The choice of drilling method depends upon:
— Cost,
—Well spacing and
—Mechanical conditions of a vertical well bore
—In addition, reservoir consideration.
—
BUILD RATES
—Ultra-short Radius
—Short Radius
—Medium Radius
—Long Radius
ULTRA-SHORT RADIUS
—45 to 90 degrees per foot
—Special equipment
—Horizontal lengths of 100’ to 200’
—Used in unconsolidated, heavy oil sands and soft formation.
—Impossible to log the open hole section.
—An ultra-short radius drain hole is drilled using endless 1¼ inch tubing.
—Uses a jet under high pressure to cut the formation and advance the endless tubing.
— twenty-four laterals can be drilled at the same horizon.
SHORT RADIUS
—1.5 to 3 degrees per foot.
—Needs special equipment
—Mechanical and motor systems are available.
—Typically used in sidetracking existing wells to bypass water producing or troublesome.
—Bending stress and fatigue can be a problem
—200’ to 1000’ horizontal section
—The horizontal section can be cased with a slotted liner or left open hole.
—Open hole logging capabilities are limited for the horizontal section.
— The first medium radius wells were drilled in 1985
—6 to 35 degrees per 100’ build rates
—Uses conventional equipment
—Horizontal section lengths have been drilled over 7000’ but typically 2000’ to 4000’
—2 to 6 degrees per 100’ build rates
—Uses conventional equipment
—Horizontal section lengths have been drilled over 10,000’ but typically 3000’ to 5000’
—No problem with bending stress, fatigue or completion equipment
—Build section is steerable, which means the motor can be rotated in the build section
—Offshore uses long radius almost exclusively since longer departures are required before the well gets to be horizontal
—Wells are more easily logged.
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