). The use of a single platform or subsea manifold from which multiple wells are drilled improves economics and simplifies production facilities. Onshore, many unconventional plays are now being drilled from well pads that include multiple wells. This approach minimizes lost time due to rig moves and can also minimize the amount of surface disturbance and the cost of pipeline connections. Some modern rigs can actually “walk” short distances from surface location to surface location without being broken down for transport (e.g., Wethe 2015).


Figure 3-11 Applications of directional drilling. (a) Multiple wells offshore or from artificial islands. (b) Shoreline drilling. (c) Fault control. (d) Inaccessible surface location. (e) Stratigraphic trap. (f) Relief well control. (g) Straightening hole and side tracking. (h, i, j) Saltdome drilling. (From LeRoy et al. 1977. Published by permission of the Colorado School of Mines.)

Onshore, wells are commonly deviated because of inaccessibility to the surface location directly over the subsurface target. Buildings, towns, cities, rivers, shorelines, and mountains are the kinds of surface obstructions that require the drilling of a deviated well. Some offshore wells are also located away from seafloor topographic complications such as escarpments or unstable conditions, requiring the drilling of deviated wells. Horizontal wells are a special type of directional well. They have many applications, most of which are designed to increase productivity rate and improve project economics. These wells are discussed in more detail in the next section.

One very important safety application of a deviated well is the drilling of a relief well to kill a well that has blown out (Fig. 3-11f). Relief wells may be required to kill a well that has blown out during drilling/completion, such as BP’s Deepwater Horizon Macondo well, or a completed well such as California’s Aliso Canyon disaster in which an old well in a natural gas storage field flowed gas for 118 days before being killed by a relief well. There are other applications of deviated wells, but they are beyond the scope of this textbook and are not discussed.

Over the last two decades, highly deviated wells and horizontal wells have become increasingly common. Horizontal wells are drilled to access both conventional and unconventional reservoirs and are the most common type of well drilled in the United States and probably the world today.

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