SPE 90829
Transition Time of Cement Slurries, Definitions and Misconceptions, Related to
Annular Fluid Migration
Murray J. Rogers, SPE, Robert L. Dillenbeck, SPE and Ramy N. Eid, SPE, BJ Services Company
Copyright 2004, Society of Petroleum Engineers Inc.
This paper was prepared for presentation at the SPE Annual Technical Conference and
Exhibition held in Houston, Texas, U.S.A., 26–29 September 2004.
This paper was selected for presentation by an SPE Program Committee following review of
information contained in a proposal submitted by the author(s). Contents of the paper, as
presented, have not been reviewed by the Society of Petroleum Engineers and are subject to
correction by the author(s). The material, as presented, does not necessarily reflect any
position of the Society of Petroleum Engineers, its officers, or members. Papers presented at
SPE meetings are subject to publication review by Editorial Committees of the Society of
Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper
for commercial purposes without the written consent of the Society of Petroleum Engineers is
prohibited. Permission to reproduce in print is restricted to a proposal of not more than 300
words; illustrations may not be copied. The proposal must contain conspicuous
acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O.
Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.
Abstract
Transition time of cement slurries is a term that has been used
throughout the oil industry for many years. During this time,
the term has been defined, redefined and misused to cover a
wide range of cementing topics. This has led to numerous
misconceptions and confusion as to what transition time really
means. For many years, this term has been directly tied to the
term right-angle-set, which relates to the speed in which
slurries undergoing continuous shear go from a pumpable to a
non-pumpable state. Once pumping is stopped, the profile of
how cement transition from a liquid, to a gel, to a set cement
changes. These changes can directly affect the performance of
cement slurries to control fluid migration.
With the advent of the Ultrasonic Cement Analyzer (UCA),
the term ”transition time” of cement slurries was redefined.
UCA’s have developed into an essential piece of equipment.
Not only can they achieve compressive strength information,
but the apparatus can also provide a continuous measurement
of how cement sets in static state. This information has
shortened wait on cement (WOC) time, and provides an
excellent profile on how fast cement develops strength.
However, the transducers in a standard UCA only provide
information after the cement develops a compressive strength
set. With improvement in computerization and transducers, a
more sensitive evaluation of gel strength development can be
studied.
Another definition for transition time is the use of a static gel
strength (SGS) analyzer to measure the time from which
cement goes from 100 lbf/100 sq. ft (48 Pa) to 500 lbf/100
sq.ft (240 Pa). It has become an industry standard that once
cement slurries reach an SGS of 500 lbf/100 sq. ft (240 Pa).,
gas or other fluids cannot be transmitted through the cement.
The faster that you achieve this optimum SGS, the less likely
that the cement will transmit gas.
This paper will establish a definition for cement transition
time and discuss the misconception of only using gel strength
development to control gas migration. Test data that exhibits
gas tight slurries with long transition and those with short
transition that allowed gas influx will be shown. Also
discussed in the paper will be the advantages of cements with
a short transition in controlling high-pressure water flows.
Introduction
The control of annular gas migration after cementing has been
the subject of many studies and papers 1-6. These include
practical approaches, theoretical approaches, mathematical
modeling and physical modeling, each concentrating on one or
two specific causes of gas migration. The one thing that all
these studies have in common is the fact that they all present
valid conclusions, and although beneficial, have all failed in
field applications at one time or another. These failures
illustrate that although we have learned a great deal about the
causes and prevention of gas migration, there is still a lot to
learn. However, before we can progress, we need to make
sure that we understand and are using the preferred
nomenclature.
The term transition time has been used to refer to the dynamic
set profile of cement slurries as exhibited on a pressurized
consistometer. In other words, slurries that provided a short
transition time were those which demonstrated what is
referred to as a “right angle set” on a thickening time chart.
Fig. 1 illustrates what is meant by right angle set. By
definition a “right angle set” is one in which the viscosity of a
slurry remains relatively low through a majority of the test and
then rapidly sets in a 20 to 45-minute time frame to more than
70 Beardon Units of Consistency (Bc)4. Work performed in
1993 by Mueller 7 demonstrated that the set profile during a
dynamic-state event is not representative of the way that some
cement slurries will develop gel forces under static conditions .
