FORMATE MATTERS
Issue no. 2 – April/May 2008
News and opinion from Cabot Specialty Fluids
www.formatebrines.com
Photoelectric
c effect
e
of cesium
formate gives surprising payoff
INSIDE
2 Cabot publishes
definitive work on
formate brines
2 First place goes to
China
3 TXM experiences
Hungarian Rhapsody
4 New research sheds
light on formate brine
stability under hydrothermal conditions
Erik Sandtorv Pedersen demonstrates the new method of log interpretation
“Logging while drilling (LWD) data using cesium formate-based fluids may lead to a more
accurate net reservoir definition and better geo-models,” says Erik Sandtorv Pedersen,
Petrophysicist at StatoilHydro.
StatoilHydro is drilling the HPHT Kvitebjørn
field in the North Sea using cesium formatebased fluids. In the early stages, StatoilHydro
was faced with a puzzling situation. According
to the interpretation of initial density log data,
which yields average matrix, fluid and gas
densities, the reservoir contained significantly
less hydrocarbons than originally believed.
The difference was so great that it was
questionable whether it was worth producing.
Something was clearly amiss.
“Based on the initial belief that there was
an error in either the logging equipment or
the log interpretation methodology, we asked
our logging contractors, Schlumberger, to
join us in an extensive joint-technology project
to help calibrate the logging tools,” says
Erik Pedersen. “The tests were run at 17 and
33% porosity fully saturated with 1.5 and
2.09 s.g. cesium/potassium formate brine.
Results confirmed that the equipment was
working fine, but all tools showed too-high
density measurements, which gave dramatic
reductions in hydrocarbon porosity and an
incorrect reservoir estimate. The next step
was to further examine and understand the
properties of cesium formate and this is when
things started to get interesting,” says Pedersen.
The ‘nuclei effect’
Cesium formate brine has a natural high density.
The weight comes from cesium ions rather
than added particles, such as barite. In traditional OBMs, the weighting agent is stopped
at the well bore wall and forms a filter cake.
With cesium formate the problem of filter
cakes are eliminated, however one needs to
correct for the drilling fluid that filtrates into
the near formation. “The traditional logging tool
algorithm is only good for elements with atomic
numbers less than roughly 24, which means
that the element has one neutron for every
proton. Cesium, with an atomic number of 55,
has considerably more neutrons than protons
in its nucleus. Therefore when measuring
electron density, which is then used to
calculate bulk density, the algorithm should
show an under-estimation of density due to
this large ‘nuclei effect’”, explains Pedersen.
“The only problem was that bulk density was
over-estimated,” he continues.
So what was the explanation? “When going
through the data I noticed an intriguing
correlation between the gamma logs and the
photoelectric factor. To cut a long story short,
higher-numbered atomic elements, such as
cesium, produce a dramatically higher photo-
electric effect. This increases the absorption
of gamma rays in the formation so that the
electron density appears higher than it is and
physical density is therefore over estimated.
This far outweighs the ‘nuclei effect’
previously mentioned,” says Pedersen.
A simple solution
Now StatoilHydro understood why the
logging results were wrong when interpreted
using methodology based on drilling fluids
with lower atomic numbers, the challenge
was to find a way of interpreting the numbers
accurately. The simplicity of the solution was
stunning. After close examination of the calibration data, a linear relationship was found
between the photoelectric factor (Pef) and
the over estimation of density. Consequently,
by consistently adjusting bulk density by the
measured Pef, porosity was correctly
calculated. “The beauty of this correction is
that it relies only on the Pef measurements,
which are logged simultaneously with bulk
density, and can therefore apply to any cesium
formate concentration,” says Pedersen.
The perfect model
The logged photoelectric factor isn’t only
useful for correcting the density curve and
estimating saturation of the invading filtrate,
but is also ideal for defining permeable
sands. Combining the photoelectric factor
and its high vertical resolution with resistivity
measurements from both the drill pass and
ream pass produces a very reliable and
accurate net reservoir definition. Furthermore, by applying a conductive drilling fluid
based on cesium formate brine in all production
wells high-quality resistivity image logs can
be run. These logs provide important
information on structural dip, depositional
environment, sedimentary features, facies
and geological correlations, all used by geomodelers to produce better reservoir models.
“The results match core porosity from different
lithologies in three different wells, so we’re
very confident that this new approach works.
Furthermore, cesium formate brine helps us
better define the net reservoir and produce
improved reservoir models. The trick is to
consider the invasion of filtrate into the
formation as a benefit and use the unique
nuclear properties of cesium to your
advantage,” concludes Pedersen.
The Kvitebjørn case is explained in detail in
SPE/IADC 105733. Please send a mail to
[email protected] for your copy.
