Innovative Approach for Lost Circulation Treatment in Surface Hole Across Naturally Fractured Limestone Formations Offshore UAE
Authors: Benberber Mohammed Rebbou , Nazih Omar , Calleia de Barros Adelson Jose , Almaazmi Ahmed Abdelrahim , De Melo Alexandre Bezerra , AbdelSattar Mohamed Ahmed , Santos Rocha Michelle Carine , Manga Patrick Ndjore , Mohammed Sherif , Basha Mohamed Ahmed , Bashandy Mohamed 
Published: October 2022

Drilling experience in the surface hole shows consistent challenges associated with hole instability in UER and Simsima carbonate formations due to the presence of a wide range of vuggy structures, natural fractures, faults, and Aquifer flow resulting in a total loss and flow scenario.

The main challenge while drilling across surface sections in UAE offshore fields is the total loss of returns. Typically, when drilling from the Jack Ups, wells are drilled with seawater and high viscosity sweeps once total losses have been encountered due to surface fluid handling problems. This results in poor hole cleaning, hole instability and risk of stuck pipes. Additionally, once the Simsima is penetrated below the UER while drilling with seawater, it has sufficient aquifer pressure to flow to the surface.

The future development of a subject reservoir dictates drilling horizontal drains in shallow un-developed reservoirs. To achieve this goal from a limited number of offshore platforms, it’s required to increase the inclination in the surface hole to +/- 50° to 60° to reach high departure targets. Multiple attempts were made to drill such a profile and the instability in the bottom UER and Top Simsima has caused the hole to collapse on the BHA resulting in multiple sidetracks till the well inclination was dropped to manage completing the section. Attempts to cure the losses in the UER to date have been unsuccessful. Conventional extended cement slurries have been widely used to cure losses while drilling but with low effectiveness.

This paper demonstrates a new lost circulation solution that combines: an LCM swelling polymer that hydrates and helps reduce flow velocity into the formation, followed by a lightweight thixotropic blend with shear-rate rheology-dependent properties. Thus, it enables plugging of large voids and fractures to deliver the wellbore integrity and proper hole cleaning required to drill high inclination surface holes, which prevents stuck pipe incidents.

The deployment of these two combined loss circulation technologies has been proven before to be very efficient to cure losses across similar aquifers in the nearest fields. The very same combination referred to in previous studies was chosen to be evaluated in these fields, considering, and leveraging all the lessons learned and good practices applied in the previous jobs performed in similar formations in the UAE.

The new proposed well design will achieve a reduction in well construction time and cost for the client, enabling a reduction in the overall AFE. This enabled the introduction of new technologies which improved performance. The drilling design consideration process in this paper can be used to provide valuable insight into future projects where a complex technical study in advance is the key to success.