Estimated Recovery System Potential (ERSP) Calculator User Manual

The ERSP, EBSP, and EDSP Calculators are intended as planning tools for estimating the potential of different oil spill response systems to mitigate (recover, burn or disperse) discharged oil relative to one another. These planning tools are NOT intended to be used as models for calculating system performance during an actual oil spill, which is affected by many factors such as the distribution of oil on the water surface, oil weathering, and other ambient on-scene conditions which are not included in these Calculators.

Prepared by BSEE and Genwest Systems, Inc.

February 2016

Contents 1. Introduction ........................................................................................................................... 4 1a. The ERSP Calculator’s Purpose and Intended Use ...................................................... 4 1b. Advancing Skimming System Components ................................................................... 5 2. Assumptions and Limitations as a Planning Tool.................................................................. 8 3. ERSP Calculator Inputs ...................................................................................................... 12 3a. Encounter Rate Inputs ................................................................................................. 13 3b. Recovery Inputs ........................................................................................................... 15 3c. Storage Inputs.............................................................................................................. 17 4. ERSP Calculator Results .................................................................................................... 20 4a. Encounter Rate Results ............................................................................................... 23 4b. Recovery Results ......................................................................................................... 23 4c. Storage Results ........................................................................................................... 24 4d. Volume Results ............................................................................................................ 25 4e. Simulation Notes .......................................................................................................... 26 5. Using the ERSP Calculator ................................................................................................. 27 5a. Calculating ERSP for a Continuous Spill Scenario ...................................................... 27 5b. Calculating ERSP for a Batch Spill Scenario ............................................................... 32 6. Equations Used in Calculations............................................................................................. 37

1. Introduction The Calculator developed in this project estimates the performance of an advancing skimming system as it encounters, contains, recovers, stores, and offloads its recovered fluids to secondary storage. The Calculator generates an “Estimated Recovery System Potential” (ERSP) value in barrels of oil recovered for each of the first three days following the instantaneous discharge of a batch oil spill, or daily for an ongoing continuous discharge of oil.

The ERSP Calculator is an HTML file, ERSP-160225.html, which runs in the following web browser versions:

PC (Win-XP, Win-7 and Win-8 environments) IE - 9, 10, 11 or greater Chrome 38 or greater Firefox 31 or greater Safari 5.1 or greater

Mac (OS 10.6 and greater) Safari 8.0 or greater Chrome 38 or greater Firefox 35 or greater

You can download the ERSP Calculator from the BSEE website. The “build” or version date of the calculator appears after the calculator name in the format -YYMMDD (see Figure 4). This date stamp can verify that you are working with the latest version of the calculator.

This User Manual provides additional guidance to the user on the various data inputs that must be entered into the ERSP Calculator regarding the skimming system configuration being evaluated, and further explains the Calculator results.

The ERSP Calculator was originally developed by Genwest Systems Inc. in consultation with and with funding from the U.S. Department of the Interior, Bureau of Safety and Environmental Enforcement (BSEE) and the United States Coast Guard.

1a. The ERSP Calculator’s Purpose and Intended Use The ERSP Calculator is primarily a planning tool for estimating the potential for mechanical recovery of spilled oil by an advancing skimming system. You can use the Calculator to evaluate the ERSP of a skimming system for two kinds of spill scenarios:

• Continuous spills, such as a well blowout, in which oil is discharged at a steady rate for a relatively long period of time.

• Batch spills, such as a spill from a tank vessel, storage tank, or pipeline, in which oil is discharged nearly instantaneously or over a relatively short period of time.

To use the Calculator, you enter configuration information about an advancing skimming system, such as its swath, on-board storage capacity, pump rates, and speed, you describe the circumstances of its operation, such as transit time to secondary storage (see Section Three, ERSP Calculator Inputs). The Calculator then estimates the amount of oil that the system could collect during the operating period of each of the first three days after a major batch spill begins, or during the operating period for each day of a continuous spill response (see Section Four, ERSP Calculator Results). These estimates of the oil collected are termed the “Estimated Recovery System Potential” (ERSP) for the given skimming system configuration. The use of the calculator tool in both spill scenarios is further demonstrated and explained in Section Five, Using the ERSP Calculator.

