*TM 5-813-1/AFM-88-10, Vol. 1
APPENDIX C
DRILLED WELLS
drill pipe, through openings in the bit, and up to the
C-1. Methods
surface in the space between the drill pipe and the wall
Drilled wells are normally constructed by one of the
of the hole, washing the drill cuttings out of the hole at
following methods:
the same time. The borehole is kept full of a relatively
-Hydraulic Rotary
heavy mud fluid. Due to its viscosity, this fluid exerts a
-Cable Tool Percussion
greater pressure against the walls of the hold than the
-Reverse Circulation Rotary
water flowing in from the water-bearing bed. Therefore,
-Hydraulic-Percussion
the mud tends to penetrate and seal the pore spaces in
-Air Rotary
the walls, and prevents caving. Water under low hydro-
These methods are suitable for drilling in a variety of
static pressure (pressure exerted by the weight of the
formations. Diameters may be as large as 60 inches for
water in the water zone) cannot force its way into the
wells constructed by the reverse circulation method.
hole.
Smaller diameter wells may be constructed by drilling to
b.
In the cable tool percussion method of
depths of 3000 or 4000 feet. For a detailed discussion of
drilling, the hole is formed by the pounding and cutting
these methods, see Ground Water and Wells by
action of a drilling bit that is alternately raised and
Johnson Division, UOP Inc. The first two methods listed
dropped. This operation is known as spudding. The drill
are the most common in well construction and a brief
bit is a club-like, chisel-type tool, suspended from a
description of each follows:
cable. As the bit is raised and lowered, the cable
a.
In the hydraulic-rotary method of drilling, the
unwinds and rewinds, which gives the bit a grinding
hole is formed by rotating suitable tools that cut, chip,
motion as well as a chisel-type action. It breaks hard
and abrade the rock formations into small particles. The
formations into small fragments and loosens soft
equipment consists of a derrick, a hoist to handle the
formations. The reciprocating motion of the drilling tools
tools and lower the casing into the hole, a rotary table to
mixes the loosened material into a slurry that is removed
rotate the drill pipe and bit, pumps to handle mud-laden
from the hole at intervals by a bailer or sand pump.
fluid, and a suitable source of power. As the drill pipe
and bit are rotated, drilling mud is pumped through the
C-1
Previous Page
