basic welltesting for dst supv

WELL TESTING(Pressure Transient Test)(Pressure Transient Test)

RESERVOIR ENGINEERING DEPT.

PERTAMINA EP REGION JAWA

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TYPICAL USE OF WELL TESTING

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BASIC REASON FOR TESTING A WELL

1. To obtain a physical sample of the fluids produced from thereservoir;reservoir;

2. To obtain a measured flow rate indicative of the productivityof the formation;

3. To obtain pressure data for the calculation of reservoirt d f th iti f t l i d dparameters and for the recognition of natural or induced

anomalies around the borehole.

WELLTEST PLAN PACKAGE

1. STATEMENT OF TEST OBJECTIVESSpecify why the well is being tested and what is thep y y gexpectation to achieves from the test data.

2. PROPOSED TEST DESIGNSpecificy type of test to be run; flow rates, duration, periods;h t i i d d ti th ti d i thshut-in periods and times; the contingency procedures in the

event that the test has to be altered in the field because ofmechanical problems.

3 MECHANICAL DESIGN3. MECHANICAL DESIGNSpecify required surface and subsurface mechanical system.Included Test interval and landing locations, well completiondiagram, surface test facilities (meter system, and the way in

hi h th d d fl id t b di d)which the produced fluids are to be disposed) .4. INSTRUMENTATION

Specify pressure and temperature measuring and recordingdevices (with backup as needed) as well as the wire linedevices (with backup as needed) as well as the wire linerecommendations.

5. SAMPLINGSpecify sampling fluids: how many samples to take, when,

Objektif ‘Well Testing’ (Press. Transient Test):

Karakterisasi ReservoirTekanan Dasar Sumur / ReservoirTekanan Dasar Sumur / ReservoirPermeabilitas ReservoirFlow EffisiensiDrajat Kerusakan formasi (DR S)Drajat Kerusakan formasi (DR, S)Type / System Porositas (single / Double i.e. Storage & Capacity )Model Daerah Reservoir Model Daerah Reservoir (Luas & Bentuk daerah Pengurasan )Reservoir boundary’ (type, jarak & arah)

2 P t i R i2. Potensi Reservoir- Produktivitas / Injektivitas (PI / II)- HC inplace (Well base OOIP or OGIP)

HC Deliverability (AOFP etc)Prinsip kerja : Mencatat respon reservoir thd gangguan yang diberikan melalui sumur

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- HC Deliverability (AOFP etc)

Type ‘Well Testing’(Ref. Teknis Operasional)( p )

1. Konventional Testing- Press. Build-Up test

P D d T t - Press. Drawdown Test

2. Multi Rate Test T R t t t- Two Rate test

- Four Point test (Gas)- (Modified) Isochronal Test

3. Multiple Well Testing- Interfference Test- Pulse Test

4. Drill StemTest (DST)

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PERALATAN UJI1. Peralatan Atas / Permukaan- Wireline Unit

Lubricator Group- Lubricator Group- BOP Group- Test Unit

2. Peralatan bawah Permukaan- Bottomhole Press. Gauge

B tt h l T G- Bottomhole Temp. Gauge- Bottomhole fluid sampler

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DOWNHOLE PRESS. - TEMP. GAUGE1. MECHANICAL

Amerada P T Bomb type- Amerada P-T Bomb type

2. Electronic Memmory Gauge (EMR) - Strain /Capacitance Gauge- Quartz gauge- Quartz gauge

3. Surface Press-Temp Read Out (SPRO)- Standard Quartz gauge- Crystal Quartz gauge- Crystal Quartz gauge

(GEOSERVICES GAUGE)

These self-contained

In most of these gauges

Mechanical gauge Electrical memory gauge

contained gauges have three essential components: a pressure-

these gauges a transducer converts pressure into an electricalpressure

sensing device, a pressure-time recorder, and a mechanical

an electrical signal that is recorded downhole. Pressure datamechanical

clock. The pressure element of a mechanical

Pressure data are available only after a gauge has been retrievedmechanical

gauge is normally a multiple-coil Bourdon-tube

been retrieved to surface.

