Latest Advances in the Development of Ecological Drilling Fluids

IBC Asia Conference 25-26
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June 2002
Offshore/Upstream Asia-Pacific 2002
Latest Advances in the Development of Ecological Drilling Fluids 1/16
John Downs, Hydro Formates
IBC Asia Conference
25th
-26th
June 2002, Sheraton Grande Sukhumvit, Bangkok
Latest Advances in the Development of Ecological
Drilling Fluids
John D. Downs
Hydro Formates
Abstract
The oil industry creates many millions of tonnes of drilling waste contaminated
with ecotoxic drilling fluid components. A number of mechanical and fluid
engineering solutions are being introduced to reduce the volume and toxicity of
drilling waste discharged into the environment. This paper looks at the required
specification and profile for the ideal fluid engineering solution to the drilling
waste problem, and identifies the formate brines as the closest match to a truly
ecological drilling fluid. A review of the use of formate brines as ecological drilling
fluids over the past 8 years, including their application in the extremely sensitive
environment of the Barents Sea, confirms their effectiveness under even the
most demanding conditions. It is concluded that the widespread adoption of
formate brines as drilling fluids will allow the oil industry to significantly reduce
both the volume and toxicity of its drilling wastes.
1. INTRODUCTION
The need for sustainable development of the world’s hydrocarbon
resources requires the oil companies and the oilfield service companies to

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continually look for ways of minimising the negative effects of their well
construction activities on the environment. The well drilling processes
alone generate many millions of tonnes of waste contaminated with toxic
drilling fluid components, and much of this contaminated waste ends up
being dumped somewhere or other in our ecosphere. The volume and
toxicity of drilling wastes produced is to a certain extent influenced by the
nature of the drilling fluids used for drilling the wells.
This paper looks at what is being done by the oil industry to develop a
truly ecological drilling fluid system that genuinely tries to minimise the
damage caused to the environment. It starts by looking at how traditional
drilling practices and conventional drilling fluid formulations tend to amplify
the negative impact of well construction operations on the environment
and how mainly mechanical engineering improvements are being
introduced to make the operations more ecological.
It then develops a specification and profile for the ideal ecological drilling
fluid and argues that the formate brines are probably the only drilling fluids
currently available that come close to matching the required performance
criteria. The paper concludes by examining how formate brines have
performed as ecological drilling and completion fluids since their first
introduction to the oil industry in 1993.
2. DRILLING OPERATIONS AND THE ENVIRONMENT
The dimensions of the negative impact that the oil companies’ well
construction activities have on the environment is largely a function of the
extent to which they continue to use traditional well bore construction
techniques to access hydrocarbon deposits.
Well trajectory and dimensions
The traditional practice of drilling individual vertical well bores directly
down to and through a hydrocarbon reservoir requires an equivalent
number of surface sites, each one having a negative impact on the
environment. In addition, the well bore diameters created by traditional
drilling methods can be larger than necessarily required to achieve the
desired hydrocarbon inflow performance. Large holes mean larger drilling
installations and more waste.
Formation damage
Traditional drilling and well construction techniques can cause significant
damage to hydrocarbon reservoirs, thereby restricting oil or gas
production. This damage might require remediation by subsequent well
stimulation operations, or more well bores might have to be constructed to
achieve the desired reservoir drainage and production rates. The
inefficient hydrocarbon recovery from wells with formation damage could

