Table of contents

Page
1.0 / Introduction / 4
2.0 / Background / 4
3.0 / DREAM model / 4
3.1 / PNEC - The Predicted No Effect Concentration / 4
3.2 / PEC - The Predicted Environmental Concentration / 4
3.3 / EIF - Environmental Impact Factor / 5
4.0 / Input data / 5
5.0 / Results / 7
6.0 / Discussion / 16
7.0 / Recommendations / 16
8.0 / References / 16

Figures and Tables

Figures
Figure 1 / Modelled area showing location and size of habitat grid
Figure 2 / Time development of the EIF for the water column for Simulation 1
Figure 3 / Footprint and vertical cross section of discharge showing the time instant with maximum risk for the water column
Figure 4 / Footprint and vertical cross section of discharge showing the time instant with minimum risk for the water column
Figure 5 / Footprint and vertical cross section of discharge showing accumulated maximum risk for the whole simulation period for the water column
Figure 6 / Footprint and vertical cross section of ‘naturally occurring’ substances only for the water column
Figure 7 / Footprint and vertical cross section of ‘added’ substances for the water column
Tables
Table 1 / Model parameters
Table 2 / Concentrations for natural components in the discharge
Table 3 / Concentrations and toxicological data for added chemicals in the produced water
Table 4 / EIF results for the water column, discharge from 6 wells at Field-centre
Table 5 / Pie-chart of EIF results for the water column, (substances >1% risk shown)
Table 6 / The 4 substances which contribute 85.5% to total risk

1.0Introduction

The backers of the DREAM Charter project wish to keep track of license holders and their proficiency in DREAM model use. To achieve this a certification system has been instituted whereby SINTEF provide input data and a basic report template which are to be completed by license holders to asses there competence in using the DREAM model. The following report relates to the use of the model for produced water.

2.0Background

DREAM and its associated EIF concept were developed by SINTEF in partnership with a number of operators in response to the Norwegian government’s White Paper no. 58 and SFTs “Zero discharge report” of 1999. The DREAM/EIF model has since become the standard tool within the Norwegian sector for assessing the environmental risk posed by PW discharges. The DREAM/EIF model is also used as a management tool for mitigating any potential harm to the environment. Further details are available at technical details can be found in Utvik, et al. (2003)

3.0DREAM model

DREAM is able to calculate the physicochemical fate of the constituent components of a discharge. This includes the ability to model factors such as dilution by seawater, local and regional mixing using time-variable 2D wind and 3D current data. The environmental persistence, bio-accumulative and toxicological properties of the components can also be modelled. The model can predict the physicochemical fate of these components in the water column and benthic sediment.

DREAM incorporates databases of oil weathering, biological, environmental and toxicological information for naturally occurring chemical groups found in produced water. Version 6.5.1 includes PNEC values correlating with the OSPAR 2012/7 Guidelines for naturally occurring chemicals. Client supplied PNEC values are used in this case. These databases are augmented by the user with similar information for any added process chemicals.

3.1PNEC - The Predicted No Effect Concentration

PNEC is the concentration of a substance below which there is not expected to be any measurable environmental harm. For added chemicals and whole effluents PNEC values are derived from toxicity testing which give EC50, LC50 or NOEC values, the most sensitive of which is then divided by an assessment factor. Assessment factors are used to account for the inherent uncertainties in using a limited number of toxicity tests to represent a substance’s influence on a complex ecosystem. Larger data sets give greater confidence in results and therefore there is an inverse relationship between number and applicability of toxicological data and assessment factors.

3.2PEC - The Predicted Environmental Concentration

DREAM uses dispersion modelling to calculate Predicted Environmental Concentration of all chemical compounds within the specified body of water through time, taking into account the compounds characteristics, fate of the compounds and local environmental conditions.

The fate of the discharge will be calculated for each component taking account of:

Density, salinity and temperature;

Evaporation at the sea surface;

Reduction of concentration due to biodegradation;

Currents - tidal, residual, meteorological forcing;

Dilution by seawater;

Local and regional mixing - horizontal and vertical.

