Click to see subtopics:With the Multilayer Allocation editor (located within the Editors pane), you can assign flow proportions for each layer in a multilayered well. Using these flow proportions, rates for each layer can be calculated from the overall well rates in the Production editor. (Typing values in this editor must be done at the well level.)
Since flow proportions are allocated on a time basis, the first step is to specify at least one calendar date. If only one date exists, then the flow proportions apply to every date in the Production editor. However, if the proportions are changing over time, then multiple dates can be typed into the Multilayer Allocation editor.
Interpolation
Interpolation is used to determine the allocation between the specified dates in the Multilayer Allocation editor. There are two interpolation options: linear and step.
1. Linear interpolation calculates an average change in flow proportions from one date to the next. This is the default setting.
2. Step interpolation keeps the proportions static until the next date is reached. When that next date is reached, the proportions instantly change.
Regardless of the specified interpolation method, any entries in the Production editor that occur before the first date in the Multilayer Allocation editor use the allocation percentages in the first row. Likewise, any production data after the last-specified allocation date continues to use that allocation.
Specifying proportions – overall
The simplest way to allocate is to specify the overall flow proportions. This method applies the same allocation to all fluids equally. The only thing that can be set is the percentage of the total fluid that comes from each layer. Percentages are set indirectly by typing values into the flow proportion fields. For example, in a two-layer well, if each layer is specified with a proportion of “1”, then 50% of the total fluid is allocated to each layer.
Specifying proportions – per fluid
By specifying proportions on a per-fluid basis, you can have greater control over allocations. For example, if you are producing only gas from one layer, and only water from another layer, then a per-fluid allocation is necessary.
By selecting Per Fluid from the toolbar, fluid proportion fields become editable (and any overall proportions are ignored).
Specifying proportions – based on kh
If you know permeability (k) and net pay (h) for each layer, you can allocate layer production based on kh. Type your known layer permeabilities, then type net pay, or click the Pull Defaults icon (
) for layer properties to bring net pay from your layer’s Properties editor.
Specifying proportions – based on khSat
If you know permeability (k), net pay (h) and fluid saturations for each layer, you can allocate layer production based on khSat. Type your known layer permeabilities, then type net pay and fluid saturations. Or, you can click the Pull Defaults icon () for layer properties to bring net pay and fluid saturations from your layer’s Properties editor, and you need to specify saturation for each of the phases that are present in the Production editor.
Special Considerations
There are special considerations for condensate and time on production / injection.
Condensate
Whenever pressure calculations are performed with condensate (Constant Rv), extra attention should be paid to the Multilayer Allocation editor. Since both gas and condensate rates can be allocated differently, the condensate-gas ratio can be quite different from one layer to the next.
In the Production editor for the well, there are two ways to control the CGR Source. When “CGR” is selected, it uses the allocated condensate volume and gas volume to calculate a CGR for each row. However, if “CGRcustom” is selected, then the per layer CGRcustom is calculated as follows:
Time on Production / Injection
Whenever a layer has none of the proportions allocated to it for a given row, it has zero allocation for the time on production (or injection). Otherwise, 100% of the time on production (or injection) is allocated.