An integrated approach to environmental decision-making
for offshore oil and gas operations



Rehan Sadiq2, Brian Veitch1, Christopher Williams3, Vanessa Pennell1, Haibo Niu1, Bo Worakanok1, Kelly
Hawboldt1, Tahir Husain1, Neil Bose1, Mukhtasor4, and Cynthia Coles1

1Faculty of Engineering and Applied Science, Memorial University of Newfoundland, St. John's, NF, Canada
2Institute for Research in Construction (IRC), National Research Council Canada, Ottawa, Ontario, Canada
3Institute for Marine Dynamics (IMD), National Research Council Canada, St. John's, NF, Canada
4Faculty of Ocean Technology, Sepuluh Nopember Institute of Technology, ITS, Indonesia


ABSTRACT

A brief overview is given of a research program on environmental risks associated with offshore
oil and gas industry discharges. The research has two major thrusts: development of
environmental risk assessment and risk management methods, and development of underwater
vehicle technology for scientific and monitoring missions. This paper focuses on the former. The
project is a joint venture between the Ocean Engineering Research Centre at Memorial
University of Newfoundland and the Institute for Marine Dynamics of the National Research
Council Canada, with the support of several Canadian companies and universities. This paper
describes several elements of the project: (a) the development of a risk management
methodology for drilling waste discharges in the marine environment, (b) development of a
probabilistic hydrodynamic model and risk-based design procedure for produced water
discharges, (c) performance characteristics of several candidate sensors for environmental effects
monitoring, (d) laboratory investigation of the settling characteristics of drill cuttings, (e)
evaluation of various offshore treatment technologies for drilling waste using multi-criteria
decision-making, and (f) evaluation of air emissions associated with the offshore petroleum
industry and environmental management practice to mitigate the impacts. The ultimate goal of
the research is to integrate current and emerging scientific knowledge and technology with the
goals of environmental protection and their associated costs in a holistic framework to guide
decision-making under uncertainty.

Keywords: Drilling waste, produced water, autonomous underwater vehicle (AUV), chemical
sensors, ecological risk assessment, environmental effects monitoring, multi-criteria decision-
making, and treatment technologies.
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Canada-Brazil Oil & Gas HSE Seminar and Workshop, March 11-12, 2002

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ENVIRONMENTAL RISK, REGULATION, AND POLICY

Offshore oil and gas operations worldwide are facing significant changes in environmental
protection regulations, which reflect the evolving values placed on the environment by society
and the subsequent adoption of these values in governmental and industrial policies. Different
jurisdictions are implementing changes at different paces, but the general direction is the same:
more attention is being focussed on environmental risk and more effort is being directed toward
mitigating it. There is no shortage of opinion on the questions that arise in this context, such as
what should be protected, and at what cost, what is an acceptable level of risk, and how does
perception match with reality. These are issues that should be debated by stakeholders in each
jurisdiction and the outcomes are not likely to be the same, nor should they be expected to be the
same.

