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The Value of Well Testing and Pressure Monitoring in Injection Site Characterization
A. Shchipanov, L. Kollbotn, R. BerenblyumInternational Research Institute of Stavanger (IRIS)Contact: [email protected]
CO2GeoNet Open Forum, 24-25 April 2018, San Servolo Island, VenicePre-Open Forum workshop organised by ENOS, 23 April 2018:
Experience-sharing focus groups: Advanced techniques for site characterisation
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Outline
› Introduction
› What is well testing and Pressure Transient Analysis (PTA)?
› Testing wells to characterize injection site
› Well test designs
› Radius of investigation
› Interpretation of injection and fall-off responses
› An example of pressure monitoring helping in characterizing site boundaries
› CO2 injection at Tubåen formation of Snøhvit field
› Time-lapse injection and fall-off pressure responses
› Lessons learned from Snøhvit
› Acknowledgements
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What is well testing and Pressure Transient Analysis (PTA)?
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Elapsed Time [hr]
Pressure Derivative
Build-up Build-up
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Production
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Production
Pressure Transient Analysis (PTA)
Well• Storage• Skin factor• Induced fracture(s) properties• Effective length (horizontal)
Reservoir• Flow capacity / permeability
(directional for horizontal well)• Areal heterogeneity• Dual porosity / permeability
Boundaries• Faults• Aquifer• Well interference
Parameters estimated from PTA
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Build-up Build-up
Model Model
Typical well test (an example from Kappa Eng.):Production and following pressure build-up
PTA is history matching of well test including pressure derivative
Pressure build-up and its derivative in log-log
Effective well length
Reservoir flow capacity
Wellbore storage
Well shut-in = pressure build-up
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Testing wells to characterize injection site
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A synthetic model of injection site (a fault block)
An aquifer fault-block (U-shape) confined by three faults (no-flow boundaries): West, North and South from the well
Pressure[bar]
N
Sealing fault =
no-flow boundary
Open for flow boundaryWell
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Well test designs: from best to more feasible
› ‘100’ (day): Long injection
› 0.4% PV (of the model) injected, may be followed by fall-off, but not necessary
› All boundaries* covered during injection
› ’10’ (day): Shorter injection – Long fall-off
› 0.04% PV injected with long fall-off (100 day)
› All boundaries may be captured during injection, fall-off serves for confirmation
› ‘1’ (day): Short injection – Long fall-off
› 0.004% PV injected with long fall-off (100 day)
› Very small volume injected short-term
› No boundaries detected from injection, all boundaries covered by fall-off
*All boundaries = 3 boundaries in this U-shape example
Shorter injection
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1, 2, 4, 8…
Design ‘1’: Radius of investigation and flow regimes
1st day:end of
injection
2nd day
4th day
8th day: and similar
picture afterwards
Long pressure fall-off (100 day)
Short-terminjection (1 day)
Fall-off response: Pressure and derivativePressure evolution in U-shape reservoir
during well test. Pressure exceeding 302 bar is colored in red to highlight pressure
evolution deeper into reservoir
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Interpretation of injection and fall-off responses
Pressure
Derivative
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1 (injection) 1 (fall-off)10 (injection) 10 (fall-off)100 (injection) 100 (fall-off)Boundary 1, 2, 4, 8 day
Injection
› Boundary dominated flow regime started after ~40 hr
› Reliable boundary indication after additional ~40 hr
Fall-off
› Beginning of boundary dominated regime depends on injection duration prior to fall-off
› 100 day: after ~80 hr
› 10: ~120 hr
› 1: ~170 hr
› Reliable boundary indication after additional ~40 hr
› Flow barriers are most quickly captured from injection pressure interpretation(quick boundary indication = minimum test duration)
› If volume to be injected is limited, fall-off is an alternative (but longer test)
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› Permanent Downhole Gauges (measuring P&T) must be installed
› A well test before the main injection phase may consist of a short water production or injection followed by long shut-in (to disclose distant flow barriers)
› Such a test gives information about critical geological features › Results may work as showstopper for the project!
› Using CO2 for injection test leads to larger uncertainty with interpretation
› PTA of pressure dynamics during the main injection phase improves site characterization
Testing wells to characterize injection site
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An example of pressure monitoring helping in characterizing site boundaries
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CO2 injection at Tubåen formation of Snøhvit field
Difference amplitude map between baseline and monitor at base of the reservoir [from Hansen et al., 2011]
Depth map of top Fuglen formation (left) and geological cross-section N-S through the reservoir sections at Snøhvit (right) [from Hansen et al., 2013]
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History of CO2 injection at Tubåen formation
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Salt precipitation followed by treatment
History periodin focus
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Time-lapse fall-off pressure transients
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Pressure DerivativeFall-off 1 Fall-off 1Fall-off 2 Fall-off 2Fall-off 3 Fall-off 3Fall-off 4 Fall-off 4
Referencefall-off
Fall-off responses / derivatives
› All faults may be captured by the shortest fall-off (10 days fall-off is already enough)
› Follow exactly the same trend indicating no changes in sealing capacity of the faults
FO 1 FO 2 FO 3 FO 4
2-year history of CO2 injection at Snøhvitmay be reproduced with analytical models matched by PTA
Four pressure fall-off responses caused by well shut-ins
All fall-offs indicate U-shape reservoir
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Model (Injection 3)
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Pressure DerivativeFall-off 1 Fall-off 1Injection 1 Injection 1Injection 2 Injection 2Injection 3 Injection 3
Time-lapse injection pressure transients
Referenceinjection
INJ 1 INJ 2 INJ 3
Injection responses / derivatives
› Rate fluctuations cause noisy pressure transients
› Spread of transients is observed even after smoothing, but they approach the same trend as fall-offs
The overall pressure build-up may be predicted with ~10% error based on the models matched to noisy injection data
Three injection pressure responses and longest fall-off response
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› PTA of real-time pressure measurements (PDG) or continuous ‘well test’ is the most efficient tool to characterize and monitor site boundary conditions
› PTA of PDG data (analytical models)
› Uses gauge data available for the most of modern wells
› Fast and cheap: minimum time, computations and data input
› Efficient in characterizing large geological domains: pressure diffuses mainly in low-compressible saline aquifer, even after CO2 plume appearance
› Site monitoring
› The above advantages makes time-lapse PTA of PDG data a perfect tool for site monitoring, e.g. CO2 reservoir containment
Lessons learned from Snøhvit
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Acknowledgements
A part of this presentation was prepared and presented at 2015 AnnualEAGE conference (paper published at EarthDoc*)The authors acknowledge Statoil Petroleum AS and the Snøhvit licensepartners for providing access to the Snøhvit data presented at the EAGEconference
*Shchipanov A., Kollbotn L., Berenblyum R. Pressure Transient Analysis in CO2 StorageProjects - From Reservoir Characterization to Injection Performance Forecast // 77th EAGEConference & Exhibition. IFEMA Madrid, Spain, 1-4 June 2015
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Derivative
Pressure
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Total Compressibility (x2)
Closer Barrier (West 1/2)
Sensitivity to flow barriers and compressibility
Sensitivity to distance to West fault and total compressibility (U-Shape case)
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Pressure Derivative1: Single 1: Single2: Parallel 2: Parallel3: U-Shape 3: U-Shape4: Chamber 4: Chamber
Sensitivity of fall-off response to number of sealing faults (no-flow boundaries)
1: Single 2: Parallel 3: U-Shape 4: Chamber