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.