In addition to evaluating the potential of an advancing oil spill skimming systems to meet various regulatory planning requirements, the ERSP Calculator can also be used to explore how to configure a skimming system to best encounter, recover, store, and offload oil more efficiently. By comparing different configurations, you may discover that increasing swath width, adding a second discharge pump, or increasing onboard storage may increase your system’s daily recovery potential. This experimentation is helpful in understanding the effects of different configurations on a system’s recovery potential.

1b. Advancing Skimming System Components The ERSP Calculator was primarily designed as a planning tool for estimating the potential of advancing skimming systems. ASTM Standard F 1780-97, Standard Guide for Estimating Oil Spill Recovery System Effectiveness, defines an advancing skimmer as a system designed to sweep out the spill area of oil. Advancing skimmers may be independent or attached to containment boom to increase sweep width. In some cases, the skimmer may not be attached to the boom, but positioned in the pocket of the boom for skimming. As long as the skimmer operates while the system is moving, it is considered to be an advancing skimming system. Some skimming systems may be used both in advancing and stationary modes. Advancing modes are especially critical in recovering spills in open water, while stationary systems are necessary for recovering oil spills in areas where the movement and removal of oil is tightly constrained by barriers such as shorelines. Figure 1 below identifies the major components of an advancing skimming system:

Figure 1. Advancing Skimming Recovery System Components.

Below are short descriptions of the various components of an advancing skimming system:

Supporting Platform Vessel – Labeled as OSRV in the diagram. This is the supporting platform for all the basic components of a skimming system including the following: containment boom, skimmer device, onboard storage, decant and offloading pumps; and (if present) berthing, messing, navigation, propulsion elements.

Containment Boom – Encounters and concentrates the oil/emulsion from the oil slick. Encounter rate is a function of the Skimming Speed, the Swath, and the oil thickness

Skimmer Device – Captures oil, emulsion, and free water (a function of the Recovery Efficiency) and transfers the Total Fluid Recovered to Onboard Storage. A portion of the oil/emulsion encountered is lost behind the system (a function of the Throughput Efficiency).

Onboard Storage – Includes tankage built into the OSRV to receive the total fluids recovered. It could also include barges or other storage that is physically connected to the OSRV so that the Skimmer can discharge directly into it. Where permitted, a portion of the free water recovered can be decanted ahead of the skimming system after settling (and physical separation and heating depending on the capability of the system). When the Onboard Storage is full, the system transits to the location of secondary storage, rigs for transfer, offloads to secondary storage, derigs and transits back to the spill site to resume skimming operations.

Pumps –Depending on the type of skimmer a subcomponent could be a pump. Also included in this component category are the pump(s) used to decant a portion of the recovered free water (if enabled) and the discharge pump(s) used to transfer recovered product from Onboard Storage to Secondary Storage.

Secondary Storage - While not shown in the diagram, secondary storage is considered a component of each skimming system. As each system fills its onboard storage it transits to the location of secondary storage.

The following diagrams illustrate some of the possible configurations of advancing skimming systems.

Figure 2. Skimming system configuration examples

Enhanced Skimming Configurations

Enhanced skimming adds a U-shaped configuration of boom with an open apex towed ahead of the skimming system. The added boom configuration increases the system’s effective swath width, and concentrates the oil/emulsion for containment and recovery by the skimmer. This configuration increases a system’s areal coverage and oil encounter rates. Enhanced skimming will require additional personnel, tow boats and enough additional boom to achieve the desired swath using a gap ratio of 1:3 (e.g. a 300 foot swath would require a minimum of 900 linear feet of boom).