Most slurries are designed to provide thickening times in the
range of 4 hours, when the actual job time may be less than 1
hour. Slurries that exhibit a right angle set after 4 hours in a
dynamic test, may demonstrate a different profile if placed
under static conditions 1 hour into the test. Once cement
movement is stopped, SGS development may occur within
several minutes to over an hour, dependent on well conditions
and slurry designs. Wellbore temperature and pressure, along
2
with slurry density and additives are the main contributing
factors determining how SGS’s develop. For these reasons,
the term “right angle set” (a dynamic analysis), should not be
used when referring to slurries with short transition times
(static-state test).
Another misconception on transition time is the use of the
initial compressive strength determination, derived from an
UCA. In some cases, the time from 50 psi to 500 psi has been
used as a determining factor for how fast slurries will
transition into a solid. The time to 500 psi is important in
reducing WOC time, but may have little to do with the SGS
development of cement slurries. Some of the confusion is
from the fact that an ultrasonic gel strength analyzer is
available on the market. This instrument is called the static gel
strength analyzer (SGSA) and will be described later in this
paper. Part of the confusion stems from the fact that the
SGSA can also be used to determine compressive strength,
while a UCA cannot be used to determine SGS.
As described by Sabins et al, “transition time is the period
during which the slurry changes from a true hydraulic fluid to
a highly viscous mass showing some solid characteristics” 8,
under static-state conditions. From this point forward, the
aforementioned definition will be used when referring to
transition time. In this work and others, it is generally
accepted that at SGS development greater than 100 lbf/100 sq
ft (48 Pa), gas or fluid intrusion into the gelled cement can
occur. This is considered the start of the transition time and is
the point in which full hydrostatic pressure transmission is
restricted. In an effort to prevent shallow water flows,
Mueller 9 proposed a program to calculate the initial transition
time based on downhole parameters. This provides a
mathamatical approach to calculate the critical gels at which
fluid intrusion can occur. The transition time ends when the
SGS increases to 500 lbf/100 sq ft (240 Pa). At this point, the
slurry developed sufficient gel strength to prevent fluid or gas
migration into the cement column.
In subsequent work,
Sabins and Sutton 10 proposed reducing the transition time
between 100 and 500 lbf/100 sq ft to less than 40 minutes.
This suggests that reducing the transition time will minimize
the time for fluid or gas intrusion into the cement. Although
the authors agree with this statement in principal,
concentrating on short transition times as your primary
approach to gas control is a one-dimensional approach to a
multi-dimensional problem. This work will demonstrate that
some slurries with short transitions can fail when tested in a
gas migration model. It will also show that in some cases
slurries with extremely long transition times can prevent
intrusion of gas, if otherwise properly designed.
Given the previous definition for transition time, a brief
description of the mechanisms to control fluid or gas
migration is needed. This paper will not attempt to establish a
cure-all for gas migration, but is intended to illusrate that this
is a multi-phase problem requiring a broader testing approach.
It is generally understood that gas migration can occur
between channels at the cement/formation interface,
SPE 90829
cement/pipe interface, cement/mud interface and through the
cement matrix itself. Assuming that the cement slurry is
designed to minimize volume reduction, the first three
mechanisms are a function of following good cementing
practices1,4. These include mud/annular conditioning, proper
centralization, casing movement, good displacement
efficiency and proper spacer design.
Good cementing
practices are an extremely important part of achieving a good
annular seal. However, it is not the intent of this work to
further explore these practices. Instead, the authors believe
that preventing flow through the cement matrix requires the
use of a fit-for-purpose cement. Designing such a cement
requires focus on multiple slurry properties that include the
following:
1. Stabilized slurry – which includes zero free fluid and
minimal particle segregation.
2. Low fluid-loss – normally fluid losses below 50 cc’s
in 30 minutes is recommended.
3. Short transition time – although a desirable property,
concentrating on transition time solely can provide a
false sense of security.
