Directive 071 - ERCB H2S Frequently Asked Questions |
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Issue: Sweet pipeline tie-in to a sour gathering system
A company is tying a sweet pipeline into one containing H2S. Since the model assumes flow from either end of the pipeline until the ESD shuts, the company assumes that there will be a possibility of H2S flowing back into the sweet line, and that therefore there could be a release. The company has tried to model this sweet line and the sour one, assuming the model will account for the backflow and provide a small EPZ for the sweet line. |
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ERCBH2S only has the capability of modelling gas that contains H2S. When a company enters 0% H2S into the model, it is forced to divide by zero, producing no answer. The key message is that the ERCB has never asked companies to account for backflow and calculate EPZs for sweet lines. The model is not built to handle that calculation. Therefore companies should assume 0 m EPZ on all sweet lines. |
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Issue: How do ESDs and check valves (CV) differ in the model?
A company indicates in its model that a pipeline has an ESD on one end of its line and a CV on the other end. Given that a CV immediately prevents backflow, the company assumed that any additional flow to the line between the time of a pipeline release and the time the ESD shut would only come from the end of the line where the ESD is located. However, when the company ran the model, a much larger EPZ than anticipated was predicted. |
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ERCBH2S treats ESD valves and check valves the same for EPZ calculations. This means that the model assumes there could be backflow into a line, when in reality there would not be. The model was written this way for simplicity. If there is enough concern from industry, we may recommend that the model be changed. |
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Issue: Large EPZs on very short lines
In some instances a line that is only 5 or 10 m in length can have EPZs several kilometres in diameter. |
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There are three main things to look for here:
- whether the company has used mitigation or not,
- what the pressure rate of change on the ESDs is, and
- what the upstream and downstream line properties are.
The model assumes infinite flow from both upstream and downstream of a pipeline. Therefore a short line with no mitigation or a very low pressure rate of change (10%) will have continual flow into it from both upstream and downstream. To mitigate this, the applicant must increase its pressure rate of change to ensure that the ESDs close sooner. |
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Issue: What does the ESD valve low pressure trigger mean? |
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The low pressure trigger is the pressure set point where the ESDs on a pipeline close. The model asks companies to enter this value as a pressure value (kPa), but it is commonly discussed in terms of percentages. A low pressure trigger of 10% means that the pipeline has to depressure to 10% of its total operating MOP before the ESDs will close. Essentially, the pipeline must be empty before the ESDs close. This means the associated EPZ will be very large, almost equal to a case using no mitigation. A low pressure trigger of 90% is generally unreasonable, as daily fluctuations in pipeline pressure would cause the ESDs to close. Many companies choose to use a low pressure trigger somewhere in the range of 50%.
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Issue: Lines with differing lengths having very similar EPZs
All other input being equal, why do lines with differing lengths have virtually the same EPZ? |
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The first this to do is check whether the company has modelled the lines using mitigation or not. If they have not (which will most likely be the case in these scenarios), the model assumes that the line will flow for 12 hours before the ESDs shut. If they have chosen “With Mitigation” but have a very low “low pressure trigger” (say, 10%), this is virtually the same as having no mitigation at all. The model assumes that the sections upstream and downstream of the ESD are infinite and will supply as much gas as needed until the pressure drops to the set point or the valves are closed manually. By selecting “With Mitigation” and entering values above the default, the EPZ becomes more sensitive to the line length. |
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Issue: The .csv file will not import into the model
After importing, the model provides a message that states “Batch import successful! 0 records imported.” |
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First, open the .csv file to make sure it looks correct and is the proper version (v1.19). The company may not have exported it correctly on its end. Instructions on how to export model runs are found on page 40 of the user guide.
If the .csv looks correct, the company may have accidentally saved it as an Excel file. Once a model run is exported, changes cannot be made to it. If you open the .csv, change something (or not), and then press “Save,” Excel will automatically change it to Excel format. Even though the suffix is still .csv, it is actually now an Excel file. The only way to make changes to a .csv file is to import it back into the model, make changes on the input page, and then reexport it.
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Issue: MOP input values
Should the MOP values be for a sustained rate or should they include very short duration high pressure anomalies? |
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The intent of the program is to calculate EPZs based on normal operating conditions, not anomalous or maintenance conditions. Therefore, all values entered should be reflective of normal operating conditions. |
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Issue: Companies want to use values lower than the default in the model
There are cases where companies want to use values that are lower than the default. Specifically, they would like to use lower than 10% for the low pressure trigger. |
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The defaults in the model are there as safety measures; therefore, even if a company enters a lower value, the model will default to the higher number. If the company feels that the default is unreasonable, it can send feedback to Directive71@ercb.ca, and ERCB staff will look at it for future model revisions.
