The Environment Impact Factor (EIF) for produced water discharges a tool for reducing environmental impacts H. Rye 1, M. Reed 1, M. Kristin Ditlevsen 1, S. Berntsen 2 & E. Garpestad 2 1 SINTEF Applied Chemistry, Trondheim, Norway 2 Conoco/PPCoN, Norway Abstract The operators on the Norwegian Continental Shelf (NCS) have agreed with the Norwegian Authorities to work towards a reduction of the environmental impact from produced water releases (and also from drill cuttings and mud releases) down to a zero release option, or a zero effects release option. In order to achieve this, an indicator for the potential impact from produced water releases has been developed, namely the EIF (= Environmental Impact Factor). This paper shows how this EIF factor has been applied to five different releases on the NCS in order to select the best option for reducing the potential impact from produced water. Keywords: modeling, environment, produced water, marine discharge. 1 Introduction When oil is produced offshore, produced water is separated from the oil stream and discharged into the sea. This produced water contains remnants of added chemicals and different natural compounds (examples are dispersed oil, some dissolved PAH s and phenols and also some heavy metals) which may represent a potential for harmful impacts on the biota in the recipient. The amounts of the produced water discharged will normally, at a later stage of production, by far exceed the amount of oil produced. The amounts of produced water discharged to the sea on the NCS have now exceeded 100 mill. tonnes per year, and have
24 therefore become a concern for the oil companies as well as for the Norwegian Governmental Bodies (SFT). The operators on the NCS have therefore developed a method for evaluating potential environmental risks from these discharges. The method gives a quantitative measure of the potential risks, and is thus able to form a basis for reduction of impacts in a systematic and a quantitative manner. This method is based on the calculation of the EIF by means of the DREAM model. The EIF method is based on a PEC/PNEC approach. That is, the concentration PEC for some compound discharged into the recipient is compared to some concentration threshold limit PNEC for that compound. When PEC is larger than the threshold PNEC, there may be a risk for damage. When the PEC is lower than the PNEC threshold, the risk for damage is considered to be acceptable. An outline of the EIF method is given in Johnsen et al. [1]. 2 The PEC The PEC (=Predicted Environmental Concentration) is the three-dimensional and time variable concentration in the recipient caused by the discharge of the produced water. The PEC is calculated for all compounds that are assumed to represent a potential for harmful impact on the biota. The calculations are made by means of the DREAM model. This model is fully three-dimensional and time variable. It calculates the fate in the recipient of each compound considered under the influence of currents (tidal, residual, meteorological forcing) turbulence and mixing (horizontal and vertical) evaporation at the sea surface reduction of concentration due to biodegradation The ocean currents are also three-dimensional and time variable, and are usually generated from hydrodynamic models. Further details on the model DREAM are presented in Reed et al. [2]. 3 The PNEC The PNEC (= Predicted No Effect Concentration) expresses the lower limit where effects on the marine biota in the recipient may be encountered. The PNEC level is given for each component (or component group) in the produced water. It is derived from laboratory testing of toxicity for each component (or chemical product) in question. The PNEC value is derived from EC50, LC50 or NOEC values from laboratory testing, where the EC50, LC50 or the NOEC value determined is divided by some assessment factor in order to arrive at the expected PNEC. The assessment factor is chosen according to EC Technical Guidance Document (EU [3]). A major data collection work has been performed in order to obtain data of sufficient reliability to be selected for determination of PNEC values. Different procedures have been selected for determination of the PNEC values for natural
