Crisman Annual Report 2009 - Harold Vance Department of ...

Cement Fatigue Failure and HPHT Well Integrity
Objectives
There have been a lot of experimental investigations
on the mechanism of fatigue failure of structures
like buildings and bridges but the fatigue behavior of
well cement is still relatively unknown to engineers.
This research tries to give a better understanding
of cement fatigue and failure, especially for high
pressure, high temperature (HPHT) wells. Through
the development of equations specific to well
cement from experimental data, we will test new
failure mechanism, crack initiation, and propagation
and failure theories, and then predict the fatigue life
of cement as related to HPHT wells.
Approach
Based on the experimental method carried out by
other fields, such as civil engineering, we will design
a specific experiment related to HPHT cementing.
The experiment involves the following steps:
specimen fabrication, test specimen preparation,
static compression tests, fatigue tests, and data
analysis. Water-cement ratio, temperature, and
pressure are the three variables to be considered.
According to obtained data, we will then develop the
failure theory and predict the fatigue life of cement.
Accomplishments
Based on the background research, the research
methods can be divided into two categories: lab
test and finite element methods. For the field of lab
testing, our representatives are K.J. Goodwin and
D. Stiles. In 1992, Goodwin built a test model for
determining conditions for cement sheath failure.
The study clearly shows that sealants that are
stiffer or possess a high Young’s modulus are more
susceptible to damage when subjected to changes
in pressure and temperature. In 2006, Stiles built
another model for testing the long term HPHT
condition on the properties of cements. For finite
element method analysis, FEM models are easy to
carry out. The right input data and choosing the
right FEM model are the most important parts of
FEM analysis. Martin Bosma and Kris Ravi did the
research on this. Their work showed that, in order
to help reduce the risk of cement failure, the cement
under downhole conditions should be compensated
for hydration volume reduction and rendered less
stiff and more resilient than conventional oilwell
cements.
The best way to study the HPHT well cement failure
was to combine the lab test and FEM methods, using
the lab data to improve and verify the FEM model
results.
Significance
Using the theory of probability, the high pressure
cement failure study showed that:
» Both cement systems show the same failure
characteristic. Without cycle load, both systems
fail in tensile strength. At this time the shear
failure and compressive failure probability is zero.
» If the tensile failure probability is high, the system
failure probability is much higher than the fatigue
failure probability.
» Compressive strength should not be the most
important parameter when designing the
cement system. Latex modified cement shows
better behavior than conventional cement,
though conventional cement has a much higher
compressive strength.
Project Information
2.3.5 Reducing the Risk of Cement Failure in High Pressure,
High Temperature (HPHT) Conditions, Rock Mechanics
Aspects through Analytical and Finite Element Method
Approaches
Contacts
Jerome Schubert
979.862.1195
jerome.schubert@pe.tamu.edu
Catalin Teodoriu
catalin.teodoriu@pe.tamu.edu
Zhaoguang Yuan
CRISMAN INSTITUTE
Crisman Annual Report 2009
49