Extended-Reach Drilling (ERD) has evolved from simple directional drilling to horizontal, lateral, and multi-lateral step-outs. ERD employs both directional and horizontal drilling techniques and has the ability to achieve horizontal well departures and total vertical depth-to-deviation ratios beyond the conventional experience of a particular field. ERD can be defined in terms of reach/TVD (total vertical depth) ratios. The definition of an ERD well depends on the results of existing drilling efforts in a particular oilfield. Local ERD capability depends on the extent of experience within specific fields and with specific rigs and mud systems.
Constraints to successful ERD include downhole drill string and casing movement, applying weight to the drill bit, possible buckling of casing or drill string, and running casing successfully to the bottom of the well. Tension may be a primary concern in vertical wells, but in ERD, torsion may be the limiting factor.

Running normal-weight drill pipe to apply weight to the bit in ERD can lead to buckling of the drill pipe and rapid fatigue failure. Conventional drilling tools are prone to twist-off, because of unanticipated failure under high torsional and tensile loads of an extended-reach well. Torque can be significantly reduced with the use of non-rotating drill pipe protectors. Advanced equipment for an ERD well may include wider diameter drill pipe, additional mud pumps, enhanced solids control, higher capacity top drive, more generated power and oil-based drilling fluids. ERD requires longer hole sections, which requires longer drilling times; the result is increased exposure of destabilizing fluids to the wellbore. The superiority of oil-based muds versus water-based muds in ERD is widely recognized. Water-based muds may not provide the inhibition or confining support of oilbased muds.

Extended-reach drill string design (planning) involves:

a) determining expected loads,
b) selecting drill string components,
c) verifying each component’s condition,
d) setting operating limits for rig team, and
e) monitoring condition during drilling.

Rig and logistics issues include storage space, setback space, accuracy of load indicators, pump pressure/volume capacity, and top drive output torque. Hole issues include hole cleaning, hole stability, hydraulics, casing wear, and directional objectives .

Conventional drill stems are about 30 ft. long and are made up of a bit, stabilizer, motor, a measurementwhile-drilling (MWD) tool, drill collars, more stabilizers, and jars. There are more than 1,600 parts to a drill string in a 24,000-foot well.

In a few cases, ERD technology has been used instead of platform installation off California, where wells are drilled from onshore locations to reach nearby offshore reserves. ERD has been instrumental in developing offshore reserves of the Sherwood reservoir under Poole Bay from shore at Wytch Farm, U.K. Other successes with ERD include the North Sea, Gulf of Mexico, South China Sea, and at Milne Point, Badami, Point McIntyre, and Niakuk fields in Alaska.

While a 6.6-mile horizontal displacement was accomplished in 1999 at Cullen Norte 1 well in Argentina (Halliburton, 1999), horizontal displacements (departure from vertical) of one-half mile to two miles are typical.

It is possible that exploration wells within the license area may be directionally drilled due to a lack of suitable surface locations directly overlying exploration targets. However, until specific sites and development scenarios are advanced and the specific conditions of drill sites are known, the applicability of directional drilling for oil and gas within the license area is unknown. Most development wells will be directionally drilled because of the cost savings realized in pad and construction, and in required facilities.


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