Drilling fluid circulation losses in petroleum drilling and well construction

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When we talk about losses is because we associate the idea that we must conserve certain factor, in the case of drilling oil wells, the circulation of drilling mud (drilling fluid) must never interrupt its circulation cycle since it leaves the suction tanks, until it reaches the bottom of the well to then return through the annular space between hole and drill pipe and then reach the active tanks so that the process is fulfilled again.

If the fluid circulation cycle is interrupted by any leakage of drilling mud into the formation, then a loss of drilling fluid circulation is occurring.

The danger is that as the level of the fluid column in the well drops due to lost circulation, the hydrostatic pressure decreases, so if the hydrostatic pressure drops dramatically, there is the possibility of a blowout occurring at the surface due to an influx of gas from the formation, because the formation pressure becomes greater than the hydrostatic pressure of the drilling fluid.

Circulation loss zones

There are two types of lost circulation of drilling fluid, as shown in the following picture:

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In the example of the well on the left side it can be seen that there is a partial loss of drilling fluid, this means that the drilling fluid that is circulating in the well returns until it reaches the surface, and that only a small volume is being lost to the formation. The example on the right side shows a well where there is no return of circulating fluid to the surface because all is being lost to the formation.

Whether the loss is partial or total will depend on the type of formation through which the circulating fluid is circulating, because if for example the lithological formation is of high permeability, then the fluid will be lost through that zone, if the loss is partial it is because there may be the probability that the formation has a medium permeability or that it is a small interval of high permeability formation.

Is high permeability the only reason why circulation losses occur?

The high permeability of the formation is not the only reason why lost circulation may occur, because if the hydrostatic pressure of the drilling fluid is higher than the formation pressure, then the lithological formation will be fractured and therefore all the drilling fluid will be lost through the induced fracture site.

Conclusión

The limitations at the moment of drilling an oil well due to circulation losses are total, that is to say, in the event of a partial or total circulation loss, a blowout may occur at the surface and/or the drilling may stop completely, since if there is no drilling fluid circulating in the well, the cuttings cut by the drill bit will not be lifted, therefore the drilling stops completely.

References

[1] Billingston, S.A. 1963. Practical Approach to Circulation Problems. Drilling Contractor.(July–August) 52.

[2] Cagle W.S. and Mathews, H.D. 1977. An Improved Lost Circulation Slurry Squeeze. Petroleum Engineer (July): 26.

[3] Clancy, L.W. and Boudreau, M. Jr. 1981. High-Water Loss High-Solids Slurry Stops Lost Circulation with Oil Mud. Oil & Gas J. (January): 99.

[4] Goins, W.C. Jr. 1952. How to Combat Circulation Loss. Oil & Gas J (June): 71.