2
F ORM AT E M AT T E R S
PEOPLE
China connect
“Introducing cesium-based formate
brines to HPHT operations across China
was a challenge I couldn’t say no to,” says
James Wang, new Business Development
Manager, China. Since establishing its
Far East office last year, Cabot Specialty
Fluids has employed James to help serve
the growing interest from the country.
James, 39, is a trained chemical engineer
with substantial experience in oilfield
technical services, project management,
R&D and marketing and sales management,
much of which comes from onshore and
offshore operations in China.
Issue no. 2 – April/May 2008
Cabot publishes definitive
work on formate brines
FACT FILE
Formate Technical Manual
contents
Part A: Chemical and Physical Properties
A1 Chemistry
A2 Brine Density and PVT Data
A3 Water Activity and Colligative Properties
A4 Brine Viscosity
A5 Crystallization Temperature
A6 pH and Buffering
A7 Thermophysical Properties
A8 Lubricity
A9 Petrophysical Properties
A10 Water Adsorption and Desorption
A11 Radioactivity
A12 Biodegradation and Biostatic /
Biocidal Properties
A13 Thermal Stability
James lives and works out of Beijing, is
married and has a three-year-old daughter.
In his spare time he plays golf, table
tennis, badminton, cooks and enjoys the
outdoor life. He can be contacted on
(86) 10 8496 4645 or by email at
[email protected].
James
Wang
New fluids engineer
Ruaridh (Ruari) Ormiston, 43, joins Cabot
Specialty Fluids as Senior Drilling and
Completion Fluids Engineer. With over
20 years’ international experience working
with IDF, Schlumberger and M-I Swaco
in Africa, the Middle East and Russia,
Ruari brings valuable expertise to Cabot’s
team of engineers. “The new technology
offered by formate fluids’ applications is
an exciting area to move into and I’m
enjoying being part of a small, dedicated
team in a high-tech world market.
Already, I’ve worked jobs in Malaysia,
Argentina and Hungary, and this will just
increase as formate use spreads around
the world”, says Ruari.
Ruaridh
(Ruari)
Ormiston
The new Formate Technical Manual
from Cabot Specialty Fluids is the most
comprehensive work on formate brines to
date. Split into three sections: chemical and
physical properties, compatibilities and
interactions, and formate field procedures, it
gives interested parties and current users a
valuable reference tool on the three formate
brines – cesium, potassium and sodium.
Author, Siv Howard PhD, says: “This manual
is an extremely useful guide to all things formate.
It combines all the existing knowledge and
data on formate brines with the results from
new tests and the experience gained from
over 500 field applications. It’s essential for
any company using or considering using
formate brines.”
Siv Howard, author of the new Formate
Technical Manual, and President of Cabot
Specialty Fluids Jim Turner, survey the
manual’s contents
The Technical Manual is provided free of
charge and is available from the following
link: www.formatebrines.com/manual. From
this page, you’re able to download the entire
manual or any single chapter that interests
you. The manual is an ongoing project and
new sections will be added and old ones
updated over time.
Any questions regarding the new
Formate Technical Manual should be
directed to Siv Howard on (44) 1224 230573
or [email protected].
Part B: Compatibilities and Interactions
B1 Compatibility with Gases
B2 Solubility of Gases in Formate Brines
B3 Diffusion of Gases in Formate Brines
B4 Compatibility with Other Oilfield Fluids
B5 Compatibility with Additives
B6 Compatibility with Metals
B7 Compatibility with Elastomers
B8 Compatibility with Cement
B9 Compatibility with Other Materials
B10 Compatibility with the Reservoir
B11 Compatibility with Shale
B12 Solubility of Minerals in Formate Brines
B13 Hydrate Inhibition
Part C: Formate Field Procedures
C1 Fluids Management
C2 Fluid Testing Procedures
C3 Other Oilfield Applications
for Formates
DID YOU KNOW?
First place goes to China
Our global society has a lot to thank the
Chinese for – the magnetic compass, paper
production, gunpowder and woodblock printing
are four of the better-known Chinese inventions. But did you know that we could also
add drilling to that list? The first oil and gas
wells were drilled well over one thousand
years ago. Metal drill bits connected to poles
of bamboo were used to drill down using the
percussive technique, similar to the churn
method used in modern day operations. A
sustained rocking movement of the pivot,
caused by several men using their combined
weight on a seesaw-like plank, lifted the drill
stem and brought it crashing down on the
rock underneath. Loose fragments and mud
were lifted from the hole using a hollow bamboo
pole with a leather foot valve attached to the
bottom. This was pushed down the hole and
into the mud, the weight of which would keep
the valve closed when it was lifted out again.
Oil and gas were piped from the hole using
hollow bamboo and often used, for example,
to burn off brine in salt production.
