Environmental aspects of the use and disposal of non aqueous ...

Environmental aspects
of the use and disposal of
non aqueous drilling fluids
associated with offshore
oil & gas operations
Report No. 342
May 2003

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Environmental aspects of the use and
disposal of non aqueous
drilling fluids associated with
offshore oil & gas operations
Report No: 
May 

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Environmental aspects of the use and disposal of non aqueous drilling fluids associated with offshore oil & gas operations
is report was produced by the Non-Aqueous Drilling Fluids Task Force.
Task force membership
Rene Bernier
ChevronTexaco
Emmanuel Garland
TotalFinaElf
Andy Glickman
ChevronTexaco
Fred Jones
Marathon
Heide Mairs
ExxonMobil
Rodger Melton
ExxonMobil
Jim Ray
Shell Global Solutions (US)
Joseph Smith
ExxonMobil
Dominic omas
Amerada Hess
John Campbell
OGP
Secretary
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Environmental aspects of the use and disposal of non aqueous drilling fluids associated with offshore oil & gas operations
Executive Summary
New technical challenges in offshore drilling have led to the requirement of drilling fluids
with drilling properties that exceed those of water based fluids. New concepts such as direc-
tional and extended reach drilling are required to develop many new resources economically.
Such drilling requires fluids that provide high lubricity, stability at high temperatures and
well-bore stability. ese challenges have led to the development of more sophisticated non-
aqueous drilling fluids (NADFs) that deliver high drilling performance and ensure environ-
mentally sound operations.
e introduction of NADFs into the marine environment is associated with fluid adhering
to discharged cuttings following treatment, since bulk discharge of NADFs is generally not
allowed. is paper does not consider bulk discharge of NADFs. Significant advances have
been made to reduce the toxicity and environmental impacts of NADFs. Where NADF
cuttings discharge is allowed, diesel and conventional mineral oils have largely been replaced
with fluids that are less toxic and less persistent. Polyaromatic hydrocarbons, the most toxic
component of drilling fluids, have been reduced from -% to less than .% for newer
fluids. New generation drilling fluids, such as paraffins, olefins and esters are less toxic and
are more biodegradable than early generation diesel and mineral oil base fluids.
e purpose of this paper is to summarise the technical knowledge about discharges of
cuttings when NADFs are used. e report summarises the results from over  publications
and compiles the findings from all available research on the subject. It is intended to provide
technical insight into this issue as regulations are considered in countries around the world.
It should aid in the environmental assessment process for new projects as it provides a com-
prehensive synopsis of what is known about the environmental impacts resulting from dis-
charge. A compilation of current regulations and practices from around the world is included
in Appendix C of this report.
As summarised in this paper, discharge is one of several options that may be considered when
deciding on waste management options. Other options include injection of cuttings or haul-
ing cuttings to shore for disposal. All waste management options have both advantages and
disadvantages with regard to environmental impact. is paper shows how environmental,
operational and cost considerations can be weighed to decide which options might be con-
sidered for given operational and local environmental conditions. e development of more
environmentally friendly fluids has been undertaken to reduce the environmental impact
associated with the discharge of drill cuttings that when NADFs are used, and make that
option more broadly acceptable. When applicable, offshore discharge is the safest and most
economical option.
is paper also covers the tools and methods available to predict the fate and effects of drill-
ing discharges. ese include laboratory techniques that have been used to address toxicity,
biodegradation and bioaccumulation characteristics of different fluids. Numerical models
that can be used to predict the distribution of cuttings that are discharged into a given envi-
ronment are also described.
A compilation of field monitoring results at offshore drilling sites reveals a relatively consist-
ent picture of the fate and effects drill cuttings associated with NADFs. e degree of impact
is a function of local environmental conditions (water depth, currents, temperature), and the
amount and type of waste discharged. Further, at sites where cuttings associated with early
generation drilling fluids were discharge, more significant temporal and spatial impacts were
observed. Cuttings discharged with newer fluids resulted in a smaller zone of impact on the
seafloor, and the biological community recovered more rapidly.
It is generally thought that the largest potential impact from discharge will occur in the
sediment dwelling (benthic) community. e risk of water-column impact is low due to the
short residence time of cuttings as they settle to the sea floor and the low water-solubility and
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International Association of Oil & Gas Producers
Environmental aspects of the use and disposal of non aqueous drilling fluids associated with offshore oil & gas operations
aromatic content of the base fluid. Impacts on the benthic biota are potentially due to several
factors. ese include chemical toxicity of the base fluid, oxygen depletion due to NADF
biodegradation in the sediments and physical impacts from burial or changes in grain size.
At sites where newer NADFs were used, field studies show that recovery is underway within
one year of cessation of discharges.
e nature and degree of impacts on the benthic community tends to reflect variability
between local environmental settings and differences in discharge practices. However, in
sediments with substantially elevated NADF concentrations, impacts include reduced abun-
dance and diversity of fauna. Recovery tends to follow a successional recolonisation, with
initial colonisation with hydrocarbon-tolerant species and/or opportunistic species that feed
on bacteria that metabolise hydrocarbons. As hydrocarbon loads diminish, other species
recolonise the area to more closely resemble the original state. e implications of potential
seafloor impacts depend on the sensitivity and significance of the bottom dwelling resources.
