Page 29 - Petroleum and Gas Field Processing

The drilling program consists of three main stages: (1) drilling the
hole to the target depth, (2) setting the various casings, and (3) cementing
the casing.

1.6.1 Drilling the Well

Well drilling has gone through major developments of drilling methods to
reach the modern method of rotary drilling. In this method, a drilling bit is
attached to the bottom end of a string of pipe joints known as the drilling
string. The drilling string is rotated at the surface, causing rotation of the
drilling bit. The rotation of the bit and the weight applied on it through
the drilling string causes the crushing and cutting of the rock into small
pieces (cuttings). To remove the cuttings from the hole, a special fluid,
called the drilling fluid or the drilling mud, is pumped down through the
drilling string, where it exists through nozzles in the bit as jets of fluid.
This fluid cleans the bit from the cuttings and carries the cuttings to the
surface through the annular space between the drilling string and the wall
of the hole. At the surface, the mud is screened to remove the cuttings and
is circulated back into the drilling string. The drilling operation is
performed using huge and complex equipment known as the drilling rig.
This is briefly described next.

The Drilling Rig
Figure 6 shows a schematic of a rotary drilling rig. It consists of two main
sections, the substructure (bottom section) and the derrick (top section).
The substructure, which ranges from 15 to 30 ft in height, is basically a
rigid platform that supports the derrick. The rig is composed of several
systems and components; the major systems are as follows:
1. Power System: It consists of diesel-engine-driven electric
generators to supply electric power to the various systems and
components of the rig. About 85% of the power generated is
consumed by the drilling-mud circulating system.
2. Hoisting System: The function of this system is to lower and
raise the drilling string into and out of the well. The main
components of the system are the crown block, the drawworks,
the traveling block, the hook, the swivel, the elevator, the drilling
line, and the dead-line anchor.
3. Rotating System: The system consists mainly of a motor-driven
rotating table that is used to rotate a pipe with a square or
hexagonal cross section, called the kelly, while allowing it to slide

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.