Bourdon tube type

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Sistim Monitoring Perekaman Data

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Press Transient Test Analysis MethodWell Testing / Pressure Transient Analysis (Methode)Press. Transient Test Analysis Method

1. Horner PlotSemilog

Pressure Transient Analysis (Methode)

- Semilog - (Tp + ∆t) / ∆t

2. Pressure Derivative (Type Curve match)- Log-log

dP/dt - dP/dt

3. Simulasi

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Integrated Linier & Log-Log Analysis

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Work Flow ‘Simulation method’ P T i t T t A l iPress. Transient Test Analysis

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‘Typical Generic Model’ Press. Transient Test Analysis

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‘Geological Model illustration’ Press. Transient Test Analysis

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Deliveriverability Test analysis

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Inflow Performance Relationship

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WELL TESTING ANALYSIS HORNER’S PLOTWELL TESTING ANALYSIS ~ HORNER’S PLOT

In a Well testing, the flow period is about the same duration as the shut-in period, and so pressure buildup data must be analyzed with the Horner plot, pws

l [(t + dt)/dt]versus log[(tp + dt)/dt]

If the shut-in period is long enough, and if wellbore storage is not dominant, a Horner plot of buildup should have a straight-line section with slope —m, where permeability calculated as :where permeability calculated as :

Or transmissibility

Th ki f t i ti t d f th f ll i i i l ti f diThe skin factor is estimated from the following empirical equation for a dimen-sionless value s denoting "skin factor."

The term log[(tp+1)/tp] is normally neglected when tp» 1 or when the skin f t i hi hfactor is high.

damage ratio (DR) which compares flow rate observed on a DST (q0) to thedamage ratio (DR), which compares flow rate observed on a DST (q0) to the theoretical flow rate without damage (qt).

An equation for calculation of DR based on the skin factor is related to the equation

DR substantially greater than 1.0 indicates damage. Eq. can be simplified byassigning average values to formation parameters. This produced an equationfor estimated damage ratio (EDR):

An equation for calculation of DR based on the skin factor relation is reported as

where pressure drop across the skin is computed as

Initial or average pressure p is estimated by extrapolating the Hornerstraight line to infinite shut-in time (tp + dt)/dt = 1 Both the first buildup plotstraight line to infinite shut-in time (tp + dt)/dt = 1. Both the first buildup plotand the second buildup plot extrapolate to the same static or initialpressure.

For practical purpose, the radius of investigation during DST is equivalent to the radius of drainage given by :

The following equation from Van Poollen may be used to estimate the radius of investigation of a particular DST in an infinite radial flow system:flow system:

A well testing was conducted on an oil well The following information was

EXAMPLE : ANALYSIS DST USING HORNER PLOT

A well testing was conducted on an oil well. The following information was reported by the DST Company. The pressure buildup data are given in tables.

Determine the following:

• Check validity and consistency of ‘WT’ data• Formation permeability, k

Ski f t d d d t ki• Skin factor and pressure drop due to skin• Initial reservoir pressure• Flow efficiency• Damage ratio

A t llb di• Apparent wellbore radius• Radius of investigation

Test type = open hole

DST DATA :Test type = open holeTotal well depth = 6550 fth = 17ft; rw = 0.33 ft; Poro = 16%; Viso = 1.O cPAPI = 36.87 API; ct = 8.0 x 10'6PSi^-1; Bo = 1.215rb/stbVu = 0.0197 bbl/ft and p = 52.78 lb/ft3M d d it 7 51b/ lMud density — 7.51b/galGauge depth = 6549 ftHole size = 7.88 in; Pipe length = 240 ft;Collar length = 240 ft; Diameter of collar = 4.5 in.Reservoir pressure @ gauge depth = 2560 psiPressure at the end of first flow = 371 psiFirst flow period = 6minFirst shut-in period = 30 minSecond flow period = 60 minSecond shut-in period = 120 minInitial shut-in pressure = 2660 psiFinal shut-in pressure = 1005 psiPressure at the end of second flow period = 643 psiFinal shut-in pressure = 1969 psi

SOLUTIONSOLUTION

To analyze pressure buildup test, follow these steps:

• Identify the MTR and find the slope of MTR p1hr and p* of the Horner plot• Identify the MTR and find the slope of MTR, p1hr, and p of the Horner plotof the second shut-in period.

• Prepare Horner plot of the first and second shut-in buildup pressures on thesame graph.

CHECK VALIDITY AND CONSISTENCY OF REPORTED DST DATA.

Hydrostatic pressure = 6549 x 0.390 = 2554 psiThe reported initial reservoir pressure at gauge depth is 2560 psi, which is ingood agreement with pi = p* = 2554 psi (extrapolated pressure from the firstshut-in straight line). The mud weight should be :

Thus the reported mud weight is correct

L l d t l tLog-log data plot.

S il H l t f d tSemilog Horner plot for data.

From the extrapolated MTR, line of the second shut-in to (tp + dt)/dt = 1

pi = p* = 2550 psi.