25 constituents in produced water and for added chemicals. Table 1 shows the actual PNEC values used for natural compounds (or component groups) in produced water. For added chemicals, the PNEC values are usually based on the information found in the HOCNF (= Harmonized Offshore Chemical Notification Format) scheme. Further details can be found in Johnsen et al. [1]. Table 1: PNEC values for natural constituents in produced water applied for the EIF calculations. Natural compounds PNEC ppb Dispersed oil 40.4 BTEX mono-aromatics 17 Naphthalenes 2.1 PAH 2-3 ring (excl. naphthalenes) 0.15 PAH 4-6 ring 0.05 Phenols C0 - C3 10 Phenols C4 - C5 0.36 Phenols C6 + 0.04 Zinc (Zn) 0.46 Copper (Cu) 0.02 Nickel (Ni) 1.22 Cadmium (Cd) 0.028 Lead (Pb) 0.182 Mercury (Hg) 0.008 4 The EIF The EIF is related to the recipient water volume where the ratio PEC/PNEC > 1 for any of the compounds or component groups considered. The ratio PEC/PNEC is related to the probability of damage on a marine recipient according to a method developed by Karman et al. [4] (and also published in Karman and Reerink [5]). When PEC/PNEC = 1, this corresponds to a level of probability of damage equal to 5 %. Figure 1 shows the relation between the PEC/PNEC ratio and the probability of damage. The EIF method has a big advantage above other screening-like methods for chemicals that it can calculate risk contributions from a sum of chemicals and/or natural compounds in produced water discharge recipient. For the total risk from a sum of compounds, the total risk is calculated from the formula P( A + B) = P( A) + P( B) P( A) * P( B) (1) where P(A) is the probability of environmental risk for compound A and P(B) is the probability of risk for compound B. For small risks (that is, P(A) and P(B) are both small), the risks can be considered to be linearly additive, approximately.
26 The total risk for a given discharge is calculated by means of the DREAM model. The total risk contribution (in %) is calculated by the DREAM model for every point (grid) in space and time within the model domain. The sum of risks (for every point in space and time) is then summarized and converted back to a corresponding PEC/PNEC value with the aid of Figure 1. The results are then presented as shown in Figure 2 (snapshot in time). The water volume indicated by the dark color then indicates the water volume where the ratio PEC/PNEC is larger than one for all compound (or compound groups) considered. Within this water volume, the risk contribution is calculated to the larger than the 5 % limit (corresponding to a total PEC/PNEC > 1). EIF is defined as the water volume where the PEC/PNEC > 1, divided by a unit volume equal to (100 x 100 x 10 =) 10 5 m 3 of recipient water. In addition, the EIF water volume is adjusted upwards by a factor of two for those compounds that have a small biodegradation factor combined with a large bioaccumulation factor. Details are given in Johnsen et al. [1]. An attractive feature of the EIF approach is that the method is also able to discriminate between the various contributors for environmental risk. In addition to show the actual number for the EIF, it can also show which of the compounds, chemicals or compound groups that contribute to the environmental risk. An example is shown in Figure 3. This makes the method attractive in particular when measures have to be chosen in order to arrive at the zero discharge option. 5 Example of application As a part of the zero discharge mindset, the operators on the NCS were asked by SFT to consider measures to be taken in order to arrive at the zero discharge option within the year 2006. One of the operators wanted therefore to consider the effects on the EIF from different measures, for reducing impacts from five different discharges of produced water, including the two techniques: Re-injection of the produced water Removal of potential harmful compounds by means of the C-Tour process. The re-injection option means that the produced water is re-injected back into the reservoir or into another geological structure below the sea floor. Although this alternative seems to be the ultimate solution, this option will still cause some discharges due to maintenance of the production flow and the re-injection system. The C-Tour option is based on a purification process of the produced water flow. The C-Tour process causes a reduction of natural compounds in the produced water by adding liquid hydrocarbon gases (natural gas fractions) to extract dispersed and dissolved (aromatic) hydrocarbons from produced water. The process differs from other solvent-extraction processes in that multicomponent hydrocarbon gases (natural gas fractions) are used as the solvent.
27 PNEC value versus environmental risk 100 Probability of environmental damage (%) 80 60 40 20 0 0,01 0,1 1 10 100 1000 10000 Ratio PEC/PNEC Figure 1: The relation between the PEC/PNEC level and the risk level (in %) for damage on biota. Based on Karman et al. [4]. Figure 2: Calculation of PEC/PNEC for the sum of various compounds in produced water. Snapshot in time. Horizontal extent (upper figure) and vertical extent (lower figure) are both shown.