In the case of wanting a low pressure trigger less than 10%, this number is already so low that it means the line will be virtually depressured before the ESDs close. If the company would like to use a lower value, it should choose “No Mitigation” instead. |
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Issue: Gas lift wells |
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Gas lift wells must be entered into the model using the release rate and H2S when the lift is operating. |
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Issue: Wells that are “suspended” but do not meet the requirements of Directive 013 |
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As these wells have not been suspended in accordance with Directive 013, companies must use the last available flow rate and gas analysis to calculate an EPZ. |
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Issue: Refined SO2 modelling |
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If the model indicates that refined SO2 modelling is required, EPA would not request it as a matter of course. However, it must be available if requested (as part of an audit or hearing review, for example). |
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Issue: CO2 modelling
Does the model take into account hazards associated with CO2? |
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The model does have an input for CO2; however, it is meant to create an EPZ for hazards associated with H2S only. If a company wishes to create a plan to deal with CO2 hazards, it will have to do its own modelling to determine an EPZ. |
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Issue: Setback designation on summary page
Why does the setback level sometimes indicate N/A? |
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Setbacks only apply to sour gas pipelines with greater than 1% H2S, not natural gas pipelines. For model runs less that 1%, N/A appears. |
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Issue: Different EPZ sizes for drilling and completions
Applicants run the model for both drilling and completions and get different results. Which .csv should be submitted with the ERP? Which EPZ should be used for the ERP? |
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If it is a drilling and completions ERP, it must be based on the larger EPZ of the two operations. The .csv for the larger operation must be submitted along with the ERP. |
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Issue: The EPZ on the Directive 056 application is for production. Does that mean the ERP should be based on that EPZ?
Directive 056 requires that companies input the EPZ for the largest of (a) drilling, (b) completions/servicing, or (c) producing/suspended in the Schedule 4.3 application. In some cases, the largest EPZ will be associated with production. |
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Though Directive 056 requires notification to be based on the largest zone, Directive 071 requirements are for drilling/completions only. Therefore, the ERCB does not expect a company’s drilling/completions plan to be based on a production EPZ, nor does it expect applicants to do their Directive 071 consultation out to the estimated production EPZ. The applicant will have to provide an explanation of why the EPZ in the application does not match that in the ERP. |
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Issue: What is the largest EPZ that the model will calculate? |
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The largest EPZ the model will calculate is 30 km. Companies can change their operating procedures to try to reduce this value. Using mitigation, especially in populated areas, is strongly recommended. In remote areas, companies will have to do an analysis of whether the benefits of a reduced planning zone outweigh the costs of additional mitigation. |
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Issue: What release rate/release volume from the model should be used for the Directive 056 application?
There are several different release rates/release volumes in the model. Which one is the correct one to use for the licence application? |
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The Land Use Setback and OLD EPZ H2S Release Rate or Volume at Licensed Conditions in column DV on the batch sheets is the number that should be used. |
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Issue: Low-end cut-off point for EPZ sizes
In the old directive, there was a low-end cut off for EPZ sized. For example, if the H2S RR was below 0.01m3/s H2S, the only requirement was for a corporate ERP (and the EPZ was 0 km as the release was likely contained on lease). In the new Directive 071, it is not clear if the minimum criteria still exists. |
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At this point, there is no low-end cut off other than those referred to in Directive 071. The ERCB recognizes that there are concerns around this issue and that a process will need to be created to deal with it. However, until this issue is dealt with through the implementation plan (in July 2009), all EPZs are valid, regardless of size. |
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Issue: Expected maximum liquid flow rate of pipeline fluid
The expected maximum liquid flow rate influences the EPZ size for the GLR<1000 model, and companies are concerned that it may be difficult to derive this value for a complex system. |
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The operator should have this information available based on production accounting. For example, if well A is assigned flow A and well B assigned flow B, then the pipeline that is joined to each well is modelled with flows A and B respectively. At the tie-in of the two lines, the flow would just be A + B.
To be conservative, one could use the total cumulative flow rate at the discharge of the gathering system for each pipeline segment in the system. For example:
Well 1 is producing 10 m3/d of oil, 5 m3/d of water, and 50 m3/d of gas
Well 2 is producing 20 m3/d of oil, 10 m3/d of water, and 50 m3/d of gas
Flow 1 = 15 m3/d
Flow 2 = 30 m3/d
Flow 3 (combined 2 & 3) = 45 m3/d
So the GLR inputs are:
Well 1 GLR = 50/15
Well 2 GLR = 50/30
Combined GLR = (50 + 50)/(15 + 30) = 100/45 |
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Issue: Pipelines with larger H2S concentrations giving EPZs smaller than pipelines with smaller H2S concentrations.
All other things being equal, why would a pipeline with 60% H2S give a smaller EPZ than one with 20% H2S? |
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The reason for this centres around buoyancy. Basically, the more H2S in a mixture, the denser it is and the less buoyant it is. Therefore, the gas would have the tendency to spread out over an area rather than disperse horizontally. In very basic terms, with 55% H2S your plume would be more circular, with 20% H2S it would be long and skinny. |
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Issue: New pipeline tying into an existing system. Is recalculation of the system required |
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When the directive was released, the ERCB stated that for well supplements or pipeline tie-in, the new operation has to be modelled and that EPZ adopted. The existing pipelines don't have to be modelled and the ERP does not have to be rewritten. Therefore, the ERCB does not require that the entire system be recalculated unless there is a significant change to the H2S or release volume. However, should a company choose to remodel the entire system (the ERCB always encourages being proactive), then it would have to complete its notification in accordance with the directive. This may result in a review and variance (R&V) application from local residents, which would be dealt with by the ERCB Law Branch. |
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