DST (DRILL STEM TEST) ~ UKLDST (DRILL STEM TEST) ~ UKL

Method of temporary completing a well to determine theproductive characteristics of a specific zone by providedp p y pprimarily indication of formation fluid content and data to helpevaluate productivity of the zone, completion practices, estimateformation properties and well bore damage.

ESTIMATED RESERVOIR CHARACTERISTICS FROM DST ANALYSIS

DST Tools

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DST Tools Evolution

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DST STRIP CHARTS S C

Good DST data should :Good DST data should :

RUNNING DSTRUNNING DST

DST Typical Chart Interpretation

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DST Typical Chart Interpretation

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a) Packer failed and could not beset

DST Strip Chart Identification

set.b) Runaway clock. Clock spring

released.c) Tool failed to close. No buildup

is obtained.d) Tool failed to Open.e) Clock stopped at shut-in drill-

stem normalstem normal.f) Effect of large superpressure.

Pressure buildup during flowand buildup period,

g) No formation permeabilitysmall amount of mud may berecovered,

h) Low-permeability formationh) Low permeability formation.

RECOMMENDATION FOR FLOW AND SHUT-IN TIME FOR DST

no ACTIVITY DURATIONRemove any excess pressure which

h lt d f tti th1 1 t Fl 5 15 t

GOALKnoval Oilwell Testing

2 1st Buildup 30-60 mnt

3 2 d Fl 60 t

may have resulted from setting the packer.

Get reliable initial reservoir pressure.

Evaluate formation characteristic for

1 1st Flow 5-15 mnt

3 2nd Flow 60 mnt

30 mnt to several hours.2nd Buildup4

some distance from the well.

Calculate transmissibility and other reservoir characteristics.

COMPARING EKSTRAPOLATED 2ND BUILDUP PRESSURE WITH INITIAL BUILDUP PRESSURE INDICATE THE SIZE OF THE RESERVOIR.

CHECKING VALIDITY AND CONSISTENCY FOR DST REPORTING DATA

1. Calculate the hydrostatic mud pressure and check agains recorded initial and final hydrostatic mud pressure.Mud Gradient (psi/ft) = 0.433 / 8.33 x ppg mud weight.Hydraulic Pressure (psi) = Well depth (ft) x Mud Gradient.Mud Weight = Hydrostatic Press x Depth x (8.33/0.433)

2. Check with reported mud weight.3. Check accuracy of Pi (estimated from extrapolated MTR Line of

the second shut-in to (tp+dt)/dt = 1.

ESTIMATION OF AVERAGE FLOW RATE (DST)

1. CALCULATE MUD GRADIENT PSIFTMGR = MUD WEIGHT (PPG) * 0.433/8.333

2. ESTIMATED FEET OF MUDFOM = INITIAL SHUT-IN PRESSURE AT THE END OF 1ST FLOW / MGR

1. CALCULATE MUD GRADIENT PSIFTMGR = MUD WEIGHT (PPG) * 0.433/8.333

2. ESTIMATED FEET OF MUDFOM = INITIAL SHUT-IN PRESSURE AT THE END OF 1ST FLOW / MGRFOM INITIAL SHUT IN PRESSURE AT THE END OF 1 FLOW / MGR

3. CALCULATE CAPACITY OF DRILL COLLAR.CDR = Cs * RHO /144

WHERE Cs WELLBORE STORAGE = 25.65* Awb(ft^2) /Rho (lb /ft3)Awb = Phi * Rp^2 Rp = ID Drill Collar

FOM INITIAL SHUT IN PRESSURE AT THE END OF 1 FLOW / MGR3. CALCULATE CAPACITY OF DRILL COLLAR.

CDR = Cs * RHO /144

WHERE Cs WELLBORE STORAGE = 25.65* Awb(ft^2) /Rho (lb /ft3)Awb = Phi * Rp^2 Rp = ID Drill CollarAwb = Phi * Rp^2 …. Rp = ID Drill Collar.Rho = fluid density (lb/ft 3̂) = 141.5 /(131.5 + SG)

4. ESTIMATE FLUID PRODUCED FROM FORMATION FPFFPR = CDR * FOM …. (FT)

Awb = Phi * Rp^2 …. Rp = ID Drill Collar.Rho = fluid density (lb/ft 3̂) = 141.5 /(131.5 + SG)

4. ESTIMATE FLUID PRODUCED FROM FORMATION FPFFPR = CDR * FOM …. (FT)

5. CALCULATE INITIAL FLOW RATE QI = FPF / (FLOWTIME * 1440 MIN/DAY) …..STBPD

5. CALCULATE INITIAL FLOW RATE QI = FPF / (FLOWTIME * 1440 MIN/DAY) …..STBPD

Terimakasih

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