28 Total risk, EIF = 0.2678 BTEX Corrosioninhibitor 0 % Zi Ni Naphthalenes 0 % Corrosioninhibitor 0 % 0 % 0 % De-emulgation chemical 0 % 4-ring+ PAH 18 % 2-3 ring PAH Scale inhibitor 47 % Phenol C0-C3 12 % Aliphatics 9 % C4+ phenol 12 % Figure 3: Pie chart for an EIF calculation. A scale inhibitor gives a contribution of 47 % of the total risk for this case. Base case EIF calculated for 2001-2020 2750 2500 2250 2000 1750 Discharge 1 Discharge 2 Discharge 4 Discharge 3 Discharge 5 EIF 1500 1250 1000 750 500 250 0 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 Figure 4: EIF calculated for 5 different discharges for the years 2001 2020. Present (2002) status with no measures on the discharges. Another feature of the process is the enhancement of the removal of dispersed oil particles over the traditional separation processes due to increased coalescence, and an induced increase in the density differences between the water and the dispersed hydrocarbon-particles. Further details are found in Henriksen et al. [6]. The results from the present status of the five discharges (the do nothing or the basecase alternative) are shown in Figure 4.
29 EIF = 2546 Phenols C6+ Phenols C0 - C3 Corrosion inhibitor 24 % Dispersed oil 16 % BTEX Naphthalenes 3 % 2-3 ring PAH 54 % Figure 5: Contributors to the EIF for discharge No. 1 expected for the year 2014. The natural compounds 2-3 ring PAH and dispersed oil give the largest contribution to environmental risk, along with a chemical (corrosion inhibitor). The basecase alternative. EIF = 389 Phenols C6+ Phenols C0 - C3 2 % Corrosion inhibitor 9 % Dispersed oil 16 % Naphthalenes 5 % 2-3 ring PAH 67 % Figure 6: Contributors to the EIF for discharge No. 2 expected for the year 2005. The natural compounds 2-3 ring PAH and dispersed oil give the largest contribution to environmental risk. The basecase alternative. The calculations show that two of the five discharges appear to contribute to the EIF, namely the discharges 1 and 2. The other three contributes with EIF s that are relatively low, compared to the other two. These two discharges will be discussed in greater detail in the following.
30 The pie charts in Figures 5 and 6 show the compounds in the produced water that contributes to the large EIF values for Discharges No. 1 and 2: While the re-injection of produced water will reduce impact for all compounds, the C-Tour process will have different effect on different natural compounds. The ability of the C-Tour process to remove water soluble compounds will be smaller, compared to the less water soluble ones. Table 2 shows the expected reduction of natural compounds in the produced water due to the C-Tour process applied in these calculations. The operator will later confirm removal efficiencies in offshore tests: Due to the effects from the re-injection (assumed 90 % efficiency) and the effects from the C-Tour process as shown in Table 2 (without re-injection), the EIF was reduced for Discharges No. 1 and 2 as shown in the Figures 7 and 8. Table 2: Expected percentage reduction of produced water natural compounds due to the C-Tour process. 6 Results from calculations Efficiency of Component group removal Dispersed oil 90 % BTEX 0 % Naphthalenes 90 % PAH 2-3 ring 90 % PAH 4-5-6 ring 90 % Phenols C0 - C3 0 % Phenols C4 - C5 90 % Phenols C6+ 90 % Both methods for reduction of EIF values (re-injection and C-Tour) appear to give significant reductions for both Discharges No. 1 and 2. The choice of method (or a combination of methods) is therefore a cost issue weighted against the benefit expressed through the reduction in the EIF value. In this particular case, the reduction of EIF turns out to be largest for discharges No. 1 and 2 in the re-injection case (Figures 7 and 8). But this is also the most costly option. The C-Tour process also gives significant reductions, and the costs for this option are also less, compared to the re-injection option. The drawback for the C- Tour option is that the water soluble fractions of the potentially harmful compounds in the discharges (typically C0 - C3 phenols and mono-aromatics) are not removed with the C-Tour process (see Table 2). This is also a drawback for reductions of water soluble chemicals used. With re-injection, all compounds are reduced along with the reduction of the amount of produced water discharged, irrespective of water solubility properties of the chemicals added or the water solubility of the natural compounds.