In many environmental settings, the bottom sediments are already anoxic, and the addition
of cuttings will have little incremental effect.
e degree and duration of impact depends on the thickness of the deposition, the original
state of the sediment and the local environmental conditions. In some settings, the cuttings
can be re-suspended eliminating any substantial accumulations. Initial deposition thickness
depends on a number of factors including the amount of material discharged, water depth,
discharge depth, the strength of currents in the area and the rate at which cuttings fall
through the water column. Greater accumulation would be expected in the case of a multiple
well development when compared with a single exploration well.
In conclusion, cuttings discharge appears to be a viable option in many environmental set-
tings. Work continues to develop and implement new technologies for cuttings treatment
to reduce fluid content on cuttings prior to discharge. Work also continues to improve and
develop a full range of disposal options.
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International Association of Oil & Gas Producers
Environmental aspects of the use and disposal of non aqueous drilling fluids associated with offshore oil & gas operations
Table of contents
1 Introduction
1
.. Processes of offshore oil & gas exploration and development drilling ...................................................
.. Exploratory, developmental and other drilling................................................................................................................
.. Drilling rigs.....................................................................................................................................................................
.. Description of drilling operations ...................................................................................................................................
.. Types of drilling fluids .........................................................................................................................
.. Drilling fluid composition...............................................................................................................................................
.. Advantages and disadvantages of NADFs .......................................................................................................................
2 Drill cuttings processing and waste disposal questions
9
. Solids control Equipment.....................................................................................................................
. Cuttings collection and handling........................................................................................................
. Cuttings disposal options....................................................................................................................
.. Offshore discharge ........................................................................................................................................................ 
.. Offshore cuttings re-injection ....................................................................................................................................... 
.. Onshore disposal........................................................................................................................................................... 
. Drill cuttings disposal options cost analysis .......................................................................................
3 Evaluation of fate and effects of drill cuttings discharge
27
. Overview of fate and effects of discharged NADF cuttings................................................................
.. Initial seabed deposition............................................................................................................................................... 
.. Physical persistence ...................................................................................................................................................... 
.. Benthic impacts and recovery........................................................................................................................................
. Laboratory studies.............................................................................................................................. 
.. Characterisation of NADF biodegradability .................................................................................................................
.. Characterisation of toxicity and bioaccumulation........................................................................................................ 
. Computer modelling of NADF cuttings discharges ...........................................................................
.. Introduction..................................................................................................................................................................
.. Model input requirements.............................................................................................................................................
.. Model uses ................................................................................................................................................................... 
.. Limitations and needs .................................................................................................................................................. 
.. Discharge modelling results .......................................................................................................................................... 
. Drilling fluid and cuttings discharge field studies ..............................................................................
.. WBF field study conclusions ........................................................................................................................................ 
.. Group  NADF cuttings discharge field study conclusions .......................................................................................... 
.. Group  NADF cuttings discharge field study conclusions......................................................................................... 
.. Group  NADF cuttings discharge field study conclusions ....................................................................................... 
.. Field survey interpretation limitations ......................................................................................................................... 
4 Conclusions
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References
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Appendix A – Table of acronyms ............................................................................................................
Appendix B – Glossary and abbreviations...............................................................................................
Appendix C – Country specific requirements for discharge of drilling fluids & cuttings ........................
Appendix D – Group II & III based fluid systems & base fluids ............................................................
Appendix E – Summary of non aqueous fluid cuttings discharge field studies........................................
E. Group  NADF cuttings discharge field studies ........................................................................................................... 
E. Group  NADF cuttings discharge field studies.......................................................................................................... 
E. Group  NADF cuttings discharge field studies .........................................................................................................
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International Association of Oil & Gas Producers
Environmental aspects of the use and disposal of non aqueous drilling fluids associated with offshore oil & gas operations
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International Association of Oil & Gas Producers
Environmental aspects of the use and disposal of non aqueous drilling fluids associated with offshore oil & gas operations
 Introduction
Exploration and development drilling activities have expanded globally into such regions
as the Caspian Sea, the UK Atlantic margin, offshore Brazil and West Africa, and the deep
waters of Gulf of Mexico as technology has improved the economics of finding and extract-
ing oil and gas. New drilling concepts, including horizontal and multi-lateral wells, enable
development to proceed with fewer platforms allowing these resources to be developed more
economically. ese techniques also have an environmental benefit of reducing the zone of
seafloor disturbance.
New drilling concepts are technically challenging and require high performance drilling
fluids† with capabilities exceeding those available from water based fluids (WBFs). As a
result, non-aqueous drilling fluids (NADFs), for which the continuous phase is primarily a
non-water soluble base fluid ie non-aqueous base fluid (NABF), have also been used exten-
sively by the petroleum industry.
e drilling process generates waste fluids and drill cuttings. Typical waste management
options include reuse, offshore discharge, re-injection and onshore treatment and/or dis-
posal. Choice of waste management options typically considers local regulations, environ-
mental assessment and cost/benefit analysis.