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June 2002
lead to premature well abandonment with the majority of reserves
remaining in place. This in turn will almost inevitably lead to more
environmental damage in the future as operators, encouraged by
improved technology or higher oil prices, return to further exploit the
abandoned wells/fields.
Drilling fluids
Traditional drilling and well construction fluids impact negatively on the
environment by increasing the volume and toxicity of waste produced in
the well-bore creation process.
Waste volume
Ideally the only significant waste that should come from the construction of
a well bore is the exact hole volume of drilled rock cuttings created by the
action of the drill bits, but often in practice the volume of waste produced
is significantly increased by the use of traditional drilling fluids.
The commonest sources of increased waste associated with the use of
traditional drilling fluids are:
• Dumping and dilution of drilling fluids to maintain fluid condition
• Loss of fluid and weighting agent from solids-control operations
• Creation of mixed fluid interfaces from displacement operations
• Increased production of cuttings from well bore cavings
• Use of different fluids for different well sections
• Use of different drilling and completion fluids
• Use of solid-weighting agents
Waste toxicity
The type of drilling fluid or well construction fluid used also has a major
influence on the toxicity of the waste produced. Water-based well
construction fluids have traditionally been based on halide salts that are
toxic to freshwater and onshore environments. Non-aqueous well
construction fluids have been based on mineral oils or synthetic
hydrocarbons, emulsified with halide brines by using powerful surfactants.
These invert emulsion fluids place a toxic burden on the environment
unless extracted from the waste before disposal. Technology is available
to extract the hydrocarbon phases from drilling wastes but it is rare to find
the other toxic elements (halide brines, emulsifiers and barite) being
removed prior to disposal.
Solid weighting agents
The use of barite in drilling fluids merits special mention in any review of
the environmental impact of well construction operations. Despite
containing 58% w/w barium, a very toxic heavy metal, large volumes of
barite are traditionally added to drilling fluids to increase their density for

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June 2002
well control purposes. These finely ground particles of barite degrade the
properties and performance of drilling fluids by:
• Spoiling the hydraulic flow properties of the base fluid
• Increasing filter cake thickness and risking differential sticking
• Having the potential to sag, causing well safety/access problems
• Creating difficulties in re-conditioning and re-cycling the fluid.
• Causing formation damage and reducing well productivity
The global barite consumption figures issued by the US government1
show
that in the year 2000 some 5 million tonnes of this mineral were used in
drilling fluids. A large proportion of this barite is discharged with drilling
wastes into the environment.
It seems that this massive pollution of the environment with a mineral
containing such a highly toxic heavy metal is only tolerated by regulators
because there is a common belief that the barium contained in the barite
is not taken into solution by drilling fluids during use and is therefore not
biologically available in drilling waste discharges as a toxicant. It is not
clear on what evidence this belief is based. Barite may only have a
relatively low solubility in fresh water (2 mg/l), but the majority of drilling
fluids contain electrolytes such as chlorides that significantly increase the
dissolution of barium from barite.
Monnin 2
has shown that under atmospheric pressure a saturated sodium
chloride brine will solubilise 50-100 mg/l of barium from barite at 50-100o
C,
and at higher temperatures and pressures the barium solubility levels can
increase to 200-400 mg/l. The same paper indicates that barite is even
more soluble in the calcium chloride brines that are routinely used as
completion fluids and as the brine phase of oil-based drilling fluids. The
barium solubilising effect of chloride brines has actually been known to the
oil industry since 1960, following the publication of work carried out by
Charles Templeton of Shell Development Company 3
.
These moderate levels of barium taken into solution by salt-containing
drilling fluids from “insoluble” barite might not sound particularly significant,
but they are way in excess of the lethal concentration for bacteria, fungi,
algae, aquatic plants (Lemma LC50=26 mg/l)4
and aquatic invertebrates
(Daphnia LC50 = 14 mg/l) 5
. Daphnia show a 50% impairment of
reproductive function at soluble barium concentrations of just 9 mg/l.
The toxicity of soluble barium to the environment is recognized by the US
Environmental Protection Agency which classifies any products or
formulations containing >100 mg/l of soluble or extractable barium as
D005 Hazardous Waste.

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It is clearly not ideal that the oil industry discharges millions of tonnes of
drilling wastes containing a toxic heavy metal that is solubilised by a
common component of drilling fluids and drilling wastes to the extent that
they could become classifiable as Hazardous Waste. More research is
needed on this subject but, no matter what the outcome of further studies
on the levels of soluble barium in drilling waste discharges, it is evident
that in waste volume terms alone barite is a strong contributor to the
negative impact of well construction operations on the environment.
3. ECOLOGICAL SOLUTIONS IN WELL CONSTRUCTION
The word “ecological”, when used in connection with a product or practice,
is defined as “tending to benefit or cause minimal damage to the
environment”. The oil industry is working towards the objective of
ecological well constructions through the development and implementation
of new technologies that include mechanical and fluid engineering
solutions (see Table 1).
4. GENERAL SPECIFICATIONS FOR DRILLING FLUIDS
Drilling fluids play a vital role in the construction of the well bores that the
oil companies use either to gather and channel produced fluids and gases
from their subterranean sources to the surface or to convey pressure
injection water/gases in the opposite direction. Some of the key properties
required of conventional drilling fluids include:
• Safe to use
• Efficiently transmit hydraulic power with minimal pressure losses
• Suspend cuttings and other solids, in static and dynamic conditions
• Control well pressures
• Stabilise the borehole, particularly in shale sections
• Minimise formation damage and blocking of sand screens
• Minimise fluid loss
• Provide lubrication between metal-metal and metal-rock surfaces
• Efficiently release cuttings in the solids-control equipment
• Minimise waste volume and waste toxicity
• Allow all forms of logging and logging interpretation
• Be compatible with all elastomers and ferrous metals
• Be compatible with other well construction fluids and preparations
• Maintain its properties at all ambient and downhole temperatures
It is remarkable that, despite almost a century of evolution, no single
traditional drilling fluid can actually meet all of these requirements. For this

