Successful Implementation of Automated Managed Pressure Drilling and Managed Pressure Cementing Techniques in the Troublesome Intermediate and Reservoir Sections of a Remote Well in the Peruvian Jungle Eliminates Wellbore Instability, Severe Fluid Losses, and Differential Sticking
Authors: Soto B. , Neyra O. , Rojas C. , Caro J. C. , Garcia S. , Rojas F. , Vera C. , Deplaude O. , Borges S. , Cortes I. , Contreras J. R. , Villar V. 
Published: October 2017

Drilling the reservoir section in the Sagari field (Peru) presents many challenges, such as wellbore collapsing in the extremely mechanically unstable Shinai formation; differential sticking in low-pressure, high-permeability sandstone reservoirs; and total losses due to the presence of natural fractures. This paper describes how the implementation of automated managed pressure drilling (MPD) and managed pressure cementing (MPC) techniques allowed overcoming those challenges in a remote location where logistics and equipment mobilization is an additional challenge.

The preliminary geomechanical study indicated that an equivalent density (ED) of 10.5-lbm/gal was required to maintain wellbore stability, while 10.8-lbm/gal could not be exceeded due to the risk of differential sticking. Additionally, eliminating pressure variations in the mechanically unstable Shinai formation would prevent wellbore collapse. The MPD strategy for drilling the original 8.5-in hole section and sidetrack consisted in using an automated MPD System to maintain the ED profile within the 10.5 to 10.7-lbm/gal window along the open hole and a near-constant pressure of 10.5-lbm/gal in the most unstable Shinai formation at all times.

Due to its reduced footprint, this automated MPD equipment package could easily be airlifted by helicopter to the remote rigsite.

The MPD strategy was implemented as per plan; it successfully prevented wellbore instability and differential sticking and contributed to the excellent condition of the wellbore. Indeed, the production liner was run down the 2,700ft of open hole smoothly in less than six hours and later well testing revealed that the mechanical skin factor in the reservoir section was equal to zero.

When drilling the last feet of the sidetrack with an ED of 10.5-lbm/gal, a natural fracture was encountered; it was immediately detected by the MPD Coriolis flow meter located at the well returns, allowing for a quick response and curing losses rapidly. However, this further reduced the operating window size. MPC allowed using a statically underbalanced drilling fluid, while ensuring well integrity and preventing wellbore collapsing during cement placement. The estimated ED on bottom was monitored in real-time and losses were successfully prevented. The coupling of the wiper plug on the landing collar was observed as per plan, and successful zonal isolation was later confirmed by cement bond log (CBL) and casing integrity test (CIT).

In addition to the application of managed pressure techniques in the production section, MPC of the intermediate 9 5/8-in casing was performed as a contingency measure, as the reduced annular flow area between the two casing strings and the narrow pore pressure -fracture pressure window would not allow cementing the casing conventionally.