Well Testing topic Pressure Draw Down Test definition,Objectives,Procedure,advantages & disadvantages

3. INTRODUCTION
• The measurement and analysis of pressure data taken after a well is put on production,
either initially or following an extended shut-in period. Drawdown data are usually
noisy, meaning that the pressure moves up and down as fluid flows past the gauges and
minute variations in flow rate take place. This is especially true for new wells, in which
well cleanup commonly occurs for days after production has begun. Such data are
difficult to interpret, and the noise often obscures regions of interest to the analyst.

4. OBJECTIVE OF TEST
• The fundamental objective of drawdown testing is to obtain the average permeability of
the reservoir rock within the drainage area of the well and to assess the degree of damage
or stimulation induced in the vicinity of the wellbore through the drilling and completion
practices.
• Other objectives are to determine the pore volume and detect reservoir homogeneities
within the drainage area of the reservoir.

5. PROCEDURE
• The well is shut in for a period of time long enough to allow the pressure to equalize
throughout the reservoir.
• The pressure equipment is lowered into the well.
• The flow is begun at a constant rate and the bottom hole pressure is measured
continuously.

6. PROCEDURE IN MORE DETAIL
• Install the equipment on a well that has been shut-in and stable.
• "Stable" is defined as the shut-in well head pressure changing at a rate of less than 1 psi per hour.
• Check for leaks in the system after installation.
• The SPIDR system must be recording for at least 15 minutes prior to opening the well (check the box for
the SPIDR system wake-up time).
• Begin flowing the well on a single choke size. If the well must be "stepped-up", try to get the well up to
full rate within 30 minutes. Continue flowing on a constant choke size for the duration of the test.
• If shut-ins or flow interruptions occur during the course of the drawdown, try to get the well back on-line
as soon as possible on the same choke size.

7. CANDIDATES OF DRAWDOWN TEST
• The drawdown test is used in the exploratory wells (new reservoirs) or the wells that
have been shut in for buildup test and those wells whose loss of revenue due to
production in buildup test can’t be tolerated.

8. ADVANTAGES
• The main advantage of pressure drawdown is that there is no loss of cash flow due to
shut in of the well during the test period.
• It also determines the boundaries of the reservoir and skin of formation.
• Suitable in new wells. With no need to lose production, reservoir size can be determined.

9. DISADVANTAGES
• The main disadvantage of drawdown test is that difficulty to flow the well at constant
rate.
• It doesn’t determine the average reservoir pressure.
• The drawback to running a drawdown is that the rate may not be constant. However,
changing the choke periodically to maintain a constant rate will cause more problems
than letting the rate fluctuate. In order to get accurate analysis on a drawdown, it is
critical that no choke changes occur during the test.

10. REFERENCES
• http://petrowiki.org/Well_test#Drawdown_test
• http://www.halliburton.com/en-US/ps/testing-subsea/reservoir-testing-analysis/data-
acquisition/spidr/drawdown-testing.page
• http://www.glossary.oilfield.slb.com/Terms/d/drawdown_test.aspx
• http://www.globalspec.com/reference/45407/203279/chapter-4-pressure-drawdown-
testing-techniques-for-oil-wells

11. THANKS FOR YOUR ATTENTION