Bamboo was used to pipe oil and gas
FO RMATE MATTERS
Issue no. 2 – April/May 2008
3
TXM experiences Hungarian Rhapsody –
Two records broken in extreme HPHT well
TXM, a subsidiary of Canada’s
Falcon Oil & Gas Ltd., and
Cabot Specialty Fluids
enjoyed a ‘champagne
moment’ after successfully
suspending Mako-6, an
extreme HPHT well located
in south-east Hungary.
Two records were broken during this
challenging well kill and suspension operation
– the deepest packer ever set in Hungary at
5,198 m/17,054 ft and the highest temperature
for cesium formate brine use. The previous
temperature record stood at 216°C/420°F,
set in January 2005, during an HPHT
completion for Walter Oil & Gas in the US
Gulf of Mexico. Now, since TXM chose
2.15 s.g./17.94 ppg cesium formate brine for
its Mako-6 well, the record has been upped
to 225°C/437°F.
Photo: Scanpix
After drilling operations started on Mako-6 in
December 2005 the well was completed in
July of the following year and temporarily
abandoned with 1.33 s.g./11.1 ppg calcium
chloride brine in the hole. Reservoir pressure
was in excess of 15,000 psi and target depth
BHST stood at 235°C/455°F. Log analysis
revealed significant gas from numerous
intervals and an extensive fraccing operation
was started in spring 2007. As part of this
process, a two-metre interval from 5,326 m to
5,328 m/17,474 ft to 17,480 ft in the
Basel Conglomerate zone was perforated.
Subsequent fraccing saw success, but after
discovery of H2S gas, a well kill operation
was initiated by M-I SWACO, TXM’s fluid
technology consultants, using cesium
formate brine from Cabot Specialty Fluids.
A total of 57 m3 cesium formate brine at
Hungarian record breaker – TXM sets deepest packer in HPHT well at 5,198 m/17,054 ft
2.147 s.g./17.92 ppg was bull-headed down
the 5½" casing to the bottom of the perforated
zone to minimise well-head pressure and
enable snubbing of a packer and test string
into the hole. The bottom of the column of
cesium formate brine was at a depth of 5,300
metres with a local temperature of
225°C/437°F. High-density cesium formate
was chosen because alternative brines with
lower densities develop much higher surface
pressures, placing more wear and tear on
the snubbing equipment and increasing
operational risk.
The cesium formate remained in the well for 39
days before a reverse circulation displacement
to a packer fluid enabled well test operations
to begin. The brine was sampled periodically
during displacement and, despite the lengthy
exposure to hydrothermal conditions,
extensive laboratory analyses showed no
significant changes in the fluid properties or
composition.
Don Wright, operations manager for TXM,
commented: “Successfully setting the packer
in Mako-6 at a record depth was a significant
achievement for us. Cesium formate provided
stable well conditions and enabled operations
to progress safely and smoothly. Crew only
needed to wear standard personal protective
equipment, something that made working
conditions much more comfortable, especially
since outdoor temperatures rose to 40°C on
occasion.”
Cesium formate brine of 2.225 s.g./18.53 ppg
has been run back into the well as a long-term
suspension fluid, while TXM make preparations
to recover a mechanically-damaged work string.
MEET US AT THESE EVENTS
Cabot Specialty Fluids is participating at a number of conferences and exhibitions over the next few months. Come and see us!
8 – 9 April
AADE Fluids Technology Conference, Houston. Papers: “Formate Brines in Extreme HPHT Well Construction Operations – Do they have limitations?”
“A New Tool for Monetizing the HSE Risk Posed by Well Construction Fluids” (Gaia Consulting)
15 – 17 April
SPE HSE Conference, Nice.
5 – 8 May
OTC, Houston (hospitality suite). Paper: OTC 19242 “An Evaluation of Perforating Techniques and Use of Cesium Formate Kill Pills to Optimise Productivity
in HPHT Wells and Minimise HSE Risks”
19 – 23 May
7th International Seminar on Drilling Fluids and Cements for Oil Wells, Isle of Margarita.
27 May
SPE 2008 Oilfield Corrosion Conference, Aberdeen.
Paper: SPE 114111 “The Hydrothermal Chemistry of Formate Brines and its Impact on Corrosion in HPHT Wells”
17 – 18 June
IBC Drilling Operation Conference, Kuala Lumpur.
Paper: “ Advances in Ecological Drilling Fluids to Reduce the Volume and Toxicity of Drilling Wastes”
4
F ORM AT E M AT T E R S
Issue no. 2 – April/May 2008
TECHNICAL FORUM
New research sheds light on formate brine
stability under hydrothermal conditions
Researchers at a leading
research institution, the
Woods Hole Oceanographic
Institution in the U.S., have
brought new insight to
understanding formate brine
stability under hydrothermal
conditions.
