01 introduction well testing

Well Test Analysis
Instructors:
Bui Tu An (PVU)
Huynh Thanh Tung (Schlumberger)
Nguyen Tuan Duong (VSP)

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

1


Course information
Credit: 02 (36 hours)
2. Grading
• In-class evaluation: 25%
• Midterm: 25%
• Final Examination: 50%
3. Text materials
1. Lee, W.J.: Pressure Transient Testing, SPE (2003).
2. Spivey John P. , Lee. W.John: Applied Well Test
Interpretation, SPE (2013).
4. Software Tools
1. Microsoft Excel.
2. Ecrin - KAPPA
1.

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

2


Course Description
 Analysis of well performance under varied reservoir

conditions including evaluation of unsteady, pseudo-steady
and steady state flow;
 Well testing methods used to determine well and reservoir

parameters;
applications
to
conventional
unconventional wells producing gas and/or liquids;

and

 The fundamentals for preparing and operating well test

equipment to monitor, measure, and gather samples for
evaluating well performance.

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

3

Course Learning Outcomes
1. Describe the terminology and the commonly-applied methods
for quantifying and predicting well performance, specifically
skin, horizontal and vertical permeability, and fracture area and
permeability;

2. Develop the ability to use diagnostic plots to identify flow
regimes and well drainage patterns;
3. Apply pressure transient well test analysis to the determination
of well and reservoir properties, i.e., skin, permeability, distance
to barriers,
4. Apply rate transient well test analysis to the determination of
well and reservoir properties, i.e., skin, permeability, reservoir
volume.

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

4


Course content
1. Introduction of well testing (2x45 minutes)
2. Review of fluid (oil & gas) properties (1.5x45minutes)

 Solution Gas-Oil Ratio, Viscosity, Density, Formation
Volume Factor, Specific Gravity, Gas Compressibility
…

3. Fundamentals

of Fluid Flow in Porous Media

(2.5x45minutes)
 Material balance, equation of state and Darcy’s Law
 Development of the diffusivity equation: Liquid and

gas systems .

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

5


Course content
4.

Solutions/models for Well Test Analysis (2x45 minutes)
 Dimensionless variables
 Steady-state, pseudosteady-state, and transient flow in

radial and other geometries
 Adding near wellbore and wellbore phenomena.
5.

Well Test Analysis (4x45 minutes)
 Analysis of pressure drawdown/buildup data for Slightly

Compressible Fluids
 Analysis

of pressure
Compressible Fluids

drawdown/buildup

data

for

 Analysis by use of Type Curves

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

6


Course content
6. Use software for the analysis of well test data

Huynh Thanh Tung (Schlumberger) (12x45 minutes)
7. Preparing and operating well test equipment

Nguyen Tuan Duong (VSP) (12x45 minutes)

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

7


What is a Well Test?
 The technique and method for the evaluation of well

conditions and reservoir characteristics.
 Investigates a much larger volume of the reservoir than cores
or logs
 Provides estimate of permeability under in-situ conditions
 Provides estimates of near-wellbore condition

 Provides estimates of distances to boundaries
 It involves producing a well at a constant rate or series of

rates, some of which may be zero (well closed in), while
simultaneously taking a continuous recording of the
changing pressure in the wellbore (at the same well or
another well) using some form of pressure recording device.
TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

8

How is a Well Test Conducted?

A well test is conducted by:
• Changing production rate at a well

• Measuring resulting pressure response at the same
well or another well

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

9


Well Test Applications
 Exploration

 Is this zone economic?
 How large is this reservoir?
 Reservoir engineering

 What is the average reservoir pressure?
 How do I describe this reservoir in order to
–
–

–

estimate reserves?

forecast future performance?
optimize production?

 Production engineering

 Is this well damaged?
 How effective was this stimulation treatment?
 Why is this well not performing as well as expected?
TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

10


Well Test Applications
 Exploration wells







Fluid sampling (Primary reason)
Measuring the initial pressure
Estimating a minimum reservoir volume
Evaluating the well permeability and skin effect
Identifying heterogeneities and boundaries.

