44 www.tcetoday.com august 2012 Ping Yang and Safina Jivraj describe a holistic, risk-based approach to meeting OSPAR’s 2020 ‘zero harm’ targets for produced water T HE fate of and biological effects associated with the marine discharge of produced water from offshore oil and gas installations are of growing environmental concern. This, coupled with a number of worldwide fields approaching ‘end-of-life’, means an increasing volume of produced water is generated, leading regulators to be more vigilant over safeguards and controls. In order to protect the marine environment of the North East Atlantic, OSPAR (the Oslo- Paris convention) has already set a target of ‘zero harmful discharge’ from produced water by 2020. With this deadline fast approaching, accepted engineering practices may need to be adapted for future produced water management, using a risk-based approach. the environmental challenge Produced water is an inseparable part of the hydrocarbon recovery process. It is produced along with oil and gas and consists of natural formation water and water which is injected into the field to force the oil to the surface. As fields mature (and become depleted), they tend to produce increasing amounts of water. In 2010, the produced water rate exceeded hydrocarbon production by 50% globally and in the UK continental shelf, this figure reached over 130% between 2011–2012. Three routes are commonly used to dispose of produced water: discharge overboard into the sea; injection back to the source reservoir; or injection to another sub-surface formation. Due to cost and operational factors, discharge overboard into the sea has been the main route across offshore operations worldwide, and as a result, regulators worldwide have shown increasing interest in understanding the risks to the marine environment from produced water discharges. Produced water contains a variety of components, both naturally occurring and those added for production purposes. While defining the composition of produced water from a specific reservoir is almost impossible (due to the complex and changing nature of its various sources), typically, it would include dispersed and dissolved hydrocarbons, production chemicals, heavy metals, suspended solids and naturally occurring radioactive material. When released to the marine environment, such contaminants may harm marine organisms through acute and chronic toxicity, with a longer term potential of bioaccumulation. legislative safeguards To mitigate the risk to marine organisms, legislative safeguards are established worldwide. For example, the North East Atlantic (which includes the UK continental Looking after the Norway lobster OSPAR’s ‘zero-harm’ targets for produced water discharge aim to protect a variety of marine species including Nephrops norvegicus (known variously as the Norway lobster, Dublin Bay prawn, langoustine or scampi), cold-water corals, sponges, redfish, saithe, cod, ling, squat lobsters, molluscs, starfish, sea pens, and sea urchins. Sue Scott
Transcript
44 www.tcetoday.com august 2012
Ping Yang and Safina Jivraj describe a holistic, risk-based approach to meeting OSPAR’s 2020 ‘zero harm’ targets for produced water
THE fate of and biological effects associated with the marine discharge of produced water from offshore
oil and gas installations are of growing environmental concern. This, coupled with a number of worldwide fields approaching ‘end-of-life’, means an increasing volume of produced water is generated, leading regulators to be more vigilant over safeguards and controls. In order to protect the marine environment of the North East Atlantic, OSPAR (the Oslo-Paris convention) has already set a target of ‘zero harmful discharge’ from produced water by 2020. With this deadline fast approaching, accepted engineering practices may need to be adapted for future produced water management, using a risk-based approach.
the environmental challenge Produced water is an inseparable part of the hydrocarbon recovery process. It is produced along with oil and gas and consists of natural formation water and water which is injected into the field to force the oil to the surface. As fields mature (and become depleted), they tend to produce increasing amounts of water.
In 2010, the produced water rate exceeded hydrocarbon production by 50% globally and in the UK continental shelf, this figure reached over 130% between 2011–2012. Three
routes are commonly used to dispose of produced water: discharge overboard into the sea; injection back to the source reservoir; or injection to another sub-surface formation. Due to cost and operational factors, discharge overboard into the sea has been the main route across offshore operations worldwide, and as a result, regulators worldwide have shown increasing interest in understanding the risks to the marine environment from produced water discharges. Produced water contains a variety of components, both naturally occurring and those added for production purposes. While defining the composition of produced water from a specific reservoir is almost impossible (due to the complex and changing nature of its various sources), typically, it would include dispersed and dissolved hydrocarbons, production chemicals, heavy metals, suspended solids and naturally occurring radioactive material. When released to the marine environment, such contaminants may harm marine organisms through acute and chronic toxicity, with a longer term potential of bioaccumulation.