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June 2002
reason it has been common for operators to have to use more than one
type of fluid to drill and complete individual wells.
5. SPECIFICATIONS FOR AN ECOLOGICAL DRILLING FLUID
A truly ecological drilling fluid is one that is not only benign but also tends
to enable the implementation of the ecological solutions (see Table 1) that
have been developed for mitigating environmental problems presented by
well construction operations. In essence the specification for an ecological
drilling fluid is the same as the general specification for the ideal drilling
fluid outlined in Section 4, but with special emphasis on:
• Dual utility as a drilling and completion fluid
• Minimal formation damage
• Optimal fluid properties for narrow bore and extended reach drilling
- maximum transmission of hydraulic power in narrow well bores
- minimal hydraulic pressure losses in extended reach well bores
• Minimal waste production
- stabilise the borehole and cuttings
- eliminate solid weighting agents
- capable of simple re-cycle with minimum losses
• Reduce waste toxicity and environmental burden
- benign, biodegradable base fluids and solutes
- low BOD and COD
6. PROFILE OF THE IDEAL ECOLOGICAL DRILLING FLUID
Based on the specifications outlined above, the profile of the ideal
ecological drilling fluid is a low-solids water-based solution containing the
absolute minimal amounts of benign biodegradable solutes of a
monovalent or non-ionic character necessary to provide the following
properties over the complete range of well bore temperatures up to at
least 200 deg. C.:
• Fluid densities up to SG 2.4 without using solids weighting agents
• Shale stabilisation
• Fluid loss control
• Drag reduction
• Solids suspension under static and dynamic conditions
• Lubrication
This minimal fluid should be compatible with the common elastomers and
steels used in well construction operations, and should allow the collection

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June 2002
and interpretation of all forms of mud logging and well bore logging data.
The fluid should also be easy to re-condition and re-use, and should be
useable in any drilling or completion operation.
Perhaps surprisingly, no commercial well construction fluid appears to
match this profile other than the formate brine systems that were
developed by Shell in the early-1990’s as high-performance ecological
drilling and completion fluids 6,7,8
.
7. FORMATE BRINES AS ECOLOGICAL DRILLING FLUIDS
The formate salts of the alkali metals are very soluble in water and form
benign brine systems with a broad range of beneficial properties8
that
make them ideally suited for use as ecological drilling and completion
fluids:
• They cover a density range between SG 1.0 and SG 2.3
• They have a good Health, Safety and Environmental profile
• They transmit hydraulic power with minimal pressure losses
• They stabilise shales
• They can be easily formulated with biodegradable biopolymers for:
- fluid loss control
- drag reduction
- solids suspension in static and dynamic conditions
• They have natural lubricating properties
• They cause minimal formation damage
• They can easily be recycled
• They allow all forms of logging and logging interpretation
• They are compatible with most elastomers and all ferrous metals
• They maintain their properties at –50o
C up to + 210o
C
The formate brines are manufactured from chemical components that are
on the OSPAR List of Substances Used and Discharged Offshore which
are Considered to Pose Little or No Risk to the Environment (PLONOR).
Data on the toxicity of formates to a selection of aquatic and marine
organisms are shown in Table 2. Benign chemicals such as formates with
LC50 and EC50 figures of > 100 mg/l are generally considered to be
practically non-toxic to the environment.
If formate brine is discharged into the environment any potassium and
caesium ions in solution will quickly become depleted by adsorption onto
soil or sediments, and the formate will be removed by microbial activity. In
standard OECD Biodegradability tests the formates are 90% biodegraded
within 15 days, and they are therefore classified as being “readily
biodegradable”8
.

