New version of Maros and Taro!
We’re pleased to announce the release of Maros 9.3.1 and Taro 5.3.1. The focus of this release is the ability to define bottlenecks in Maros with further debottlenecking capability, previously available in Taro.
Previously, Maros has validated the production profile of all product streams against the design capacity of each node and its respective parallel blocks. This makes sense during the design-phase where analysts are planning to design an unconstrained production system. However, during the operational-phase, design is fixed which does not give flexibility to change the capacities. To overcome this challenge, Maros is now able to run with bottlenecks defined in the system with further debottlenecking capability.
We would like to say thank you to Chevron ETC for their contribution in the development of this new feature.
Please visit DNV GL Software’s Customer Portal to download the latest version of the products:
Debottlenecking in Maros
The following case study is used to explain the use of bottlenecks in Maros. An offshore production facility is under operation (past the design phase) described using the following block flow diagram:
The main assumptions for this case study are listed below:
- The node design capacities are indicated in parenthesis. Each export node has the node design capacity of
- Oil export: 100 mbbls/day
- Water production: 100 mbbls/day
- Gas compression: 100 mmscf/day
- Two systems are defined: Compression and Pumping system
- Each system is formed with parallel blocks with one equipment item
- Each parallel block unit are using the following capacities:
Table 1:Parallel Block capacity per unit
|Parallel Block||Equipment||Unit 1||Unit 2|
|Compression||Compressor||75 mmscf/day||75 mmscf/day|
|Pumping system||Pump||60 mbbls/day||60 mbbls/day|
The reservoir profile is described using the following production profile:
A new reservoir profile is calculated where the water production has increased considerably for the next 10 years.
Adding this new production profile at the Flow Grid in Maros will prompt the following error message in the Water Production Node:
As the error indicates, the node capacity of 100 mbbls/Day is not sufficient to handle the newly defined flow of 125 mbbls/day. Maros will identify all nodes where the system is unable to process the production rates defined at the Flow Grid.
As the error message indicates, this problem can be resolved by:
- Change the Node Design Capacity to meet the peak production rate for the associated stream in the Flow Grid or;
- Select the option to “Allow Bottlenecks” in the Settings tab
The first solution is not feasible for assets that are under operations – design configuration is fixed. Thus, to allow the model to run with this current bottleneck, the user needs to select the option to “Allow Bottlenecks” in the Settings tab:
This will convert the error message into a warning message. The red icon indicates an error message and you cannot run the model . The yellow icon indicates a warning which will allow you to run the model but made you aware of a specific issue in the model.
This will impact mainly two areas of the flow calculation:
- Bottlenecked production caused by the inability to flow all the water production and the requirement to maintain the gas and oil ratio (GOR)
- Spare capacity available when the nodes are not 100% utilized
The following section discuss the impact of these different changes to the flow calculation:
The bottlenecked production can be easily identified by playing the animation mode. The flow of water is bottlenecked in year 6, as described in the error message:
The water production is bottlenecked by 80%. This is calculated by referring the Node Design Capacity for node which is to meet the potential production demand. In this case, the water production node design capacity is 100 mbbls/day and the potential flow is 125 mbbls/day i.e. 100/125 = 0.8.
To maintain the gas and oil ratio, this bottleneck is spread to all the nodes in the block flow diagram:
- Oil export node is now showing a production of 80 mbbls/day (i.e. 80% x 100 mbbls/day) and;
- Gas export node is now showing a production of 60 mmscf /day (i.e. 80% x 75 mmscf/day).
This will obviously cause an impact to the main Key Performance Indicators in the system. It is important to note that Maros will always report the Production Efficiency. Production efficiency is defined as the total volume produced at the export node to that which would have produced had all equipment run without failures throughout the system life.
Production Efficiency = Production of Export Node / Potential Production of Export Node
Taking this case study, the last three years of the platform are constrained by the water production node. So, after removing events that would cause production loss, the maximum production efficiency this platform can achieve is 92%. This can be easily calculated by taking the production profile of oil and referring to the actual profile:
The total production for the actual production volume is 3,358,000 mbbls and the total potential production volume is 3,650,000 mbbls.
To assist users on understanding the impact of bottlenecks to the system, a new KPI has been introduced to the performance summary: Volumetric Production against Plant capacity.
For the case where there is no production loss, this KPI will be showing 100%. This KPI can be used as a reference point to the overall efficiency of the model without looking at the bottlenecked production.
Spare capacity change
When comparing base case and the new water production profile, one noticeable difference is transient spare capacity. The importance of identifying spare capacity for the different product streams is thoroughly discussed in Chapter 9.
The impact of the flow change to the spare capacity is discussed in the following section.
Let’s start by taking the example of failures in the Compression system during the first 3 years of operation, when the production rate is equal to 100 mmscf per day. The failure of one of the parallel block units, which can produce up to 75% of the Node Design Capacity (i.e. 75 mmscf per day), will reduce the production for all streams proportionally. In this case, the system is constrained to produce at 75% of its capacity – 75 mmscf/day is available of 100 mmscf/day of potential.
Now considering failures in the Water production system during the same period. In this case, because the system is not fully utilizing the Node Design Capacity, no production loss is computed.
Running the same analysis for the period where the gas production is reduced to 75 mmscf per day will follow the same logic. This is shown in the next screenshot:
Analysing the water production profile for the same period will show the maximum water is 40 mbbls per day. This means that, similarly to the compression system, failures to the water production system will not cause any production loss. Same logic applies – because the system is not utilizing its full capacity, the spare capacity can maintain production, avoiding production loss.
However, the reviewed production profile now predicts a maximum production of 90 mbbls per day for this period of time. This means that a failure in the water production will now constraint the water production system which will then impact the production of all other product streams.
The production loss associated with this failure can be computed by calculating how much the system is constrained and mapping out the using the gas and oil ratio.
In this case, the Water production system is required to produce at 90 mbbls per day and it is now constrained to 60 mbbls per day. This means a 33.3% of reduction which is then passed into all other nodes. This results in:
- Oil export system is now producing at 66.67 mbbls per day
- Gas export system is now producing at 50 mmscf per day.
For the last step of the simulation, where the Water production system is bottlenecked, the impact of decreased spare capacity must be combined. This will provide the overall view of production losses which are associated with the bottlenecked production.
Controlling the bottleneck
Maros provides the ability to define two types of bottlenecks in models:
- Node design capacity bottlenecks: those nodes which are unable to meet the production profile defined at the Flow Grid
- Transient Rate Profiles: ability to control the flow for a specific node
The following section describes how this will impact the model and its results:
Node design capacity bottlenecks
Bottlenecks that involve Node Design Capacity will impact mainly the flow calculation for nodes where the Production rate defined at the Flow Grid is higher than the Node Design Capacity. It is important to note that, changing the Node Design Capacity will change the reference point for the Capacity Loss factor defined at the Failure Mode, Scheduled Activity and Trigger set level. Another important change will be the model’s inability to boost the system to production rates that were previously available.
This new feature allows the user to define the required flow running through a specific node. This is an additional set of information which will be used to constrained the production to a certain level for specific nodes. Now, the user can define transient changes for nodes that need to be controlled for its flow.
This bottleneck will be spread throughout the different nodes in the model. Similarly to bottlenecks caused by Node Design Capacity, this change will mainly impact those nodes where the Production rate defined at the Flow Grid is higher than Transient Rate Profile. One important difference is that this will not change the reference point for the calculation of Capacity Loss as the Node Design capacity remains the same. The same restriction to boosting operations is expected.