No flaring well testing
(Injection Fall-off testing)
Arild Fosså | Expro Norway AS
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Traditional well testing
• Low actual emissions, but aesthetically un-appealing
• Important data for development decisions
• Are there real alternatives ??
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Background
Dynamic Well Test data is used as input data for the following;
• Reservoir Model
• Well performance Model, and
• Pipeline and Facilities Models
Key data provided are;
• Pressures,
• Temperatures
• Flow rates
• Fluid data (both PVT and large volume)
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Well Bore
Pressure transient
from a Well Test
Example of conseq. from missing data
K Field knowledge
Reservoir evaluation
Development strategy
Miss understand :
Poor estimate :
Wrong decisions for
recovery mechanism
• heterogeneity org.
• K anisotropy
• Reserves
• Production profiles
(gas/water injection,
gas cycling/depletion)
Business
Less Profits /
Lose money
Overestimate :
Underestimate
heterogeneity size
Miss or not quantify
extra permeability
(fract. , dissolution)
• sweeping efficiency
• reserves
• Underestimate
Production profiles
• Poor estimate
segregation effects
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Overestimate Facilities
Underestimate :
• Facilities
• Profitability
Lose money
• Less Profits
• Project
abandonment
Backdrop on the Barents Sea
• The big picture for the Barents Sea area is characterized as follows;
– Same formal rules & reg’s as the rest of the NCS.
– High focus from environmental groups
– High focus on spill prevention from the authorities
– High Political focus – (spills, blow-out risk, ice-edge, public
opinion, etc. etc.)
• Due to this an alternative way of testing wells could be of interest.
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
What is needed for a Well Test?
•
•
•
•
Porosity
Viscosity
Flow rates
Pressures
From cores
From Fluid Samples
From Surface (normally)
From Bottom Hole
The “simple” option…..
• In addition it is important to minimize
the accumulator effect downhole
inside the string – Well Bore Storage
effects.
Gas test - Westhope, North Dakota, January 07
• Due to this there is great freedom in
how you achieve the above.
The elaborate option…….
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Bideford Dolphin plant - 2010
Injection Fall-off testing
• One of the parameters we have freedom
over is the flow rate. Which is used to
induce the pressure transient.
• There is nothing stopping us from doing an
injection period rather than a flow period
to get the pressure transient going.
• The equivalent to the normal pressure
build-up would be a pressure Fall-off.
• Gives the same type of data as a normal
well test.
– Except Fluid Data - obtained during open
hole logging.
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Classic Injection Fall-off test.
Injection Fall-off application
• Traditionally Injection Fall-off tests have been used for;
– Water zones and water-flood projects.
• Measure pressure increases to accurately predict pressure
rises from long-term fluid injection.
– Verify that reservoir zones are «non-migration» types – i.e. no
communication between reservoir zones.
– Changes in permeability and skin over time.
– Geothermal wells
– Water disposal wells
– Traditionally used for Gas Storage wells
• There isn’t anything stopping a wider use.
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Injection Fall-off issues
• Issues associated with Injection Fall-off testing vs. normal Well Tests
– First, the character of the system changes.
• Instead of single-phase flow, we are now faced with two-phase water/oil
flow governed by relative permeability's
– Second, injection of cold water induces temperature changes in
the formation
• This complicates the pressure behaviour through temperature effects on
the oil and water viscosities.
– Third, injection of water may result in the formation accidentally
fracturing and in coupling of rock mechanics and fluid flow
problems.
• It is critically important for successful test interpretation to avoid
accidental fracturing and to inject water at below the formation fracturing
pressure.
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Mitigation #1
System character change
• Issue - Introduction of two-phase
fluids in the reservoir affecting the
relative permeability's
• Mitigation – Use theoretical «twobank» and «multi-bank» models.
– handles the two-phase aspect of
an Injection Fall-off test.
– addresses changing saturation
gradients, which has a significant
impact on the pressure transients.
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Horner plot example illustrating
the effectsaturation
of bankingprofile
on an side view
Schematic
analytical plot
Schematic saturation profile top view
Mitigation #2
Reservoir cooling
• Issue - cold water reduces formation
temperature, hence oil & water viscosities
• Mitigation – Research show that for
pressure transients governed by a moving
thermal front, one should use fluidproperties corresponding to the cold
injection fluid to analyse the results
correctly.
– Prior PVT data a plus for job planning
– Extensive Fluid Sampling program for
Wireline Formation Tests
– Bulk sample issue for facilities &
pipeline models not solved fully.
(Limitation with method)
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Pressure transient data for
injection of 95°C water into a
250°C reservoir
Mitigation #3
Formation fracturing
• Issue – Risk of accidental
formation fracturing, possibly
fracturing the cap rock.
• Mitigation – Good control of
the Fracture Gradient, plus
injectivity modelling before a
job.
– Requires general good area
knowledge.
– Possibly that Injection-FallExample simulation of BHP for
Injection Fall-off job
off method is best suited for
appraisal wells.
Generic Pore-pressure & Frac gradient curve
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Mitigation #3.1
Formation fracturing - vacuum
• Other issue – In case a water-injection well is fractured, the wells
often go on surface vacuum, where the fluid level can fall below
surface, making surface pressure data monitoring impossible.
• Mitigation – Normally the vacuum would stem from fracture
propagation, which limits the issue. However, dealing with this
complication requires bottom hole pressure recorders (memory or
Surface Read-Out).
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Injection Fall-off application
• It is not recommended to do Injection Fall-off tests for
rank exploration wells.
• However, we would recommend it as a possible Appraisal
Well technique, provided the following;
– Prior fluid data obtained from earlier exploration wells
– Fluid properties available for reduced reservoir
temperatures
– Sufficient fluid sampling planned on actual well during OH
logging
– Porosity from earlier cores available
– Core saturation experimental results available from earlier
wells
– Fracture gradient is well known for the target formation
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Other
• To plan a successful Injection Fall-off test the following is needed;
– More simulations than normal to model pressure transient
responses to ensure correct job design.
– A plan for bulk samples for pipeline and facility model
experiments
• Can you live without?
• Can it be obtained from the Initial Flow period to surface
tanks?
– Bottom Hole gauges must be used for data gathering.
• Equipment and services required are the same as for a normal DST,
with the exception of Fluid Sampling.
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Has it been done before?
• Source:
NPD + Press release
– http://factpages.npd.no/factpages/Default.aspx?culture=no
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•
•
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Well bore:
Rig:
Time frame:
Formation:
7122/7-4S Klappmys
Polar Pioneer
November 2006
Kobbe (1911-1927 m)
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway
Thank you!
Arild Fosså | Expro Norway AS
[email protected]
2015 - SPE Workshop in Arctic Norway
March 11th – 12th 2015 | Harstad, Norway