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PETE 613(2005A)
Slide — 1Well Testing —Historical Perspectives
T.A. Blasingame, Texas A&M U.Department of Petroleum Engineering
Texas A&M UniversityCollege Station, TX 77843-3116
+1.979.845.2292 — [email protected]
Petroleum Engineering 613Natural Gas Engineering
Texas A&M University
Lecture 08:Well Testing —
Historical Perspectives
PETE 613(2005A)
Slide — 2Well Testing —Historical Perspectives
Well Testing — Historical PerspectivesOrigin of the "Deliverability" (or Backpressure) RelationEmpirical.Used to assess "open flow" potential of gas wells.Does not provide a "time-dependent" behavior.
Multi-Rate TestingHistorically, 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 AnalysisExpected Results: Pressure Transient Analysis (PTA).Example Data Sets: PTA and Production data.Basic Plots: Lee Text Example 2.2 (Pressure Buildup).
PETE 613(2005A)
Slide — 3Well Testing —Historical Perspectives
Well Testing — Historical PerspectivesOrigin of the "Deliverability"(or Backpressure) Relation
Origin of the "Deliverability" Relation
PETE 613(2005A)
Slide — 4Well Testing —Historical Perspectives
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 toProduction Practices — Rawlins andSchellhardt (USBM Monograph, 1935).
History of the "Deliverability" Equation
nwfppCgq )( 22
PETE 613(2005A)
Slide — 5Well Testing —Historical Perspectives
Well Testing — Historical PerspectivesMulti-Rate Testing
Multi-Rate Testing
PETE 613(2005A)
Slide — 6Well Testing —Historical Perspectives
Deliverability Testing: Basics
a. "Standard" 4-point test deliverability test — notethat 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 thateach "buildup" is not required to achieve pi.
d. Governing equations for "deliverability" testanalysis/interpretation.
PETE 613(2005A)
Slide — 7Well Testing —Historical Perspectives
Deliverability Testing: Orientation
a. Basic "pressure-squared" relationthat is presumed to describe gasflow — analogous form can bederived from steady-state flow theory(Darcy's law).
b.Traditional "deliverability" plot —probably derived from empiricalplotting of data.
PETE 613(2005A)
Slide — 8Well Testing —Historical Perspectives
Deliverability Testing: Orientation
a."Rate-squared" (or velocity-squared) formulation — analogousform can be derived from steady-state flow theory (ForchheimerEq.).
b. Modified "deliverability" plot —note that bqsc
2 must be known (...need alternative approach).
PETE 613(2005A)
Slide — 9Well Testing —Historical Perspectives
Well Testing — Historical PerspectivesExpected Results:
Pressure Transient Analysis (PTA)Production Analysis (PA)
Origin of the "Deliverability" Relation
PETE 613(2005A)
Slide — 10Well Testing —Historical Perspectives
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 flowregime is a characteristic behavior derived from an analytical solution —e.g., the constant pressure derivative function for infinite-acting radialflow (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 toperform simultaneous analysis/modelling procedures. Provides estimatesof dynamic formation properties: (i.e., model parameters)Radial Flow: k, S, CDFractured Wells: k, xf, FCD, CfDHorizontal Wells: kr, kr/kv, hwell, (effective length) zw (position), ChDDual porosity reservoir properties: ,
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
PETE 613(2005A)
Slide — 11Well Testing —Historical Perspectives
Expected Results of Production Analysis (PA):— "Conventional" decline curve analysis: (Arps, etc.) — empirical relations
used to provide estimates of recovery and forecasts of futureperformance.
— "Model-based" analyses: Using analytical/numerical reservoir models toperform simultaneous analysis/modelling procedures. Providesestimates of dynamic formation properties (k, S, xf, dual porosityproperties, 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
PETE 613(2005A)
Slide — 12Well Testing —Historical Perspectives
Well Testing — Historical PerspectivesReservoir Performance Analysis:
PTA and PA Data Quality and Data Artifacts
PTA and PA Data Quality and Data Artifacts
PETE 613(2005A)
Slide — 13Well Testing —Historical Perspectives
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
Pro
du
ctio
nR
ate,
MS
CF
D
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Su
rfac
eP
ress
ure
,psi
g
Gas FlowrateWellbore Pressure
Production Data: Example 1
PETE 613(2005A)
Slide — 14Well Testing —Historical Perspectives
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
Producing Time, days
Gas
Pro
du
ctio
nR
ate,
MS
CF
D
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Cal
cula
ted
BH
P,p
sia
Gas FlowrateWellbore Pressure
Production Data: Example 2
PETE 613(2005A)
Slide — 15Well Testing —Historical Perspectives
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: (t format) Pressure drop andpressure drop derivative versus shut-in time(Bourdet (SPE 12777)).