 Producing wells







Verifying permeability and skin effect
Identifying fluid behavior
Estimating the average reservoir pressure
Confirming heterogeneities and boundaries
Assessing hydraulic connectivity

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

11


Well Test Objectives
 Define reservoir limits

 Distances to boundaries
 Drainage area
 Estimate average drainage area pressure

 Characterize reservoir

 Permeability & Skin factor
 Dual porosity or layered behavior
 Diagnose productivity problems

 Permeability
 Skin factor
 Evaluate stimulation treatment effectiveness

 Skin factor
 Fracture conductivity & half-length
TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

12


Types of Well Tests

q

Single-Well
TALENTS FOR DEVELOPMENT

Multi-Well
@MSc. Bui Tu An

13

Single well tests
 Drawdown test – Produce a well at constant rate (or

multirate) and measure the pressure response.

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

14


Single well tests
 Buildup test – Shut in a well that has been producing

and measure the pressure response.

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

15


Single well tests
 Injection test – Inject fluid into a well at constant rate

and measure the pressure response.

 Injection-falloff test – Shut in an injection well and

measure the pressure response.
TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

16


Multi-well tests
 Interference test – Produce one well at constant rate and
measure the pressure response at one or more offset
wells.

 Pulse test – Alternately produce and shut in one well and
measure the pressure response at one or more offset
wells.
TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

17


Well Test Methods
The primary ways to test a well are covered in the
following sections.

1. Open hole and cased hole, no completion
 Conventional deliverability tests, involving extensive surface

and downhole equipment, are designed to simulate the
production characteristics of new wells.

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

18


Well Test Methods

Figure 1 shows a
typical surface
offshore layout for
an exploration
well test and a
sketch of the
drillstem test
(DST) string of
downhole testing
tools.

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

19

Well Test Methods
2. Wireline formation tests (WFT)
Wireline tests (Repeat Formation Tester - RFT or Modular Formation
Dynamics - MFD) are performed mostly in open hole using a cable-operated
formation tester and sampling tool anchored at depth while reservoir
communication is established through one or more pressure and sampling
probes. Figure 2 shows typical configurations for testing and sampling with
the MDT.

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

20


Well Test Methods
3. Production or injection test with completion string in place
 Production and injection well tests, performed using production
logging tools, are conducted to obtain pressure and optional flow
measurements. Figure 3 shows a sketch of a basic version of the PS
Platform* new-gener-ation production services platform, equipped
with a gas holdup sensor.

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

21

Well Test Methods
4. Mini-DST
 The Mini-DST tool uses the conventional Wireline Formation Tester

(WFT) configured with a dual-packer module and downhole pump.
 The operation of mini-DST tool requires much less time than the

classic DST, and multiple zone tests can be conducted to assess
individual zone deliverability.
 On the other hand, the mini-DST has definitely increased reliability

and the success rate of pressure transient tests.

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

22


Well Testing - Data Acquisition
 Downhole Recorders

 Record pressure and temperature
 Components
−

Pressure Gauge

−

Power Source

−

Memory unit

 1 to 2 recorders used
 Surface pressure readout (Wireline link)

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

23


Well Test Data Analysis

 Diffusivity Equation
 Model Recognition

 Interpretation



Straight-Line



Type-Curve



Simulation and History Matching

TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

24


To sum up : Well Test
 A properly designed, executed, and analyzed well test

can provide information:
 formation permeability
 reservoir initial or average pressure

 sand-face condition (well damage or stimulation)
 volume of drainage area
 boundary and discontinuities
 reservoir heterogeneity
 distance or extension of the fracture induced

 validation of geological model.
 Further, it is important to determine the ability of a

formation to produce reservoir fluids and underlying reason
for a well's productivity.
TALENTS FOR DEVELOPMENT

@MSc. Bui Tu An

25