Page 32 - Petroleum and Gas Field Processing

grade must be selected such that the casing string will not fail under all
loads to which it will be subjected during drilling, setting casing, and
production.
To set a casing string, the drilling operation is stopped when the
desired depth is reached and the drill string and the pit are pulled out of
the hole. The casing string is then lowered into the hole, joint by joint,
using the hoisting system of the rig, until the total length of casing is in
the hole. A round, smooth object called the guide shoe is attached to the
bottom of the first joint of casing to ease and guide the movement of
the casing into the hole. The casing is then cemented to the wall and
drilling operation is resumed until the target depth for the next casing
string is reached. Normally, before setting the production casing, the
petroleum formation is logged and evaluated. The casing will be set only if
the logging results indicate the presence of a productive formation.
Otherwise, the well will be abandoned.

1.6.3 Cementing the Casing
To cement the casing, the annulus between the casing and the wall of the
hole must be filled with cement. To achieve this, the required volume of
the cement slurry (prepared on location) is pumped through the casing.
A special rubber plug is normally inserted ahead of the cement to separate
it from the mud and prevent any contamination of the cement with mud.
Another plug is inserted after pumping the specified volume of cement.
This is followed by pumping a fluid (normally mud) to displace the
cement. When the first plug reaches the bottom, pumping pressure is
increased to rupture the plug and allow the flow of cement behind the
casing. When the top plug reach the bottom, the cement must have filled
the annulus to the surface. The cement is then left undisturbed until it sets
and acquires enough compressive strength before resuming the drilling
operation for the next casing string.
Once the casing is cemented, it becomes permanently fixed into the hole.
It is very important to have a good cement bond between the casing and the
wall of the hole. For this purpose, a special log (cement bond log) is conducted
to check the integrity of the cementing operation. Failure to have a good
cementing job will necessitate expensive remedial cementing operations.

1.7 RESERVOIR ENGINEERING ROLE AND FUNCTIONS

Reservoir engineers play a major role in field development and operation.
Some of the major functions of reservoir engineering are discussed next.

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