Scope

The focus of the work presented here is significantly narrower in scope. It concentrates on the
scientific and technical aspects of environmental risks related to the major marine discharges
associated with the offshore petroleum industry. The goal of the research is to integrate current
and emerging scientific knowledge and technology with the goals and costs of environmental
protection in a holistic framework to guide decision-making under uncertainty.
This work is being pursued by a partnership consisting of the Ocean Engineering Research
Centre at Memorial University of Newfoundland and the Institute for Marine Dynamics of the
National Research Council Canada, with the support of several Canadian companies (Petro-
Canada, International Submarine Engineering, Applied Microsystems) and universities
(University of Victoria).
Most of this work is being carried out under a major project entitled Offshore
Environmental Risk Engineering Using Autonomous Underwater Vehicles, which has two major
thrusts: development of environmental risk assessment and risk management methods, and
development of underwater vehicle technology for scientific and monitoring missions. This
paper concentrates more on the former and describes several elements of the project: (a) the
development of a risk management methodology for drilling waste discharges in the marine
environment, (b) development of a probabilistic hydrodynamic model and risk based design
procedure for produced water discharges, (c) performance characteristics of several candidate
sensors for environmental effects monitoring, (d) laboratory investigation of the settling
characteristics of drill cuttings, (e) evaluation of various offshore treatment technologies for
drilling waste using multi-criteria decision-making, and (f) evaluation of air emissions associated
with the offshore petroleum industry and environmental management practice to mitigate the
impacts.
While much of this work is relevant in an international sense, the project is particularly
concerned with the developments off the East Coast of Canada. Of the various discharges to the
environment, produced water and drill cuttings are the main focus of this work.
Produced water is a combination of formation and injection water and can be a complex
mixture of inorganic and organic compounds, which has the potential to be toxic to the ocean
environment. Constituents of concern include metals, petroleum hydrocarbons, nutrients,
radionuclides and treatment chemicals. Typical discharge rates for produced water can be high.
Over the life of the producing field, the quantity of discharge can be typically 10 times as high as
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the volume of hydrocarbons produced. Models of the produced water discharge tend to predict
that produced water will be rapidly diluted and dispersed when discharged into the ocean,
however, real data with which to corroborate these assertions are scant (Mukhtasor 2001).
Produced water is treated continuously and then discharged. Discharge limits of oil in
water in the US Gulf of Mexico and the OSPAR (Oslo and Paris) convention countries are 29 mg/l
and 40 mg/l, respectively, for a 30 day average. OSPAR plans to move to a 30 mg/l limit within 4
years. New draft regulations for the East Coast of Canada have followed the OSPAR limit of 40
mg/l, but have put operators on notice that this might be reduced to 30 mg/l at the next regulatory
review (CNOPB 2002).
Drill cuttings are a product of exploration and production drilling operations and are
typically discharged and settle on the seabed. For the most part, cuttings are small rock particles,
but some amount of the drilling mud adheres to the rock particles. The drilling fluid (mud) is a
mixture of water, base fluids, special clays, minerals, and chemicals that is pumped downhole
through the drill string and is ejected through nozzles in the drill bit at high pressure. The jet of
fluid lifts the cuttings off the bottom of the hole and away from the bit. The drilling fluid is
circulated to the surface through the annulus between the drill string and casing. At the surface,
the drill cuttings, silt, and sand are removed from the drilling fluid before it is returned downhole
through the drill string.
The cuttings, sand, and silt are separated from the drilling fluid by a solid separation
process. Some of the drilling fluid remains attached to the cuttings after treatment. After solid
separation, the cuttings are disposed of in a manner that depends on the type of drilling fluid
used, the oil content of the cuttings, and the regulatory regime. The disposal methods include
transport to shore for land-based disposal, ocean discharge, and re-injection. The early focus of
efforts to reduce the environmental impacts of cuttings discharges was centered on reducing the
volumes of drilling fluids discharged with the cuttings, as well as the generic toxicity of the base
oil itself. By 1985 it became clear that regardless of the inherent levels of toxicity of the base
oils, the cuttings piles persisted and continued to pollute for many years due to leaching of
chemicals into the ambient environment (Hall 2000).
The U.S. EPA (1999b) suggested product substitution, e.g., synthetic based fluids (SBFs)
instead of oil based fluids (OBFs), as the best way of reducing environmental impacts. The oil
industry has developed many base materials, such as vegetable esters, to increase the efficiency
of drilling operations. With these improved characteristics, the U.S. EPA (1999a) is still
proposing controlled discharge of the cuttings associated with SBFs. SBFs are less dispersible in
nature and sink to the seafloor, and may be a potential environmental concern to the benthic
community. It is believed that environmental impacts include smothering by the drill cuttings,
changes in grain size and composition, and anoxia caused by the decomposition of organic
matter (U.S. EPA 1999a). The environmental impacts associated with the zero discharge of
OBFs can be more harmful than the discharge of SBFs due to non-water quality environmental
impacts, like air pollution and ground water pollution in the case of incineration and land based
disposal, respectively (U.S. EPA 1999a).
In addition to the marine discharges, air emissions are coming under increasing scrutiny.
Emissions of gases associated with the production of oil and with refining operations are a cause
of concern at the local and at the global level. Flaring or venting of associated natural gas,
including methane and other light hydrocarbons, is a major contributor to the build up of green
house gases directly linked with global warming problems. The adverse impacts of global
warming are expected to have a particularly marked effect on the environment.
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RESEARCH PROJECT