3.3EIF - Environmental Impact Factor

The EIF concept is used to measure the potential environmental risk posed by offshore PW discharges. The individual components can be quantified, identifying the compounds which pose the greatest potential harm. Thus allowing benefit comparisons of any potential mitigating measures. EIF refers to a volume of water, 100m long by 100m wide by 10m deep, in which the PEC/PNEC ratios of all substances have been calculated. An EIF of 1 equates to this volume of water in which at least one chemical compound’s PEC/PNEC ratios is greater than one. A PEC/PNEC ratio of >1 in this volume of water equates to a 5% probability that the most sensitive species in an ecosystem will be adversely affected by the PW discharge or that there is a 5% potential for ecological risk.

Using the PEC calculated by the model, it is possible to sum up the total risk to the environment surrounding the discharge point by building a risk map which can show the ‘typical’ (time-averaged) risk and a momentary maximum risk to the environment.

4.0Input data

Table 1 – Model parameters

Model parameters
Model duration (days) / 30
Liquid/solid particles / 5000
Dissolved particles / 5000
Concentration grid dimensions (m) / 100 x 100
Output interval (hours) / 3
Time step interval (minutes) / 5
Area of study (grid) / 25km x 25km
Metocean data (wind) / Gullfaks.wnd
Metocean data (tide) / NSEA.dir
Model initiation date / 01 May 1990*
Geographical position of discharge location / 59° 9.5' N 2° 27.5' E
Discharge depth below water surface / 15m
Discharge volume / 4,500,000 tonnes/year
Discharge rate / 1233tonnes/day

* SINTEF approved date for the above metocean data as it represents a period of calm climactic conditions which will give a ‘worst case scenario’.

Table 2 - Concentrations for natural components in the discharge

EIF component
name / Component
group / Concentrations
mg/l / PNEC
ppb
EIF_BTEX / BTEX / 16.9 / 17
EIF_NAPHTHL / Naphthalenes / 2.08 / 2.1
EIF_PAH1 / PAH 2-3 / 0.41 / 0.15
EIF_PAH2 / PAH 4+ / 0.0058 / 0.05
EIF_PHENOL1 / Phenols C0-C3 / 10.01 / 10
EIF_PHENOL2 / Phenols C4-C5 / 0.12 / 0.36
EIF_PHENOL3 / Phenols C6-C9 / 0.0046 / 0.04
EIF_ALIFATER / Dispersed oil / 41.1 / 40.4
EIF_CADMIUM / Cadmium (Cd) / 0.00023 / 0.028
EIF_COPPER / Copper (Cu) / 0.002 / 0.02
EIF_LEAD / Lead (Pb) / 0.0013 / 0.182
EIF MERCURY / Mercury (Hg) / 0.000071 / 0.008
EIF_NICKEL / Nickel (Ni) / 0.002 / 1.22
EIF_ZINC / Zinc (Zn) / 0.0245 / 0.46

Table 3 - Concentrations and toxicological data for added chemicals in the produced water

Chemical
name / Component / Concentration
(mg/l) / LogPow / Biodeg
% 28 dg / PNEC
ppb / Weight
factor
Chemical-1 / Component 1 / 14 / 0 / 58 / 8.5 / 2*
Chemical-2 / Component 1 / 0.650 / 1.3 / 71 / 125 / 1
Chemical-2 / Component 2 / 0.00047 / 2.3 / 83 / 50 / 1
Chemical-2 / Component 3 / 0.004 / 3 / 64 / 51 / 1
Chemical-2 / Component 4 / 0.033 / 0 / 27 / 700 / 1
Chemical-2 / Component 5 / 0.187 / 0 / 81 / 2.3 / 1
Chemical-3 / Component 1 / 8.070 / 0 / 36 / 1000 / 1
Chemical-4 / Component 1 / 0.212 / 0.4 / 21 / 1000 / 1
Chemical-5 / Component 1 / 0.7 / 0 / 67 / 0.25 / 1

*Weight factor which is used to put an extra weight on “red” and “black” chemicals as designated by Klif for Norwegian waters.

Figure 1 - Modelled area showing location and size of habitat grid

5.0 Results

Using the input data listed above it was found that the produced water simulation produced a time averaged EIF of 8 with a maximum computed EIF of 14. When a weighting factor is applied to chemicals we find that the EIF rises to 16.

