Post on 12-Nov-2014
description
2009
WELL TESTING COURSE
Francesca VERGA – POLITECNICO DI TORINO
Introduction to well testing
types
objectives
equipment
Recap of flow equations for an infinite acting porous medium
Flow equations for closed reservoirs
Tests description and interpretion for oil and gas wells
Drawdown periods
Buildup periods (Horner plot)
Recap of well productivity and deliverability
Introduction to the pressure derivative method
Pressure derivative analysis: interpretation models for early, middle and late time
Excercises on well tests interpretation (Interpret by Paradigm/Saphir by Kappa)
Tutorials
Real cases
Numerical well testing (Saphir by Kappa)
Basics on unconventional well testing
Decline curves
Tutorials (Topaze by Kappa)
Course Program
S(well + reservoir)
INPUT
Production/Injection flow rates Bottom Hole Pressure
Well Testing
The principle of Well Testing is… to analyze the output signal of a wellon which a known input signal has been applied.
OUTPUT
Rate and Bottom Hole Pressure vs Time
Standard Well Testing
Main Targets of Well Testing
Reservoir description:
define nature of produced fluids;
estimate (initial) static pressure pi (ps )
estimate permeability (horizontal and vertical k);
analyse reservoir heterogeneities (natural fractures, layering, change ofcharacteristics);
evaluate reservoir size (drainage area);
Well description:
define production potential (Productivity Index, well deliverability)
well damage (skin factor S);
design remedial jobs (i.e.: acid treatment, gravel pack, fracturing);
verify completion efficiency;
design surface production facilities;
optimize drilling technique by choosing the best mud in order to minimize formationdamage (for new infilling wells)
Types of Well Test
Mini DST – MDT (Modular Dynamic Tester)
Standard Production Test
Limit Test
Interference Test
areal interference
vertical interference
Mini DST – MDT
Well Test Type
WELL: exploration
COMPLETION: Open/Cased hole DST string
DURATION: very short (few hours)
OBJECTIVES: formation pressure, fluid samples, mobility
MDT – Mini DST
DESCRIPTIONIt is possible to test the fluids in an open hole or cased hole(perforations h=30 cm) by setting packers above and belowthe interval of interest. This way a well interval is isolated (1m) and the formation fluids are allowed to flow into the wellby using a downhole pump. The tools can be run in hole bywireline or drill pipes. The formation pressure and fluidmobility (thus permeability) can be measured and theformation fluids sampled.
Courtesy of Schlumberger
Production test with DST string
Well Test Type
WELL: exploration
COMPLETION: DST string + TCP
DURATION: variable (2-7 days)
OBJECTIVES: formation pressure, fluid samples, permeability, well damage, ……
DESCRIPTIONA drill stem test is a test which uses special tools mounted onthe end of the drill string, comprising a downhole valve,pressure gauges, and fluid samplers.The well can be perforated in underbalance conditions,avoiding mud invasion. The well is opened to flow by a valveat the base of the test tool, and reservoir fluid flows up thedrill string.A common test sequence is to produce, shut in, produceagain and shut in again. DST can be quite short, since thepositive closure of the downhole valve avoids wellborestorage effects.
Courtesy of Schlumberger
WELL: production
COMPLETION: final
DURATION: variable (2-7 days)
OBJECTIVES: formation pressure, permeability, well damage, reservoirboundaries, well deliverability
Standard production test
Well Test Type
BuildUpDrawDown
1
Standard P.T.
Well Test Type
BUDD
DRAWDOWN PERIODA well that is static, stable and shut-in is opened to flowand the downhole pressure measured as the pressuredeclines. For the purposes of traditional analysis, theflow rate is supposed to be constant. Many of thetraditional analysis techniques are derived using thedrawdown test as a basis. However, in practice, adrawdown test may be rather difficult to achieve underthe intended conditions. In particular:(a) it is difficult to make the well flow at constant rate,even after it has (more-or-less) stabilized;(b) the well condition may not initially be either static orstable, especially if it was recently drilled or had beenflowed previously.
