Directional Drilling
"E&P technologies have literally redefined reserves. Oil and gas at depths recently considered unreachable can now be tapped. Smaller accumulations once thought to be uneconomic can now be produced profitably. Fields under wetlands or cities can be accessed without disruption of the surface" (U.S. Department of Energy)
Directional Drilling - also called Horizontal, Deviated, or Slant Drilling - is the process of drilling an indirect path to a reservoir that cannot be reached directly beneath the drilling site. Although the technique has been around since 1939, early applications were severely limited by low build rates and short lateral extension capabilities. Deviated drilling, also known as slant drilling, is a fairly old method in which it often took up to 2,000 feet for the well to complete the transitional curve from vertical to horizontal. With modern technology, however, experienced drillers can make a 90 degree turn in less than 100 feet!
Increasing Recovery Rates and Extending Production Life
Horizontal wells generally increase productivity to at least 2-3 times that of vertical wells. For wells which would have otherwise been considered marginal or uneconomic, horizontal drilling often enables successful reservoir development. The oil or natural gas in some types of reservoirs can be most thoroughly recovered by horizontal drilling. The following reservoir types are excellent examples of conditions that benefit from this technology:
- Thin reservoirs: In cases where hydrocarbon deposits are wider than they are thick, vertical wellbores are only able to extract oil and gas from a small area surrounding the wellbore. However, horizontal wells use lengthy lateral arms to extend into these long, flat reservoirs and drain a significantly larger area.
- Reservoirs with natural vertical fractures: Fracturing within the formation causes little "pipelines" through which the hydrocarbons can flow. Encountering the fractures at an angle perpendicular to the wellbore improves productivity.
- Locating isolated and bypassed oil and gas reservoirs: Horizontal wells can be used to search for overlooked reserves within a field. In an existing field, vertical wells are often re-entered and drilled horizontally to reach those isolated and bypassed reserves. According to a study by the U.S. Department of Energy, "Since 1990, the vast majority of reserve additions in the United States-89 percent of oil reserve additions and 92 percent of gas reserve additions-have come from finding new reserves in old fields"(Environmental Benefits of Advanced Oil and Gas Exploration and Production Technology, 1999).
- Accessing reserves in environmentally sensitive areas: In some areas, drilling is restricted for environmental reasons or because a rig cannot be set up on the proposed pad site. This often occurs when the targeted formation is under a building, below a shallow lake, or in a protected wildlife habitat. In cases where a vertical well cannot be used, horizontal drilling can access the targeted reservoir while leaving the surface habitat undisturbed.
Reduced Capital and Operating Costs
In addition to draining the same amount as three or four vertical wellbores, a horizontal well costs significantly less than drilling several vertical wells in the same area. The operating costs associated with infrastructure, wellhead equipment and maintenance are also significantly reduced.