legislative safeguards To mitigate the risk to marine organisms, legislative safeguards are established worldwide. For example, the North East Atlantic (which includes the UK continental
Looking after the Norway lobster
OSPAR’s ‘zero-harm’ targets for produced water discharge aim to protect a variety of marine species including Nephrops norvegicus (known variously as the Norway lobster, Dublin Bay prawn, langoustine or scampi), cold-water corals, sponges, redfish, saithe, cod, ling, squat lobsters, molluscs, starfish, sea pens, and sea urchins.
Sue
Sco
tt
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shelf), is guided by the OSPAR convention to prevent and eliminate marine pollution. OSPAR has two main mechanisms to regulate produced water discharges: • Performance standards which prescribe limits on allowable levels of hazardous substance discharged. The current OSPAR limit is 30 mg dispersed oil/l of produced water. But produced water contains many pollutants, other than dispersed oil, hence a limit on dispersed oil does not adequately inform on environmental harm. In addition, the use and discharge of production chemicals are controlled by the Harmonised Mandatory Control Scheme, which requires substance level toxicity pre-screening and site specific environmental risk analysis. • Guiding principles, which underline the approach to achieve performance standards, such as the application of best available techniques (BAT) and best environmental practice (BEP).
change is imminentThe momentum for change is OSPAR’s 2020 target of ‘zero harmful discharge’ from produced water. OSPAR describes this target as “near background concentrations in the marine environment for naturally-occurring substances and close-to-zero concentrations of synthetic substances” but does not provide a clear picture of what constitutes ‘harmful.’ Operators need clear rules to decide how to assess the risk of harm so that they can identify and prioritise actions to make stepwise progress. In response, over the past four years, OSPAR has been formulating a recommendation for a risk-based approach (RBA) which takes a more holistic approach to achieving the target, rather than solely focussing on levels of dispersed oil in produced water. While the implications of this are not yet defined, it’s likely that requirements will include undertaking risk characterisation, either on a substances-based approach, a whole-effluent approach, or a combination of the two. The risk characterisation would require an assessment of the inherent capacity of the substances and the whole effluent in the discharge to cause adverse effects. An assessment of the sensitivity of the ecosystem for exposure to produced water either as a whole or from its components will also be needed. This will almost certainly involve comparing predicted environmental concentrations (PECs – ‘natural’ environmental concentrations) to predicted no effect concentrations
Figures 1 and 2: DREAM resultsBy comparing the maximum and instantaneous risk to acceptance criteria, the DREAM results of the environmental risks of produced water can be used to decide on a corrective course of action. Some of our modelled cases for non-routine discharges overboard have presented an environmental risk. These environmental risks rapidly disperse to <5% at the end of the release, reflecting the highly dispersive environment in this example. More advanced features of the model allow impacts on plankton to be examined, and the body burden in fish to be calculated at different life cycle stages.
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Figure 1: Instantaneous environmental risk of produced water discharge
Figure 2: Maximum environmental risk of produced water discharge
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(PNECs – concentrations that produce no adverse effects). It’s likely, then, that the regulatory system will require toxicity testing, modelling of the discharge and an interpretation of the results, which discusses the potential environmental impact. It’s expected that the operators will be required to demonstrate compliance with OSPAR’s recommendation as part of the ongoing renewal of their discharge consents. This is likely to be achieved by whole effluent testing (WET) or various models which employ compositional analysis data. OSPAR’s recommendation states that “where unacceptable environmental risks have been identified, contracting parties should review management options, evaluate measures and develop and implement site-specific actions to reduce the risks to an acceptable level.” Operators will therefore need to show that positive steps are being taken to adequately manage impacts achieved through the demonstration of BAT as defined by OSPAR. While operators in OSPAR contracting countries are free to implement the regime before any OSPAR deadlines, it’s recognised that an updated, if not new, set of tools and knowledge base will be required, to resolve issues such as: • screening criteria for detailed assessment;• acceptance criteria that can collaborate with observed results;• an approach to account for the physical, chemical and biological fate of discharged substances; and• a coherent WET test method.
