The importance of the Reynolds number calculation in petroleum engineering is that by calculating it we can estimate whether the flow behavior of the drilling mud will be laminar or turbulent.
What is the benefit of knowing whether the drilling fluid is laminar or turbulent?
In the case that we calculate the Reynolds Number and it gives us less than 4000, it means that the flow is laminar, the laminar flow behavior is not convenient for drilling a well, since there will not be a good transport of cuttings while drilling, therefore problems of sticking of pipes may occur.
That is why it is convenient to adjust certain properties of the fluid such as viscosity and density of the drilling fluid, there are other parameters that although they are not properties of the drilling fluid, must also be controlled because they depend on the Reynolds number going up or down. For example, if we want to obtain a drilling mud that has a turbulent behavior in order to obtain an effective cleaning of the hole, then we can lower the flow rate of the fluid, simply by lowering the flow rate of the mud pumps.
What are the characteristics of turbulent flow behavior that promote cleanup and transport of drill cuttings from the bottom of the hole to the surface?
A drilling fluid in turbulent conditions will exhibit low viscosity rates, which, coupled with low gel strength, provides some ease in transporting cuttings from the bottom of the hole to the surface while drilling.
The same turbulence characteristics of the drilling mud allow the drill cuttings to be suspended and not blow back and fall to the bottom of the hole.
The important thing about having a low viscosity drilling fluid is that we can reduce the resistance to flow that occurs when viscosity is high.
Turbulent drilling fluids have low gel strength, this means that the gel will allow even when the mud circulation stops, the cuttings will not flow back to the bottom of the well.
How is the Reynolds number calculated?
If we calculate the Reynolds number in the units of measurement of the English petroleum system shown in the Reynolds number equation, then the Reynolds number will give us dimensionless.
In the case that the Reynolds number gives us: Re<4000, then we can lower the average circulation velocity of the drilling fluid, this is achieved by lowering the pump flow rate values. We can also lower the dynamic viscosity of the drilling fluid, this is achieved by adding some chemical additives to the drilling fluid.
You can also increase the density of the drilling fluid and thereby increase the Reynolds number value to seek the turbulence of the drilling fluid, however, this may not be as advisable, because if the density is very high, there is a probability that the hydrostatic pressure of the drilling fluid is greater than the fracture pressure of the formation.
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