4. Minimize volume reduction – Several papers 2, 3, 11 on
gas migration discuss volume reduction during the
plastic-state, which is controlled primarily by the
slurries fluid loss and is relatively small. More than
95% of the hydration volume reduction occurs after
initial set. The entry rate for gas or fluid can never be
more than the total cement volume losses rate.
5. Reduced internal slurry permeability – Although
Sutton and Ravi 2 present a good case that slurry
permeability has a direct relationship to fluid loss, in
our work we noted variances in the permeability
during the initial hydration of the slurry. These
variances may be attributed to the type of fluid loss
additive used or to an increase in permeability during
the induction period. We observed that the use of
materials which reduce permeability of the cement
can help to minimize flow paths for gas or fluid.
Figure 2 demonstrates this increase in permeability.
The fluid loss for this slurry was approximately 12
cc’s using a convensional fluid loss cell and API
procedures. During the hydration of the slurry, the
permeability appeared to increase. There was also a
simultaneous increase in filtrate production, causing a
voulume reduction.
Test Equipment Description
The cement slurries examined in the laboratory for this work
were subjected to a variety of tests. Those tests included
standard API HTHP thickening times, and Fluid Loss testing,
as well as non-API gas migration model, and SGS testing.
Thickening Time: All HTHP slurry thickening times were
performed following API RP-10B testing standards, on HTHP
pressurized consistometers using API test schedules
appropriate for the simulated well depth and specific
temperature gradient.
Fluid Loss: The HTHP slurry fluid loss tests were all
performed following API RP-10B standards in standard HTHP
SPE 90829
stirred fluid loss cells, at temperatures reflective of the wells
for which the slurries were being tested.
Gas Migration: For testing a slurry's resistance to internal gas
flow during setting, a gas flow test model similar to one
described by Beirute and Cheung 6 was utilized. An
operational diagram of the actual test cell is illustrated in
Figure 3. This gas flow model is equipped to measure the
permeability of the cement while being subjected to
pressurized gas intrusions from the reservoir. In the subject
test cell, three distinct pressures are applied to the cement
slurry during the test.
The hydrostatic pressure that would normally be transmitted to
the top of the cement column by the fluids above the cement
(such as drilling mud and/or cement spacers) is simulated by
mineral oil from a pressurized storage vessel. This oil is
pushed to the top of a traveling piston, which in turn rests on
top of the slurry in the test cell. Normally, 1,000 psi is used to
simulate the hydrostatic head on the cement slurry. The
travelling piston contains a small port in its center and is fitted
with a 325/60 mesh stainless steel screen across its face that
makes contact with the cement slurry in the test cell. On the
backside of the traveling piston, the central port is connected
to a 0.25-in. diameter stainless steel tube, which is 10.0-in.
long. This tube is used to introduce the second of the three
pressures.
In this case, it delivers pressurized nitrogen gas to simulate the
effect of a reservoir gas being injected into setting slurry in the
annulus of a well. The screen across the face of the travelling
piston is used to simulate a high-pressure, high-permeability
gas zone. For testing, a constant pressure of 500 psi is used to
simulate this high-pressure interval.
The third pressure used in the test is introduced to the cell via
a port in the bottom of the assembly. This bottom port is
covered with the same type of 325/60-mesh stainless steel
screen as the face of the travelling piston. Once again,
nitrogen gas is utilized via this port and screen. A pressure
regulator, is utilized to hold a constant 300 psi to simulate a
lower pressure, high-permeability formation.
The
performance of the regulator is similar to a check valve. If the
pressure on the test cell side of the regulator is greater than
300 psi, then the regulator allows fluids (either cement filtrate
or Nitrogen gas) to leak off. Once the test cell is filled with
cement slurry and the desired temperature and pressure
conditions simulated, the test can be run.