31 Results from impact reductions for Discharge No. 1 3000 2500 Basecase C-tour Reinjeksjon 2000 EIF 1500 1000 500 0 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Year Figure 7: Results from re-injection or the C-Tour process for reduction of the impacts from produced water discharge on the recipient, expressed through the value of the EIF, Discharge No. 1. Results from impact reductions for Discharge No. 2 450 400 350 300 Basecase C-tour Reinjeksjon EIF 250 200 150 100 50 0 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year Figure 8: Results from re-injection or the C-Tour process for reduction of the impacts from produced water discharge on the recipient, expressed through the value of the EIF, Discharge No. 2. The conclusion from this work is therefore that a re-injection or the C-Tour process for the discharges No. 1 and 2 appears to be the most attractive option for reduction of environmental impact in a cost-effective manner. Tests is planned to be carried out on the C-Tour process in order to determine its efficiency more accurately. The EIF method has thus demonstrated that efforts have been re-directed towards the discharges where the environmental benefit will be largest (that is, discharges No. 1 and 2). Then efforts can be saved (or optimized) by giving less priority to the other three discharges (No. 3-5) where the environmental benefit (in terms of reduced EIF) will be moderate anyway.
32 7 Definitions and acronyms DREAM Dose related Risk and Effect Assessment Model EC50 The concentration where a specific effect is observed for 50% of the test specimen EIF Environmental Impact Factor HOCNF Harmonised Offshore Chemical Notification Format LC50 The concentration which causes lethality for 50% of the test specimen LOEC Lowest Observed Effect Concentration NCS Norwegian Continental Shelf NOEC No Observed Effect Concentration PAH Poly-Aromatic Hydrocarbons PEC Predicted Environmental Concentration PNEC Predicted No Effect Concentration SFT Norwegian State Pollution Control Authority TGD Technical Guidance Document (EC [3]) References [1] S. Johnsen, T.K. Frost, M. Hjelsvold and T.R. Utvik, 2000: The Environmental Impact Factor a proposed tool for produced water impact reduction, management and regulation. SPE paper 61178 presented at the SPE International Conference on Health, Safety and Environment in Oil and Gas Exploration and Production, Stavanger, Norway, 26 28 June 2000. [2] M. Reed et. al., 2001: DREAM: a Dose-Related Exposure Assessment Model. Technical Description of Physical-Chemical Fates Components. Paper presented at the 5 th Int. Marine Environmental Modelling Seminar, New Orleans, USA, Oct. 9-11 2001. [3] EU, 1996: Technical guidance document in support of commission directive 93/67/EEC on risk assessment for new notified substances and commission regulation (EC) No. 1488/94 on risk assessment for existing substances. Part i to IV, Office for official publications of the European Communities. ISBN 92-827-8011-2. [4] C.C. Karman et. al., 1994: Ecotoxicological Risk of Produced Water from Oil Production Platforms in the Statfjord and Gullfax Fields. TNO Environmental Sciences. Laboratory for Applied Marine Research, den Helder, The Netherlands. Report TNO-ES, February 1994. [5] C.C. Karman and Reerink, H.G., 1997: Dynamic Assessment of the Ecological Risk of the Discharge of produced Water from Oil and Gas producing Platforms. Paper presented at the SPE conference in 1997, Dallas, USA. SPE paper No. SPE 37905. [6] I.B. Henriksen et. al., 1999: The CTour Process. Cost-effective Extraction Process for Removal of Dissolved and Dispersed Hydrocarbons from Produced Water. 10 th Int. Oil Field Chemicals Symposium, 28/2 3/3 1999, Fagernes, Norway.