Influence of formation pressure on oil well drilling planning

Planning the drilling of an oil well involves a series of elements that are influential in such planning, however among all the elements that we can consider there is one that is paramount, since the safety of drilling operations will depend on it, this element is the formation pressure, also called pore pressure, its affectation and influence make that it must be considered in the well plan, the objective of this consideration lies in the fact of how much can impact the formation pressure in the normal functioning of the drilling operations, especially considering that the formation pressures range from those considered normal, which are formation pressures with which you can work without any fear of fluids such as gas and / or oil entering the well, also considering the abnormal formation pressures, which are called abnormal because they are high pressures that can cause an onslaught of fluids such as gas and oil to the well and subsequently cause a blowout, finally in the planning should be considered the subnormal formation pressures, which are below normal, and rather than being able to cause an operational problem, its value should be considered in the planning of the well in order to prepare an action plan to take care of the future productivity of the well.

When we refer to the future productivity of the well, it is because in the future the productivity of an oil well can be affected by the damage caused to the formation, but for this the following question should be asked:

When does the damage to the formation occur?

This generally occurs when the drilling fluid has a hydrostatic pressure higher than the formation pressure, so if low values of formation pressure are considered, it is because it is intended to foresee in the design of the drilling fluid hydrostatic pressure values that do not exceed by far the low values of formation pressure.

If we perform the planning of a well considering that the formation has normal pressure, then we must know that the wells to be drilled with normal pressure do not generate any problems that alter the elaboration of a functional planning, since the hydrostatic pressure generated by the mud densities makes the drilling fluid used handle densities between the range of 8.5 to 9.5 lbm/gal, which are very common density values and that without variation are very easy to supervise.

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It is important that the planning design always considers the possibility of kicks and blowouts, since a normal formation pressure condition can change to abnormal or subnormal.

The other important thing to consider in the well planning is that being able to take into account the formation pressure is very important to know how to choose the casing that can withstand such formation pressure.

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Wells to be drilled in low formation pressure reservoirs must not only consider the evaluation of the formation damage and the possible impact on its future productivity, but also consider a planning design that contemplates the additional and necessary amount of casing to cover the geological zone in the low pressure subsurface.

References

Data collection for well planning

PEH:Introduction_to_Well_Planning