BUILDUP PERIODA well which is already flowing (ideally at constant rate)is shut in, and the downhole pressure measured as thepressure builds up. Analysis of a buildup test oftenrequires only slight modification of the techniques usedto interpret drawdown test. The practical advantage of abuildup test is that the constant flow rate condition isachieved (since the flow rate is zero).Buildup tests also have disadvantages:(a) It may be difficult to achieve the constant rateproduction prior to the shut in.(b) Production is lost while the well is shut in.
2
1
2
Running gaugein hole
Real Well TestDrawdown Period
Buildup Period
Pulling out gauge
Limit Test
Well Test Type
WELL: exploration/appraisal
COMPLETION: provisional or final
DURATION: variable (days-weeks)
OBJECTIVES: investigate reservoir boundaries, estimate reservoir size
Areal Interference
Well Test Type
FIRST WELL: active (producing) well
SECOND WELL: observation/spy well(s) (shut-in)
COMPLETION: final
DURATION: variable (days-weeks)
OBJECTIVES: recognise reservoir continuity between wells
DESCRIPTIONInterference tests require long-duration production or injection ratechanges in the active well. Theassociated pressure disturbancerecorded in the observation well(s)yields information regarding thedegree of hydraulic communicationwithin the interwell region.
Observation well
Q
tp
tp
t
Areal Interference
Well Test Type
producing well
observation well
observation well
Dt = time lag
Vertical Interference
Well Test Type
FIRST POOL: active (producing) pool
SECOND POOL: observer pool (shut-in)
COMPLETION: final – dual completion
DURATION: variable (hours-days)
OBJECTIVES: recognise comunication between the pools or at the well
DESCRIPTIONThese tests are conducted todetermine crossflow between twolayers separated by a low-permeability layer or to detectleaks behind the casing due topoor cementation or through thepaker.
Courtesy of Schlumberger
Well Testing
Field Data
Field Data
SurfaceData
BottomData
ProducedFluids
WellheadPressure
WellheadTemperature
T p
Flow Rates
Field FluidProperties
Separators
DWT
SRO MemoryGauge
Well Testing Equipment
Surface Equipment:
Downhole Gauges:
electronic (Memory , SRO) gauges
bi – three phase separator
choke manifold
Dead Weight Tester (DWT)
heater
piping/burners
Courtesy of Schlumberger
Bottom Pressure / Temperature :
Always check the coherence of the instrumental response in terms of both pressureand temperature (option “Validation Gauges“)
Always check gauge pressure against the corresponding wellhead pressures (DeadWeight Tester) taken as a reference.
Flow Rate:
The flow rates selected in the Rate History must be homogeneous with thecorresponding bottomhole pressures ( option “Validation Rates“)
Field Data Quality Control
Well Testing
Downhole Gauge Specifications
Mechanical Gauges (Amerada)…
…are at home to enjoy their pension!
Downhole Gauge Specifications
Electronic Gauges (Memory / SRO)
Max W.P.: 20 kpsia
Max W.T.: 185 – 190 °C
Resolution: 0.2 psia
Accuracy: 10 psia
Drift: 3 psi/1° day or 1.5 psi/week
Strain Gauge Quartz Gauge
Resolution: 0.01 psia
Accuracy: 2 psia
Drift: negligible
Memory-The gauge is placed downhole, there is no connection to the surface during the
test. Batteries provide energy to make the tool work. Data are recorded andstored during the test. The gauge is recovered when the test is over. Low cost but
no possibility to monitor the test.
Surface Read Out- Connection to the surface and data transferring is maintained during
the test through an electric wireline cable. High cost (surface wireline unit andpersonnel) but possibility to intervene changing the test sequence if needed.
Downhole Gauge Specifications
Courtesy of Schlumberger
Courtesy of Schlumberger
Microsystems Technology