Underbalanced drilling techniques when foamed drilling fluids are the most important.

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Overweight drilling is the most common drilling technique; however, it has several disadvantages such as formation damage, mud losses and stuck pipe-challenges that are common in high-permeability zones and highly fractured formations. To overcome these problems, the underbalanced drilling method could be implemented.

It is important to mention that the underbalanced drilling technique is a technique that allows drilling wells keeping the drilling fluid pressure below the formation pressure values (reservoir pressure), however it is well known that for safety reasons, the technique mostly used to drill oil and natural gas wells is the overbalanced technique, that is, the technique in which the drilling fluid pressure is above the formation pressure values.

The question that many may be wondering is:

If the most commonly used drilling technique is overbalance drilling, why do you drill with the underbalanced drilling technique?

The answer is that the overbalance drilling technique offers greater security, since the higher pressure of the drilling fluid keeps fluids such as gas and oil within the oil formation, thus avoiding that these fluids can migrate to the surface and that an explosion can occur, however beyond that advantage there are only very marked disadvantages, For example, there is damage to the formation, since maintaining a fluid pressure that exceeds the formation pressure causes a certain volume of that fluid to penetrate the walls of the well and thus damage occurs to the oil formation, causing this in the future may reduce the permeability rates of the producing rock which in turn causes very low productivity rates.

Although there are other disadvantages from the operational point of view in the drilling of a well when the overbalanced drilling technique is used, I only mentioned the disadvantage of low productivity rates in the future, since everything that is done operationally during the drilling of an oil well should impact positively and not negatively on its future productivity. All this leads us to conclude preliminarily that the underbalanced drilling technique is a technique that among many things comes to cover a solution that is to maintain the high productivity of the wells in the future during their productive life.

The underbalanced drilling technique (UBD) is a technique that requires extensive knowledge in the sense that the engineers in charge of drilling a well know how to apply the correct methodology in its application, since for example there are geological conditions that favor its application, Among the candidate reservoirs for its application are the oil fields that have hard formations that have low pressure, which in many cases are highly fractured formations that would not withstand high pressures of a drilling fluid because it would cause damage to the formation that would subtract future productivity to the well.

Once the engineer has identified the ideal geological conditions such as the oil reservoir has a hard formation with very low formation pressures, the field production has made the oil reservoir depleted, the formation is suddenly highly fractured, then it could be assured that the reservoir is a good candidate to be drilled using the underbalanced drilling technique.

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What fluid should be used to drill using the underbalanced drilling technique?

Logically the same fluids that are used to drill by the overbalance technique cannot be used in this technique of underbalanced drilling, since they are fluids that have a high content of solids that increase their density and therefore increase the circulation pressure causing damage to the formation.

On the contrary, the correct thing to do would be to use fluids with low density that generate very low pressures that make the drilling fluid pressure equal or lower than the formation pressure. Among these low-density fluids are single-phase and two-phase fluids, single-phase fluids include air, nitrogen and natural gas, and two-phase fluids include mist and foam.

In this UBD technique, I would advise the use of foamed fluids for several reasons, among which are their low density and their ability to transport the riprap that is cut by the drill bit as the wellbore is drilled deeper.

The most outstanding physical property of foamed fluids is their viscosity, since it is due to their high viscosity that they have the capacity to drag the cuttings from the bottom of the well to the surface. In addition to this, it also has low density, which allows it to be underbalanced, which in turn translates into high rates of future productivity in the well.

The conclusion of the case is that the foamed fluid is a great option to use the underbalanced drilling technique, as long as the well to be drilled is from an oil field that meets the conditions mentioned above, and that due to its high viscosity and low density in a fluid that provides operational benefits in drilling as long as it has the corresponding safety equipment in case there is an onslaught of fluids such as gas and oil into the well.

References

A review of foam-based fracturing fluids applications: From lab studies to field implementations

Investigating synergism and antagonism of binary mixed surfactants for foam efficiency optimization in high salinity