Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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T 5709 CAN
Peb
FOAM CEMENT SAMPLING DEVICE AND METHOD
The invention relates to a device and a method for obtaining a
foamed cement sample at elevated pressure.
Foamed cement consists of a cement slurry into which a gas has
been injected. A number of the physical properties of the foamed
cement appear to be dependent on the gas bubble size and distribu-
tion. Hence, if foamed cement is used, for example, for providing a
cement annulus around a steel casing in an oil or gas production
well, field samples must be obtained to verify if foamed cement's
properties in the field are the same as those studied in the
laboratory. Thus, there is a need for some means of foam cement
quality control in the field.
It is therefore an ob~ect of the present invention to provide
a foam cement sampllng device and method which are suitable to
obtain in a cost-effective and reliable manner representative
samples of foamed cement during well cementation operations.
The method according to the invention comprises the steps of:
- providing a sampling device comprising a tubular body which
contains a removable sleeve, said body being provided at the ends
thereof with removable flanges, one of said flanges comprising a
fluid inlet port provided with an inlet gate valve, the other of
said flanges comprising a fluid outlet port provided with an
outlet gate valve,
- connecting said inlet gate valve to a cement line vla which a
foamed cement slurry is pumped at an elevated pressure during
placement of a cement lining in a well,
- opening said inlet and outlet gate valves while pumping cement
through said line, thereby diverting a portion of the cement
slurry flow through the sampling device,
- allowing the sampling device to be filled with the cement slurry
and then closing said outlet gate valve and subsequently closing
said inlet gate valve,
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- allowing the foamed cement to cure under elevated pressure,
- removing at least one of said flanges from the tubular body,
- removing the sleeve containing the cured cement sample from said
body, and
- removing the cured cement sample from the sleeve.
The sampling device according to the invention comprises:
- a tubular body which contains a removable sleeve,
- a pair of removable flanges removably mounted at the ends of said
body, one of said flanges comprising a fluid inlet port provided
with an inlet gate valve, the other of said flanges comprising a
fluid outlet port provided with an outlet gate valve,
- means for connecting said inlet gate valve to a cement line.
In use the sampling device may be connected to either the
cement mixing line so as to collect a cement sample before the
cement is pumped downhole or to an annulus vent line in order to
collect a cement sample after it returns to the surface.
The key to the sampling device and method according to the
invention is that an in-line sample of the field mixed cement is
collected and allowed to cure under in-situ pressure.
The sampling device according to the invention allows for easy
removal of the used cement without breakage and is constructed in a
manner which allows for easy clean-up and maintenance.
The invention will now be explained in more detail with
reference to the accompanying drawing, in which:
Fig. 1 shows a longitudinal sectional view of a sampling
device according to the invention.
The sampling device shown ln Fig. 1 comprises a steel tubular
body 1 with terminal flanges 2 and 3 at both ends.
A first disk-shaped flange 4 is secured to one of said
terminal flanges 2, 3 by a series of nuts 5 and tension rods 6.
Said first disk-shaped flange 4 comprises a central fluid inlet
port 7 which can be opened or closed by an inlet gate valve 8. The
inlet gate valve 8 is connected to a cement bleeding conduit 9,
which is provided with a bleed off valve 10 and a flange 11 which
can be mounted on a T-joint (not shown) of either a cement mixing
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line or annulus vent line. The cement bleeding conduit may further
be equipped with a pressure gauge (not shown) for pressure
reference.
A second disk-shaped flange 12 is secured to the other
terminal flange 3 of the tubular body l by a series of tension rods
13 and nuts 14. The second disk-shaped flange 12 comprises a
central fluid outlet port 15 which can be opened or closed by an
outlet gate valve 16. Sealing between the disk-shaped flanges 4, 12
and the terminal flanges 2, 3 of the tubular body i5 provided by
steel ring gaskets 18.
A plastic tube 20 is arranged inside the tubular steel body l
such that the cement samples obtained by the sampling device can be
withdrawn and handled easily. The plastic tube 20 is greased before
inserting it in the tubular steel body 1 and subsequently slipped
in and out the steel body l a few times to ensure that the steel
body's interior is coated with grease.