Figure 3. Open apex enhanced skimming configuration example

2. Assumptions and Limitations as a Planning Tool The ERSP Calculator was developed to provide an encounter-rate based estimate of daily recovery potential for advancing skimming systems operating in open waters, in warm or cold climates, without the effects of ice, debris or extreme weather conditions. The calculator accommodates a broad range of skimming system configurations and addresses response activities including the accessing, containment and recovery of oil. The calculator also accounts for the storage and possible decanting of recovered free water, the transiting of a skimming system to and from secondary storage, and the offloading of recovered fluids. The goal was to provide a computer tool that could facilitate the calculation of a “Planning Standard”, not a “Performance Measure”.

The following is a list of assumptions and limitations inherent to the design of the ERSP Calculator, that are readily acknowledged as conditions accepted in order to keep the Calculator a simple and easy to use planning tool:

• Ambient Conditions: Estimates made by the Calculator assume that conditions are generally conducive to effective skimming operations. Its output is designed to serve as a guide for planning the deployment of skimming systems and estimating their recovery potential in order to meet plan holder needs. • Default Values: Generally, conservative default values are built into the Calculator. A default value is conservative if it is more likely to be an underestimate than an overestimate. • Skimming Downtime: No downtime due to maintenance or repair is considered. • Oil Types: The Calculator does not differentiate outputs based on the type of oil or product being recovered. Its design assumptions most closely approximate the spreading and emulsion characteristics of Group II, III, and IV oils. As a result, the calculator is a less accurate predictor for the availability of non- persistent Group I type oils, such as gasoline or diesel fuel. Group I oils tend to NOT form stable emulsions. Group I oils also tend to form much thinner slicks than Group II, III, and IV oils even in very large discharge quantities. • Use of Constant TFRR Values: Skimming systems are assumed to be collecting at a constant recovery rate. Actual recovery of oil/emulsion by skimmers is likely to be more intermittent in nature (as necessary to accumulate sufficient thicknesses of oil) in order to maximize the efficiency of recovery operations. At any point the Total Fluid Recovery Rate (TFRR) cannot exceed Maximum Total Fluid Recovery Rate of the system. If this occurs, the Calculator will reduce the Swath so that the TFRR = Maximum Total Fluid Recovery Rate. • Skimming in Waters with Restricted Maneuverability: The ERSP calculator does not discern between ocean or offshore operating areas and inshore operating areas. While the ERSP algorithms apply equally in all areas, skimming systems with large swath widths and large tethered storage arrangements are likely to be less effective in inshore operating areas, where water depths and restricted maneuverability are likely to become a critical factor. It is up to the ERSP Calculator user to apply operational knowledge and common sense in selecting values for their skimming configuration that match the needs of the operating environment (as opposed to entering values for poorly matched configurations that would maximize the ERSP at the expense of operational feasibility). • Three Day Window for Calculating ERSP for a Batch Spill Scenario: The three-day ERSP calculation period for batch spill scenarios was selected for several reasons. After the first three days, there is a reduced availability of oil because the majority of the oil has weathered and spread to the point where continued on-water skimming operations may become an ineffective response option. Another factor is the operational reality that three days after an incident