The gas flow test model actually records (automatically, via
microprocessors) the (static) fluid loss, transition time, and
permeability of the setting cement. As well as all pressures,
the volume of any cement filtrate and/or whole gas that passes
through the cement is also recorded. Additional pressure
monitoring ports in the cell allow for the recording of the
actual pore pressure of the cement slurry as it cures. This
particular pressure reading is critical during the test, as a gas
tight slurry will typically show a gradual decline of the slurry
pore pressure as the slurry sets and no longer transmits the
simulated hydrostatic pressure of the fluid above the cement
3
top. However, in instances where gas is actually working
through the slurry matrix, the slurry pore pressure will
typically cease its decline over time and begin to rise again, as
high-pressure formation gas forces its way into the setting
cement slurry matrix. At the same time, data recording will
typically indicate excess slurry filtrate being forced from the
setting slurry, and in some instances, whole gas will be
detected flowing through the slurry and out of the test cell.
As originally discussed by Beirute and Cheung 6, in order for a
slurry to be considered gas tight in a test with the model, the
slurry pore pressure needs to continue to decline until the
slurry is fully set and there should be no gas flow through the
setting slurry. Figure 4 illustrates the results from the model
with a slurry that maintained low permeability during
transition and resisted flow of the high pressure gas. Figure 5
illustrates a test where the slurry was not able to resist gas
flow and therefore the test was deemed a failure.
Since the original development of the model, field results with
slurries designed to pass the gas model have shown good
correlations to results obtained from field applications.
Static Gel Strength: As previously mentioned, currently there
are not any industry recognized standard methods for the
determination of SGS in oilfield cement systems. However,
ISO is evaluating three different types of laboratory test
devices in order to attempt to develop such standards. One of
the test devices being evaluated is an ultrasonic test device
(SGSA) that uses interpretation of ultrasonic transmissions
passing through the cement slurry to determine the developing
SGS.
A second device being evaluated is a vane device. This device
is essentially a “Vane type rheometer” that operates with an
intermittent shear. Unlike other equipment available to
measure SGS, the vane device is limited to about 800 psi
pressure.
The third device works in a very similar fashion to an HTHP
consistometer, in that the slurry is brought up to bottomhole
pressure and temperature over time, while being continuously
sheared at a rate consistent with slurry placement in a well.
After being conditioned under bottomhole conditions for a
time approximately equal to that required for placement in a
well, the test device then is transitioned over into the SGS test
mode. In this mode, the SGS of the slurry is continuously
monitored over time by means of a special paddle immersed in
the slurry inside a pressurized vessel. The resistance on the
paddle rotated at a continuous shear of 0.26°/min, is measured
by a strain gauge.
For this work, all SGS determination was preformed with a
device that functions in the same manner as the third type of
tester described above. This modified piece of tabletop
laboratory equipment functions both as a standard HTHP
consitometer, as well as a SGS analyzer. Figure 6 shows the
entire machine. In the thickenong time mode, it can actually
function as a fully capable HTHP consistometer. However, in
SGS testing, this mode is typically used only to simulate the
4
SPE 90829
shearing of the slurry during placement into the annulus of a
well. As described previously, once the slurry has been
conditioned in the placement simulation mode, the device is
then switched over into the SGS testing phase of the test.
Figure 7 shows a close-up of the control panal, which by
means of a microprocessor instrumentation column and a thin
lanyard, as shown on Figure 8, takes over the very precise
drive of the paddle from the large motor used in the
consistometer/conditioning mode. This instrumented column
controls the rate of rotation of the paddle. Although capable of
vaiable rotation rates, 0.26o/minute was used as a standard for
our testing, which is roughly equal to one complete rotation in
about 23 hours. It is the drag of the slurry on this very slowly
turning paddle that is used to compute the SGS. Typically,
once a slurry has obtained an SGS of 500 lbf/100 sq ft (240
Pa), the test is considered to be finished and is terminated.
Data Presentation:
Although the authors have observed numerous examples of
slurries that support their findings, four designs were chosen
to demonstrate the typical misconceptions with regards to
transition time as defined previously. These slurries are:
1.
Portland Class H + GMR + DA + EA + FWC mixed
at 16.2 ppg in fresh water
2.
Portland Class H + GMR + DA + LTR + KCl mixed
at 15.7 ppg in fresh water
3.
Portland Class H + GMR + DA + FLA mixed at 16.5
ppg in fresh water
4.
LSC mixed at 15.8 ppg that provides low fluid loss
properties.