The sampling device operates as follows. The flange 11 of the
cement bleeding line 8 is mounted on a T-ioint of a suitable cement
line (not shown) before the cement injection is started. Optionally
a Hamer valve (not shown~ may be arranged between the flange 11 and
T-joint in order to enable disconnection of the sampling device
from the cement line before terminating the well cementation
procedure.
During starting of the cementation procedure the bleed-off
valve lO and either said Hamer valve (not shown) or the fluid inlet
valve 8 are closed while waiting for foamed cement passage through
the cement line at the T-joint. When cement slurry passes through
the cement line at a desired pressure, e.g. 150 kPa, the Hamer
valve and the inlet and outlet gate valves 8 and 16 are opened,
while the bleed-off valve 10 is closed. As soon as the sampler is
filled with foamed cement and the cement slurry flows out of the
sampler via the outlet gate valve 16 said outlet valve 16 is closed
followed by the inlet gate valve 8.
After closing the gate valves 8 and 16 the Hamer valve is
closed and the bleed-off valve 10 is opened thereby emitting cement
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slurry from the cement bleeding conduit 9. Subsequently the flange
10 is disconnected from the Hamer valve and then the device is
stored ln an upright position for e.g. 24 hours while the gate
valves 8 and 16 are kept closed so as to allow the cement sample
trapped in the sampling device to cure under the same pressure as
the pressure at which the sample was taken from the cement line.
Upon termination of the 24 hours curing period the gate valves 8,
16 are slightly opened to depressurize the sample. Subsequently the
disk-shaped flanges 4 and 12 are removed from the tubular body 1
and then the plastic sleeve 20 containing the cured cement sample
is removed from the tubular body e.g. by pushing it out with
another identical plastic sleeve. Then the cured cement sample is
removed from the sleeve by splitting the sleeve 20 which leaves a
cylinder of foamed cement. Finally the sampling device is cleaned
up and greased for the next cement job.
FIELD TEST OBSERVATIONS
A first foam cement sample, collected at 105 kPa from an
annulus vent line~ was obtained and withdrawn perfectly. On the
second cement job the sample was caught at 230 kPa but leaking was
noticed at the outlet gate valve. A bullplug was placed in the
outlet end to try to maintain pressure in the sampler. The
sampler's inlet gate valve leaked on its third job, however, the
outlet gate valve sealed perfectly. No leaking was observed on the
fourth sample collected at 860 kPa. A watery slurry was present at
the inlet end when this sample was withdrawn. The fifth sample was
collected at 1020 kPa but leakage occurred at the inlet gate valve.
This sample sei~ed in the sampler, so it was removed by pressuring
it out with water.
On average, preparing the sampler for a cement job took 90
minutes and setting up the sampler took 20 minutes. Sample collec-
tion took about 1-2 minutes. After the sample was withdrawn, the
gate valves were soaked in a vinegar solution for 12 hours and the
lodged cement broke down to a sludge. A rubber O-ring on the bleed
off valve was replaced because it was damaged on the sampler's
third job. The volume of foamed cement returns flowing onto the
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ground during sample collectlon was negligible. The leaking inlet
gate valve was replaced after the fifth cement job. No further
leaks were encountered during sampling.
The field tests revealed that the sampling device according to
the invention is suitable to collect representative foam cement
samples at various foam pressures and that the time associated with
samples operation is minimal.
The field test furthermore revealed that the sampling device
can be used to take a foam cement sample at a pressure higher than
the pressure occurring in the cement line during cementing opera-
tion. This may be desired in order to take into account the hy-
draulic head of the cement column in the well annulus.
To obtain a sample at a pressure higher than the pressure in
the cement line during cementing operations the cement line section
lS comprising the T-joint and the bleeding line 9 may be pressured up
with water upon termination of the ce~enting operations during
which a cement sample has been trapped in the sampling device. When
the desired increased pressure is reached in the cement bleeding
line 9 the inlet gate valve 8 is opened and then closed again,
whereupon the sample is allowed to cure at said increased pressure.
The sampling device may be connected to any suitable cement
line such as the cement mixing line or annulus vent line, depending
where the sample is desired. In any case an in-line sample of the
field mixed cement is collected and allowed to cure under in-situ
pressure. The sampling device is constructed for easy clean-up and
maintenance and allows for easy removal of the cured cement sample
without breakage.
