P613_05A_Lec_08_WT_Historical_Perspectives_(050408).ppt

Well Testing —
Historical Perspectives
PETE 613
(2005A)
Slide — 1
T.A. Blasingame, Texas A&M U.
Department of Petroleum Engineering
Texas A&M University
College Station, TX 77843-3116
+1.979.845.2292 — t-blasingame@tamu.edu
Petroleum Engineering 613
Natural Gas Engineering
Lecture 08:
Well Testing —

Well Testing —
PETE 613
(2005A)
Slide — 2
Well Testing — Historical Perspectives
Origin of the "Deliverability" (or Backpressure) Relation
 Empirical.
 Used to assess "open flow" potential of gas wells.
 Does not provide a "time-dependent" behavior.
Multi-Rate Testing
 Historically, VERY popular — still used quite often,
especially on new wells to estimate deliverability and
"non-Darcy" flow effects.
 Keep it simple — a "4-point" test is appropriate.
 Isochronal testing is very difficult to implement.
Pressure Transient Analysis
 Expected Results: Pressure Transient Analysis (PTA).
 Example Data Sets: PTA and Production data.
 Basic Plots: Lee Text Example 2.2 (Pressure Buildup).

Well Testing —
PETE 613
(2005A)
Slide — 3
Origin of the "Deliverability"
(or Backpressure) Relation
Origin of the "Deliverability" Relation

Well Testing —
PETE 613
(2005A)
Slide — 4
Gas Well Deliverability:
 The original well deliverability
relation was completely empiri-
cal (derived from observations),
and is given as:
 This relationship is rigorous (i.e.,
it can be derived) for low pres-
sure gas reservoirs, (n=1 for lami-
nar flow).
From: Back-Pressure Data on Natural-
Gas Wells and Their Application to
Production Practices — Rawlins and
Schellhardt (USBM Monograph, 1935).
History of the "Deliverability" Equation
n
wf
p
p
C
g
q )
( 2
2



Well Testing —
PETE 613
(2005A)
Slide — 5
Multi-Rate Testing
Multi-Rate Testing

Well Testing —
PETE 613
(2005A)
Slide — 6
Deliverability Testing: Basics
a. "Standard" 4-point test deliverability test — note
that the rates increase (to protect the reservoir).
b. "Isochronal" test sequence — note that each
"buildup" is required to achieve pi.
c. Modified "Isochronal" test sequence — note that
each "buildup" is not required to achieve pi.
d. Governing equations for "deliverability" test
analysis/interpretation.

Well Testing —
PETE 613
(2005A)
Slide — 7
Deliverability Testing: Orientation
a. Basic "pressure-squared" relation
that is presumed to describe gas
flow — analogous form can be
derived from steady-state flow theory
(Darcy's law).
b.Traditional "deliverability" plot —
probably derived from empirical
plotting of data.

Well Testing —
PETE 613
(2005A)
Slide — 8
Deliverability Testing: Orientation
a."Rate-squared" (or velocity-
squared) formulation — analogous
form can be derived from steady-
state flow theory (Forchheimer
Eq.).
b. Modified "deliverability" plot —
note that bqsc
2 must be known (...
need alternative approach).

Well Testing —
PETE 613
(2005A)
Slide — 9
Expected Results:
Pressure Transient Analysis (PTA)
Production Analysis (PA)
Origin of the "Deliverability" Relation

Well Testing —
PETE 613
(2005A)
Slide — 10
 Expected Results of Pressure Transient Analysis (PTA):
— "Conventional" PTA: Use of semilog and other specialized plots to
estimate reservoir properties from a particular "flow regime" (i.e., a flow
regime is a characteristic behavior derived from an analytical solution —
e.g., the constant pressure derivative function for infinite-acting radial
flow (IARF)). Examples of other specialized plots: square-root and fourth-
root of time plots for fractured wells.
— "Model-based" analyses: Using analytical/numerical reservoir models to
perform simultaneous analysis/modelling procedures. Provides estimates
of dynamic formation properties: (i.e., model parameters)
 Radial Flow: k, S, CD
 Fractured Wells: k, xf, FCD, CfD
 Horizontal Wells: kr, kr/kv, hwell, (effective length) zw (position), ChD
 Dual porosity reservoir properties: w, l
 Data Requirements/Assessment/Review:
— Typically involves very accurate measurements of bottomhole pressures
(this is a priority).
— Rate history is most often the weakest link — must perform "due
diligence" and obtain the best possible rate history.
— Should use downhole shut-in device to minimize wellbore storage.
Expected Results from PTA

Well Testing —
PETE 613
(2005A)
Slide — 11
 Expected Results of Production Analysis (PA):
— "Conventional" decline curve analysis: (Arps, etc.) — empirical relations
used to provide estimates of recovery and forecasts of future
performance.
— "Model-based" analyses: Using analytical/numerical reservoir models to
perform simultaneous analysis/modelling procedures. Provides
estimates of dynamic formation properties (k, S, xf, dual porosity
properties, etc.)
— "Model-based" forecasting: A direct extension of model-based analysis
— generation of a time-dependent pressure and/or rate forecast.
 Data Requirements/Assessment/Review:
— Are production data available? (BOTH rates and PRESSURES!)
— Is the well completion history available? (review for issues)
— PVT and static reservoir properties? (must be assessed/included)
— Is the production "analyzable?" (can major issues be resolved?)
Expected Results from PA