Slurry 1: Represents a multi-functional slurry designed to
provide a short transition time, control fluid or gas intrusion
and exhibit a right angle set on the HPHT consistometer. This
design is considered an ideal case scenario, since it addresses
most of the causes of gas migration, as previously discussed.
The slurry composition is a blend of Portland cement
containing additives that provide gas migration reduction
(GMR). These materials aid in fluid loss control, free fluid
prevention, bonding and internal slurry permeability
reduction. GMR additives can consist of a broad range of
materials such as latex, polyvinyl polymers, silica fume
blends, etc. This design also included a cement dispersant
(DA), an expanding additive (EA) and a free water control
additive (FWC).
Basic testing criteria for this slurry used a bottomhole
circulating temperature (BHCT) of 110°F (43.3°C), an initial
pressure of 400 psi, a final pressure of 2,900 psi and a ramp
rate of 20 minutes. All slurry preparation and conditioning
was done according to API RP 10-B specifications.
For Gas Flow Testing, the slurry was mixed and ramped up to
bottomhole circulating temperature (BHCT) on an
atmospheric consistometer. Once conditioned and stable at
temperature for 20 minutes, the slurry was transferred into a
pre-heated cell jacket (of same temperature). As described in
the equipment section, a pressure of 1,000 psi was used to
simulate the hydrostatic head. Pressures of 500 psi and 300
psi, respectively, were used to simulate high and low-pressure
zones. Although these pressures can be altered to simulate
actual well conditions, it was found that these parameters
provide a standardized test procedure under a worse case
scenario. The slurry was then kept static at temperature and
pressure for the duration of the test, normally 24 to 48 hours.
The parameters discussed above, along with the fluid loss,
volume reduction and gas volume, were automatically
monitored and recorded for the duration of the test. The data
was transferred to a computer where it was plotted against
time as seen in Figure 9.
The SGS of the slurry was then tested as described in the
equipment section of this work. The slurry was ramped up to
pressure and temperature while being sheared at 150 rpm
(such as it would be in an HPHT thickening time test). After
conditioning for 2 hours, (which is the time to mix, pump and
displace the slurry), the top-drive motor was turned off and the
secondary motor was activated and attached to the strain
gauge to initiate SGS testing. A lanyard attached the strain
gauge to the paddle, which pulled it through a rotation of 0.26
°/min. The force required for that rotation was then monitored
through the data acquisition system and plotted on a chart
recorder. As mentioned previously, the time from 100 lbf/100
sq ft (48 Pa) to 500 lbf/100 sq ft (240 Pa) is the measure of
transition time. Figure 10 exhibits the results of this test.
This final test of the slurry was a thickening time
determination on a conventional HTHP consistometer to
record its set profile. The same pressure and temperature
parameters were also used for this test. The consistency of the
slurry was measured and the test stopped when it reached 70
Bc. The results of this testing can be seen in Figure 11.
Slurry 2: Represents a multi-functional slurry design that
exhibits a satisfactory transition time, yet allows gas intrusion
when tested on the Gas Model. This slurry is similar to Slurry
1, with the addition of Potassium Salt (KCL) and a low
temperature retarder (LTR). In this case, the GMR was not of
sufficient quantity or type to prevent gas influx.
Basic testing criteria for this slurry used a BHCT of 138°F
(58.9°C), an initial pressure of 550 psi, a final pressure of
4,900 psi and a ramp rate of 40 minutes. All slurry preparation
and conditioning was done according to API RP 10-B
specifications.
The Gas Model test was conducted first, using the same
procedure discussed previously. Figure 12 shows the results
of this Gas Model test.
The SGS of the slurry was then tested as described in the
equipment section of this paper with the temperature and
pressure ratings listed for Slurry 2. In this case, the slurry was
conditioned for 4 hours to simulate total job time. After
conditioning the motor was switched to SGS mode, as
SPE 90829
described for Slurry 1. The results of this testing is shown in
Figure 13.
