Environmental Engineering Reference
In-Depth Information
12
Cement Bond Logging
Cement bond logging (CBL) is an important part of a well-completion program and
is also recommended for most workover programs. Most of the cementing-related
problems encountered can be diagnosed by use of the CBL. However, successful
interpretation of a CBL depends on certain minimum requirements:
The tool must be run strictly centralized.
A transit-time curve must be recorded.
A wave train or VDL display must be available.
Before explaining these requirements in detail, however, it is worthwhile to
review the principles of oil-well cementing, since many problems can be traced
back to the primary cement job and the way it was conducted.
Principles of Oil-Well Cementing
Oil-well cementing is the process of mixing a slurry of cement, water, and additives
and pumping it down through steel casing to the annular space between the well bore
and the outside of the casing. Figure
12.1
illustrates the conventional cementing pro-
cess. Sometimes it is advisable to cement a well in two or more stages in which case
a more complex completion string is required, as shown in Fig.
12.2
. This technique
is employed when two or more zones have different cement requirements.
Cement has three principal functions in a well:
To restrict fl uid movement between formations
To bond the casing to the formation
To provide support for the casing
As long as an effective hydraulic seal is provided between porous and permeable
zones in the well, a cement job may be considered as good. Important examples include
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