The following outlines the components which contribute to the total EIF, the table outlines all of the components, natural and added, while the pie chart gives the 12 which achieve a greater than 1% contribution to total.

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Table 4 – EIF results for the water column, discharge from 6 wells at Field-centre

Components / Concentration
ppm / PNEC
ppb / Contribution
to risk / Contribution
EIF / Weight / Weighted
contributions / Weighted
EIF / Contribution to overall risk (%)
Total / 16.29154
BTEX / 16.9 / 17 / 2.18 / 0.3053526 / 1 / 0.3053526 / 1.87430 / 1.9
Naphthalenes / 2.08 / 2.1 / 4.62 / 0.6471234 / 1 / 0.6471234 / 3.97214 / 4.0
PAH 2-3 / 0.41 / 0.15 / 28.32 / 3.9667824 / 1 / 3.9667824 / 24.34872 / 24.3
PAH 4+ / 0.0058 / 0.05 / 0.86 / 0.1204602 / 1 / 0.1204602 / 0.73940 / 0.7
Phenols C0-C3 / 10.01 / 10 / 4.1 / 0.574287 / 1 / 0.574287 / 3.52506 / 3.5
Phenols C4-C5 / 0.12 / 0.36 / 2.48 / 0.3473736 / 1 / 0.3473736 / 2.13223 / 2.1
Phenols C6-C9 / 0.0046 / 0.04 / 0.85 / 0.1190595 / 1 / 0.1190595 / 0.73081 / 0.7
Dispersed oil / 41.1 / 40.400002 / 9.31 / 1.3040517 / 1 / 1.3040517 / 8.00447 / 8.0
Cadmium / 0.00023 / 0.028 / 0.04 / 0.0056028 / 1 / 0.0056028 / 0.03439 / < 0.1
Copper / 0.002 / 0.02 / 0.73 / 0.1022511 / 1 / 0.1022511 / 0.62763 / 0.6
Lead / 0.0013 / 0.182 / 0.03 / 0.0042021 / 1 / 0.0042021 / 0.02579 / < 0.1
Mercury / 0.000071 / 0.008 / 0.04 / 0.0056028 / 1 / 0.0056028 / 0.03439 / < 0.1
Nickel / 0.002 / 1.22 / 0 / 0 / 1 / 0 / 0.00000 / 0.0
Zinc / 0.0245 / 0.46 / 0.36 / 0.0504252 / 1 / 0.0504252 / 0.30952 / 0.3
Total % risk from naturally occurring compounds / 46.4
Chemical-1 Comp-1 / 14 / 8.5 / 16.32 / 2.2859424 / 2* / 4.5718848 / 28.06294 / 28.1
Chemical-2 Comp-1 / 0.65 / 125 / 0.02 / 0.0028014 / 1 / 0.0028014 / 0.01720 / < 0.1
Chemical-2 Comp-2 / 0.00047 / 50 / 0 / 0 / 1 / 0 / 0.00000 / 0.0
Chemical-2 Comp-3 / 0.004 / 51 / 0 / 0 / 1 / 0 / 0.00000 / 0.0
Chemical-2 Comp-4 / 0.033 / 700 / 0 / 0 / 1 / 0 / 0.00000 / 0.0
Chemical-2 Comp-5 / 0.187 / 2.3 / 0.51 / 0.0714357 / 1 / 0.0714357 / 0.43848 / 0.4
Chemical-3 Comp-1 / 8.07 / 1000 / 0.04 / 0.0056028 / 1 / 0.0056028 / 0.03439 / < 0.1
Chemical-4 Comp-1 / 0.212 / 1000 / 0 / 0 / 1 / 0 / 0.00000 / 0.0
Chemical-5 Comp-1 / 0.7 / 0.25 / 29.18 / 4.0872426 / 1 / 4.0872426 / 25.08813 / 25.1
Total % risk from added compounds / 53.6

*Weight factor which is used to put an extra weight on “red” and “black” chemicals as designated by Klif for Norwegian waters.