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June 2002
It is interesting to consider that the universal adoption of formate brines
as drilling fluids would reduce barium heavy metal discharges from drilling
operations by some 3 million tonnes/year.
The density range of the formate brines can be extended, if necessary, up
to SG 3.0 by the addition of caesium tungstate brine – another discovery
made by this author while working for Shell back in 1990.
8. ECOLOGICAL APPLICATIONS OF FORMATE BRINES
Formate brines have been successfully used as ecological drilling and
completion fluids in many hundreds of wells in at least 14 countries since
1993. The high-density caesium formate brines have so far been used in
a total of 46 wells, including 6 reservoir drill-ins by BP and Statoil.
In many cases the formate brines have enabled the implementation of the
ecological solutions described in Section 3:
Formation damage reduction
Field results obtained over a period of 8 years have confirmed that oil and
gas wells drilled and/or completed with formate brines have invariably
shown higher than expected production rates. Figures published in the
public domain suggest that typical production rate increases are in the 30-
40% range 9,10,11,12
, but in some instances the productivity indices (PI) and
actual oil production rates have been 300-400% higher than expected 30
.
The ecological benefit of these increased production rates is that fewer
wells have needed to be drilled to achieve the operators’ production
targets.
Reduction in heavy metal discharges
Formate brines have only been used in few hundred of the approximately
600,000 wells drilled in the world over the past decade, but even so in this
period they have probably reduced heavy metal (barium) discharges to the
environment by around 50,000 tonnes.
Narrow well bore drilling and completion
Formate brines were originally identified as having the ideal characteristics
for use as the basis of ecological drilling fluids for deep drilling and slim
hole drilling13
.
The perceived advantages for formate brines in these applications were:
• Maintenance of solids carrying capabilities at high temperatures
• Elimination of solids sag at high down hole temperatures
• Minimal circulating pressure losses

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• Low potential for differential sticking (very thin filter cakes)
• Low Equivalent Circulating Densities in long/narrow boreholes
• Maximum power transmission to mud motors and bits
• Non-hazardous
• Compatible with reservoir minerals and liquids (i.e. non-damaging)
• Compatible with drilling/completion hardware and elastomers
• Environmentally responsible and readily biodegradable
The first recorded field use of formate brines was by NAM in the
Netherlands who formulated a sodium formate brine as a coiled-tubing
drilling fluid in a well side-tracking operation in the Berkel field. This, and
subsequent coiled–tubing field trials in UK and Norway by Shell and
Statoil with virtually solids-free potassium formate brines 14,15
, established
the true advantages of the formates for narrow-bore drilling in reservoirs.
In 1995, after experiencing hole problems using conventional drilling
fluids, Mobil used potassium formate brine for the first time as a high
temperature drilling–in fluid in a deep slimhole horizontal gas well in
Northern Germany 16
. Mobil had previously obtained favourable results
with potassium formate brine as a completion and workover fluid earlier in
the field development campaign. Mobil reported that the use of the
formate drilling-in fluid effectively “eliminated most of the previous hole
problems and significantly reduced well costs” 12
. The specific benefits
realised with the formate system included:
• Excellent polymer stability at 310o
F
• Effective hole cleaning
• ROP increased by 20%
• No formation damage (skin factor=0)
• Thin, easily removable filter cake
• Good inhibition of formation clays
• No corrosion
• Low differential sticking potential
• Low treatment costs during drilling
Mobil has drilled and completed another 15 deep slim hole wells with
potassium formate brine in Germany and has concluded 17
:
“ Formate-based fluids have been applied as high density, temperature
stable, low solids, environmentally friendly, non-damaging, non-corrosive
drilling and reservoir drilling fluids. Replacing high solids drilling fluids with
low-solids formate-based fluids has resulted in a dramatic increase in
drilling performance and hydraulics. Since the use of formate-based fluids
has been implemented, the productivity of wells has increased compared
to wells drilled with the traditional fluids ”