b.Rate History: (te format) Pressure drop andpressure drop derivative versus Agarwalsuperposition 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
Dp
and
Dp
',p
si
Pressure DropPressure 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+02Dt , hr
Dp
and
Dp
',p
si
Pressure DropPressure Drop Derivative
Pressure Transient Data: Example 1
PETE 613(2005A)
Slide — 16Well Testing —Historical Perspectives
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+03Dt , hr
Dp
and
Dp
',p
si
Pressure DropPressure Drop Derivative (L=0.2)Pressure Drop Derivative (L=0.3)Pressure Drop Derivative (L=0.4)Simulated Pressure DropSimulated Pressure Drop Derivative
PETE 613(2005A)
Slide — 17Well Testing —Historical Perspectives
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
1000
0
1100
0
Producing Time, days
Oil
Pro
du
ctio
nR
ate,
ST
BD
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Est
imat
edB
HF
PP
ress
ure
,psi
a
Oil FlowrateWellbore Pressure
Pro
rate
dP
rod
uct
ion
Init
ial
Dep
leti
on
(no
pre
ssu
resu
pp
ort
)
Rec
om
ple
tio
n
Aci
dS
tim
ula
tio
n
Co
nve
rsio
nto
Jet
Pu
mp
p wf assumed constant
Data Artifacts: Example 1
PETE 613(2005A)
Slide — 18Well Testing —Historical Perspectives
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
Producing Time, days
Oil
Pro
du
ctio
nR
ate,
ST
BD
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
Est
.BH
FP
ress
ure
,psi
a
Oil FlowrateWellbore Pressure
Pu
mp
Ch
ang
e
p wf not synchronouswith rate profile
Data Artifacts: Example 2
PETE 613(2005A)
Slide — 19Well Testing —Historical Perspectives
Data Artifacts Example 3: Canada Gas Wellpwf 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
Producing Time, days
Gas
Pro
du
ctio
nR
ate,
MS
CF
D
0
500
1000
1500
2000
2500
3000
3500
Cal
c.B
HF
Pre
ssu
re,p
sia
Gas FlowrateWellbore Pressure
qo
and
pw
f
incr
easi
ng
p wf variations notsynchronized with q g
Data Artifacts: Example 3
PETE 613(2005A)
Slide — 20Well Testing —Historical Perspectives
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
Producing Time, days
Gas
Pro
du
ctio
nR
ate,
MS
CF
D
05001000150020002500300035004000450050005500600065007000
Su
rfac
eP
ress
ure
,psi
g
Gas FlowrateWellbore Pressure
Flo
wu
pA
nn
ulu
s
Flow up Casing
Flow up Tubing
Data Artifacts: Example 4
PETE 613(2005A)
Slide — 21Well Testing —Historical Perspectives
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: (t format) Pressure versus shut-in time (South Texas Gas Well (US)) — Packerleak (most likely cause).
b.Log-log Plot: (t format) Pressure drop andpressure drop derivative versus shut-in timetime (South Texas Gas Well (US)) — Packerleak (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
pw
f,p
sia
PressureSanger 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
Dp
and
Dp
',p
si
Pressure DropPressure Drop Derivative
Data Artifacts: Example 5
PETE 613(2005A)
Slide — 22Well Testing —Historical Perspectives
Data Artifacts: Example 6
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
Pse
ud
op
ress
ure
Dro
p, D
pp
and
Dp
p',
psi
Pressure DropPressure Drop Derivative
PETE 613(2005A)
Slide — 23Well Testing —Historical Perspectives
Well Testing — Historical PerspectivesWell Test Analysis — Basic Plots
Well Test Analysis — Basic Plots
PETE 613(2005A)
Slide — 24Well Testing —Historical Perspectives
Well Test Analysis: Basic Plots (Lee Text Example)
a. Log-log "preliminary analysis"plot — wellbore storage andradial flow (Cs, k).
b. Cartesian "early-time" plot —used to analyze wellborestorage (p0, Cs).
d. Semilog "middle-time" plot —used to analyze radial flowbehavior (k, s).
e. Horner "middle-time" plot —used to analyze radial flowbehavior (k, s, p*).
f. Log-log "summary" plot —summary of all analysis (Cs, k,s, A, etc).
c. Cartesian "Arps" plot — usedto estimate average reservoirpressure.
PETE 613(2005A)
Slide — 25Well Testing —Historical Perspectives
Basic Plots: "Preliminary" Log-Log PlotPressure drop function does not give much resolution.Pressure drop derivative function shows wellbore storage/radial flow.
Basic Plots: "Preliminary" Log-log Plot
PETE 613(2005A)
Slide — 26Well Testing —Historical Perspectives
Basic Plots: Early Cartesian PlotUsed to estimate wellbore storage coefficient (slope of trend).Pressure at start of the test estimated from extrapolation.
Basic Plots: Early Cartesian Plot
PETE 613(2005A)
Slide — 27Well Testing —Historical Perspectives
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)
PETE 613(2005A)
Slide — 28Well Testing —Historical Perspectives
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)
PETE 613(2005A)
Slide — 29Well Testing —Historical Perspectives
Basic Plots: Horner Semilog PlotCORRECTED for rate history.Used to estimate permeability, skin factor, average reservoir pressure.
Basic Plots: Horner Semilog Plot
PETE 613(2005A)
Slide — 30Well Testing —Historical Perspectives
Basic Plots: "Summary" Log-Log PlotUsed to show simulated reservoir response (based on analysis).Multiple data functions used to orient analysis/interpretation.
Basic Plots: "Summary" Log-log Plot
PETE 613(2005A)
Slide — 31Well Testing —Historical Perspectives
Given data — Lee text (1st edition),Example 2.2.
Module 4: Well Test Analysis — Work Relations
Working relations — Lee text (1stedition), Example 2.2).
PETE 613(2005A)
Slide — 32Well Testing —Historical Perspectives
T.A. Blasingame, Texas A&M U.Department of Petroleum Engineering
Texas A&M UniversityCollege Station, TX 77843-3116
+1.979.845.2292 — [email protected]
Petroleum Engineering 613Natural Gas Engineering
Texas A&M University
Lecture 08:Well Testing —
Historical Perspectives(End of Lecture)