The design of the wells in Cuervito Field is generally composed of three casings, in order to access the highest yielding sands. Drilling operations are characterized by the presence of a balloning effect, causing the loss of circulation that occasionally difficult meeting the planned target for the well.
The balloning effect, breathing formation or phenomenon of loss and gain, is an elastoplastic behavior of the walls of a well that usually originates in impermeable formations. When circulating drilling fluids it creates an additional pressure that is commonly defined as the equivalent circulation density (ECD), which when imposed on the walls of the well, causes them to dilate. When circulation is stopped, the ECD decreases, the diameter of the hole shrinks along with the pressure, creating a flow return to the well. High temperatures also play a role in the balloning effect. The expansion and contraction of the holes in the Cuervito Field is highly remarkable.
In order to minimize the encountered problems and to optimize drilling operations, a series of steps were prepared in order to study Cuervito Field’s 16 wells. This study contains geological and geopressure information. As a result of this study two different options were encountered: (i) Adding an additional casing or (ii) An unconventional drilling technique.
The first alternative (adding an additional casing to the well) proved to be a more complex and less elegant solution when compared to the unconventional drilling technique.
The unconventional drilling technique known as Managed Pressure Drilling (MPD), enables the control of the annular pressure profile and monitors the bottom pressure limits in order to maintain them at a constant level, while minimizing drilling fluid loss and drilling downtime.
During the drilling of the well 17 of Cuervito Field the effect balloning was presented in large scale and was implemented a pilot project to evaluate the technique of MPD. The result was successful and was applied in the following three wells in the Field, achieving the elimination of the typical problems of the area.