The major elements of the research project Offshore Environmental Risk Engineering Using
Autonomous Underwater Vehicles are outlined in Figure 1. This research has two major parts:
methodology development for environmental modeling and risk assessment, and development of
techniques for environmental effects monitoring (EEM). Environmental modeling research is
subdivided into water quality and non-water quality (waste emissions from stacks and flares).
Water quality modeling is again subdivided with respect to type of waste discharged. Drilling
waste and produced waters are the two major groups. Both waste discharges require fate and
transport modeling and ecological risk assessment steps. The development of an autonomous
underwater vehicle (AUV) is focused on environmental monitoring and scientific sampling
missions.



Modeling
Monitor/Experiment


Non-water quality
Water quality
Autonomous underwater
Lab experiments on

vehicle (AUV)
environmental impacts
environmental impacts
drilling waste


B
i
o

a
Settling behavior
v
a

Drilling waste
Produced water
i
l
a
discharges
b

discharges
i
l
i
t
y
Fate

Hydrodynamic modeling
modeling

Ecological risk assessment (ERA)

Human health risk assessment HHRA

Evaluation of offshore treatment technology
Cost estimation
Risk management for decision-making



A risk based design for
offshore discharges/emissions


Tasks already completed



Tasks under study


Tasks planned for future research



Figure 1. An integrated approach for risk based design for offshore oil operations.
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Drilling waste discharges in the marine environment – A risk based decision methodology

The main aim of this work is to develop a risk management framework for determining the best
drilling waste discharge scenario for disposal in the marine environment (see Figure 2). The
specific objectives are:

(a) development of probabilistic contaminant fate modeling methodology using fugacity and
aquivalence based approaches;
(b) development of an ecological risk assessment methodology using probabilistic concepts;
(c) development of human health cancer and non-cancer risk assessment methodologies using
probabilistic concepts;
(d) development of a fuzzy composite programming framework for risk management by
integrating environmental risk, cost estimates, and technical feasibility for various treatment
options; and
(e) an application of the developed risk management framework to a hypothetical case study.

Fate modeling is performed using fugacity and aquivalence based concepts. A chemical
specific approach is employed for contaminant fate modeling. A steady state non-equilibrium
water and sediment interaction model with probabilistic inputs is used to determine the
contaminant concentrations in the water column and pore water. The uncertainty and variability
in the model inputs are expressed by statistical distributions. The concentrations in the water
column and pore water are estimated using Latin Hypercube sampling (LHS) based Monte Carlo
(MC) simulations. The concentrations in the water column and pore water follow lognormal
distributions. Estimated parameters of lognormal distribution for known discharge conditions are
used for performing multiple regression analyses. The highest 95th percentile is used as the
predicted environmental concentration (PEC). The uncertainties in the PEC are expressed by the
coefficients of regression models.
The PEC values are converted into exposure concentrations (EC) by adjusting for
bioavailability and probability of exposure. The whole ecological community is defined as
assessment endpoints. The toxicity assessment analyses are based on the lognormally distributed
predicted no effect concentrations (PNEC). The lowest 10th percentile on PNEC distributions is
used as a safety level, or PNEC criteria value. Bootstrapping is performed on original PNEC data
to determine the uncertainty in the PNEC criteria values. The hazard or risk quotients (HQ/RQ)
are calculated by dividing EC with PNEC criteria values. The CHARM model's approach is used
to convert HQ/RQ into risk estimates for each contaminant. The composite ecological risk for
drilling waste is determined by integrating the individual risk estimates assuming statistically
independent events.
The human health risk methodology is based on the consumption of contaminated seafood.
A probabilistic framework for human health risk assessment is used for cancer and non-cancer
risk estimates. The chronic daily intake rate (CDI) is established based on fish ingestion rates,
lipid content, bioconcentration factors, exposure duration, and exposure frequency. The LHS
based MC simulations are performed to estimate the CDI. Arsenic is the only proven human
carcinogen in the drilling waste stream. The composite hazard index for non-cancer risks is
calculated by simple addition for a given exposure scenario.
A risk management methodology using fuzzy composite programming (FCP) is used. The
costs of treatment, drilling fluid loss due to discharge, and ecological and human health damages
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are estimated. The technical feasibility of various solid control devices is also included from a
performance viewpoint. The environmental risk reductions, cost saving and technical feasibility
indices are grouped using FCP methodology. A double weighting scheme is employed in FCP.
The final utility and centroidal values of the system improvement indices are calculated through
fuzzy ranking methods to determine the best management alternative.
The risk management framework was applied to a hypothetical case study on the East
Coast of Canada. Five discharge scenarios, or management alternatives were selected for the
analysis: 10.0%, 8.5%, 7.0%, 5.5% and 4.0% attached base fluids to wet cuttings. Sensitivity
analysis was performed using four different weighting schemes to account for human
subjectivity.
This study has introduced a new concept of integrating probabilistic fate modeling with
ecological and human health risk assessment methodologies within a risk management
framework to determine the best management alternative under conflicting objectives. It has
provided a framework for a decision support system for the selection of the best drilling waste
marine discharge option under any known regulatory and technical constraints. The results of
this research can be seen in Sadiq (2000, 2001) and Sadiq et al. (2000, 2001a-b, 2002a-d).