Early applications of NADFs used diesel or crude oil as the base fluid. Later, to lessen envi-
ronmental impacts when cuttings were discharged, mineral oils replaced diesel and crude.
More recently, low toxicity mineral oil based fluids, highly refined mineral oils and synthetic
fluids (esters, paraffins and olefins) have been used as base fluids. ese fluids are generally
less toxic due, in part, to reduced concentrations of aromatic compounds, and are less persist-
ent in the environment.
In many jurisdictions, regulations to deal with the full range of NADF technology have
not yet been developed. However, this is expected to change in the future since a number of
countries have either drafted or are actively working on new regulations. Worldwide regula-
tions on drilling discharges are summarised in Appendix C.
is document provides information useful for the development of technically based waste
management practices that consider both environmental risks and the balance of cost and
benefit associated with drilling discharges. Access to a full range of drilling fluid technology
is necessary to achieve drilling performance objectives and providing cost-effective develop-
ment, especially in deep water or where horizontal or extended reach drilling is employed.
Consequently, it is essential to understand the potential environmental issues and effects
associated with marine discharge of drilling wastes and the full life cycle analysis of imple-
menting alternative options.
To this end, this document discusses what is known about the fate and effects of drilling
discharges associated with the use of NADFs. In the following text, the process of oil and gas
drilling is described along with the technical advantages and disadvantages of NADFs. is
is followed by discussion of drill cuttings processing and waste disposal options, along with
guidelines for conducting cost analyses of options. e fate and effects of drilling fluids on
discharged cuttings are discussed next. Finally, the tools available to evaluate the environ-
mental performance of NADFs, including laboratory testing, computer modelling and field
studies are described along with the results of such studies.
† ril ing fluids are often referred to as muds or dril ing muds
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International Association of Oil & Gas Producers
Environmental aspects of the use and disposal of non aqueous drilling fluids associated with offshore oil & gas operations
1.1. Processes of offshore oil & gas exploration and development drilling
1.1.1 Exploratory, developmental and other drilling
e two primary phases of drilling operations conducted as part of the oil and gas extrac-
tion process are exploration and development. Exploratory drilling involves drilling wells
to determine whether hydrocarbons are present. Once hydrocarbons have been discovered,
additional appraisal or delineation wells may be drilled to determine the size of the hydro-
carbon accumulation. When the size of a hydrocarbon accumulation is defined sufficiently
for commercial development, field development is started. Development wells are drilled for
later production during this phase. Although the facilities used for each type of drilling may
differ, the drilling process for each well is generally similar.
Exploration activities are usually of short duration, involve a relatively small number of
wells, and are conducted from mobile drilling rigs. Development drilling usually occurs
over a longer interval of time and involves multiple wells to different parts of the reservoir.
Development wells are drilled to produce the hydrocarbon contained in the reservoir effi-
ciently. ey are drilled both as the initial means of producing the field and over the field’s
life, to manage withdrawal of reserves properly and replace wells that have experienced
mechanical problems.
1.1.2 Drilling rigs
Different types of facilities are commonly used for different drilling scenarios. Offshore,
drilling operations are performed either from mobile offshore drilling units (MODUs) or
permanent production platforms. MODUs facilitate moving drilling equipment from one
drilling site to another. e two basic types of MODUs are bottom-supported units and
floating units. Bottom-supported units include submersibles and jack-ups and are typically
used for drilling in waters up to around  metres. Floating units include semi-submersibles,
either anchored or dynamically positioned (Figure .) and ship-shaped vessels. Floating units
are typically used when drilling in deeper waters and at locations far from shore.
Permanent production platforms include fixed platforms or compliant towers (CT) or float-
ing facilities such as tension leg platforms (TLP), or spar platforms (Figure .) and FPSOs.
In addition to providing a platform for drilling wells, the fixed or floating platform provides
space for production facilities and living quarters.
Exploratory drilling is usually accomplished using a MODU. For development, fixed plat-
forms represent the minimum cost solution for drilling in shallow water. When the water
depth exceeds about  metres, development drilling is usually conducted from floating
drilling units or floating production facilities.
e type of facility used for drilling will have some influence on waste management options.
For example, the location of the wellhead can affect the ability to apply certain drilling
waste disposal options, particularly cuttings re-injection. When drilling is being conducted
from a fixed or floating platform or jack-up rig, the wellhead is located on the surface, above
the water level. When drilling is being conducted from a semi-submersible, the wellhead
is located on the seafloor. Technologies for injection into sub-sea wellheads are not mature
and are discussed in more detail in Chapter . In addition, space and weight limitations of
MODUs may limit the capability to store drilling wastes or to incorporate cuttings process-
ing or handling equipment more so than would be the case for fixed or floating platforms.

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