A Formation Water Viscosity Calculator is an engineering tool used to estimate the viscosity, or resistance to flow, of water found in subsurface rock formations. The viscosity of formation water is not constant; it changes significantly with temperature and the amount of dissolved salts (salinity). This calculator uses established empirical formulas to predict the water's viscosity based on these two key parameters. Reservoir engineers and geoscientists depend on this value for building accurate reservoir simulation models, forecasting how fluids will move through rock, predicting water production rates, and designing enhanced oil recovery projects like waterflooding. Consequently, calculating water viscosity is a fundamental step in understanding and managing the behavior of a petroleum or geothermal reservoir.
formula of Formation Water Viscosity Calculator
The viscosity of formation water is typically calculated using empirical correlations developed from extensive laboratory measurements.
A general formula structure is:
Where:
- μ = dynamic viscosity in centipoise (cP)
- T = temperature in degrees Celsius
- A, B, C = empirically derived constants that change based on the water's salinity.
A more direct and commonly used empirical correlation for brine (saline water) is:
μ = 0.42 + 0.0037 × S + 1.4 / (T + 22)
Where:
- μ = viscosity in centipoise (cP)
- S = salinity in grams per liter (g/L) or parts per thousand (ppt)
- T = temperature in degrees Celsius (°C)
This specific formula provides reliable estimates for conditions commonly found in reservoirs:
Salinity: 0–200 g/L
Temperature: 20–150 °C
Estimated Water Viscosity (cP) at Various Temperatures and Salinities
This table provides quick estimates for formation water viscosity in centipoise (cP) under different conditions, helping to visualize the impact of temperature and salinity.
| Temperature (°C) | Fresh Water (0 g/L) | Seawater (35 g/L) | Brine (100 g/L) | Heavy Brine (200 g/L) |
| 25 | 0.89 cP | 1.02 cP | 1.22 cP | 1.59 cP |
| 50 | 0.55 cP | 0.68 cP | 0.88 cP | 1.25 cP |
| 75 | 0.38 cP | 0.51 cP | 0.71 cP | 1.08 cP |
| 100 | 0.28 cP | 0.41 cP | 0.61 cP | 0.98 cP |
| 125 | 0.22 cP | 0.35 cP | 0.55 cP | 0.92 cP |
Example of Formation Water Viscosity Calculator
A reservoir engineer needs to estimate the viscosity of formation water to input into a simulation model. The reservoir conditions are known.
First, the engineer gathers the required data.
- Formation Temperature (T): 90°C
- Formation Water Salinity (S): 150 g/L
Next, the engineer uses the direct empirical formula.
μ = 0.42 + 0.0037 × S + 1.4 / (T + 22)
μ = 0.42 + 0.555 + (1.4 / 112)
μ = 0.42 + 0.555 + 0.0125 = 0.9875 cP
Therefore, the estimated viscosity of the formation water under these reservoir conditions is approximately 0.99 cP.
Most Common FAQs
As temperature increases, the water molecules gain kinetic energy and move around more vigorously. This increased movement makes it easier for the molecules to overcome the intermolecular forces that hold them together, allowing the fluid to flow more easily and thus reducing its viscosity.
When salts dissolve in water, they break apart into ions. These ions are larger than water molecules and create more "frictional" drag within the fluid as they move. This increased internal resistance makes it more difficult for the water to flow, which results in a higher viscosity.
In a reservoir, oil and water flow together through the tiny pore spaces in the rock. The relative ability of each fluid to flow depends heavily on its viscosity. By accurately calculating the water's viscosity, engineers can better predict how water will move in relation to the oil. This is critical for forecasting how much water will be produced alongside the oil and for designing efficient recovery systems.