Hydrodynamic modeling and ecological risk based design of produced water discharge

In the context of produced water discharges, environmental risk assessment (ERA) has usually
been directed at monitoring. Mukhtasor (2001) considered the engineering design of a discharge
outfall for produced water from an offshore platform using hydrodynamic modelling and
considerations of ecological risk assessment. The specific objectives of this research were:

1. Develop an initial dilution model;
2. Integrate the developed initial dilution model with a far field model;
3. Develop a methodology for probabilistic hydrodynamic modeling;
4. Identify methodologies for ERA of produced water;
5. Develop a framework for risk-based design; and
6. Apply the framework to a case study.

Conceptual and numerical problems associated with presently available initial dilution
models were identified and a new approach to initial dilution modeling was proposed based on
the hypothesis of additive shear and forced entrainment combined with nonlinear regression. The
proposed approach is systematic and provides an objective means of evaluating the initial
dilution model. The new model is more robust than previous models and is conceptually and
numerically more defensible. It gives a unique, continuous solution of centreline dilution.
Further, it does not assume that the current has no effect in the buoyancy dominated near field
(BDNF), which other models do; in the buoyancy dominated far field (BDFF) region the model
has one parameter fewer that an existing model, but is no less accurate; in the transition region it
gives a unique solution, which asymptotic models do not; it has approximately the same
precision for all regions (BDNF, BDFF, transition); and it can also be presented in a probabilistic
form that permits calculation of failure probability for specified model inputs and a threshold
dilution.

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Selection of a disposal option: drilling waste discharge in ocean environment

C

o

•
n
Drilling waste characterization
t
a
•
m
Defining discharge scenarios

i
n
a
n
t

f

• Estimating pollutant loading rates
a
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• Application of fugacity/aquivalence models

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• Exposure assessment
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• Estimating uncertainty in
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• Estimating HQ
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Defining basic events, e.g., ecological risk, human health risk, status

d
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of technology, cost estimates
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Technical
Cost
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Estimates
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Estimating final system index and utility functions
(
F
C
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)


Ranking various alternatives


Selecting best alternative after making tradeoff analysis

Final disposal limitations on SBFs discharge

Figure 2. An integrated approach for risk management of drilling waste discharges.
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Hydrodynamic modeling was carried out by integrating the near and far field models. The
initial dilution model was used as the near field model. The far field model and control volume
approach for connecting near and far field models were adapted from published methods. A
comparison using a case study showed that the proposed hydrodynamic model and the CORMIX
model are generally in good agreement, particularly in estimating average effluent
concentrations. The new model also provides the concentration field in the x-y directions so that
it may also be applicable for analysis of mixing zones, which in some cases is defined in terms of
the horizontal area around the discharge location. The new model can also be used in a
probabilistic analysis to take into account the uncertainty associated with the model inputs,
coefficients, and error term. The probabilistic analysis was done using Latin Hypercube
Sampling (LHS) based Monte Carlo (MC) simulations.

