Well-Mixed Inventory Method
The Well-Mixed Inventory method mixes the inputs and outputs at the start of each time slice.
Note: The routines for Baffled and Well-Mixed are the same, but the mixing steps are in a different order.
Well-Mixed Inventory Method Example
An inventory initially has 2000 bbl 50%A: 50%B. There are three time slices during the accounting period. During time slice 1 a quantity of 2000 bbl 40%B: 60%C enters and 1980 bbl are extracted. During time slice 2 a quantity of 1000 bbl is extracted and 3000 bbl 33.3%B: 66.7%C enters. During time slice 3 1000 bbl are extracted and 500 bbl 100%A are added. Minimum tracking level is set such that any compositions less than or equal to 10 bbl are removed. The packet number signifies the order the packets entered into the inventory.
The calculation procedure is described below.
- Assume that the inputs are mixed with the inventory contents at the start of each time slice.
- Add the quantities of each material entering the inventory in new columns to the right.
- Calculate the percentage of each material in the inventory. If any materials are below the minimum tracking level at the last time slice, then push these out first.
- Calculate the percentage of each material in the inventory.
- Multiply the composition percent by the transfer quantity leaving for each material during the time slice.
- Subtract the quantity of each material from the columns in the table.
- For the last time slice, check columns to see if any are below minimum tracking level. If there are, then redo the time slice by flushing out these products first.
- Re-index all packet numbers.
The results are illustrated in the tables below.
Inventory has opening volume of 2000 bbl and a starting composition of 50%A:50%B.
The Col 1, Col 2, …column syntax is Packet number.; material; quantity (bbl).
Initial Inventory Reading
| Inventory | Col 1 | Col 2 |
|---|---|---|
| 101 | 1;A;1000 | 1;B;1000 |
Time Slice 1 After 2000 bbl Input of 40% B:60% C
| Inventory | Col 1 | Col 2 | Col 3 | Col 4 |
|---|---|---|---|---|
| 101 | 1;A;1000 | 1;B;1000 | 2;B;800 | 2;C;1200 |
Time Slice 1 After 1980 bbl Output
| Inventory | Col 1 | Col 2 | Col 3 | Col 4 |
|---|---|---|---|---|
| 101 | 1;A;505 | 1;B;505 | 2;B;404 | 2;C;606 |
Time Slice 2 After 3000 bbl of 33.3% B:66.7%C
| Inventory | Col 1 | Col 2 | Col 3 | Col 4 | Col 5 | Col 6 |
|---|---|---|---|---|---|---|
| 101 | 1;A;505 | 1;B;505 | 2;B;404 | 2;C;606 | 3;B;1000 | 3;C;2000 |
Time Slice 2 After 1000 bbl Output
| Inventory | Col 1 | Col 2 | Col 3 | Col 4 | Col 5 | Col 6 |
|---|---|---|---|---|---|---|
| 101 | 1;A;404.4 | 1;B;404.4 | 2;B;323.5 | 2;C;485.3 | 3;B;800.8 | 3;C;1601.6 |
Time Slice 3 After 500 bbl Input of 100.0% A
| inventory | Col 1 | Col 2 | Col 3 | Col 4 | Col 5 | Col 6 | Col 7 |
|---|---|---|---|---|---|---|---|
| 101 | 1;A;404.4 | 1;B;404.4 | 2;B;323.5 | 2;C;485.3 | 3;B;800.8 | 3;C;1601.6 | 4;A;500 |
Time Slice 3 After 1000 bbl Output - Ending Result
| inventory | Col 1 | Col 2 | Col 3 | Col 4 | Col 5 | Col 6 | Col 7 |
|---|---|---|---|---|---|---|---|
| 101 | 1;A;314.9 | 1;B;314.9 | 2;B;251.9 | 2;C;377.9 | 3;B;623.6 | 3;C;1247.4 | 4;A;389.4 |
Inventory has an ending volume of 3520 bbl and a composition of 20%A:33.8%B:46.2%C.