Slurry 3: In this test, the authors investigated the ability of a
slurry that exhibits an extremely long transition time to control
annular gas migration. This slurry consisted of a blend of
Portland cement containing a GMR, DA and fluid loss
additive (FLA). The fluid loss of Slurry 3 was controlled to
less than 50 cc’s/ 30 minutes. The combination of the low
fluid loss to control volume reduction and the GMR to reduce
the matrix permeability of the slurry during hydration, has
been shown to aid in preventing gas migration.
The test criterion used for Slurry 3 was identical to that used
for Slurry 2.
The Gas Model was conditioned and run similar to those tests
previously mentioned for Slurry 1 and 2. The result of the gas
model for this slurry is shown in Figure 14.
The SGS or transition time was run using the procedure
described previously in this work. Job time for this specific
design was 3 hours prior to starting the SGS test. The result
for this test is shown in Figure 15.
Slurry 4: The final slurry design was chosen to exhibit the
typical misconception that SGS development (transition time)
and a ‘‘right-angle-set’’ demonstrated on the conventional
HPHT consistometer are related. In this example the slurry
used is known as a liquid storable cement (LSC) system.
Although initially developed for use in remote locations, its
unique properties have established a broader market in many
parts of the world. For some specific jobs, a long transition
time is the main requirement requested by the operator. The
composition of this slurry was a mixture of Portland cement, a
combination of silica flour (325 mesh) and sand (100 mesh),
cement plasticizer, retarder, FLA, anti settling agent and an
intensifier, for activation.
For this application the slurry was ramped to a BHCT of
180°F (82°C) in 1 hour at an initial pressure of 700 psi and a
final pressure of 7700 psi. The slurry temperature was held
constant for 1 hour to simulate job time. After this period the
slurry was ramped to BHST of 222°F (105.5°C) over a 3 hour
period. This is following guidelines established by the
operator to simulate actual job conditions.
Since this is a special slurry design it is not mixed in
accordance with API procedure. A standard laboratory
procedure has been established to provide mixing instructions
that more closely simulate field applications. This procedure
has been used successfully, to mix and store LSC, for over 8
years. The thickening time profile is shown in figure 16.
The transition time was conducted using the procedure
established earlier in this work. A condition time of 2 hours
was used prior to initiating the SGS mode. The result of this
test is shown in figure 17.
Discussion
5
As noted in figure 9 for slurry 1, the hydration of the slurry
began to occur about 4 hours into the gas model test. At this
time the filtrate production leveled out at approximately 40
cc’s. The pore pressure of the cement slurry continued to drop
for 7 hours after the initial pressure drop was noted. No influx
of gas was recorded during this 24-hour evaluation.
Figure 10 of slurry 1 exhibits the transition time of this slurry
design.. The SGS development from 100 lbf/100 sq ft (48 Pa)
to 500 lbf/100 sq ft (240 Pa) was 47 minutes. Although at the
upper limits of what would normally be considered acctable
by the authors, this design provided satisfactory SGS results.
The last figure 11 is a scanned image of the thickening time
chart for slurry 1. The slurry exhibited a thickening time of
3:30 hours. For the first 2 1/2 hours of the test the slurry
exhibited a consistency of 10 Bc. Once it began to set it took
approximately 15 minutes to go from 40 Bc to 70 Bc. This set
profile would be considered a ‘right angle set’.
The slurry provided a pass scenario for all three catergories
evaluated. Although, this may be desirable it is not always
practical considering the varability and quality issue with the
numerous cements on the market. It is important not to
dismiss a specific design that has a long transition time, if the
slurry is still capable of passing a gas flow test.
Figure 13 of slurry 2 demonstrate an excellent transition time
of 33 minutes from 100 lbf/100 sq ft (48 Pa) to 500 lbf/100 sq
ft (240 Pa). Although the transition time exhibited by slurry 2
is considered satisfactory to prevent fluid or gas intrusion, it
can be observed in figure 12 that the slurry exhibited gas
migration 7½ hours into the gas flow test. It also should be
noted that the slurry design exhibited less than 40 cc’s fluid
loss in the standard fluid loss cell. In the gas model more than
85 cc’s of filtrate was produced for the duration to the test.
The last 20 cc’s of filtrate was made during the onset of
hydration, which has been observed in many failed tests over
the years. A possible explanation for this is that the rapid
volume reduction caused by increased permeability during
initial hydration allowing gas influx into the matrix of the
slurry.