Performance characteristics of candidate sensors for environmental effects monitoring

Several candidate autonomous underwater vehicle missions have been proposed. At this early
stage, these missions serve as both trials of the AUV technology, and an opportunity to gather
information to validate predictive models, such as the produced water fate models described
above. Conventional strategies for ocean sampling involve the collection of samples of water and
biological specimens using equipment that is usually deployed over the side of a ship, and the
return of these samples to land laboratories for analysis. Such methods are tedious and
sometimes inaccurate, as volatile chemicals will disappear quickly. Thus in-situ chemical
analysis of samples is desirable in order to keep the quality of the samples high. This could be
achieved by equipping an AUV with suitable sampling and chemical analysis equipment.
An AUV is a self-propelled submersible robot capable of carrying out pre-programmed
tasks without human intervention. AUVs are particularly suited for applications in hazardous
environments because they do not require a human support team nearby or a tether to the surface.
These vehicles provide a platform for a wide variety of offshore tasks, including oceanographic
sampling and research, environmental monitoring, under-ice mapping, pipeline inspections and
surveys, and offshore oil and gas systems maintenance and support. In the present context, an
AUV might provide a suitable platform for sensors to detect the presence of chemicals in drilling
wastes and produced waters, and for validation of numerical models that predict the
consequences of these discharges.
In a recent trial, a mass spectrometer was used for identifying the chemical constitution of
a substance by means of the separation of compounds according to their differing mass and
charge. The Applied Microsystems Limited (AML) mass spectrometer is an innovative
underwater mass spectrometer first developed at the Center for Ocean Technology at the
University of South Florida. The subsequent development of the mass spectrometer at AML is an
on-going process that continually changes to suit the needs of the mission.
The underwater mass spectrometry system is housed in three separate pressure vessels that
are connected in series for deployment. The front vessel serves as the sample collection system
and contains a pump and a flow injection system. Sample water is continuously pumped into a 1-
ml sample loop, the contents of which are periodically swept into the membrane introduction
mass spectrometer (MIMS) system in the central vessel by switching the flow injection valve.
Pumping deionized water from a reservoir bag into the MIMS interface probe displaces samples.
In this manner changes in ion intensities for selected masses can be continually compared to
background levels in the mass spectrometer. It is possible to use a carbon filter rather than
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deionized water that will reduce the complications associated with the reservoir bag and related
plumbing. In addition, a continuous mode of sampling can be used. This type of sampling will
eliminate the need to switch the flow injection valve, which will reduce sample time.
A continuous mode of sampling was chosen for the trials. The continuous sample mode
does not compare samples against a background level to give discrete values. Instead, it
compares changes in concentration as the mass spectrometer is moved through the water stream.
The central pressure vessel contains the main components of the mass spectrometer. These
components include the vacuum chamber and mass analyzer with membrane introduction probe,
associated electronics, turbo molecular vacuum pump and controller, CardPC motherboard
with 72MB DiskOnChip memory, and a power distribution board which can be interfaced with
an external computer that activates the various components in sequence. The third vessel
contains two dry diaphragm pumps in series that serve as backing pumps for the turbo pump.
The practical depth of deployment for this system is presently limited to 30 m.
The trials were conducted over a three day period from February 4 through February 6,
2002 in Burrard Inlet, near Vancouver, BC. The AUV used for the trials was the ARCS vehicle
supplied by International Submarine Engineering in Port Coquitlam, BC. The first step was to
install the mass spectrometer on the AUV. There were no complications in adding the equipment
to the payload bay of the AUV. The mass spectrometer was also user-friendly. The software
included with the instrument is Windows based and allows for easy control of the mass
spectrometer. A picture showing the mass spectrometer installed on the AUV is presented in
Figure 3.
Dimethyl sulphide (DMS) was used as a chemical tracer for this experiment. It was
pumped into the inlet at a rate of about 7 l/h. The AUV support staff programmed ARCS to do a
mission with the mass spectrometer on board. The captain and crew of the research vessel
estimated the current direction, and ARCS was programmed to do a lawnmower pattern back and
forth perpendicular to the current direction. The reason for this choice was that the current was
the means of transport for the DMS. Initial results indicate that the mass spectrometer detected
the DMS during the sea trials. This result shows the potential for the use of such an instrument
for environmental monitoring of chemicals in an effluent plume. The picture in Figure 4 shows
the ARCS vehicle on its mission.





