The oil in water ratio (OWR) is a measure used in oilfield drilling to express the relative amounts of oil and water in an oil-based mud. It is not simply the percentage of oil and water present; rather, it's the ratio of the oil volume percentage to the water volume percentage.
Here’s how it’s calculated, according to the provided reference:
- Retort Analysis: The OWR is derived from a retort analysis, a test performed on a drilling mud sample to determine its composition.
- Volume Percentages: The retort analysis provides the volume percentage of oil and water in the mud.
- OWR Calculation: The ratio is determined by dividing the oil volume percentage by the sum of the oil and water volume percentages. The same operation is done for water. Then, the oil percentage is written first, followed by a forward slash, then the water percentage.
Calculating the OWR
Let's break down the calculation with the example provided:
- Example Mud: Imagine a drilling mud containing 60% oil and 18% water by volume.
| Component | Volume Percentage |
|---|---|
| Oil | 60% |
| Water | 18% |
- Calculate the percentage attributed to oil: [60/(60 + 18)] *100 = 76.92%. For the sake of the example, this will be rounded to 77%
- Calculate the percentage attributed to water: [18/(60 + 18)]*100 = 23.07%. For the sake of the example, this will be rounded to 23%
- Express as a Ratio: The oil-in-water ratio for this sample is expressed as 77/23. This is not a fraction, but a ratio.
Why is OWR Important?
- Mud Properties: OWR is a key indicator of the mud's overall characteristics, impacting viscosity, density, and fluid loss control, all crucial for efficient drilling.
- Performance: Proper control of the OWR ensures the drilling mud performs as intended, preventing issues like stuck pipe and formation damage.
In conclusion, the oil-in-water ratio is not just the simple percentage of oil and water. Instead, it's a ratio expressed by dividing the percentage of oil by the sum of the percentage of oil and water in the sample.