Up until now, no satisfactory laboratory
experiments have successfully predicted
what happens to formate brines at the bottom
of a HPHT well. Frustratingly enough, there’s
no correlation between minor changes in
formate brine composition in the field and
formate decomposition measured in standard
laboratory autoclaves. But why? There are
many differences between laboratory testing
conditions and conditions in deep oil and gas
wells; one of the less obvious being the
presence of a headspace gas in the laboratory
environment. The presence of a gas cap
allows gaseous products of hydrothermal
decomposition to escape from solution. This
has the undesirable effect of shifting the point
of equilibrium, which increases the degree
and duration of decomposition. Performing
laboratory testing in a HPHT environment
without the presence of a headspace gas is
difficult, something that made Cabot Specialty
Fluids seek assistance from outside experts.
Jeff Seewald (PhD), one of the world’s leading
experts on the hydrothermal reactivity of
organic acids1, was put on the case. Seewald
says: “In our laboratory, the test fluid is
placed in a gold test cell immersed in a highpressure high-temperature autoclave filled
with water. The gold test cell has the advantage
of being flexible so that experiments can be
operated and sampled without the need for a
gas headspace.”
A first set of HPHT exposure experiments
with cesium formate brine was conducted in
this test cell to identify if and where thermal
decomposition equilibria would establish.
A very high temperature of 270°C and a
moderate pressure of 5,000 psi represent
one of the worst-case scenarios for formate
brines as lower temperatures and/or higher
pressures create a more favourable environ-
ment for formates. As this initial test was
designed to look at equilibria only and not
reaction rates, no catalytic material was
present in the test cell (the presence of
catalytic surfaces increase the reaction rates,
but does not influence the place where the
equilibrium establishes).
Testing at Woods Hole has yielded some very
interesting results:
- The decomposition of formate brines will,
under realistic hydrothermal conditions,
reach equilibrium relatively soon.
- The major product of formate decomposition
is bicarbonate, which is already present in
formate brine as a component of the pH
buffer. Some carbonate is also formed,
which is the second pH buffer component.
- By adding extra carbonate/bicarbonate
buffer to the brine, it should be possible to
formulate a ‘thermally stable’ formate fluid.
Such a fluid reaches equilibrium after just
a very minor degree of decomposition.
Future testing using the gold test cell will
investigate the influence of equilibria on compatibility between formate brines and metals.
Jeff Seewald with the gold test cell. This
allows for experimentation without a gas
headspace
1. McCollom, T.M. and Seewald, J.:
Constraints on the Hydrothermal Reactivity
of Organic Acids Anions: I: Formic Acid and
Formate”, Geochemica et Cosmochimica
Acta, Vol. 67, No. 19, pp. 3625-3644, 2003.
Boxed in
Unscramble each group of letters to discover seven words
associated with drilling and completion. Then fit them across the
grid to spell out another word reading down the highlighted
boxes. This is your answer! The first correct answer drawn out of
the hat receives a digital photo frame from Philips. Perfect for
letting you bring your electronic photos into the living room! The
following fifty correct entrants drawn from the hat all receive a
Maglite Solitaire. (Limited to one per person.) Please remember
to add your name, company and address for delivery of the gift.
Good luck!
DILFU
GOL
RIDLL TIB
DANMERL
REKHAS
GUSTINCT
Please send completed entries to Ellena Paterson at
[email protected] or fax (44) 1224 870089
by 1 June 2008.
Congratulations to all those who solved the word search in the
previous issue of Formate Matters. The lucky winner is Tony
Kraychy from Calgary. For the correct answer to the word search,
SIGN UP FOR YOUR FREE COPY!
If you would like to receive further copies of Formate Matters
please send an email to [email protected]
or call (44) 1224 897229.
CENRES
or for the complete rules for this competition, please contact
Ellena Paterson using the email noted earlier.
AND FINALLY…
“The only limits are, as always, those of vision.”
James Broughton, poet and filmmaker, 1913-1999
For further information please contact Cabot Specialty Fluids Ltd., Cabot House, Hareness Circle, Altens Industrial Estate, Aberdeen. AB12 3LY. UK. T: (44) 1224 897229. E: [email protected]
NOTICE AND DISCLAIMER. This newsletter is designed to provide information of a general nature and is not intended as a substitute for professional consultation and advice in a particular matter. The opinions and interpretations expressed within are
those of the author only and may not reflect those of other identified parties. Cabot Specialty Fluids Ltd. does not warrant the accuracy and completeness of this newsletter, nor endorse or make any representations about its content. In no event will
Cabot Specialty Fluids Ltd., Cabot Corporation or any of their subsidiaries, affiliates, officers, directors or employees be liable for any damages whatsoever arising out of the use of or reliance on the contents of this newsletter.
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