has occurred, most of the necessary response resources would be on-scene or ordered, and spill specific response planning would be in place. • Oil Spreading and Thickness Values: Computer models, such as the Response Options Calculator (ROC) developed by Genwest, along with other sophisticated models described in the EDRC project final report, were used to establish nominal oil thicknesses for each of three days following a major spill (typically thousands to tens of thousands of barrels). The ROC predicts that, in a batch spill, oil thicknesses within the slick generally will decline over time. The spreading and weathering of a broad range of oil types and volumes were simulated under varying wind/sea conditions and water temperatures. The analysis of the results of these simulations revealed nominal representative thickness values that are used to estimate the oil encounter rates for each day of a significant spill. The results of hundreds of computer simulations suggested that 12 hours after the discharge of a large oil spill (assumed mid-day on Day 1), the nominal oil/emulsion thickness could be estimated at 0.1 inch. The mid-day thicknesses for each of Days 2 and 3 could be represented by 0.05 inch (after 36 hours) and 0.025 inch (after 60 hours). In the ERSP Calculator the Operating Period is defined as the length of time in hours each day (centered on noon) where conditions allow a skimming system to conduct removal operations. Real-world oil/emulsion thicknesses can span several orders of magnitude for the many different oil types and environmental conditions that could actually occur during a spill. However, the three selected values reflect reasonable representative thicknesses which are used for the Operating Period in each of the first three days for the recoverable portion of a batch discharge of oil for “planning” purposes. For significant continuous discharges, the nominal oil/emulsion thickness for the designated Operating Period in Day 1 (.1 inch) of a batch spill is used for each day of the response to a continuous spill. • Use of Best Practices for Skimming: The ERSP Calculator assumes responders will use best practices, for example, the use of airborne spotters and remote sensors in order to actively direct and keep skimming systems continuously operating in the thickest available concentrations of recoverable oil. ERSP also assumes that personnel are available and trained to deploy and effectively operate the skimming system in the manner necessary to achieve the maximum potential. • Emulsification: Many oil releases involve emulsified oil (emulsions of water in oil). During real oil spills, emulsification proceeds at different rates and to different degrees depending on such things as oil type and environmental conditions. Based on a number of simulations, the Calculator specifies the percentage of emulsification as 35% in Operating Period 1, 55% in Operating Period 2, and 75% in Operating Period 3 for batch releases, 35% for all operating periods of a continuous release. In any ERSP Calculator run, the recovered fluids are assumed to be a mix of oil/emulsion and free water. However, ERSP is a calculated estimate of the volume of oil recovered.

• Asset Mobilization: It is assumed that the skimming system is rigged and ready to operate with empty Onboard Storage at the beginning of each Operating Period. The ERSP Calculator does not account for the time necessary at the beginning of a spill for notification, mobilization, and transit time to the location of the oil slick. These factors need to be addressed separately in each plan as required by the relevant agency regulations. • Offloading in between Operating Periods: At the end of each Operating Period it is assumed that any fluids remaining in onboard storage will be removed before the next Operating Period begins. If the Calculator determines that this offloading cannot be done in the time available between Operating Periods, then a Simulation Note (Simulation Notes are described in more detail in Section 4) will be generated - “Offload not achievable between Operating Periods - Reduce Operating Period [hrs]”. Using the same system configuration, the user can reduce the Operating Period and recalculate until the Note no longer appears. Adding Discharge Pump capacity or making other configuration changes could also impact the required offload time.

3. ERSP Calculator Inputs This section provides a general description, and in many cases amplified guidance, for each of the input fields and the variables that a user must enter into the Calculator. The graphic below is an illustration of the input screen that a user will see and use to enter their skimming system information into the Calculator.

Figure 4. ERSP Calculator Input Screen

Discharge Type (Continuous Spill and Batch Spill): The user must identify the type of spill for which the system is being evaluated. This selection will determine the format of the output that the ERSP Calculator will display.

Skimming System Identifiers:

These screens are useful for both planners and regulators to identify and track the ERSP Calculator input and output data associated with major equipment configurations.

• Name of System: Entry field for the name or other form of identifier for the skimming system (up to 48 characters). • Skimmer Details: Enter configuration details including the type of platform, skimmer, pump, and boom being used and other key information to identify this simulation.

The Use of Default and Alternate Values: The Calculator, and its default values for many of the key inputs, was intended to be “conservative” in nature. In some cases, an advancing oil skimming system’s tested performance will be able to exceed the default values for specific inputs. Plan holders or OSROs may submit requests for the use of alternate values in the ERSP Calculator to the appropriate regulatory agency. The regulatory agencies will consider each request based on the merits of the documentation provided. Operators should expect that the use of approved alternate values may be subject to validation efforts by regulators. Plan holders and OSROs may be required to satisfactorily demonstrate the practical