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Table 5 - Pie-chart of EIF results for the water column, discharge from 6 wells at Field-centre (substances1% risk shown)

Table 6 – The 4 substances which contribute 85.5% to total risk

Components / % contribution to
overall risk
Chemical-1 Component 1 / 28.1
Chemical-5 Component 1 / 25.1
PAH 2-3 e.g.
Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene,
including C1-C3 alkylhomologues, Anthracene and Dibenzothiophene / 24.3
Dispersed oil / 8.0

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Figure 2 - Time development of the EIF for the water column for Simulation 1, (discharge from 6 wells at Field-centre)

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Figure 3–Footprint and vertical cross section of discharge showing the time instant with maximum risk for the water column, (discharge from 6 wells at Field-centre)

Arrow indicates position of transectused to create vertical cross section through plume

Figure 4 – Footprint and vertical cross section of discharge showing the time instant with minimum risk for the water column

Arrow indicates position of transect used to create vertical cross section through plume


Figure 5 - Footprint and vertical cross section of discharge showing accumulated maximum risk for the whole simulation period for the water column

Arrow indicates position of transect used to create vertical cross section through plume

Figure 6 - Footprint and vertical cross section of ‘naturally occurring’ substances only for the water column

Arrow indicates position of transect used to create vertical cross section through plume

Figure 7 - Footprint and vertical cross section of ‘added’ substances for the water column

Arrow indicates position of transect used to create vertical cross section through plume

6.0 Discussion

Using the input data in tables 1-3 it was found that the produced water simulation produced a time averaged EIF of 8 with a maximum computed EIF of 14. This means that over the 30 days modelled the average volume of water to be significantly environmentally harmed (>5% risk) was 800,000m3 (8 x (100m x100m x 10m)), and at the moment of maximum harm 1,400,000m3 (14 x (100m x 100m x 10m)) were effected. When the weighting factor is applied to the chemicals (in this case Chemical-1 compound 1) we find that the EIF rises to 16 as the weighted chemical (Chemical-1 compound 1) makes the single largest contribution to EIF. The worst case scenario is therefore that 1,600,000m3 (16 x (100m x 100m x 10m)) of water suffers environmental harm.

The majority of risk is created by 4 components (Table 6) Chemical-1 Component 1 (28.1%), Chemical-5 Component 1(25.1%), PAH 2-3 (24.3%), Dispersed oil (8.0%).

Figure 2 shows that there are major fluctuations in the EIF e.g. over an 18 hour period between days 10 and 11 the EIF fluctuates by 13 units. The periods of lowest EIF are often associated with increased wind speeds. Highest EIF figures are achieved when the plume is at it’s most concentrated e.g. Figure 3 and lowest EIF figures are achieved when the plume is at it’s most dispersed e.g. Figure 4.

Figure 5 shows the accumulated maximum risk for the whole simulation period for the water column. The greater than 5% risk area is approximately ovoid in shape, mostly NNW of the discharge point. The area of greatest risk is approximately 11 x 5 x 3 EIF cells or 1,100m x 500m x 30m.

Figures 6 & 7 show the accumulated maximum risk for the whole simulation period for naturally occurring and added chemicals respectively, as can be seen they have very similar patterns, which is also reflected in the near 50:50 split in their contribution to risk (Table 4).

7.0 Recommendations

53% of the total risk is caused by two substances ‘Chemical-1 Component 1’ and ‘Chemical-5 Component 1’, if either of these could be substituted for less harmful substances then an improved environmental result could be achieved. Chemical-1 Component 1 has a weighting factor of 2 suggesting it is a chemical which already requires substitution.

The other area for improvement would be improved oil and water separation, insoluble oil contributes only 8% to the overall risk however the soluble components such as PAH 2-3 and Phenols added a further 37% to the total risk. Re-injection of the produced water to the well would obviously also reduce the impact of the produced water.

8.0 References

Utvik, T. R., Frost, T. K., & Johnsen, S. (2003). OLF Recommended Guidelines - A Manual for

Standardised Modelling and Determination of the Environmental Impact Factor.

OSPAR Commission (2012). Recommendation 2012/5 for a risk-based approach to the Management of Produced Water Discharges from Offshore Installations

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