Norwegian example Norway, a pioneer in adopting a risk-based approach for produced water management, is setting the example on how the industry
Figure 3: Time development and component contribution chart, showing the large predicted risk presented by H2S scavengers
could prepare itself for such a move. As early as 1996, the Norwegian government issued a white paper requiring the Norwegian oil industry to reach the goal of ‘zero discharge’ to the marine environment by 2005, which was later interpreted as ‘zero harmful discharge’. To quantify the potential risk to the marine environment, the Norwegian oil and gas industry developed the environmental impact factor (EIF), an eco-toxicological risk indicator, to be used on risk-based produced water management. An EIF=1 is a volume of 100 m x 100 m x 10 m of recipient water containing concentrations of one or more substances which may negatively impact more than 5% of the most sensitive species. EIF has been used by the industry to demonstrate progress toward ‘zero harmful discharge’ and to assure the regulator of its compliance status. The substances having the most potential to cause harm can also be identified, enabling systematic decision-making on investing the most optimal and cost-efficient mitigation measures to reducing risk to the marine environment. In addition, the DREAM (dose-related risk and effect assessment) model has been developed to simulate the three-dimensional and time-variable concentration field and EIF from produced water discharge. DREAM has the capability to calculate the fate of compounds or whole effluent under the influence of:• currents (tidal, residual, and affected by weather);• turbulent mixing (horizontal and vertical);• density (difference through salinity and temperature);• evaporation at the sea surface;• adsorption / desorption dynamics; and • reduction of concentration due to biodegradation.In parallel, efforts have been taken to classify substances based on their persistence, biodegradability, and toxicity characteristics. This enables decisions to be made on prohibiting and substituting hazardous production chemicals along with optimising chemical dosage.
is the UK ready?In 2010 the UK’s offshore regulator, the Department of Energy and Climate Change (DECC), along with the offshore industry, began preparing for the ultimate implementation of RBA. DECC has been formulating a proposal on a four-tiered assessment process involving a stepwise process with the possibility of screening installations by risk. To give operators an overview of how the process can be applied, worked examples have used OSPAR sampling data for chemical and toxicity properties of produced water. The final output
Operators need clear rules to decide how to assess the risk of harm so that they can identify and prioritise actions to make stepwise progress.
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is a produced water management plan based on the risk profile generated from the assessment. From the operators’ perspective, a strategy for future regulatory requirements is crucial so that the need for pre-investment can be assessed. A proven risk management tool such as DREAM will be useful in conducting cost-benefit analysis and informing a risk reduction strategy. Figures 1 and 2 show DREAM results which assess environmental risk from produced water discharge for a UK oil & gas operator. The results have been used to support option selection by comparing the maximum and instantaneous risk to acceptance criteria. Some of our modelled cases for non-routine discharges overboard have presented an environmental risk. These environmental risks rapidly disperse to <5% at the end of the release, indicating low persistence which is unlikely to cause cumulative effects. Further, major contributors to the risk can be identified. Where it is shown that production chemicals are a greater contributor to the risk than the naturally-occurring components, these can be adjusted. In one example, it was found that H
2S
scavengers accounted for approximately 80%
of the predicted risk (Figure 3). Therefore, the risk reduction measures should focus on less toxic or reduced dosage of H
2S scavenger.
RBA-readyWhilst imminent, at the time of writing this article, the final draft of the OSPAR Recommendation on RBA has not yet been published. However, it would be prudent for operators to begin planning for this new approach in produced water management, particularly for new projects. This is to allow risk reduction measures to be incorporated at an early stage of design. Although the applicability of OSPAR requirements are limited to the North East Atlantic Region, the concept of using a risk-based approach in produced water management offers oil and gas operators a means to demonstrate good operator stewardship and to deliver consistent environmental performance across all major projects worldwide. tce
Ping Yang is principal environmental engineer; Safina Jivraj ([email protected]) is environmental skills group manager, both at Genesis.
Current OSPAR requirements use 30 mg dispersed oil /l of produced water as the limit. Many constituents are not found entirely within the dispersed oil, but are dissolved in the produced water itself.
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