Slurry 3 is a classic case of a gas flow test that passes (figure
14) and a transition time that fails (figure 15).. The slurry
pore pressure drop started at approximately 4½ hours into the
test, and continued for 10 hours before stabilizing. The
transition time chart demonstrates what is considered to be a
very slow gel strength development. Basically it took 4:19
hours to go from 100 lbf/100 sq ft (48 Pa) to 500 lbf/100 sq ft
(240 Pa).
Slurry 4 was a special case in which it was necessary to design
a slurry to provide an extremely long transition time. This
was accomplished by use of a special LSC system. Figure 17
shows the results of the transition time or SGS test. It can be
noted that the slurry obtained 100 lbf/100 sq ft (48 Pa) within
30 minutes after switching to the SGS mode. However, it took
nearly 24 hours to reach 500 lbf/100 sq ft (240 Pa). This slow
gel development would not have been anticipated under
accepted ideaology, given the right angle set exhibited in
6
SPE 90829
figure 16. The thickening time chart exhibits a slurry that
produced a consistency of less that 8 Bc for over 40 hours and
then increased to 70 Bc in 10 minutes. This is considered a
true right angle set. Figure 16 and figure 17 are a good
indication that right angle sets and short transition times do
not necessarily correlate to each one another.
Conclusions
From the investigations and results discussed in the paper, the
authors propose the following conclusions:
1.
2.
3.
4.
Even though the SGS can be critical for the
prevention of shallow water flows in deep water
cementing operations, data does not indicate that the
SGS is singularly critical for preventing gas
migration through a hydrating cement slurry.
The occurrence of a “right angle set” in a slurry
during HTHP thickening time testing does not
necessarily equate to the same slurry possessing rapid
development of SGS, or yielding a particularly high
SGS.
Gas migration model testing does not support the
theory that Ultra-low fluid loss control in a cement
slurry is singularly critical for preventing gas
migration through a hydrating cement system.
The slurries that were deemed to have successfully
passed the gas flow model used in this work also
exhibited low permeability throughout slurry
transition.
Nomenclature
API
Bc
BHCT
BHST
0
C
cc
DA
0
F
FLA
FWC
GMR
HPHT
ISO
- American Petroleum Institute
- Beardon Units of Consistency
- Bottom Hole Circulating Temperature
- Bottom Hole Static Temperature
- Degrees Centigrade
- Cubic Centimeter
- Cement Dispersant
- Degrees Fahrenheit
- Fluid Loss Additive
- Free Water Control
- Gas Migration Reducer
- High Pressure High Temperature
International
Organization
for
Standardization
KCl
- Potassium Chloride
lbf
- Pounds Force
LSC
- Liquid Storable Cement
LTR
- Low Temperature Retarder
Pa
- Pascal
ppg
- Pounds per Gallon
psi
- Pounds per Square Inch
sq. ft. - Square Feet
SGS
- Static Gel Strength
SGSA - Static Gel Strength Analyzer
UCA - Ultrasonic Cement Analyzer
WOC - Wait on Cement
Acknowledgement
The authors would like to thank BJ Services for their
support and permission to publish this paper. The authors
would also like to thank Scott Bray and Chris Perez for
their assistance in generating the data used in this paper.
Additional thanks are extended to Doris Porter and Harold
Brannon for their assistance in finalizing and proofing this
paper.
References
1. Stewart, R. B. and Schouten, F. C., “Gas Invasion
and Migration in Cemented Annuli: Causes and
Cures”, paper IADC/SPE 14779, presented at the
1986 IADC/SPE Drilling Conference, Dallas, 1012 February, 1986.
2. Sutton, D.L. and Ravi, K.M., “New Method for
Determining Downhole Properties That Affect
Gas Migration and Annular Sealing”, paper SPE
19520, presented at the 1989 64th Annual
Technical Conference, San Antonio, 8-11
October, 1989.
3. Sabins, F. and Wiggins, M.L., “Parametric Study
of Gas Entry Into Cemented Wellbores”,
published in the SPE Drilling and Completion,
September 1997.