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June 2002
Mobil have also carried out a series of frac jobs in a deep high
temperature gas well using potassium formate brine.
Horizontal and multilateral well drilling and completion
In 1993-94 Shell and Statoil in Norway conducted the first applications of
sodium and potassium formate brines as full bore reservoir drilling-in and
completion fluids, confirming their non-damaging properties in the
construction of a number of extremely productive open hole horizontal
wells18,19
.
The later application of blended sodium/potassium formate brines as
drilling-in and completion fluids for open hole multilateral horizontal wells
in The Netherlands would show that “the minimal residual drilling-induced
damage increased production capacity 40% over that expected, with a
near-zero mechanical skin” 9
.
Statoil have recently demonstrated the benefits of drilling and completing
a series of 6 high angle open hole reservoir sections in the HT/HP Huldra
field with SG 1.90 potassium/caesium formate brine 20
. Statoil report
positive effects on well control/safety (elimination of barite sag), hole
cleaning, hole stability, ECD and well performance.
Extended reach drilling and completing
For a number of years Shell in the UK has been drilling and completing
extended reach horizontal wells in the Schooner, Ketch, Barque, Galleon,
Skiff, Brigantine and Inde fields using sodium/potassium formate brine
blends. Horizontal reservoir sections of up to 7,000 ft have been drilled
with the formate brines and then completed in the formate brines with
Expandable Sand Screens 21
.
Universal fluids
Formate brines have powerful shale-stabilising properties 22,23,24,25,26
and
can therefore be used as universal fluids to drill entire wells from top to
bottom, thus avoiding the creation of additional wastes associated with
using different fluids for drilling each of the various well sections.
Since 1999 potassium formate brines have been used as multi-purpose
shale drilling and reservoir drilling fluids in land wells in Alberta, Canada.
Over 200 wells have now been drilled and the users claim that the formate
anion plays an important role in stabilising the Canadian shales 27
.
The most powerful demonstration of the universal capabilities of the
formates was provided in 2000 when Norsk Agip drilled the intermediate
12 ¼-in and the 8 ½-in reservoir sections of their offshore Goliath and
Gamma discoveries in the environmentally-sensitive Barents Sea using
SG 1.3 –1.4 sodium/potassium formate brines 28
. The use of the formate
brines avoided polluting the Barents Sea fishing grounds with barium

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June 2002
heavy metal, and the brines were re-cycled and re-used in consecutive
wells. Agip noted that the quality of the young and highly reactive shale
cuttings brought up from downhole by the formate brines was comparable
to those seen when drilling with oil-based muds.
9. NON-AQUEOUS FORMATE FORMULATIONS
Until convinced otherwise a section of the drilling community will continue
to have reservations about contacting shales or oil reservoirs with water-
based drilling and completion fluids such as the formate brines. To satisfy
the requirements of these reactionary elements a number of non-aqueous
drilling fluid systems based on formates are either in development or are
already in field use. While clearly not meeting the same ecological
specifications of straight formate brines each of these hybrid systems
represents some improvement on traditional drilling and completion fluids.
Novel chloride-free invert emulsions
Many thousands of wells have been drilled in Canada over the past 10
years with invert oil emulsion drilling fluids containing calcium nitrate brine
as the internal phase. More recently this technology has been updated
and improved by using potassium formate in place of calcium nitrate as
the internal brine phase. These formulations still contain oil, emulsifiers
and barite but their toxicity to the local onshore environment has been
diminished somewhat by the substitution of the conventional chloride brine
internal phase with firstly a nitrate brine and now a formate brine.
Novel high-density invert emulsions
Norsk Hydro in Norway has field tested a novel completion fluid
comprising an SG 1.6 solids-free invert oil emulsion fluid containing
caesium formate brine as the internal brine phase and weighting
agent 29,30
.
The first oil wells in the Visund field completed with conventional bromide
brines had Productivity Indices (PI) of just 60-70 Sm3/d/bar. After using a
caesium formate invert emulsion as the alternative perforating fluid in well
A-23H a greatly improved PI of 200-300 Sm3/d/bar was achieved. Very
recently a further well perforated in the caesium formate invert emulsion
came in with a PI of 1000 Sm3/d/bar. The production from the two wells
completed in caesium formate brine will be enough to load the Visund
platform production treating facility to its maximum capacity of 100,000 bbl
oil/day.

