Civil Engineering Reference
In-Depth Information
American Petroleum Institute (API), and are used as
de facto
standards all over the world.
However, formal ISO international standards for oil well cementing are currently under
development (Bensted, 1995). API Specification 10A,
Specifications for Well Cements,
divides oil well cements into several classes. Of these, classes G and H are the basic oil
well cements, used most widely. Classes D, E, and F include retarded oil well cements,
and Class C is a rapid-hardening cement. Class J includes special cements developed for
high-temperature well cementing.
27.1
CLASS G AND CLASS H OIL WELL CEMENTS
Class G and Class H oil well cements are the most important ones in the API
classification system, and are the most extensively used for cementing oil and gas wells.
They can be tailored to cope with a wide range of well-cementing conditions by the
addition of suitable additives to their slurries.
The chemical, physical and performance requirements for Class G and Class H oil well
cements are summarized in Table 27.1. The requirements are identical for both classes,
with one exception: the water/cement ratio to be used in the tests performed in
determining the performance characteristics of these cements. The reasons for this
distinction are historical (Bensted, 1992b), and will not be discussed in detail here.
In general, Class H cements are more coarsely ground than Class G cements; the
specific surface area of Class H cements is typically in the range 220-300 m
2
/kg,
whereas that of Class G is in the range 270-350 m
2
/kg. Class H cement was designated
for lower water/cement ratios, and will hydrate more slowly than its Class G counterpart.
Both Class G and Class H cements are available in moderately sulfate resistant (MSR)
and high sulfate resistant (HSR) grades, which differ mainly in their C
3
A content.
Table 27.1
API specifications for class G and class H oil well cements.
Chemical requirements
Cement type:
MSR
HSR
MgO (max.)
6.0
6.0
SO
3
(max.)
3.0
3.0
Loss on ignition (max.)
3.0
3.0
Insoluble residue (max.)
0.75
0.75
C
3
S
48-58
48-65
C
3
A (max.)
8
3
C
4
AF+
2x
C
3
A (max.)
-
24
Na
2
O equivalent (max.)
0.75
0.75