Well Testing —
PETE 613
(2005A)
Slide — 12
Reservoir Performance Analysis:
PTA and PA Data Quality and Data Artifacts
PTA and PA Data Quality and Data Artifacts

Well Testing —
PETE 613
(2005A)
Slide — 13
 Production Example 1: Sewell Ranch No. 1 (North Texas (US))
 Rate and pressure data affected by water loading.
 Late-time data affected by line pressure (other wells in flow system).
Sewell Ranch Well No. 1 — Barnett Field (NorthTexas)
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
0 500 1000 1500 2000 2500 3000 3500 4000
Producing Time, days
Gas
Production
Rate,
MSCFD
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Surface
Pressure,
psig
Gas Flowrate
Wellbore Pressure
Production Data: Example 1

Well Testing —
PETE 613
(2005A)
Slide — 14
 Production Example 2: UPR22 Gas Well (Mid-Continent (US))
 Rate and pressure data affected by fluid loading.
 Seasonal cycles in demand/production.
UPR22 Gas Well — Mid-Continent (US)
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
0 250 500 750 1000 1250 1500
Gas
Production
Rate,
MSCFD
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Calculated
BHP,
psia
Gas Flowrate
Wellbore Pressure
Production Data: Example 2

Well Testing —
PETE 613
(2005A)
Slide — 15
 Pressure Transient Example 1: Bourdet (SPE 12777)
 Production history effects are obvious.
 Interpretation should consider "no rate" and "rate" history cases.
a.No Rate History: (Dt format) Pressure drop and
pressure drop derivative versus shut-in time
(Bourdet (SPE 12777)).
b.Rate History: (Dte format) Pressure drop and
pressure drop derivative versus Agarwal
superposition time (Bourdet (SPE 12777)).
Bourdet Example (SPE 12777) (Dt e Format)
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02
Dt e , hr
D
p
and
D
p'
,
psi
Pressure Drop
Pressure Drop Derivative
Bourdet Example (SPE 12777) (Dt Format)
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02
Dt , hr
D
p
and
D
p'
,
psi
Pressure Drop
Pressure Transient Data: Example 1

Well Testing —
PETE 613
(2005A)
Slide — 16
Pressure Transient Data: Example 2
 Pressure Transient Example 2: DaPrat (SPE 13054)
 Dual porosity/naturally fractured reservoir (PSS interporosity flow).
 Illustrates the sensitivity of the pressure derivative function.
DaPrat Example (Well Mach 3X, SPE 13054) (Dt Format)
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03
Dt , hr
D
p
and
D
p'
,
psi
Pressure Drop
Pressure Drop Derivative (L=0.2)
Simulated Pressure Drop
Simulated Pressure Drop Derivative

Well Testing —
PETE 613
(2005A)
Slide — 17
 Data Artifacts Example 1: Womack Hill Field (Alabama (US))
 Note the various events (value of annotated production records).
 No pressure data (typical).
Womack Hill Well No. 1633 — Womack Hill Field (Alabama)
1.E+01
1.E+02
1.E+03
1.E+04
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
Oil
Production
Rate,
STBD
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Estimated
BHFP
Pressure,
psia
Oil Flowrate
Wellbore Pressure
Prorated
Production
Initial
Depletion
(no
pressure
support
)
Recompletion
Acid
Stimulation
Conversion
to
Jet
Pump
p wf assumed constant
Data Artifacts: Example 1

Well Testing —
PETE 613
(2005A)
Slide — 18
 Data Artifacts Example 2: Told Well 3 (Colombia)
 pwf NOT synchronous with qo (pwf from fluid levels).
 Note that effect of pump change is captured by pwf and qo.
Well Told 3 — Colombia (South America)
1.E+02
1.E+03
1.E+04
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Oil
Production
Rate,
STBD
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
Est.
BHF
Pressure,
psia
Oil Flowrate
Wellbore Pressure
Pump
Change
p wf not synchronous
with rate profile

Well Testing —
PETE 613
(2005A)
Slide — 19
 Data Artifacts Example 3: Canada Gas Well
 pwf NOT synchronous with qg at early/intermediate times.
 Dispersion in pwf at middle times not reflected in the qg function.
Gas Well (Poor Early Time Data) — (Canada)
1.E+02
1.E+03
1.E+04
1.E+05
0
50
100
150
200
250
300
350
400
450
500
550
600
Gas
Production
Rate,
MSCFD
0
500
1000
1500
2000
2500
3000
3500
Calc.
BHF
Pressure,
psia
Gas Flowrate
Wellbore Pressure
q
o
and
p
wf
increasing
p wf variations not
synchronized with q g