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June 2002
Development work is underway on solids-free invert emulsions containing
high volume ratios of caesium formate to oil that could be taken to fluid
densities of up to SG 1.8. The use of caesium tungstate brine as the
internal brine phase of these formulations might allow the creation of
solids-free invert emulsions with fluid densities up to SG 2.0 or higher.
Novel non-aqueous formate “brines”
In 1997 researchers in Norsk Hydro’s laboratories in Norway discovered
that potassium formate and caesium formate are highly soluble in non-
aqueous polar organic fluids such glycerol and glycols. This discovery has
opened up the possibility of making benign high-density water-free and
hydrocarbon-free fluids for use as novel drilling and completion fluids.
These fluids will place a greater burden (e.g. oxygen demand) on the
environment than aqueous formate brines, but they represent an
interesting improvement over traditional brines.
10. CONCLUSIONS
Although the oil industry has made many incremental improvements in the
environmental acceptability of drilling fluids by modifying conventional
formulation technologies it seems clear that only the formate brines break
the mould and meet the criteria for classification as genuine ecological
drilling fluids with universal utility throughout the various stages of the well
construction process. Most importantly, the formate brines enable the
implementation of various mechanical engineering solutions that have
been introduced to make well construction operations more ecofriendly.
Eight years of rigorous field-testing of formate brines has validated their
performance under the most demanding conditions and proven their worth
in sensitive environments such as the Barents Sea. The future should see
formate brines being adopted as the preferred ecological drilling fluids on
a global basis, allowing the oil industry to significantly reduce both the
volume and toxicity of its drilling wastes.
Formate brines also have a bright future in downstream segment of the oil
industry as “green” substitutes for glycols and methanol in gas dehydration
and hydrate inhibition processes.
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June 2002
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-21st
February 1997.
27. Hallman, J.H., SPE, Mackey, R., Schwartz, K.:” Enhanced Shale
Stabilization With Very Low Concentration Potassium
Formate/Polymer Additives”, paper SPE 73731 presented at the SPE
International Symposium and Exhibition on Formation Damage Control
held in Lafayette, Louisiana, 20–21 February 2002.

th
June 2002
28. Zuvo, M., Asko, A.: “Sodium/potassium formate brine used as drilling
fluid in sensitive Barents Sea wells”, Offshore Magazine, August 2001,
64-66 and 181.
29. Jiang, P., Taugbol, K., Mathisen, A.M., Alteras, E.: “New Low-Solids
OBM Demonstrates Improved Returns as Perforating Kill Pill”, paper
SPE 73709 presented at the SPE International Symposium and
Exhibition on Formation Damage Control held in Lafayette, Louisiana,
20–21 February 2002.
30. Mathisen, A.M.:” Development and Application of Low Solid Oil-Based
Perforation Fluids to Maximise Well Productivity”, paper presented to
IQPC Drilling and Completion Fluids Conference held in Ardoe House
Hotel, Aberdeen, 20-21 March 2002.
Table 1 – Ecological solutions in well construction operations
Objective Solution
Reduction in well numbers Reduction in formation damage
Horizontal wells
Reduction in surface
footprint
Extended reach wells
Multilateral wells
Coiled-tubing drilling
Reduction of waste volume Slim holes
Improved solids control
Elimination of solid weighting agents

th
June 2002
Universal drilling/completion fluid
Cuttings re-injection
Reduction of waste toxicity Benign drilling fluids
Table 2 – Toxicity of Formates to Aquatic and Marine Organisms
Species Test type Sodium
formate
(ppm)
Potassium
formate
(ppm)
Caesium
formate
(ppm)
Zinc
bromide
(ppm)
Scophthalmus
maximus
LC50 96
hours
6,100 1,700 260 8
Acartia tonsa EC50 48
hours
3,900 300 340 2
Skeletonema
costatum
EC50 72
hours
1,600 3,400 1,000 0.3
Oncorhynchus
mykiss
LC50 96
hours
10,000 3,500 2,100 1
Daphnia
magna
LC50 48
hours
1,000 540 350 6
Mysidopsis
bahia
LC50 96
hours
7,130 522 307 1.5

Latest Advances in the Development of Ecological Drilling Fluids

Latest Advances in the Development of Ecological Drilling Fluids

Latest Advances in the Development of Ecological Drilling Fluids

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