petroleum enginer 2012 dst 8

8/10/2019 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 Shut in Pressure


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


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 Shut in Pressure


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DST PROCEDURE

Measurement steps

Final Flow Pressure

Final Shut In Pressure


The pressure recorder

records the pressure

increasing gradually up to

the Final Shut In Pressure


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The Packer is disanchored.


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 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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