Figure 3. Mass spectrometer in ARCS vehicle.
Figure 4. The ARCS AUV on trial mission.
Canada-Brazil Oil & Gas HSE Seminar and Workshop, March 11-12, 2002
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Laboratory investigation of the settling characteristics of drill cuttings

The settling behaviour of drilling waste is uncertain and will undergo a number of physical-
chemical processes upon discharge. The fate of these discharged drilling wastes (cuttings and
fluids) will depend upon the local oceanographic conditions, quantities and conditions of
discharge, amount, type and concentration of fluids on cuttings, and fall velocity of cuttings
particles. The synthetic base fluids (SBFs) are not water miscible and tend to aggregate and fall
rapidly through the water column. To predict the fate of SBF drilling cuttings, it is important to
understand how they behave upon discharge. A detailed risk management study for drilling
waste has already been conducted (see above) in which some assumptions were made to
determine the fate of drilling waste in the marine environment. Additional work is underway in
order to improve the knowledge of the physical characteristics of the cuttings waste stream in
order to improve fate modeling.
A number of mathematical models have been used to assess drilling discharge during the
past three decades. Many of the available models for the various processes were developed based
on simple concepts and have had limited testing. Predictions made by different models differ
significantly. For example, Huang (1992) conducted laboratory investigations on the transport
properties of water based drilling fluids (WBFs), including resuspension, flocculation, and
settling speeds.
In the current project, flocculation properties of drilling waste will be examined by using a
blade type flocculator, which can generate a wide range of turbulent shear. Typical values of
shear rate in the ocean environment are in the range from 0.01 to 10 s-1 (David et al. 1994). The
cohesive fine particles (d<38 µm) will be sieved out from the SBF cuttings slurry and diluted to
5, 10, 25, 50, 100, 200, 500, and 1000 mg/l by mixing with synthetic seawater. The flocculator
will be run at a series of constant rotational speeds to generate fluid shear in the samples. At
specific time intervals, the flocculator will be stopped and samples put into a 2.5 m high settling
column for a particle size analysis and settling speed test. High resolution and high speed digital
photographs will be employed to track the falling particles. The recorded images will be used to
determine the particle size distribution and settling speed of each particle. Both the non-cohesive
and cohesive particles will be tested. Through the analysis of experimental data, the flocculation
time, floc size distribution with flocculation conditions, and the settling velocity-size relationship
in quiescent water will be obtained.
The setup for the quiescent water settling experiment has been tested using sand particles.
The experimental results for terminal velocity are compared with the settling velocities of glass
spheres (Gibbs et al. 1971) and sand particles (Sleath 1984) in Figure 5. The settling of fine
particles was found to reach a constant speed (terminal velocity) in a very short time after
discharge. Even very coarse particles were found to approach their terminal velocity within a few
seconds. It was also shown that the shape of particles has a strong effect on the terminal settling
velocity and this effect is more significant for large particles. The shape of SBF drilling cuttings
varies a lot, especially when flocculation occurs.
Turbulence in the water body has a significant effect on the settling of suspended particles.
These turbulence effects have been studied by number of investigators, but inconsistencies in
results have been reported (Peter 1993). In order to investigate the turbulence effect on settling
and the dispersion of drilling particles in dynamic conditions, tests in a wave tank may be done.


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Document Outline

• ABSTRACT
• RESEARCH PROJECT

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