By Walter K. Merschat Exploration Geologist, Unocal, 1969-76; Geoscientist, Gulf Research, 1976-84; Consultant, Scientific Geochemical Services, 1985-present
WHAT IS DIRECTIONAL DRILLING? Directional drilling is an advanced technology that allows oil and gas resources to be tapped a long horizontal distance away from the well site. For the purposes of this report, “directional drilling” will encompass all forms of drilling where the endpoint of the well is distant from the drill site, rather than directly beneath it. Under this definition, slant-hole wells, S-turn wells, and horizontal wells are all considered forms of directional drilling. The term “directional drilling” can also be used to describe drilling to lay subsurface pipelines beneath rivers and other sensitive areas; this application of A brief synopsis of directional well types follows, of the various directional well types. Slant-Hole Wells Slant-hole wells are drilled at an angle from the vertical, using a tilting drilling rig. Slant-hole wells can be completed without making any bends at all, resulting in the equivalent of a conventional vertical well that is tilted on its axis. Alternately, slant-hole wells can be combined with a horizontal bend that is drilled in much the same way as traditional horizontal wells
Sometimes known as “deviated wells,” Sturn wells start out in a near-vertical orientation, have a long near-horizontal or diagonal section, and finish by approaching the vertical once again. This well type has been used in extendedreach applications. For example, the Sacate Sa-1, an offshore California well, achieved a horizontal distance of over 3½ miles from the well site using this drilling technique (Elks and Masonheimer 2002). Horizontal Wells Horizontal wells are defined as wells deviated more than 75 degrees from vertical (Lacy et al. 1992); they often depart from the horizontal in order to track the dip of the target formation. These wells have a characteristic “J” shape, with the horizontal section following the oil- or gas-bearing rock to maximize production. Short-Radius Short-radius wells feature a sharp, abrupt turn from the vertical to the horizontal plane. A comprehensive review of short-radius horizontal drilling found that “[r]eservoir management applications, water and gas coning, injection wells, irregular formations and coal degasification [coalbed methane production] are becoming more economically feasible” (Leazer and Marquez 1995). This study found that short radius horizontal wells make it easier to avoid problem formations above the pay zone. And with short-radius wells, submersible pumps can be placed deeper in the wellbore, improving pumping efficiency and extending pump life. The study concluded that “[s]hort radius technology has evolved to the point where it is a common occurrence to drill a 45-ft radius curve into a 10-ft target and achieve displacements in excess of 1,000 ft.” These wells are not typically used to drill long horizontal distances from the well site. Medium Radius Medium-radius wells make their turn from the vertical to the horizontal at an intermediate rate, and the horizontal length is often longer. By the early 1990s in the United States, mediumradius wells were the most widely used and productive of horizontal wells (USDOE 1993). In 1990, the longest horizontal displacement for a medium-radius horizontal well reached 4,164 feet (Moritis 1990). This drilling style figures Figure 1. Different types of directional wells. Slant-Hole Slant- Hole S-Turn Short-Radius Medium-Radius Long- Radius Stacked Laterals Opposing Laterals Sidetracking from Vertical Well Horizontal Wells Single Wells Multilateral Wells Horizontal from
So yes it all stacks up to a Horizontal flow DYOR Go NWE you good thing Cheers Janus
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