petroleum enginer 2012 dst 8
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DRILL STEM TEST
The Drill Stem Test is defined as the way to test thereservoir. The main objective is to evaluate the flow rate
of the payzone. In the meantime, a sample of fluid
contained in the formation is brought to the surface.
This sample is analyed in the lab and many informationsrelated to the reservoir will result.
A chart pressure recorder is interpreted, characteristics
such as reservoir pressure, porosity, permeability,
saturationare evaluated.
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DST PRINCIPLE
While drilling, the borehole walls are controlled by the
pressure exerted by the column of drilling fluid.The DST is to allow the fluid contained in the formation to
flow from the reservoir to the well.
So, the pressure exerted by the mud must be cancelled and
the formation to be tested must be isolated.
Specific equipents are used :
Packer to isolate the formation to be tested.
Tester : kind of valve to be opened to allow the formation
fluid to flow.
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Formation
PfPw
H
Pw is the well pressure
exerted by the drilling
fluid.
Pw = H x Mud Weight
While drilling, Pw is
slighty greater than Pf.The DST is to make Pf
greater than Pw.
Thus, the fluid in the
formation can flow to the
well.
This needs to reduce Pw.
The use of Pacher is
required.
Mud
Pressures before DST
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Formation
PfPw
H
Packer
Tester
Drill
Stem
The well pressure Pw is
considerably reducedbecause of the column H
under the packer.
The formation pressure
Pf becomes greater than
Pw.
The fluid can flow easily
to the well.
Pressures after Packer
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Schematic Layout of a Test
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Drill Stem Test ASSEMBLY
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THE PRESSURE RECORDER
The most important information during test is the pressure
recordings.
At least 2 recorders placed at different locations are inserted in the
test assembly.
This is to interpret the result and explain any recording anomalies.
Example of Chart
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THE PACKER
The packer is an
important tool in testassembly. It closes off
the annulus space
betwwen the hole and
the drill pipe. This
permits to reduce thehydrostatic pressure
front of the formation.
The packer has a
rubber sealing elementthat is compressed by
applying weight of one
ton per inch diameter.
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THE SAFETY JOINT
The safety joint is very
useful tool in test
assembly. It is used in
case of stuck of the drill
string assembly.
If a stuck occurs, the
tester can be retrievedby disconnection at the
safety joint.
The safety joint has odds
big threads connection.
It may be unscrewed
easily just by rotation of
less than 5 revoultions.
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THE HYDRAULIC JAR
The Jar is inserted in thetest assembly above the
safety joint. This is to
attempt to unstuck before
to unscrew at the safety
joint. The type of jarcommonly used is
actuated hydraulically.
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The Pressure Equalizing Valve
The Pressure Equalizing
Valve also called Bypass is
used to equalize thepressures above and below
the packer. While running
the test assembly, the valve
is open to reduce surge
pressure caused by thelarge diameter of the
packer seal element.
The valve is closed during
the whole test then opened
to equalize the pressuresabove and below the
packer.
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THE TESTER VALVE
The Tester Valve is the main component of the test assembly. The
function of this valve is to alternate opening and closing of the
assembly dowhole in order to get periods of flow and recompressionof the fluid contained in the formation pores.
There are 2 types of Tester Valve
MFE : Multi Flow Evaluator
PCT : Pressure Control Test
In MFE type, the valve is opened and closed by a downward
movement due to the weight of the drill collars.
In PCT type, the valve is opened and closed by pressure in the
annulus. This type is practically commonly used by DST
Companies. It is suited to off shore platforms and horizontal wells.
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The Reverse Circulation Valve
The Reverse Circulation Valve also
called DCIPV (Dual Closed In Pressure
Valve) is located from 9 to 30 meters
above the tester. It allows
communication with the annulus as the
operation test completed.
The most common type of reverse
circulation valve is break off plug.
While running in hole, the lateral ports
are plugged by a hollow sleeve fixed to
the body with a shear pin.
Before to start pulling out of hole, an
iron ball is sent inside the drill string
and will seat on the sleeve. Under an
increase of pressure, the shear pin will
break and the sleeve will slide down.
The lateral ports are opened and make
communication with the annulus.
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Lateral Ports
Close Open
Sleeve
BallShear
Pin
Reverse Circulation Valve
While Running In
Hole
Before Pulling Out
Of Hole
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DST PROCEDURE
The Reverse Circulation Valve
is closed
The Tester Valve is closed
The Bypass is open
While running in hole, the
pressure recorder records the
hydrostatic pressure at different
depths. There are small intervall
times due to making connection of
the stand drill string.
Running In Hole
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The Test Assembly is at Bottom
Hole.
The Reverse Circulation Valve isclosed.
The Tester Valve is closed.
The pressure recorder records
the Hydrostatic Pressure.
DST PROCEDURE
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DST PROCEDURE
The Packer is
anchored to the walls of
the hole by applying aweight of 8 to 10 tons.
The pressure recorder
records a slight increase
pressure.
The Tester Valve will
be opened in a very
short time.
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DST PROCEDURE
Measurement steps
The Pacher is anchored.
The Tester Valve is opened.
There is a large pressure drop.
The pressure recorder records the
Initial Flow Pressure. The fluid
contained in the formation starts toflow.
Initial Flow Pressure
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DST PROCEDURE
Measurement steps
Initial Flow Pressure
Initial Shut in Pressure
The Tester Valve is closed.
There is an increase pressure.
This pressure will be stabilized
at a pressure called Initial Shut
in Pressure.
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DST PROCEDURE
Measurement steps
The Tester Valve is closed.
There is a drop pressure till the
initial flow pressure.
The fluid in the formation starts to
flow.
The pressure recorder recordes the
flowing pressure increasing graduallyup to Final Flow Pressure.
Final Flow Pressure
Initial Flow Pressure
Initial Shut in Pressure
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DST PROCEDURE
Measurement steps
Final Flow Pressure
Final Shut In Pressure
The Tester Valve is closed.
The pressure recorder
records the pressure
increasing gradually up to
the Final Shut In Pressure
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The Packer is disanchored.
The Tester Valve is closed.
The pressure increase up to
Final hydrostatic pressure.
Final hydrostatic pressure
Final shut in pressure
DST PROCEDURE
Measurement steps
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The Packer is disanchored.
The Reverse CirculationValve is open to make
communication with the
annulus.
The Tester Valve is closed.
The Test Assembly is pulling
out of the hole.
PULLING OUT THE
TESTER ASSEMBLY
CA C A S
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TYPICAL CHART TEST
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