Abstract

A giant oilfield offshore Abu Dhabi is being further developed with artificial islands and extended reach drilling (ERD). Several lost returns events while drilling the intermediate intervals using non-aqueous fluid (NAF) have occured. NAF and high mud weights are required to stabilize the shale intervals in the overburden due to high inclinations, but have increased the frequency and severity of the mud losses.

To prevent losses while drilling with higher mud weights, combinations of sized ground marble, fibers, and resilient graphite are used to reinforce the NAF fluid to control losses in the formation. With the reinforcement material added to the NAF losses were still experienced on some wells.

Traditional leak off type loss circulation material (LCM) pills were trialed but unsuccessful. Due to the NAF damaging the permeability of the rock, treating losses with NAF mud are difficult because the leak off rates are reduced. Reverse gunk was selected as a good option to treat losses in NAF due to the fact that it does not require leak off to cure the losses. The reverse gunk pill relies on downhole mixing to build integrity.

Reverse gunk pills were used successfully in wells to build sufficient integrity to maintain shale stability mud weight. This enabled drilling through the unstable shales and to casing point. The successful application of the reverse gunk prevented the need for the contingency liner, which eliminated a hole section and allowed use of the originally planned completion size.

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