An Innovative Approach to Cementation of Monobore Completion Tubing to Maximise Access to the Bottom Most Reservoirs

Abstract

Cementation of the monobore completion strings for Total in Tunu field of Indonesia is a balancing act. The bottommost reservoir sands are within 30-ft of a high-pressure zone. Therefore, having a conventional length of shoe track, two to three tubing joints, will block the access to the bottom sands. Furthermore, any error in displacement volumes of these cement jobs would lead to costly remediation. Drilling out cement inside the small tubing sizes would force Total to use special drilling techniques, and displacing extra mud volumes would wet the shoe, which could jeopardize the well integrity. To tackle the challenges, shoe track length was minimized with the float shoe and collar placed only 1 m apart. A custom-made calibration plug, with proper burst disc pressure rating, was designed and used prior to cementation; this plug allowed the tubing volume to be measured physically. Based on observing the pressure spikes on the rig floor, the displacement volumes for all the cement jobs are known prior to the cement job. As it is proven to be valuable, this innovative cementation method continues to be used by Total ever since its introduction. The calibration plug has been used in more than 200 wells with the total depths of 13,000-ft to 17,000-ft. The cement displacement was done accurately, and top plug was bumped successfully. This has saved 100-ft—the conventional shoe track length—of drilling on each well. Also, the plug contributes to the safe exploitation of the bottom targets without encountering the high-pressure zones. This innovative technique is applicable to cementation of all completion strings with reservoir targets close to the tubing shoe. It has been proven to be a reliable method in eliminating the shoe track and can be applied to any similar cementation operations.