4. Grant, W.H. et al, “Simplified Slurry Design
Increases Wellsite Success”, paper SPE/IADC
16135, presented at the 1987 SPE/IADC Drilling
Conference, New Orleans, 15-18 March, 1987.
5. Pornpoch Tiraputra, et al, ‘Overcoming ShallowGas Drilling Difficulties in the Gulf of Thailand”,
paper IADC/SPE 87179, prepared for the 2004
IADC/SPE Drilling Conference, Dallas, 2-4
March, 2004.
6. Beirute, R. M. and Cheung, P. R., “A Method for
Selection of Cement Recipes To Control Fluid
Invasion After Cementing”, paper SPE 19522,
published in the SPE Production Engineering,
November, 1990.
7. Mueller, D.T., “An Investigation of The StaticState Properties of Right-Angle-Set Cements”
prepared for the Southwestern Petroleum Short
Course, 1993.
8. Sabins, F.L., et al, “Transition Time of Cement
Slurries Between the Fluid and Set States”, paper
SPE 9285, presented at the 1980 SPE Annual
Technical Conference and Exhibition, Dallas, 2124 September, 1980.
9. Mueller, D. T., “Redefining the Static Gel
Strength Requirements for Cements Employed in
SWF Mitigation”, paper OTC 14282, prepared
for the 2002 Offshore Technology Conference,
Houston, 6-9 May, 2002.
10. Sabins, F.L. and Sutton, D. L., “The Relationship
of Thickening Time, Gel Strength, and
Compressive Strength of Oilwell Cements”, paper
SPE 11205, presented at the 1982 SPE Annual
Technical Conference, New Orleans, 26-29
September, 1982.
SPE 90829
7
Time
11. Sabins, F.L. and Sutton, D.L., “Interrelationship
Between Critical Cement Properties and Volume
Changes During Cement Setting”, paper SPE
20451, presented at the 1990 SPE Annual
Technical Conference, New.
Class H + FLA + Retarder @ 16.5 ppg tested at 180°F
TT – 3:45 hrs
FL – 12 cc’s
FW - Zero
0
5
10
DC VOLTAGE
Figure 1 – Right Angle Set
Figure 3 – Gas Model Schematic
15
Figure 2 – Gas model chart showing the rapid filtrate
increase during cement hydration
8
SPE 90829
Figure 4 – chart showing a gas flow test that passed
Figure 5 – chart showing a gas flow test that failed
Figure 6 – Tabletop HTHP consistometer conversion to SGS tester.
SPE 90829
9
Figure 7 – Microprocessor instrument panel used for modified
tabletop SGS tester
Figure 8 – Lanyard assembly used to converte the SGS
tester to gel testing mode
Cement Pore Pressure
500 lbf/100 sq ft
Cement Filtrate
100 lbf/100 sq ft
Figure 9 –Gas Flow Model chart for Slurry 1 (Passed)
Start SGS test mode
Figure 10 – SGS chart for Slurry 1
10
SPE 90829
Figure 11 – Thickening time chart of Slurry 1
Cement Filtrate
Cement Pore
Pressure
Gas Volume
Figure 12 – Failed Gas Flow Model chart for Slurry 2
SPE 90829
11
500 lbf/100 sq ft
100 lbf/100 sq ft
Start SGS test mode
Figure 13 – SGS chart of Slurry 2
Cement Pore Pressure
Cement Filtrate
Figure 14 – Gas Flow Model chart of Slurry 3 (Pass)
12
SPE 90829
500 lbf/100 sq ft
Folded Chart - approximately 90
minutes of chart not shown.
100 lbf/100 sq ft
Start of SGS test mode
Figure 15 – SGS chart of Slurry 3 (Long Transition Time)
SPE 90829
13
Right Angle Set
Folded Chart - approximately 37
hours not shown
Figure 16 – Thickening time chart of Slurry 4 (Right Angle Set)
14
SPE 90829
Folded Chart - approximately
19 1/2 hours not shown
100 lbf/100 sq ft
Figure 17 – SGS chart of Slurry 4 (Long transition time)