introducton to drill stem test (DST), DST overview, Primary Function of DST, Objectives of DST, Tools of DST (dril stem test), Procedure of DST

1. INTRODUCTION TO
DRILL STEM TEST (DST)
RAO MUBARAK ALI
mubarik.ali43@yahoo.com
international member of
SPE 4353073

2. PRESENTATION CONTENT
• Introduction
• Overview
• Primary Function of DST
• Objectives
• Tools
• Procedure

3. INTRODUCTION
• When a well is ready to produce for the first time, the
production staff has an estimate of what will come out---, Oil,
Gas, or a combination. Still, they want to know how much and
under what pressure, to better understand the reservoir’s
mechanics and to design the facilities needed to process the
production. In order to evaluate a well’s productivity there are
number of direct and indirect tests but DST or Drill Stem Test is
the most authentic test of them all.

4. OVERVIEW
• Drill Stem Testing – DST is a procedure to determine the
potential productivity, pressure, permeability or extent of an oil
or gas reservoir before the permanent completion equipment is
installed. Drill stem testing is essentially a flow test, which is
performed on isolated formations of interest to determine the
fluids present and the rate at which they can be produced.
• DST bottom hole assembly BHA consist of a packer or packers,
which act as an expanding plug to be used to isolate zones of
the well for the testing process, valves that may be opened or
closed from the surface during the test, and down hole sensors
used to acquire reservoir information.

5. PRIMARY FUNCTION OF DST
• Isolate the target zone
• Control the flow of the well
• Conduct the fluid to surface
• Obtain Down hole information
• Evaluate the reservoir potential productivity

6. OBJECTIVES
Reservoir characteristics that may be estimated from DST analysis include:
• Average effective permeability: This may be better than core permeability since much
greater volume is averaged. Also, effective permeability rather than absolute permeability
is obtained.
• Reservoir pressure: Measured, if shut-in time is sufficient, or calculated, if not. It also
gives an accurate measure of bottom hole pressure and temperature.
• Composition: Fluid (Oil, Water and Gas) produced and sampled during test helps to design
surface facility accordingly.
• Wellbore damage: Damage ratio method permits the estimation of what the well should
make without damage.
• Barriers, permeability changes, and fluid contacts: These reservoir anomalies affect the
slope of the pressure buildup plot. They usually require substantiating data to
differentiate one from the other.
• Radius of investigation: An estimate of how far away from the wellbore the DST can "see".
• Depletion: Can be detected if the reservoir is small and the test is properly run.

7. DST TOOLS
Depending on the type of test and
well bore conditions there are
number of different tools that are
staked over one another to get the
desired results. But generally a
common study purpose considered
tools are illustrated below.

8. TOOLS
• Reverse Circulation Valve: Just below the drill pipes there is a mechanically
activated valve that provides communication between Drill Pipe and
Annulus. Its purpose is to circulate out any produced hydrocarbons after the
test is complete by pumping drilling mud down the annulus and then up to
the drill pipe.
• Multi-flow evaluator: It contains a sample chamber and a valve that can be
opened and closed multiple times during the test to allow flow when
required and stop it as well whenever needed.
• It has also got inside pressure recorders.
• Master Valve: Below the sampler there is a master valve that is designed to
open and close just once during the test. It activates with a delay of 5
minutes after the command is send to it working as a master control valve
for the test.
• Bypass Valve: This valve allows the drilling mud already present in the well
bore to pass out the annulus from the inside of DST assembly blow it while
tripping in to avoid swabbing. The same application is used to avoid surging

9. TOOLS
• Hydraulic Jar: This is an optional component of DST stem. Basically it
is a hydraulic jack that gives an upward shock to free a stuck pipe (if
any).
• Slip Joint: In case the hydraulic is unable to free a stuck pipe then we
have no option left than to leave the components blow slip joint in
the well bore and retrieve out the filled sampler. Slip joint is an anti-
threaded sub that screws open to retrieve out the above free
components.
• Packer: It is used to isolate the Annulus from the test zone.
• Perforated anchor: It provides a base support on the bottom of the
hole for the packer to be activated by weight as well as perforations
to allow the flow. It is also mounted by outside pressure recorders.

10. PROCEDURE
The DST tools are gradually lowered in the well bore
and the pressure recorder reads an increase of
pressure due to the increasing height of mud column
above it. Then the packer is set in place. Master valve
and multi-flow evaluator valve are opened one by one.
As the fluid is allowed to flows the pressure drops. This
first flow lasts 3 to 10 minutes to ease out any build up
pressure in the formation while setting the packer.
Then the multi-flow evaluator valve is closed for the
first shut-in period till the pressure stops going up and
stabilizes with time. This pressure is considered to be
the actual reservoir shut-in pressure. After that the well
is again made to flow for 1 hour in open hole and for 3
hours in a cased hole to collect a sufficient sample and
pressure data. Finally the master valve is closed and
the test is complete. The produced hydrocarbons are
circulated out to the surface through reverse circulation
sub and packer assembly is inflated off which again pts
the load of above mud column on the pressure
recorder showing a vertical increase of pressure. The

11. THANK YOU………….!