Well Testing —
PETE 613
(2005A)
Slide — 20
 Data Artifacts Example 4: Southeast TX Gas Well (US)
 Multiple completion changes.
 Issues related to pressure profile — measure bottomhole pressure?
Gas Well with Evolving Condensate — (Southeast TX (US))
1.E+02
1.E+03
1.E+04
1.E+05
0
50
100
150
200
250
300
350
400
450
500
550
600
Gas
Production
Rate,
MSCFD
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
Surface
Pressure,
psig
Gas Flowrate
Wellbore Pressure
Flow
up
Annulus
Flow up Casing
Flow up Tubing

Well Testing —
PETE 613
(2005A)
Slide — 21
 Data Artifacts Example 5: South Texas Gas Well (US)
 Gas well with anomalous pressure "jump" — packer leak?
 No "reservoir" mechanism (other than injection) could produce feature.
a.Semilog Plot: (Dt format) Pressure versus shut-
in time (South Texas Gas Well (US)) — Packer
leak (most likely cause).
b.Log-log Plot: (Dt format) Pressure drop and
pressure drop derivative versus shut-in time
time (South Texas Gas Well (US)) — Packer
leak (most likely cause).
Sanger Gas Well Case (South Texas (US))
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03
Dt , hr
p
wf
,
psia
Pressure
Sanger Gas Well Case (South Texas (US))
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03
Dt , hr
D
p
and
D
p'
,
psi
Pressure Drop

Well Testing —
PETE 613
(2005A)
Slide — 22
 Data Artifacts Example 6: Mid-Continent Gas Well (US)
 Changing wellbore storage and condensate banking (very high skin).
 Interpretation depends on understanding of reservoir and fluids.
Dunn Prefracture Pressure Buildup (Condensate Banking)
(Mid-Continent (US))
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02
Shut-In Pseudotime, Dt a , hr
Pseudopressure
Drop,
D
p
p
and
D
p
p
'
,
psi
Pressure Drop

Well Testing —
PETE 613
(2005A)
Slide — 23
Well Test Analysis — Basic Plots
Well Test Analysis — Basic Plots

Well Testing —
PETE 613
(2005A)
Slide — 24
Well Test Analysis: Basic Plots (Lee Text Example)
a. Log-log "preliminary analysis"
plot — wellbore storage and
radial flow (Cs, k).
b. Cartesian "early-time" plot —
used to analyze wellbore
storage (p0, Cs).
d. Semilog "middle-time" plot —
used to analyze radial flow
behavior (k, s).
e. Horner "middle-time" plot —
used to analyze radial flow
behavior (k, s, p*).
f. Log-log "summary" plot —
summary of all analysis (Cs, k,
s, A, etc).
c. Cartesian "Arps" plot — used
to estimate average reservoir
pressure.

Well Testing —
PETE 613
(2005A)
Slide — 25
 Basic Plots: "Preliminary" Log-Log Plot
 Pressure drop function does not give much resolution.
 Pressure drop derivative function shows wellbore storage/radial flow.
Basic Plots: "Preliminary" Log-log Plot

Well Testing —
PETE 613
(2005A)
Slide — 26
 Basic Plots: Early Cartesian Plot
 Used to estimate wellbore storage coefficient (slope of trend).
 Pressure at start of the test estimated from extrapolation.
Basic Plots: Early Cartesian Plot

Well Testing —
PETE 613
(2005A)
Slide — 27
 Basic Plots: Late Cartesian Plot (Pressure Buildup)
 NOT a universally valid plot (ONLY valid for very late times).
 Average reservoir pressure estimated from extrapolation.
Basic Plots: Late Cartesian Plot (PBU)

Well Testing —
PETE 613
(2005A)
Slide — 28
 Basic Plots: Semilog Plot (Miller-Dyes-Hutchinson)
 NOT corrected for rate history.
 Can be difficult to interpret (semilog straight line needs orientation).
Basic Plots: Semilog Plot (MDH)

Well Testing —
PETE 613
(2005A)
Slide — 29
 Basic Plots: Horner Semilog Plot
 CORRECTED for rate history.
 Used to estimate permeability, skin factor, average reservoir pressure.
Basic Plots: Horner Semilog Plot

Well Testing —
PETE 613
(2005A)
Slide — 30
 Basic Plots: "Summary" Log-Log Plot
 Used to show simulated reservoir response (based on analysis).
 Multiple data functions used to orient analysis/interpretation.
Basic Plots: "Summary" Log-log Plot

Well Testing —
PETE 613
(2005A)
Slide — 31
Given data — Lee text (1st edition),
Example 2.2.
Module 4: Well Test Analysis — Work Relations
Working relations — Lee text (1st
edition), Example 2.2).

Well Testing —
PETE 613
(2005A)
Slide — 32
T.A. Blasingame, Texas A&M U.
Department of Petroleum Engineering
College Station, TX 77843-3116
+1.979.845.2292 — t-blasingame@tamu.edu
Petroleum Engineering 613
Natural Gas Engineering
Lecture 08:
Well Testing —
(End of Lecture)

P613_05A_Lec_08_WT_Historical_Perspectives_(050408).ppt

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