Post on 02-Nov-2015
description
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
Well testing part
Books (available @ DITAG library):
Horne R., 2001. Computed aided well test analysis
Bourdet D., 2002. Well test analysis: the use of advanced interpretation models. Elsevier.
Papers (SPE One-Petro library available from DITAG computers)
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 well on 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 of characteristics);
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 formation damage (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 (minutes)
OBJECTIVES: formation pressure, fluid samples, mobility
MDT Mini DST
DESCRIPTION It is possible to test the fluids in an open hole or cased hole (perforations h=30 cm) by setting packers above and below the interval of interest. This way a well interval is isolated and the formation fluids are allowed to flow into the well by using a downhole pump. The tools can be run in hole by wireline or drill pipes. The formation pressure and fluid mobility (thus permeability) can be measured and the formation fluids sampled.
Courtesy of Schlumberger
Production test with DST string
Well Test Type
WELL: exploration
COMPLETION: DST string + TCP
DURATION: variable (hours)
OBJECTIVES: formation pressure, fluid samples, permeability, well damage,
DESCRIPTION A drill stem test is a test which uses special tools mounted on the 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 valve at the base of the testing tool, and reservoir fluid flows up the drill string. A common test sequence is to produce, shut in, produce again and shut in again. DST can be quite short, since the positive closure of the downhole valve avoids wellbore storage effects.
Courtesy of Schlumberger
WELL: production
COMPLETION: final
DURATION: variable (2-7 days)
OBJECTIVES: formation pressure, permeability, well damage, reservoir boundaries, well deliverability
Standard production test
Well Test Type
BuildUp DrawDown
1
Standard P.T.
Well Test Type
BU DD
DRAWDOWN PERIOD A well that is static, stable and shut-in is opened to flow and the downhole pressure measured as the pressure declines. For the purposes of traditional analysis, the flow rate is supposed to be constant. Many of the traditional analysis techniques are derived using the drawdown test as a basis. However, in practice, a drawdown test may be rather difficult to achieve under the 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 or stable, especially if it was recently drilled or had been flowed previously. BUILDUP PERIOD A well which is already flowing (ideally at constant rate) is shut in, and the downhole pressure measured as the pressure builds up. Analysis of a buildup test often requires only slight modification of the techniques used to interpret drawdown test. The practical advantage of a buildup test is that the constant flow rate condition is achieved (since the flow rate is zero). Buildup tests also have disadvantages, the main being that production is lost while the well is shut in.
2
1
2
Running gauge in hole
Real Well Test Drawdown 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
DESCRIPTION Interference tests require long-duration production or injection rate changes in the active well. The associated pressure disturbance recorded in the observation well(s) yields information regarding the degree of hydraulic communication within the interwell region.
Observation well
Q
t p
t
p
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
DESCRIPTION These tests are conducted to determine crossflow between two layers separated by a low-permeability layer or to detect leaks behind the casing due to poor cementation or through the paker.
Courtesy of Schlumberger
Well Testing
Field Data
Field Data
Surface Data
Bottom Data
Produced Fluids
Wellhead Pressure
Wellhead Temperature
T p
Flow Rates
Field Fluid Properties
Separators
DWT
SRO Memory Gauge
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 pressure and temperature (option Validation Gauges)
Always check gauge pressure against the corresponding wellhead pressures (Dead Weight Tester) taken as a reference.
Flow Rate:
The flow rates selected in the Rate History must be homogeneous with the corresponding 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 and stored 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 and personnel) but possibility to intervene changing the test sequence if needed.
Courtesy of Schlumberger
Microsystems Technology